Powering the Future: Progress and Hurdles in Developing Proton Exchange Membrane Fuel Cell Components to Achieve Department of Energy Goals—A Systematic Review

Abstract

This comprehensive review explores recent developments in Proton Exchange Membrane Fuel Cells (PEMFCs) and evaluates their alignment with the ambitious targets established by the U.S. Department of Energy (DOE). Notable advancements have been made in developing catalysts, membrane technology advancements, gas diffusion layers (GDLs), and enhancements in bipolar plates. Notable findings include using carbon nanotubes and graphene oxide in membranes, leading to substantial performance enhancements. Innovative coatings and materials for bipolar plates have demonstrated improved corrosion resistance and reduced interfacial contact resistance, approaching DOE targets. Nevertheless, the persistent trade-off between durability and cost remains a formidable challenge. Extending fuel cell lifetimes to DOE standards often necessitates higher catalyst loadings, conflicting with cost reduction objectives. Despite substantial advancements, the ultimate DOE goals of USD 30/kW for fuel cell electric vehicles (FCEVs) and USD 600,000 for fuel cell electric buses (FCEBs) remain elusive. This review underscores the necessity for continuous research and innovation, emphasizing the importance of collaborative efforts among academia, industry, and government agencies to overcome the remaining technical barriers.

1. Introduction

Energy is a cornerstone of human civilization and progress. Throughout history, the need for energy has grown in tandem with the advancement of civilization. The global energy demand is inextricably linked to population growth, urbanization, and modernization. The global energy demand proliferates with increasing population, urbanization, and modernization [1]. The global energy demand is projected to experience exponential growth in the coming years. An annual statistical review showed that global energy consumption is estimated to be growing at an average of 2.3% per year [2]. As per BP’s Energy Outlook, energy utilization is presumed to rise by 34% between 2014 and 2035. The global population and quality of life have led to a rapid rise in energy demand, and fossil fuels have been the most significant contributors to the global energy demand. Fossil fuels continue to serve as the dominant energy source, propelling the global economy, contributing to approximately 60% of the increase in energy consumption, and accounting for around 80% of the total energy supply projected for 2035. Natural gas is expected to exhibit the most rapid growth among fossil fuels [3].

On the contrary, coal is expected to experience a significant decline in its prominence. Despite holding a substantial share in 2000, coal’s growth has declined. By 2035, coal’s contribution to essential energy is projected to be minimal, with natural gas surpassing it to become the second-largest energy source. Meanwhile, renewables (including biofuels) are anticipated to rapidly expand among non-fossil fuels, increasing their share in primary energy from approximately 3% today to an estimated 9% by 2035 [4,5]. The demand for the transportation of people and goods is a significant driver of the global energy demand. The transportation sector accounts for about 26% of global energy consumption, as presented in Figure 1 [6]. As the number of vehicles per capita and distance traveled per vehicle approach saturation level in industrialized countries, an increase in population and income per capita and industry globalization can result in an off-trend accelerated growth of vehicles.

Almost one-third of the world’s energy reserves are utilized by the transportation sector, which predominantly relies on fossil fuels. However, this dependence on fossil fuels is not a viable long-term solution. The planet’s finite fossil fuel resources are being depleted, and their extraction and conversion into usable fuels also contribute to environmental pollution [7]. Furthermore, technology in the transportation sector is accountable for more than one-third of the worldwide emissions of Green House Gases (GHGs), resulting from the combustion of fossil fuels in internal combustion engines [8]. Consequently, there is a growing search for alternatives to traditional petroleum-powered vehicles, with fuel cell vehicles emerging as leading contenders [9]. As concerns regarding the exhaustion of petroleum-based energy reserves and climate change continue to mount, there has been a notable surge of interest in fuel cell (FC) technologies in recent years. This heightened attention is due to their impressive efficiency and minimal emissions. Fuel cells offer superior energy densities compared to other energy devices, making them well-suited for extended-range applications in the transportation sector. These advantages have consequently accelerated the research and advancement of FC-driven vehicles [10].

Of the various applications for PEMFCs, the automotive sector stands out as the most competitive and promising. Concerns like air pollution, climate change, and fuel sustainability have emerged in the rapidly expanding global vehicle market. These concerns are closely linked to conventional engines, specifically internal combustion engines (ICEs), which rely on hydrocarbon fuels. PEMFCs can probably restore ICEs because they can achieve better efficiency and reduce GHGs [11,12]. Furthermore, they boast compact dimensions and a higher weight-to-power ratio, rendering them exceptionally well suited for automotive and portable applications. This explains why significant organizations have opted for PEMFCs to power all hydrogen-fueled buses and cars currently available [13]. The power output of these vehicles, from passenger cars and buses to utility vehicles, typically falls within the range of 20 kW to 250 kW [14]. According to data from the U.S. DOE, a single fuel cell electric bus (FCEB) in the U.S. has achieved a remarkable drive time exceeding 29,000 h. At the same time, nine other buses have surpassed the 20,000 h mark, albeit with notable repairs or replacement of their FC stacks [15].

PEMFCs are the most auspicious technologies in clean energy resources. This is due to their exceptional attributes, which include zero emissions, minimal operating temperature, rapid startup, and an impressive efficiency rate of 60% [16,17,18]. The primary domain of PEMFCs centers on transportation, primarily due to their potential to significantly mitigate environmental impacts, notably in curbing GHG emissions. Additionally, PEMFCs find applications in dispersed and compact power generation [19]. Many prominent automotive manufacturers exclusively focus on advancing PEMFC technology owing to its notable advantages, such as high power density and superior dynamic characteristics compared to other types of fuel cells. PEMFCs, falling under the category of low-temperature systems, are characterized by their utilization of a thin, penetrable polymeric membrane as a solid electrolyte [20].

PEMFC technology operates efficiently at temperatures as low as 80 °C, requiring minimal warm-up time. This efficiency is attributed to the use of a thin membrane and exceptionally lightweight platinum materials on either side of the permeable membrane [21]. The structure of PEMFC is shown in Figure 2. At the anode of a PEMFC, hydrogen ions (H₂) are supplied and subsequently undergo a process whereby they are separated into electrons and protons. These protons then migrate across the electrolyte to the cathode while the electrons proceed via a peripheral circuit, producing direct current. At the cathode, oxygen responds with the hydrogen ions, resulting in the formation of water. In this electrochemical process, platinum serves as anode and cathode electrodes. The results at the anode and cathode in the PEMFC are depicted by Equations (1) and (2):

$${\mathrm{H}}_2+2{\mathrm{H}}^{+}\to 2{\mathrm{e}}^{-}$$

(1)

$$0.5{\mathrm{O}}_2+2{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}\to {\mathrm{H}}_{2}O$$

(2)

The electrical efficiency of PEMFCs is 40–60% and can produce a theoretical voltage of 1.2 V; however, in a practical scenario, the voltage output ranges from 0.6 to 0.8 V. This capability enables PEMFCs to efficiently generate electrical power spanning from 5 kW to 250 kW, all while maintaining a compact and lightweight structural profile, rendering them suitable for a wide array of applications, notably in the automobile domain. After reaching the condition of technological readiness, numerous automotive organizations like Toyota, Honda, and Hyundai are commercially selling fuel cell electric vehicles. These presently guarantee the speed refueling time, driving reach, and durability of vehicles that will compete with conventional combustion engines. Importantly, they operate at relatively low temperatures, simplifying containment and minimizing thermal losses [22].

Though several benchmarks have been achieved, substantial endeavors are still required to lower costs and enhance durability. Extensive research has been conducted on energy consumption analysis and various fuel options, encompassing alternative fuel systems that promise further fuel technology advancements. These advancements can potentially decrease the use of petroleum in the transportation sector [23].

To ensure PEMFC technology can rival ICE vehicles in cost-effectiveness, longevity, and performance, the U.S. DOE has established PEMFC targets for MEA and catalysts, membrane electrolytes, and bipolar plates, as outlined in

Table 1. The 2025 DOE targets for MEA and catalysts used for PEMFCs [24].

Characteristics	Units	Status	Aim for 2025
Pt group metal (PGM)	rated G/kW	0.125:1.05 (150, 250 kPa)	≤0.10
Durability with cycling	hrs	4100	8000
Performance at 0.8 V	mW/cm2	306	300
Rated power		890, 1190 (150, 250 kPa)	1800
Demise in catalytic activity	%	40	≤40% initial loss
Deficiency at 0.8 A/cm2	mV	20	≤30
Constancy of electrocatalyst support	%	Not Available	≤40
Deficiency at 1.5 A/cm2	mV	>500	≤30
Mass activity	mgpgm at 900 more-free	0.6	0.44
Free catalyst action of PGM	A/cm2 at 900 more-free A	0.021	0.044

,

Table 2. The 2025 DOE targets for membrane electrolytes used for PEMFCs [24].

Characteristics	Units	Status	Aim for 2025
Max. working temperature	°C	120	120
Area-specific proton resistance at 120 °C and water partial pressure of 40 kPa	Ω cm2	0.054 (40 kPa) 0.019 (80 kPa)	0.02
Area-specific proton resistance at 95 °C and water partial pressure of 25 kPa	Ω cm2	0.027 (25 kPa) (at 80 °C 0.02 at 25 kPa, 0.008 at 45 kPa)	0.02
Area-specific proton resistance at 30 °C and water partial pressure of 4 kPa	Ω cm2	0.018	0.03
Area-specific proton resistance at −20 °C	Ω cm2	0.2	0.2
Max. H2 and O2 crossover	mA/cm2	1.9 and 0.6	2 and 2
Min. electrical resistance	Ω cm2	1635	1000
Mechanical durability	Cycles w/<10 sccm crossover	24,000	20,000
Chemical stability	Hours with <5 mA/cm2 crossover or <20% loss in OCV	614	500

and

Table 3. The 2025 DOE targets for bipolar plates used for PEMFCs [24].

Characteristics	Units	Present Status	2025
Weight of plate	kg/kW	<0.4	0.18
Plate H2 permeation	Std cm3/sec.cm2Pa @ 80 °C, 3 atm 100% relative humidity (RH)	<2 × 10−6	2 × 10−6
Corrosion at anode	µA/cm2	Not reaching the peak	<1 and no active peak
Corrosion at cathode	µA/cm2	<0.1	<1
Conductivity	S/cm	>100	>100
Flexural modulus	MPa	>34 (carbon plate)	>40
Elongation	%	20–40	40

. These targets were established in collaboration with the U.S. DRIVE Partnership. This coalition includes automotive and energy groups focusing on FC Technical Team input. The element-level targets provide valuable guidance for developers to assess their progress even before testing complete FC systems.

FC technology faces two primary challenges: cost and durability. The U.S. DOE has established ambitious targets for its 2020 FC system initiative. These objectives include achieving a cost of USD 40/kW, attaining a peak power efficiency of 65%, and reducing the platinum (Pt) content to 12.5 g/system. These targets aim to enable the yearly production of 500,000 automotive FC systems, as illustrated in Figure 3. A detailed cost breakdown analysis of PEMFC stacks reveals that catalysts, most likely referring to platinum catalysts, account for a substantial portion of the total cost, approximately 40%. This significant cost contribution can be attributed to various factors, including materials processing expenses and manufacturer markups. Specialized Pt catalysts, designed for optimal performance, often come at a significantly higher price than untreated Pt metal. Interestingly, the increased production scale has led to notable cost reductions in PEMFCs, with progress comparable to the advancements in lithium-ion batteries [25].

Moreno et al. pointed out that a substantial reduction of 30% in the membrane electrode assembly size could achieve the cost target of USD 40/kW by 2020. This reduction would lower the catalyst and membrane cost to under USD 4/kW and USD 1/kW. However, it is significant to note that the catalyst cost represents a substantial portion of the overall material price and may not decrease with an increase in the annual production of systems [26]. Therefore, a key challenge is to decrease the reliance on expensive Pt-based catalysts while ensuring the endurance of FC systems. To address this challenge, several strategies can be employed. These include finding catalyst materials with enhanced oxygen reduction reaction (ORR) activity, increasing the surface area of the catalyst, and minimizing mass transportation loss at peak current density. These approaches aim to decrease the volume of platinum required while maintaining the performance and longevity of the fuel cell. The evolution and projected cost of automotive fuel cells are depicted in Figure 3. The bars in the figure represent the cost of PEMFC stacks in USD and the total cost of the FCEV for the specified year. The figure also shows the cost distribution for various FC components, focusing on a yearly production scale of 500,000 FC systems.

Figure 3. Automotive FC costs [27].

Figure 3. Automotive FC costs [27].

The primary objective of this paper is to explore the recent advancements made in PEMFCs to reach the technical targets of the U.S. DOE, as carried out by various academic and industrial researchers. In addition, the various barriers and challenges involved in the commercialization of the PEMFC are also summarized. Exploring recent advancements in PEMFC technology and understanding the barriers and challenges in commercialization are necessary to drive progress toward the technical targets set by the U.S. DOE. This knowledge enables researchers and industry stakeholders to focus on developing cost-effective, durable, and efficient PEMFC systems, ultimately contributing to a sustainable and clean energy future.

This study establishes inclusion and exclusion criteria to guide the systematic review. The inclusion criteria encompassed literature published between 2010 and 2022, specifically focusing on PEMFCs and their integral components, including catalysts, membranes, gas diffusion layers, and bipolar plates. Research articles, review articles, and conference papers exploring the advancements, challenges, and prospects of PEMFC technology are considered. Additionally, literature aligning with the technical targets outlined by the U.S. DOE for PEMFC components and studies that offer valuable insights into the performance, durability, and cost aspects of PEMFCs were sought out. Furthermore, literature discussing alternative fuel systems, vehicle emissions, engine technology advancements, and eco-driving strategies in the context of PEMFCs is included to provide a comprehensive perspective. The exclusion criteria comprised literature published before 2010 or after 2022, studies unrelated to PEMFCs or their constituent parts, non-English language publications, patents, theses, and dissertations. These studies primarily focus on other types of fuel cells or energy storage technologies, and literature that did not contribute substantial insights or relevance to the topic of PEMFCs and their development was also excluded. These criteria were rigorously applied to select pertinent sources for the present investigation, ensuring the quality and relevance of the included studies.

2. U.S. DOE

The U.S. DOE is a federal agency established in 1977 with the primary responsibility of overseeing the nation’s energy policy. Its mission includes the promotion of energy efficiency and the advancement of renewable energy sources. Within the DOE, there are various offices and programs, each with specific areas of focus:

National Nuclear Security Administration (NNSA): This division is primarily tasked with managing and safeguarding the nation’s nuclear energy resources, ensuring their safety and security.

Office of Environmental Management (EM): The EM office oversees waste management and environmental cleanup activities at inactive or decommissioned facilities, particularly concerning past nuclear energy activities.

Office of Fossil Energy (FE): The FE office is pivotal in developing energy policies and regulations related to fossil fuels, namely, coal and natural gas. It also concentrates on advancing technologies to make fossil fuel use cleaner and more efficient.

Power Marketing Administrations (PMAs): These regional power administrations, operating under the DOE, are responsible for transmitting electric power generated from federal hydroelectric projects. They ensure the reliable distribution of electricity across different regions of the U.S.

These DOE offices and programs collaborate to address a wide array of energy-related challenges, encompassing energy security, environmental sustainability, and the promotion of clean and sustainable energy sources. The DOE is a cabinet-level association with significant energy and national security-related missions. The foundation of the DOE goes directly back to World War II and the Manhattan Project. The Manhattan Project was a top-secret program that began efforts to produce and stockpile U.S. nuclear weapons. Today, energy authorities oversee laboratories that were once essentially responsible for producing weapons of mass destruction and implementing strategies to strengthen U.S. energy resources. The DOE promotes U.S. national, economic, and energy security by implementing nuclear, fossil fuel, and alternative energy strategies. The DOE is tasked with advancing science and technology in all energy sectors and purifying the country’s nuclear weapons complex.

Table 4. Technical targets for MEA and catalysts [21,28,29,30].

Characteristics	Units	2020 Targets	Current Status	2025 Targets
Total content of PGM	g/kW rated	0.125	0.125	≤0.10
Durability with cycling	Hours	5000	4100	8000
Performance at 0.8 V	mW/cm2	300	306	300
Performance at peak power	mW/cm2	1000	890	1800
Mass loss	%	<40	40	≤40% loss of initial
Performance loss	mV	<30	20	≤30
Electrocatalyst support stability	% mass activity loss	<40	40	≤40
Loss in performance	mV	<30	>500	≤30
Activity of mass	mgpgm @ 900 mVIR-free	0.44	0.6	0.44
Free catalyst activity of PGM	A/cm2 @ 900 mVIR-free A	0.044	0.012	0.044

,

Table 5. Technical targets for membranes [21,28,29,30].

Characteristics	Units	2020 Targets	Current Status	2025 Targets
Max. operating temperature	°C	120	120	120
Area-specific proton resistance at 120 °C and water partial pressure of 40 kPa	Ω cm2	0.02	0.054	0.02
Area-specific proton resistance at 95 °C and water partial pressure of 25 kPa	Ω cm2	0.02	0.027	0.02
Area-specific proton resistance at 30 °C and water partial pressure of 4 kPa	Ω cm2	0.03	0.018	0.03
Area-specific proton resistance at −20 °C	Ω cm2	0.2	0.2	0.2
Max. O2 crossover	mA/cm2	2	0.6	2
Max. H2 crossover	mA/cm2	2	1.9	2
Min. electrical resistance	Ω cm2	1000	1635	1000
Mechanical durability	Cycles w/<10 sccm crossover	20,000	24,000	20,000
Chemical stability	Hours with <5 mA/cm2 crossover or <20% loss in OCV	>500	614	500

and

Table 6. Technical targets for bipolar plates [21,28,29,30].

Characteristics	Units	2020 Targets	Current Status	2025 Targets
Weight of the plate	kg/kW	0.4	<0.4	0.18
H2 permeation in the plate	Std cm3/sec.cm2.Pa @ 80 °C, 3 atm 100% Relative Humidity (RH)	<1.3 × 10−14	<2 × 10−6	2 × 10−6
Corrosion anode	µA/cm2	<1 and no active peak	no active peak	<1 and no active peak
Corrosion cathode	µA/cm2	<1	<0.1	<1
Conductivity	S/cm	>100	>100	>100
Flexural modulus	MPa	>25	>34	>40

provide a comprehensive overview of the targets set by the U.S. DOE for PEMFC components for 2020 and 2025. These targets have been established in collaboration with the U.S. DRIVE Partnership, a coalition that includes locomotive and power organizations. The FC Technical Team within this partnership has played a significant role in shaping these guidelines. These component-specific targets are essential benchmarks for individual FC component developers. They offer a framework for evaluating progress and performance without testing complete FC systems.

3. Recent Developments in Fuel Cell Technologies

The U.S. DOE has invested in various research and development projects (R&D) to meet the ambitious FC performance targets. These projects address critical aspects of FC components’ cost, durability, and overall performance. One critical area of focus for the DOE’s efforts is membrane R&D. This strategic emphasis on membranes aims to enhance the cost-effectiveness and durability of PEMFC systems. It is worth noting that the cost of components within PEMFC stacks currently falls short of the long-term cost targets set by the U.S. DOE. For instance, consider the Toyota Mirai PEMFC system as an example. It is projected to cost approximately USD 233/kW to mass produce 100 stacks annually.

In contrast, the U.S. DOE has set an ambitious goal of achieving a system cost of just USD 30/kW by 2025. This significant cost reduction is critical in making FC technology more competitive and widely accessible. To attain this target, ongoing research and development initiatives are crucial, particularly in improving the efficiency and cost-effectiveness of PEMFC components [31,32]. The U.S. DOE established the FC Performance and Durability (FC-PAD) consortium in 2015. This consortium brings together a diverse and multi-disciplinary team with a specific mission: to enhance PEMFCs’ PAD. The elementary goal of this collaborative effort is to work towards achieving the transportation cost targets set by the U.S. DOE.

The FC-PAD consortium represents a significant R&D initiative to advance PEMFC technology. By improving the performance and durability of these fuel cells, the consortium contributes to the broader objective of making fuel cell-based transportation more cost-competitive and sustainable. The multi-disciplinary approach of FC-PAD likely involves experts from various fields, including materials science, engineering, chemistry, and energy technology, all working together to address the challenges associated with PEMFCs. As a result, significant advances have been made in developing PEMFC components, and R&D has been conducted in PEMFC performance.

Recently, a cost assessment of automotive fuel cells has revealed that the cost of the membrane can represent a substantial portion of the total charge of the FC pack for FCEVs, particularly during lower production. In this analysis, it was projected that at low production volumes, such as 1000 systems per annum, the membrane’s cost could account for as much as 45% of the overall price of the FC stack. This finding underscores the significance of decreasing the cost of the membrane component, as it plays a pivotal role in the system’s cost structure. Addressing membrane costs and making advancements in membrane technology and manufacturing processes makes it possible to make FCEVs more economically viable, mainly when production volumes are limited.

3.1. Advancements in MEA

In 2017, the U.S. DOE established a specific technical target for PGM usage in fuel cells. The goal was to reduce the total loading of PGMs to less than 0.125 mg/cm² by 2020. This reduction in PGM loading aimed to make FC technology more cost-effective and sustainable by minimizing costly and rare Pt-based catalysts. Additionally, the DOE set a target activity level for the reversible hydrogen electrode (RHE) of 0.44 A/mg_PGM for the PGM catalyst. This target activity level is associated with a current density of 44 mA/cm² for the PGM-free catalyst. These specifications were part of the DOE’s efforts to enhance the performance and efficiency of FC catalysts while reducing their reliance on precious PGM [33]. Although the Pt load at the anode can be easily reduced to below 0.05 mg/cm² [34], the electrode catalyst’s stability and performance at the cathode is significant. Under acid and corroding conditions at the cathode of a fuel cell, platinum (Pt) nanoparticles tend to aggregate and grow over time. This phenomenon leads to a reduction in the available surface area of the Pt catalyst, which can negatively impact the performance and efficiency of the fuel cell.

Though some research studies have successfully met the 2020 targets set by the U.S. DOE for reducing the Pt loading in fuel cells, commercial fuel cells used in vehicles have not yet achieved these targets. Specifically, commercial fuel cells typically operate with a platinum loading of approximately 0.35 mg_Pt/cm². The challenge of reducing platinum usage while maintaining or improving FC performance remains a significant focus of R&D efforts within the FC industry. Reducing platinum loading is essential for making FC technology more cost-effective and competitive for widespread adoption in various applications, including transportation [35].

Over the last decade, exceptional advances have been made in the initial ORR activity of the non-PGM catalyst, but the stability is significantly lagging. Today, the volumetric ORR activity of a 0.9 A/cm² carbon catalyst layer (CCL) is maintained in the membrane electrode assembly (MEA) for less than a day [36,37], whereas the vehicle must last more than ten years. State-of-the-art non-Pt group metal (non-PGM) catalysts in FC technology typically consist of active sites composed of transition metals, nitrogen, and carbon. One of the most widely acknowledged degradation mechanisms for these non-PGM catalysts involves the active sites targeted and attacked by the byproduct of the ORR, hydrogen peroxide (H₂O₂) [38]. This degradation mechanism can substantially impact the long-term performance and endurance of non-PGM catalysts in fuel cells. Researchers are actively investigating ways to mitigate this degradation and improve the stability of non-PGM catalysts for more reliable and long-lasting FC operation [39].

A significant dual challenge exists to advance FC technology: the need to enhance activity and stability by orders of magnitude concurrently. Specifically, this implies achieving an initial activity at 0.9 V of 90–270 A/cm² for the CCL or more than 0.4 A/cm² for the MEA. This level of improvement is notably more demanding than the U.S. DOE 2025 target, which aims for a MEA activity of more than 0.044 A/cm². Meeting these stringent requirements for increased activity and stability represents a formidable challenge for researchers in the field [33].

Meeting the challenging targets for non-PGM catalysts in fuel cells may necessitate a novel material design approach that differs from the current M/N/C catalysts. Presently, PGM-based catalysts demonstrate impressive performance metrics, such as high mass activity, in various testing environments:

• In half-cell testing, PGM-based catalysts have exhibited a high mass activity, with [40] reporting more than 13 A/mg_Pt at 0.9 V.
• In H₂-O₂ fuel cells, an MA of 1.77 A/mg_Pt at 0.9 V has been achieved [41], surpassing the DOE target of 0.44 A/mg_Pt.

However, it is essential to note that PGM-free M-N-C catalysts used in FC membrane electrode assemblies (MEAs) have demonstrated impressive current densities, exceeding 30 mA/cm² at 0.9 V [42]. Although this performance surpasses the DOE target of 44 mA/cm², it is essential to acknowledge that PGM-free catalysts typically require a higher loading than commercial Pt/C catalysts. The comparison spotlights the need for continuous R&D to bridge the performance gap between PGM-based and PGM-free catalysts while addressing factors like catalyst loading to make non-PGM catalysts more competitive in FC applications.

Platinum alloys added on a porous carbon layer are the preferred technology for PEMFCs, because they provide high performance and extended operational lifespans. These alloys are often represented as a slurry of Pt and Co precipitated on a high-surface area carbon (HSC) layer, as demonstrated in various studies [43,44,45]. For example, in the case of the catalyst used in the Toyota Mirai, this modeled catalyst configuration has been employed, resulting in a stack achieving an impressive energy output of 1095 mW/cm² [46,47]. In a FC stack with a power output of approximately 100 kW, about 30 g of Pt were required [27]. Based on this factor and the active area, this translates to a platinum stacking density of 0.32 mg/cm² or 0.29 g/kW_net.

Furthermore, it is worth noting that Tu et al. conducted research indicating that adding tungsten (W) to Pt-Cu catalysts improved their stability after 3000 potential cycles. However, the performance of the catalysts did diminish significantly after 5000 cycles [48]. This highlights the importance of conducting adequately long endurance tests to assess the robustness of the ORR catalyst. It is suggested that the potential cycles proposed by the DOE (10,000 cycles) may not indicate the catalyst’s long-term durability, as indicated by Tu et al.’s findings.

Ganesan and Narayanasamy have developed a catalyst using a synthesis method that yields Mass-Specific Power Density (MSPD) values exceeding 5 mWµg⁻¹Pt at potentials greater than 0.65 V [49]. This achievement positions this catalyst as a promising candidate to meet the U.S. DOE 2020 target for FC performance. He et al. introduced a Fe-N-C catalyst obtained from ZIF-8 with atomically dispersed FeN4 sites. Conducted tests demonstrated the superior performance of this new Fe-N-C catalyst, achieving a current density of 0.004 A/cm² at 0.87 V in a voltage vs. irreversible voltage-free (ViR-free) condition [50]. This result aligns with the DOE target of 0.044 A/cm² at 0.9 V. Under conditions of H₂ air at one bar pressure, current density reached 75 mA/cm² at 0.8 V.

Currently, platinum-based electrocatalysts are the preferred choice for PEMFCs owing to their high ORR activity and permanency in the acid and corroding surroundings of the PEMFC cathode. The U.S. DOE has established an ORR mass activity (MA) target of over 0.44 A/mg_PGM at 0.9 V in a PEMFC MEA. Numerous Pt-based electrocatalysts have met or exceeded this target during the beginning-of-life (BOL) phase [51,52].

The impact of phosphoric doping levels in the membrane of a high-temperature PEMFC was investigated. The authors found that current density increased from 1.011 A/cm² to 1.372 A/cm² when the doping level increased from 5 to 11 [53]. Bae et al. used a Nafion membrane of the linear type with a Pt loading of 0.2 mg/cm² and found that the cell performance was significantly improved, especially when the voltage was below 0.6 V of the planar membrane. The quantity of Pt loading was generally based on the type of application. In the electrodes of fuel cells, the typical Pt loading has historically ranged from approximately 0.4 to 0.8 mg_Pt/cm² [54]. However, the U.S. DOE instituted a more stringent target of 0.125 mg_Pt/cm² for 2020 and 2025 to promote cost reduction and efficiency improvements.

Research conducted by Kongkanand [55] and Han et al. [56] focused on analyzing the catalyst’s behavior of dealloyed Pt-CO, Pt-Ni, and Pt-Cu within MEA testing environments. Their findings exposed that the unalloyed Pt-CO exhibited a superior power density over the Pt-Ni catalyst. This research is significant in identifying catalyst materials that can enhance the efficiency and performance of fuel cells while potentially reducing the reliance on expensive platinum materials. Improving catalyst behavior makes it possible to work towards achieving the DOE’s stringent Pt loading targets and advancing the technology.

The Pt-Ni catalyst’s power density was superior to the Pt-Cu catalyst. The Pt-CO catalyst MEA has shown the ability to produce 1 kW with 0.16 g of Pt loading, which is closer to the U.S. DOE target of 0.125 gPGM/kW. The effect of Pt loading and particle radius was considered in the investigation by Carcadea et al. [57], because these are the critical parameters to improve the electro-catalytic activity and the entire performance of the PEMFC. Concerning the Pt loading, the current trend in developing catalyst layers for the PEM FC has been reduced to 0.125 mg Pt/cm². The U.S. DOE has set targets for the catalyst referred to at the MEA level: an initial MA of more than 0.44 A/mg_Pt at 0.9 V vs. RHE and less than 40% activity loss after 30,000 voltage cycles [33]. The operating current density of 1.6 A/cm² at an output voltage of 0.65 V is considered achievable for commercial applications, based on the knowledge gathered from various researchers. However, in alignment with the U.S. DOE targets set before 2020, there is a more ambitious goal of achieving an operating current density of 3.0 A/cm² at an output voltage of 0.8 V. It is worth noting that there is a noticeable technical gap between the current operating current density and the DOE target. Increasing the operating current density is deemed crucial for advancing FC technology. However, one of the limitations in achieving higher current density levels is often related to the insufficient supply of oxygen to the catalyst layer (CL), as observed in the research conducted by [58]. Improving the oxygen supply to the CL and addressing related challenges is a critical area of focus for researchers to bridge the technical gap and meet or exceed DOE targets for FC performance.

Haragirimana et al. researched PEMFCs using a mixture of four sulfonated polyacl aryl ether sulfone (SPAES) copolymers with varying sulfonate levels. They developed enhanced mechanical, thermal, oxidative, and hydrolytic stability membranes. Specifically, the B4 membrane exhibited notable characteristics like a high proton conductivity of 203.1 mS/cm at 90 °C and 169.2 mS/cm at 94.1% relative humidity, an impressive current density of 1050 mA/cm², and a strong power density of 467.98 mW/cm² [59]. This research demonstrated the potential for these improved membranes to enhance the performance of PEMFCs. Additionally, Suzuki et al. [60] conducted a study that focused on the pore structure and its impact on mass transfer in the electrode of fuel cells. Their findings likely contribute to a deeper understanding of how the internal structure of FC components, such as electrodes, can influence mass transport processes, which is crucial for optimizing FC performance.

Kang et al. [61] researched PEMFCs and investigated the degradation rate of these fuel cells to temperature. They observed that initially, the degradation rate of the PEMFC was low, but it later increased rapidly over time. This understanding of temperature-dependent degradation can help to inform strategies for mitigating degradation and improving the long-term stability of PEMFCs. Sutradhar et al. [62] developed a sulfonated poly phenylene benzo phenome (SPPBP) membrane using C-C coupling polymerization. This membrane exhibited high thermal properties, chemical stability, and a proton conductivity of 92.90 mS/cm, making it a potential candidate for enhancing PEMFC performance. Neethu et al. [63] explored a novel PEM design incorporating activated carbon extracted from coconut shells (ACGS). This design aimed to improve proton exchange through high porosity, superior specific surface area, and the incorporation of natural clay. The use of ACGS also contributed to reducing the overall cost of the membrane to approximately USD 45/m². Manufacturers seeking to meet the U.S. DOE targets for PEMFC membranes have proposed a consistent approach. This involves producing composite membranes with low equivalent weight (EW) and short side chains. The target is to reduce the EW value to 600–800 for membranes with high proton conductivity. This approach aligns to enhance the efficiency and cost-effectiveness of PEMFCs.

According to the latest 3 M progress report from 2014, the EW value of the nanofiber-reinforced multi-acid side chain membrane reached 725, and the thickness of the membrane decreased to 14–20 µm [64]. However, the durability and resistance of the membrane at 80 °C and 120 °C were slightly less than the 2020 DOE targets. The impedance and H₂ permeation of the membrane at 20 °C and 30 °C were higher than the 2020 DOE targets. The utilization of graphene oxide (GO) was also investigated, and MEA made with GO Nafion showed excellent cell performance of 1.27 A/cm² at 100% relative humidity compared to 0.435 A/cm² for the pristine Nafion membrane [65]. With some modification in the graphene increase, the proton conductivity of the Nafion membrane increased by five times more than the pristine Nafion membrane, and a power and current density of 300 mW/cm² and 760 mA/cm² at 70 °C were achieved [66,67].

3.2. Advancements on GDL

The GDL in PEMFC has numerous roles, such as acting as a connection bridge between the MEA and the bipolar plates (electrically and physically), offering a route for gas diffusion and drainage, and providing mechanical support to the membrane electrode assemblies. Though GDL plays a multifaceted role in PEMFCs, it is noteworthy that the advancements achieved in this component toward meeting the stringent targets set by the DOE are not notably substantial in quantitative terms.

Su et al. [68] developed various types of GDLs using Nafion, PVDE, FEP, PBI, and PBI/PVDF and observed that the PVDE and PTFE offer better performance than other types. Their current and power densities are 0.52 A/cm² and 0.61 A/cm² at 0.6 V and 160 °C, which was 120% higher than Nafion and PBI-based GDL. The PEMFC model was analyzed using a multi-serpentine flow field configuration. Specifically, they examined the performance of PEMFCs with 3- and 9-pass multi-serpentine flow field designs using COMSOL 5.5A software. Their findings indicated that the 6-pass serpentine flow field configuration yielded the highest power output and current density. At operating conditions of 1.4 bar pressure and an applied voltage of 0.4 V, this configuration achieved a maximum power density of 0.4761 W/cm² and a maximum current density of 1.1902 A/cm². These results suggest that the 6-pass serpentine flow field design was the most efficient in generating electrical power from the PEMFC under the specified operating conditions [69]. This type of analysis can provide valuable insights for optimizing FC designs to enhance their performance and efficiency.

The impact of PTFE deposition in the GDL was investigated by Chen et al. [70]. A 10% PTFE incorporation is recommended as an optimal value for HT PEM, since it has been shown that a lower percentage of PTFE loading leads to improved cell performance yet has a detrimental influence on the mechanical qualities of the GDL. The qualities of GDLs used in HTPEM fuel cells need more development before they can be optimized.

The GDL of carbon nanotubes (CNT) was developed, whose thickness was only one-third of the MEA made with conventional GDL. The volume and weight-specific power density of the GDL was increased to 15,600 W/L and 9660 W/L. The authors concluded that high cell performance was obtained for the thinner GDL layer [71]. This was in line with the conclusion made by Chun et al. [72], who studied the impact of the GDL thickness layer through numerical simulation and found that the cell’s performance was low for the thicker GDL, as shown in Figure 4. This was because the saturation of the liquid increased rapidly, whereas the concentration of oxygen near the catalyst layer decreased as the thickness of the GDL increased.

MPL-coated GDL containing hydrophilic CNT was developed, and it was observed that the MPL-coated GDL with 4% CNT offers higher performance in low and high humidity conditions [73]. The U.S. DOE is a pioneer in developing the PEM fuel cell’s technological targets and components. According to recent research [33], the U.S. DOE has outlined technical targets for bipolar plates, including cathode and anode corrosion resistance, electrical conductivity, and area-specific resistance. Remarkably, these targets were already met by 2015 [74]. Nevertheless, there are specific design parameters that demand further enhancement. Of particular note is the cost aspect, which necessitates a reduction from the current USD 7/kW to a demanding target of USD 2/kW by 2025. This cost reduction presents a notable challenge in the field.

3.3. Advancements in Bipolar Plates

An interdigital flow field model for PEMFCs was investigated using the ANSYS 14.5 software package. The study specifically focused on examining the effect of various landing-to-channel widths. The findings indicated that the optimum power density achieved at a specific aspect ratio (L*C) of 2.2 was 0.4086 W/cm². This optimal performance was obtained at a temperature of 323 K, a voltage of 0.55 V, and an operating pressure of 2 bars [75]. This research highlights the importance of flow field design and geometry in influencing the performance of PEMFCs. By optimizing the flow field configuration, researchers can enhance fuel cells’ power density and overall efficiency, which is crucial for their practical application in various industries.

The use of porous carbon inserts with high porosity levels ranging from 80% to 90% in both uniform and zig-zag pin-type flow field designs for PEMFCs was explored. The aim was to assess the impact of these inserts on the fuel cell’s performance. The research demonstrated that including porous carbon inserts led to significant improvements in power densities. Specifically, in a 25 cm² PEMFC, the power density increased by 9.5% when using these inserts compared to a conventional serpentine flow field design. In a larger 70 cm² PEMFC, the power density improvement was even more substantial, with a 12.1% increase for the uniform pin type and a remarkable 20.6% increase for the zig-zag pin type compared to the conventional design [76]. These findings highlight the potential benefits of using porous carbon inserts in flow field designs to enhance the performance of PEMFCs. Improved power densities are crucial for making FC technology more competitive and efficient for various applications. In a similar vein, quoting the role of nanostructured porous graphite is quite significant here [77].

A new zig-zag flow channel with a cooling plate of 150 mm × 150 mm and a machined zig-zag flow channel with 37 coolant inlet was examined. A cooling plate thickness of 2 mm, channel width of 2 mm, rib width of 2 mm, channel depth of 1 mm, and channel diameter of 1.33 mm were considered. The thermal performance of the zig-zag model was increased by 5–23% [78]. Tanaka et al. suggested using the metal sheet GDL of the SS-316l with the simulation software STARCCM+ (Version 10.04.011, CD-adapco, N.Y.) and found that metallic GDL gives adequate strength and thickness to the structure of GDL. The risk of corrosion is one drawback of using the metallic GDL, which shortens the cell’s lifetime [79].

The electrochemical characteristics of the 316L SS with carbon films like C-Cr-N, C-Cr, and pre-carbon in a modeled PEMFC were analyzed. They found that the C and C-Cr-N films’ ICR values were more advanced than the U.S. DOE target of 20 mUcm² [80]. The ICR value of the C-Cr film was within the satisfactory range. The inclusion of carbon nanotubes as a material for GDL will significantly improve the performance and durability because of their high transport rates due to the inherent smoothness of the nanotubes [81].

A comprehensive analysis concerning potential candidates aligned with the DOE 2020 targets was presented. This study identified carbon-based and metal nitride coatings as viable candidates [82]. Achieving mass production of bipolar plates through an ‘in-line’ process has been explored, involving rolling and stamping techniques [83,84]. Furthermore, Haye et al. [85] made a notable advancement by applying a 50 nm chromium nitride coating onto a 316L stainless steel foil. This coating was meticulously optimized to align with DOE specifications, particularly regarding interfacial contact resistance (ICR) and corrosion resistance. The results included an interfacial contact resistance (ICR) of 8.4 mΩ/cm² at 100 N/cm² and a corrosion rate of 0.10 μA/cm² in a 0.6 M H₂SO₄ solution at 0.48 V. Furthermore, these materials exhibited exceptional properties even after undergoing high deformation, allowing for the stamping of bipolar plates from coated foils.

The chemical stability and electrical conductivity of various bipolar plate materials were investigated. These materials included SS304, SS316L, and nickel-based alloys 6020, 3127, and 5923. The interfacial contact resistance (ICR) measurements revealed a ranking order for the materials under a pressing force of 220 N/cm² as follows: SS304 > SS316L > BMA5 graphite bipolar plate > 6020 NiBs > 5923 NiBs ≈ 3127 NiBs > XM9612 graphite bipolar plate [86]. According to Leng et al. [82], it was observed that conventional uncoated stainless steel materials failed to meet the DOE targets concerning corrosion resistance and ICR for bipolar plates. In a study by Lin et al. [87], a high-density columnar single-phase Pt3Fe coating was applied to a 316 SS substrate. This Pt₃Fe coating exhibited exceptional electrical conductivity and corrosion resistance, aligning with DOE requirements and enhancing the performance of PEMFCs. Furthermore, Ni-Mo and Ni-Mo-P alloys were introduced to coat AISI-304 SS substrates through the electrodeposition method [88].

Applying Ni-Mo and Ni-Mo-P coatings led to a significant reduction in ICR, with ICR values approximately eight times lower than SS substrates under a compaction force of 220 N/cm². A tantalum coating with a thickness of 30 μm was employed on SS316l bipolar plates using CVD. A long-term polarizing test conducted at a clamping pressure of 140 N/cm² achieved an ICR value ranging from 22.34 to 32.6 mΩ.cm² [89]. Various research efforts have been dedicated to enhancing the corrosion protection of metal bipolar plates and reducing surface contact resistance, as demonstrated in the studies cited in [90,91,92]. Another critical approach involves the modification of bipolar plate surfaces to mitigate interfacial contact resistance and corrosion current density, thereby enhancing the performance and lifespan of PEMFCs [93]. Additionally, the airbrushing technique was utilized to coat stainless steel bipolar plates, achieving current densities ranging from 0.11 μA/cm² to 0.54 μA/cm², thus meeting the DOE target of less than 1 μA/cm² [94].

A spraying method was employed to coat the samples to a thickness of 270 nm and surface roughness of 80 nm, and it was found that using the arc process in thermal spraying provides good metal protection, particularly in an aquatic environment [95]. The thermal spray was used on the metal plate with thicknesses of 0.6 nm and 0.8 nm and achieved an I_corr value of 1.10 × 10 A/cm², higher than the DOE technical targets [96]. The corrosion kinetics and coating structure of the Zr-C/a-C film were investigated utilizing electrochemical impedance spectroscopy. The authors discovered that multi-layered Zr-C/a-C film possesses higher charge transfer resistance than the SS316l with enhanced corrosion resistance. An ICR value of 3.63 mU/cm² and a corrosion current value of 0.49 mA/cm² were achieved for the Zr-C/a-C film bipolar plate, which met the DOE 2020 targets [97].

Despite the conventional graphite and metal-based plates, polymer composites offer the potential to reduce the weight and cost of bipolar plates while maintaining mechanical strength. However, achieving the required electrical conductivity while balancing mechanical properties remains challenging [98].

Table 7. Summary of recent developments in PEMFC components.

Authors	Components	Observations	Conclusions
Su et al. [68]	GDL	At an operating voltage of 0.6 V and a temperature of 160 °C, the power density reached 0.61 W/cm2, with a corresponding current density of 0.52 A/cm2.	The obtained power and current density value of the GDL are higher than the 2020 and 2025 DOE targets.
Gago et al. [96]	Bipolar plate	An Icorr value of 1.10 × 10 A/cm2 was achieved.	The obtained Icorr value was higher than the DOE technical targets.
Lee et al. [65]	Membrane	A current density of 1.27 A/cm2 at 100% RH was achieved.	The obtained current density value was higher than the DOE technical targets of 2020 and 2025.
Muthukumar et al. [69]	GDL	The power and current density are 0.4761 W/cm2 and 1.1902 A/cm2 at 1.4 bar pressure and 0.4 V.	The obtained power and current density value of the GDL are higher than the 2020 and 2025 DOE targets.
Gercel et al. [99]	Membrane	The membrane’s power density was assessed at 23.7 mW/cm2 when tested at 80 °C.	The obtained power density value of the membrane does not meet U.S. DOE 2020 and 2025 targets.
Vinothkannan et al. [66]	Membrane	A power density of 300 mW/cm2 was achieved at 70 °C.	The obtained power density values met U.S. DOE 2020 and 2025 targets.
Bi et al. [97]	Bipolar plate	An ICR value of 3.63 µ/cm2 and corrosion current value of 0.49 mA/cm2 were achieved for Zr-C/a-C film.	The ICR value of the bipolar plate met the DOE 2020 targets.
He et al. [50]	Catalyst	A current density of 0.004 A/cm2 at 0.87 ViR-free was achieved.	The obtained current density value did not meet DOE targets of 2020 and 2025.
Li et al. [53]	Membrane	A current density of 1.372 A/cm2 at a cell voltage of 3 V was achieved.	The obtained value met the DOE targets of 2020 and 2025.

shows the summary of recent developments in PEMFC components.

The data analysis from the table reveals an essentially promising performance of various fuel cell components. The GDL, bipolar plates, and most membrane evaluations have consistently exceeded or met DOE targets for 2020 and 2025. However, a notable exception exists in the catalyst case, for which the reported current density value did not meet the DOE targets. These findings underscore the potential for significant advancements in fuel cell technology, with particular components exhibiting impressive capabilities to meet or even exceed critical performance targets set by the Department of Energy.

4. Current Status and Technical Barriers

Overall, the primary challenge is reducing dependence on expensive PGM materials, improving the performance, stability, and endurance of catalysts and membranes, and bridging the performance gap between Pt-based and non-Pt catalysts to make PEMFC technology more competitive and cost-effective. Endurance is yet another significant hurdle to the global implementation of the PEMFC. It is confounding to simultaneously encounter the U.S. DOE endurance and price goals, as modern fuel cells become less durable as the load on expensive electrode catalysts is reduced. The Toyota Mirai FCEV is priced at around USD 60,000, even after factoring in inducements [100]. This pricing is notably higher than that of conventional gasoline vehicles.

Additionally, an FCEB costs approximately USD 1 million. To address this challenge, as recommended by Seselj et al. [101], research and development efforts should focus on finding alternative catalyst materials that are abundant, cost-effective, and exhibit comparable or better performance than Pt-based catalysts. This includes exploring non-PGM catalysts such as transition metal oxides, carbon-based materials, and metal-free catalysts. Enhancing non-Pt catalysts’ catalytic activity and stability can be achieved through various methods, such as alloying, doping, nanostructuring, and surface modification. These techniques can improve the catalyst’s performance and durability and reduce degradation over time. Developing advanced ion-conducting membranes with improved proton conductivity, chemical stability, and mechanical strength is essential [102]. Additionally, research should focus on materials like high-temperature polymer electrolytes, composite membranes, and anion exchange membranes to enhance the overall performance and durability of the fuel cell system [103].

Optimizing the integration of catalysts, membranes, and other components within the fuel cell system is crucial. This involves designing efficient gas diffusion layers, flow field plates, and electrode structures to enhance mass transport, reduce overpotentials, and improve overall system performance [104]. Exploring innovative manufacturing techniques like additive manufacturing (3D printing) can enable the production of complex geometries, reduce material waste, and enhance the performance and cost-effectiveness of catalysts and membranes [92]. Developing strategies to mitigate catalyst and membrane degradation is essential for improving the long-term stability and endurance of PEMFCs. This includes understanding degradation mechanisms, optimizing operating conditions, and implementing effective catalyst and membrane regeneration techniques. Increasing the production scale and implementing cost-effective manufacturing processes can significantly reduce the overall cost of PEMFC technology [38]. This involves optimizing material usage, streamlining manufacturing processes, and leveraging economies of scale [105]. By pursuing these strategies, researchers and engineers can work towards reducing the dependence on expensive PGM materials, improving the performance, stability, and endurance of catalysts and membranes, and bridging the performance gap between Pt-based and non-Pt catalysts [106]. This will make PEMFC technology more competitive and cost-effective, enabling its broader adoption in various applications.

Regarding durability, the DOE testing revealed that the Toyota Mirai completed a 3000 h driving test. However, it faced challenges during DOE Accelerated Stress Test (AST) protocols. After undergoing 5000 cycles, the vehicle’s performance experienced a significant decline, and the cathode’s catalyst layer (CL) thickness decreased from 10 to 3 μm in the 1.0–1.5 V cycle AST [107]. However, this is common, and researchers are working to address it. Scientists are developing better technologies to address issues such as durability, increasing driving range, weight reduction, cost reduction, and charging time. The design of a battery system from lithium-ion cells presents particular challenges to thermal management in integrated hybrid PEMFC systems [108]. Proper thermal management can help improve the durability of the battery. Accurately predicting strength and durability is a fundamental requirement, especially when developing electric vehicles with a heavy battery pack that alters the mass distribution and creates different loads [109]. Engineers typically face three significant challenges relating to strength and durability analysis: knowing the loads, understanding specific stresses and strains, and accounting for material properties. Addressing these challenges can help improve the durability of the battery.

The set lifetime targets for FCEVs and FCEBs are 8000 h and 25,000 h, respectively. The current status indicates a cost of USD 50/kW for 100,000 units and USD 45/kW for 500,000 units per year, which is approximately 50% higher than the ultimate target of USD 30/kW. The DOE targets for 2020 and 2025 are USD 30/kW for FCEVs and USD 600,000 for FCEBs. Furthermore, data from various FC developers suggest that equipment costs are approximately six times higher than the target of USD 1000/kW [110]. For micro combined heat and power (mCHP) applications, Panasonic has succeeded by developing 700 W units with a lifetime of 90,000 h, surpassing the DOE’s 2025 target of 6000 h [111].

Eventually, PEMFC components, encompassing the membrane, catalysts, and bipolar plates, must exhibit robustness to endure the challenging operational conditions inherent in their applications. The longevity and durability of these components are imperative for ensuring the commercial viability of PEMFC technology. Several critical factors influence the overall durability of PEMFCs. Catalyst decay, marked by the progressive degradation of catalyst materials over time, is a prime concern, directly impacting performance. The lifetime of the proton exchange membrane is intrinsically linked to the endurance of catalysts, electrode plates, gas diffusion layers, and efficient water management [103]. Contaminants from the ambient environment can exert deleterious effects on PEMFC performance, emphasizing the need for stringent fuel purification protocols [112]. Elevated operating temperatures threaten component stability and functionality, warranting effective thermal management strategies. Inadequate or excessive water levels can curtail performance and power output, necessitating precise water management techniques [113]. To bolster durability, advancements in component design aimed at heightened resilience and resistance to degradation are pivotal. Durability testing protocols, providing insights into PEMFC lifetime degradation, are instrumental for in-depth evaluation and analysis. Effective thermal management and water management techniques, such as microporous layers, have demonstrated their capacity to enhance durability [114].

Furthermore, diligent fuel purification practices safeguard against impurities’ adverse impact on PEMFC performance. Mitigating the repercussions of harsh operating conditions on electrode degradation represents an additional avenue toward enhancing the overall durability of PEMFCs [112]. In summation, the assurance of PEMFC component durability remains an indispensable prerequisite for attaining commercial viability, and the multifaceted interplay of catalyst decay, membrane decay, contaminants, temperature, water management, and fuel purification underscores the significance of proactive strategies for improvement.

5. Enhancing PEMFC Lifetime for Commercial Viability

Recent significant developments have been focused on overcoming a pivotal challenge hindering the widespread commercialization of PMEFCs, namely, extending the lifetime of proton exchange membranes (PEMs) [115]. The longevity and durability of PEMs are instrumental in ensuring the commercial viability of PEMFC technology, particularly as stringent U.S. Department of Energy (DOE) targets for heavy-duty vehicle applications demand lifetimes of 30,000 h by 2030 and an ambitious 60,000 h by 2050 [116]. One remarkable field advancement is developing a groundbreaking lifetime prediction method for PEMFCs. This innovative approach leverages current degradation laws to optimize the utilization of degradation information tied to current density. Doing so provides a wealth of data indispensable for the comprehensive evaluation and in-depth analysis of PEMFC lifetime degradation [117]. Complementing this, establishing durability testing protocols tailored to PEMFCs has proved instrumental in rigorously assessing their long-term resilience. These well-defined protocols provide an invaluable means to gain insights into the complex factors influencing PEMFC lifetime degradation, thereby enabling a more holistic approach to evaluating and analyzing this critical aspect [118].

Material innovation is a primary principle in the quest for enhanced durability. This involves ongoing research and development efforts to create superior materials that can significantly contribute to extending PEMFC lifetimes. Novel materials with enhanced properties like improved chemical stability, enhanced mechanical strength, and increased resistance to degradation promise to elevate PEMFC components to new levels of longevity and performance [107]. Simultaneously, system engineering approaches play an integral role in fortifying the durability of PEMFC components. Skilled engineers are actively engaged in the design and optimization of robust systems. These systems are meticulously crafted to enhance the overall longevity of PEMFCs by addressing operational and environmental challenges. Innovative designs can encompass advanced thermal management systems, improved water and gas management techniques, and optimized balance-of-plant systems [119].

Moreover, developing mitigation strategies demonstrates the commitment to resolving challenges related to degradation and durability in PEMFCs. These strategic interventions encompass enhancements aimed at reducing the adverse impact of operating conditions on electrode degradation. Additionally, integrating predictive maintenance systems ensures early detection and prevention of potential issues, further safeguarding PEMFC longevity [120]. Together, these new approaches provide a holistic plan to overcome the obstacle of increasing PEMFCs’ service lives. They include revolutionary lifespan prediction methodologies, durability testing protocols, material advancements, cutting-edge system engineering, and realistic mitigation solutions to meet DOE objectives. The commercial feasibility of PEMFC components may be significantly increased by this concerted effort, hastening the shift toward cleaner, more sustainable energy sources.

6. Challenges and Solutions for Meeting U.S. DOE’s 2035/2050 PEMFC Targets

The formidable barriers associated with the U.S. DOE’s ambitious 2035/2050 targets for PEMFCs emphasize the critical challenges in achieving these targets. Lifetime and durability represent a paramount challenge, given the need to attain a 40,000 h lifetime for PEMFC systems [121]. The inherent degradation of PEMFCs over time, driven by operating conditions and catalyst deterioration, highlights potential solutions such as advanced durability testing protocols, predictive maintenance systems, and innovations in catalyst and membrane durability [122]. The quest to reduce costs to USD 40/kW by 2035 and USD 30/kW by 2050 constitutes another formidable task, with material costs and manufacturing expenses being pivotal contributors [123]. Proposed solutions revolve around material innovations, streamlined manufacturing processes, and the realization of economies of scale [26]. Performance and efficiency targets are equally demanding, necessitating advancements in catalysts, ion-conducting membranes, system engineering, water, and thermal management [124]. Challenges in expanding the hydrogen infrastructure, addressing the environmental impact, establishing regulatory and policy support, and enhancing the technology readiness level (TRL) are comprehensively highlighted by Lindorfer et al. [125], underscoring the need for a concerted, collaborative effort among government agencies, research institutions, and industry partners. However, the omission of supply chain considerations is a deliberate decision regarding focus and scope within this review article, which concentrates primarily on technical, economic, and environmental facets while acknowledging that supply chain discussions, which can be extensive, may warrant a dedicated review of their own.

7. Conclusions

In conclusion, this review underscores the substantial progress in developing PEMFC components while highlighting the persistent challenges. Notably, the focus has been on achieving the ambitious targets set by the U.S. DOE for cost, durability, and performance.

Numerous advancements have been made in the field, particularly in catalyst development, membrane design, GDLs, and bipolar plates. Key findings include successfully utilizing carbon nanotubes and graphene oxide in membranes, significantly enhancing performance. Additionally, innovative coatings and materials for bipolar plates have improved corrosion resistance and reduced interfacial contact resistance, moving closer to DOE targets. However, the durability–cost trade-off remains a formidable obstacle. Extending the lifetime of fuel cells to meet DOE goals often necessitates a higher loading of expensive catalysts, which conflicts with cost reduction objectives. Balancing these factors is a crucial challenge.

Furthermore, though significant strides have been made in meeting the DOE’s technical targets for various components, achieving USD 30/kW for FCEVs and USD 600,000 for FCEBs remains elusive. This review underscores the need for continued research and innovation to address the remaining technical barriers, especially in achieving long-term durability while reducing costs. Collaborative efforts from academia, industry, and government agencies are essential to drive PEMFC technology closer to widespread commercialization, ultimately contributing to a sustainable and clean energy future.