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Review

Perovskite-Based Nanocomposite Electrocatalysts: An Alternative to Platinum ORR Catalyst in Microbial Fuel Cell Cathodes

by
Gopa Nandikes
1,
Shaik Gouse Peera
2,* and
Lakhveer Singh
1,*
1
Department of Environmental Science, SRM University-AP, Amaravati 522502, Andhra Pradesh, India
2
Department of Environmental Science, Keimyung University, Daegu 42601, Korea
*
Authors to whom correspondence should be addressed.
Energies 2022, 15(1), 272; https://doi.org/10.3390/en15010272
Submission received: 12 November 2021 / Revised: 14 December 2021 / Accepted: 28 December 2021 / Published: 31 December 2021
(This article belongs to the Special Issue Recent Developments and Emerging Trends in Chemical and Biological Fuel Cells)
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Abstract

:
Microbial fuel cells (MFCs) are biochemical systems having the benefit of producing green energy through the microbial degradation of organic contaminants in wastewater. The efficiency of MFCs largely depends on the cathode oxygen reduction reaction (ORR). A preferable ORR catalyst must have good oxygen reduction kinetics, high conductivity and durability, together with cost-effectiveness. Platinum-based electrodes are considered a state-of-the-art ORR catalyst. However, the scarcity and higher cost of Pt are the main challenges for the commercialization of MFCs; therefore, in search of alternative, cost-effective catalysts, those such as doped carbons and transition-metal-based electrocatalysts have been researched for more than a decade. Recently, perovskite-oxide-based nanocomposites have emerged as a potential ORR catalyst due to their versatile elemental composition, molecular mechanism and the scope of nanoengineering for further developments. In this article, we discuss various studies conducted and opportunities associated with perovskite-based catalysts for ORR in MFCs. Special focus is given to a basic understanding of the ORR reaction mechanism through oxygen vacancy, modification of its microstructure by introducing alkaline earth metals, electron transfer pathways and the synergistic effect of perovskite and carbon. At the end, we also propose various challenges and prospects to further improve the ORR activity of perovskite-based catalysts.

1. Introduction

Energy plays a vital role in the modern era as there is an excess need for energy due to rapid industrialization and the increased global population. Increasing energy demands trigger substantial research to explore cost-effective renewable energy building technologies with improved efficiency [1]. The prevalence of pollutants in aquatic systems and wastewater is another serious concern due to their negative impact on the environment and ecosystems [2]. Microbial fuel cells (MFCs) are considered a favorable technology for simultaneous wastewater treatment together with bioelectricity generation, as they can use wastewater as a source for producing bioenergy [3,4]. Sharing the similar working principle of electrochemistry with common fuel cells, an MFC is designed to have a set of anode–cathode segments [5]. In MFCs, the electrochemically active microorganisms, also called exoelectrogens, attach to the anode and metabolize organic matter in the wastewater to produce electrons and protons. As a result of microbial respiration, electrons are generated and they are transferred to the anode electrode, which further performs the electrical work by passing through the circuit, and protons are transferred to the cathode via a proton exchange membrane. At the cathode, the protons and electrodes are combined in the presence of oxidants such as oxygen to generate water as the final product [6]. By this combined bio–electrocatalytic reaction, the wastewater is treated at the anode, together with the useful energy output (Figure 1). Membrane-free MFCs are proven to be more efficient and cost-effective, but there are a few challenges, such as the reduced coulombic efficiency, distance between the electrodes and limitations in the design of single-chambered MFCs (SCMFCs). Proton exchange membranes such as Nafion 117, which is expensive, have been replaced by sulfonated polyether ether ketone (SPEEK) [7], sulfonated SiO2 and sulfonated polystyrene ethylene butylene polystyrene (SSEBS), etc. [8]. These membranes can overcome the limitations and even provide better outputs, as indicated in recent studies [9,10]. The performance of MFCs is reliant on several factors, such as the type of electrode material at the anode, the type of exoelectrogens in the wastewater, the type and efficiency of the cathode, enzymes and operational conditions [2,7,11,12]. The capability of a cathode for reduction reactions is an important aspect for the overall energy output from the microbial fuel cell. A vast number of cathode materials have been tried and tested in MFCs, in which perovskite-based nanocomposite electrocatalysts have gained much attention in recent times. This study reviews the perovskite electrocatalysts that have been used in the MFC system, their unique reaction pathway and the feasibility of maximizing the energy output through changes in perovskite’s elemental type and composition.

2. ORR Catalysts

There are various elements in MFCs that pertain to their efficiency. Among all, the type of anode electrode and efficient ORR cathode electrocatalysts are believed to be the most influential factors, which decide the practical power generation capacity of MFCs [13]. In particular, a highly catalytically active ORR cathode catalyst is essential for the continuous generation of bioenergy. An ideal ORR catalyst must be relatively affordable, abundant, environmentally safe and maintain consistent catalytic activity and stability [14]. The cathodic ORR should ideally result in direct four-electron transfer, in contrast to the undesirable two-electron process [15]. Generally, electrocatalysts that contain noble metals such as Pt follow a direct four-electron transfer reaction, whereas electrocatalysts made up of transition metals such as Co, Fe, Mn, Ni, etc., follow a dominant four-electron pathway or a mixed two- and four-electron pathway. A two-electron pathway results in a lower electron transfer rate and onset potential, therefore leading to a considerable energy loss [14,15,16].

2.1. Pt-Based Catalyst

For decades, the platinum catalyst has been known to be the most ideal catalyst for bio–electrochemical cells, especially MFCs [17]. Even though the Pt catalyst is considered a highly active solution and a benchmark for ORR catalysts, its major drawback is its high cost and limited availability [6]. In addition, Pt-based catalysts are susceptible to catalytic poisoning and a loss in activity, and the stability decreases over time. Hence, research has shifted to explore low-cost metals and efficient materials to be used as ORR catalysts [18].

2.2. Non-Pt-Based Catalysts

In recent years, non-precious metals have been tested as possible options for ORR catalysts in MFCs. Platinum group metal-free (PGM-free) catalysts are a class of catalysts that include transition metals (Fe, M, Mn, Cu) [19,20,21] and heteroatom-doped carbon-based materials. Ideally, most of these catalysts have confirmed excellent electrocatalytic activity. In particular, activated carbon [21,22], graphite [23,24], carbon nanotubes [25], nitrogen-doped carbon and carbon black [26] have achieved vast recognition due to their increased surface area and electrical conductivity. Biochar has been used as an ORR catalyst lately due its availability, cost-effectiveness and ideal physical and chemical characteristics [23]. Biochar’s properties assists in major nutrient cycles in microorganisms and improve their growth [27,28,29]. Transition metal oxides (TMOs) constitute a broad family of electrocatalysts that constitutes single- and mixed-metal oxides [30]. When compared to Pt-based catalysts, TMO-based catalysts have several advantages, such as being economical and more abundant, ease of synthesis and eco-friendliness [31]. Transition metal oxides acquire multiple valence states, which results in a variety of oxides having distinctive crystal structures. Transition metals of VII and VIII group elements have multiple valences and several oxides, enabling them to have various electrocatalytic applications [32,33,34,35,36,37,38].

2.2.1. Single-Metal Oxides

Generally, single-metal oxides have less electrical conductivity. Hence, providing them with a conductive substrate or matrixes such as carbon or graphene material have proven to be crucial in raising their catalytic performance.
Manganese oxides such as Mn2O5−δ have gathered attention as a demanding single-metal oxide catalyst because of their variable valence states and variable structures, proving their exceptional redox electrochemistry. Manganese oxides can function simultaneously as an ORR as well as OER catalyst [34], thus making them an interesting bifunctional catalyst for oxygen electrochemistry. Recently, the introduction of oxygen vacancies into the Mn oxide was found to be an efficient strategy to further improve the ORR activity of Mn-oxide-based catalysts, which increased the proportion of more active Mn3+ and increased the electrical conductivity. Nevertheless, the ORR activity of Mn-based oxides overall has been either similar or, in some cases, better than that of Pt/C [38].
Cobalt oxide is another good candidate for ORR that has several advantages over other oxide candidates because of its tunable composition, high electrocatalytic activity and low cost [35]. Co3O4 has a spinel structure, where Co2+ and Co3+ act as a redox couple and occupy tetrahedral and octahedral voids to facilitate electron transfer; in particular, the exposure of active Co3+ is found to play a key role in the ORR reaction [36].
Vanadium pentoxide (V2O5) has been successfully used as an alternative to platinum cathode catalysts in a single-chambered MFC. V2O5 was synthesized through a hydrothermal method and electrochemical measurements proved that V2O5 is comparable in performance by up to 55% to that of Pt/C [31].

2.2.2. Mixed-Metal Oxides

Mixed-metal oxides are an amalgam of stable metals, which can be bi-metal, tri-metal, or multi-metal systems. These metals possess different valence states and have been used extensively used as ORR catalysts [39]. Within the mixed-metal oxides category, spinel-type oxides and perovskite oxides are the most investigated systems.

Spinel-Type Oxides

These fall within the category of mixed-metal oxides having a AB2O4 chemical formula, where A is taken as a divalent metal ion such as Mg, Co, Ni, Zn, Fe or Mn. A trivalent metal ion is used as the B element, such as Cr, Mn, Co, Al or Fe. Cations of different valency states help in reducing the activation energy associated with the electron exchange reaction by the hopping process during the ORR reaction. Ideal spinel structures are cubical with closely packed oxides, besides the two tetrahedral and the four octahedral points in the formula unit. B3+ ions occupy four octahedral sites and A2+ occupy the two tetrahedral sites. This type of structure is called a “normal spinel”. If B3+ ions take up all the tetrahedral sites and a pair of the octahedral sites, and the remaining octahedral sites are occupied by A2+ ions, then it is called an “inverse spinel” structure [40,41,42,43].

3. Perovskite Oxides

The perovskite oxides are a family of mixed-metal oxides with a general compositional formula of ABO3, in which A-site elements are of rare earth and alkaline earth elements, whereas the B site constitutes a transition element. Perovskites are best known for their advantages of substituting A- or B-site cations to produce active and stable electrocatalysts [41]. This substitution of A or B sites with various atoms introduces abundant oxygen vacancies in the anion network, which helps oxygen molecules to bond together during ORR. Various elements can be introduced in the perovskite oxide’s B site and can be altered on the basis of structure and composition in order to enhance the electrical conductivity and oxygen vacancy of the perovskites [43]. Thus, indicating a suitable transition metal at the B site can prevent the morphological deformation of the high oxygen vacancy and gives an optimal D band center for the whole B site [44,45]. This will enhance the overall catalytic performance of perovskite composites (Figure 2).
Perovskite oxides have a cubic structure in which A atoms occupy the corners of the cubic cell. In the central six-fold coordination, there are B atoms occupied by an octahedron of six anions, with the O2 atoms situated in the center of the faces [44]. The B site is comparatively smaller than the A-site cation. Apart from the simple perovskite ABO3 structure, modification can be achieved by integrating two different kinds of B ions with separate charge and proportion. Equiatomic portions of two different ions in the B site are often replaced, making the formula of the perovskite ABB′O6. The two developed B ion units can be observed as doubled within the three axes. In most cases, B and B’ charges may be different. In this scenario, oxygen atoms marginally shift towards the more charged ones. However, this process does not alter the octahedral symmetry of the perovskite [45].

3.1. ORR Mechanism of Perovskite-Type Oxides

Typically, ORR takes place through two types of pathways, either a direct four-electron reduction pathway or an indirect 2 + 2 electron reduction pathway into two water molecules in an acidic environment or four OH in an alkaline medium. A direct four-electron reduction is highly required to maintain the high energy output.
Alkaline electrolyte 4e− pathway:
O2 + 2H2O + 4e−→ 4OH−
Acidic electrolyte 4e− pathway:
O2 + 4H+ + 4e−→ 2H2O
Perovskites are known to perform a direct four-electron reduction of O2 to four OH− ions. If the ORR takes place through a two-electron reduction process, it leads to the formation of undesired H2O2 and HO2−. Jin et al. [46] proposed a possible catalytic ORR cycle in alkaline medium on a perovskite catalyst, as shown in Figure 3.
Due to the abundance of OH− ions in an alkaline environment, the perovskite’s surface is always adsorbed and covered by OH− ions at the B site. The first step in the ORR process is the adsorption of O2 at the B site by replacing the pre-adsorbed OH− ion in the presence of one electron (Figure 3) [47]. In the associative ORR reduction pathway, it is the B site of the ABO3 perovskite onto which O2 is adsorbed. The second step would be the addition of a proton to the previously adsorbed O2 to form a peroxide (OOH−). In a consecutive reaction of OOH− at the B site, there would be three possibilities: (3A) the formed OOH− can desorb from the B site and enter the bulk solution; (3B) two OOH− on nearby sites would collectively undergo the hydrogen peroxide chemical disproportionation (HPCD) reaction to form two OH− and one O2 molecule; (3C) the most desirable reaction, in which OOH− undergo reduction electrochemically (hydrogen peroxide electrochemical reduction reaction (HPER)) to form O2−, which further reacts with H2O and e− to form OH−, completing the one cycle of ORR. The selectivity of the OOH− reaction among the three possibilities depends on the composition of perovskites and electrode parameters [48]. In order to quantify the electron transfer rates and to distinguish two-electron and four-electron pathways, a rotating ring disk electrode (RRDE) is used. It recognizes the electrons exchanged by counting the hydroperoxides found at the ring [49,50].

3.2. Application of Perovskite-Based ORR Electrode in MFCs

Based on the above knowledge, various researchers have developed a variety of perovskite-based catalysts for ORR and for application in MFCs. In a study by F. Shahbazi Farahani and group [51], the authors developed a bimetallic Fe-Mn perovskite-type oxide supported on carbon Vulcan (C/FeMnO3) and graphene oxide (GO/FeMnO3) by a chemical/thermal reduction method. The produced bimetallic FeMnO3 phase having the perovskite structure was found to be homogeneously dispersed on the carbon support. GO/FeMnO3 and C/FeMnO3 composites exhibited good catalytic activity towards ORR both in alkaline and acidic environments, as depicted by hydrodynamic voltammetry, RRDE, cyclic voltammetry and EIS. The ORR charge transfer resistance of C/FeMnO3 was found to be much lower than that of GO/FeMnO3, signifying a low ORR kinetic rate for GO/FeMnO3 (Figure 4). This is due to the restacking of graphene oxide sheets during the formation of the catalyst, which affected both the available metal oxides and the metal-oxide-assisted interaction negatively. In a typical setup, MFCs should be able to work in variable process states in terms of functioning and also fuel composition. Catalysts should be able to cope with the changes and show stable results. Hence, the authors conducted an accelerated stress test, in which C/FeMnO3 presented excellent stability in simulated conditions. The kinetic data in terms of power and voltage displayed better performance than that of the Pt-based MFC. Despite these findings, the longevity of these metal oxides with carbon hybrids is, however, a concern that needs further study [51].
In a recent study [52], a Zn doping strategy was used to alter the microstructure and produce oxygen vacancies on perovskite in an attempt to enhance the ORR activity (Figure 5). Zn was doped together with iron to form a CaFe0.7Zn0.3O3 perovskite oxide that showed good catalytic activity, with a porous structure and improved surface area. Moreover, Zn and Fe showed an impressive synergy in improving the formation of oxygen vacancies, together with the formation of a mixed valence state of Fe2+/Fe3+. Zn-doped perovskite oxides (CaFe0.7Zn0.3O3) displayed excellent ORR kinetics, onset potential (0.194 V vs. Ag/AgCl), and half-wave potential (−0.219 V vs. Ag/AgCl) in alkaline conditions, outperforming the Pt/C ORR catalyst. This exemplary performance is likely due to three main factors, one being the doping of the Zn element uniformly in the perovskite oxide. This leads to the generation of mesoporous pores via high-temperature carbonization evaporating the Zn in the mixture, forming a hierarchically porous assembly. The second is B-site doping with Zn ions, which creates more oxygen vacancies by elevating the oxygen unavailability rates and increasing the conductivity. The third important factor is the mixed valence state of Fe2+/Fe3+, which helps to stabilize the perovskite’s catalytic activity, in addition to the presence of the Fe3C active phase in the catalyst. Moreover, CaFe0.7Zn0.3O3 follows the ideal four-electron pathway of ORR, which delivered a maximum power density of 892 mWm−3 with excellent stability over 160 h of operation time. The inferences from the study confirm the feasibility of the CaFe0.7Zn0.3O3 catalyst as a substitution for a Pt cathode catalyst [52].
F. Nourbakhsh et al. [5] used LaCoO3 (LC), LaMnO3 (LM) and LaCo0.5Mn0.5O3 (LMC) perovskite oxide nanoparticle-based cathode catalysts as a substitute for a platinum cathode (Figure 6). The Lanthanum-based perovskite-type oxide cathode catalysts produced were tested for their catalytic efficiency in a dual-chambered MFC. The LC, LM and LMC were tested individually for their morphology, structure and electrochemical properties. LaMnO3 delivered a maximum power density higher than 13.9 mWm−2 in the two-chambered MFC, a value that is twice as high as that of carbon cloth (CC) used as a cathode in similar circumstances. The internal resistance of these MFCs with different ORR cathodes was recorded. Carbon cloth had the highest internal resistance, followed by LC, LMC and LM. The reduced internal resistance of La-based perovskites, especially LM and LMC, leads to a lower activation energy of ORR in a neutral medium, which supports the catalyst reaction [53]. Transition metal cation participation and its valency largely influence ORR and the electrocatalytic activity of the perovskite-type oxides.
Xin Wang and group [53] used La0.4Ca0.6Co0.9Fe0.1O3 (LCCF) perovskite, a carbon-supported Ca and Fe double-doped LaCoO3. The reverse micelle technique was used to synthesize the LCCF. Finely dispersed carbon was used as a support matrix for the LCCF particles. A comparative study of the LCCF/C cathode and C cathode was conducted, using Pt as a control, at ambient temperatures and with a neutral electrolyte in a single-chambered MFC. The LCCF/C ORR catalyst followed a hybrid electron pathway of both four electrons and two electrons due to the presence of carbon. The LCCF/C perovskite oxide’s structure provides oxygen vacancies and, in turn, gives oxygen mobility and reduces biofilm coverage. The advantage of the LCCF/C catalyst is that, after 15 cycles, it displays the lowest decay rate (2%) in open-circuit voltage compared to carbon (22%) and Pt (4%), proving that it can attain stable performance against biofouling (Figure 7).
Farhan Papiya et al. [1] used Al2O3–rGO as an alternative to a platinum ORR catalyst in a single-chambered MFC. Cobalt nanoparticles of different weight percentages were added to the alumina and graphene oxide mixture. The study conducted was with four different weight percentages, along with Pt/C as a standard reference. Catalyst B, having 80 wt% of cobalt metal, was proven to show the highest power density of 548.19 mWm−2. Catalyst A had 70 wt% Co, Catalyst C had 90 wt% Co and Catalyst D had 80 wt% Co but no Al2O3. Cyclic voltammetry and open-circuit voltage experiments proved that 80 wt% Co (Catalyst B) resulted in the highest electrocatalytic activity compared to the other catalysts. The ORR activity of the different catalysts was in the order D < C < A < Pt/C < B (Figure 8). Oxygen adsorption on the surface of the catalyst was also high for Catalyst B, proven through the BET surface test. The ratio of 80:20 (Co/Al2O3:rGO) worked the best out of the different catalytic materials tested on the MFC.
BaMnO3 perovskite coated with carbon and its electrocatalytic properties for the oxygen evolution reaction and oxygen reduction reaction were studied by Yujiao Xu et al. [54]. A bifunctional catalyst has a wide range of applications in the field of batteries, fuel cells, etc. The study was conducted in two stages: initially, the catalytic properties of the bare BaMnO3 nanorods were examined; later, the same tests were carried out with a thin layer of carbon coating on the BaMnO3 nanorods. The results showed a large improvement in the peak current density, which was −0.94 mAcm−2 on the bare BaMnO3 nanorods and −2.5 mAcm−2 on the carbon-coated BaMnO3 nanorods. Carbon-coated BaMnO3 nanorods delivered a better positive shift in the onset and half-wave potential compared with the bare BaMnO3 nanorods. An electron transfer rate of 3.8 was observed in the carbon-coated BaMnO3 nanorods, compared to 3.4 in the latter. The study proves that a thin layer (5%) of carbon coating can improve the stability of BaMnO3 as a bifunctional catalyst (Figure 9).
In a study conducted by L.J. Bai et al. [55], a LaxSr1-xCoO3 perovskite nanocatalyst was introduced as a cathode catalyst in an anaerobic fluidized bed microbial fuel cell. The experiment was carried out at different concentrations of catalyst, such as La0.7Sr0.3CoO3, La0.3Sr0.5CoO3 and La0.8Sr0.2CoO3, in which La0.7Sr0.3CoO3 produced the maximum power output of 104.59 mWm−2 and open-circuit voltage of 594.0 mV. The results show that La0.7Sr0.3CoO3 achieved the best concentrations of lanthanum and strontium in the perovskite oxide, as it was more efficient in the comparative study. Table 1 summarizes the electrocatalytic properties of the various perovskite-Based Nanocomposite Electrocatalysts developed for cathodic ORR In MFCs.

4. Summary and Perspectives

The perspective on perovskite-type oxide-based cathodes in MFCs has been discussed. The literature and the vast array of information we have on their molecular mechanisms, characteristics and behavior offer a basic understanding of perovskite cathodes. The modification of the perovskite crystal structure through doping of the A and B site has proven to be a sensible technique in improving the ORR performance. Replacing the A site with a lower-oxidation-state cation or instigating an A-site cation deficiency is indicated as a practical method to generate oxygen vacancies for ORR. The electrocatalytic properties of perovskites are also primarily dependent on the choice of B-site metal cations. The increase in ORR kinetics is associated with an optimal balance of ionic mobility, surface electron transfer and oxygen vacancies as aided by the synergistic effects of B sites. The combination of elements such as Zn and Fe will produce a synergic effect at the B site, which helps the composite to perform better and achieve excellent electricity flow rates. By introducing Zn and Co, oxygen vacancies and oxygen surface adsorption could be increased, which are beneficial to the ORR reaction by enhancing the charge transfer kinetics between the catalyst and gaseous O2 reactants. The mesoporous and microporous composition of perovskite oxides contribute various porous channels for the exchange of electrons, and the mass transfer process is shortened. This reveals that Zn-, La- and Mn-doped perovskite-type oxides could be ideal electrocatalysts with enhanced corrosion resistance, stability and outstanding onset potential and half-wave potential. These modified perovskite oxides will display excellent ORR activity and facilitate an evident four-electron pathway that can display remarkable durability even if compared to the benchmark Pt/C catalysts. An understanding of the different reaction pathways and various key parameters influencing the perovskite oxide ORR catalysts has proven to be pivotal. In recent studies, relatively improved ORR activity has been observed for perovskite-oxide-based catalysts with carbon added. Advancements in the field of electrocatalysis and the development of more ideal combinations of perovskite nanocatalysts will prove to be a solution for MFCs with low ORR activity and power output. This, in turn, will provide a promising replacement for the expensive Pt ORR catalyst.

Author Contributions

Conceptualization: G.N. and L.S.; writing—original draft preparation: G.N. and S.G.P.; writing—review and editing: G.N., L.S. and S.G.P. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not Applicable.

Informed Consent Statement

Not Applicable.

Data Availability Statement

Not Applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Graphical representation of a single-chambered MFC with perovskite ORR catalyst having a four-electron pathway.
Figure 1. Graphical representation of a single-chambered MFC with perovskite ORR catalyst having a four-electron pathway.
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Figure 2. Crystal structure of perovskite oxide with ABO3 composition. (Concept adopted with permission from [43]. Copyright 2020, MDPI, Open Access).
Figure 2. Crystal structure of perovskite oxide with ABO3 composition. (Concept adopted with permission from [43]. Copyright 2020, MDPI, Open Access).
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Figure 3. Representation of ORR mechanism in perovskite. (1) represents the initial step of ORR with adsorption of O2 on B site, (2) peroxide formation with addition of proton in O2, (3A) release of peroxide from surface, (3B) electrochemical reduction, (3C) chemical disproportionation. (Reprinted with permission from [47]. Copyright 2021, ACS Publications, Open Access).
Figure 3. Representation of ORR mechanism in perovskite. (1) represents the initial step of ORR with adsorption of O2 on B site, (2) peroxide formation with addition of proton in O2, (3A) release of peroxide from surface, (3B) electrochemical reduction, (3C) chemical disproportionation. (Reprinted with permission from [47]. Copyright 2021, ACS Publications, Open Access).
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Figure 4. LSV curves at different electrode rotation rates of (a) C/FeMnO3 and (b) GO/FeMnO3 in O2-saturated neutral PBS (scan rate:10 mVs−1), with Koutecky–Levich plots obtained at ~0.6 V as an inset; (c) polarization and power density (PD) curves of MFCs assembled with C/FeMnO3, GO/FeMnO3 and Pt/C cathodes fed with 1 mgL−1 sodium acetate in neutral PBS; (d) voltage cycles under 1 kΩ external resistance as a function of time. (Reprinted with permission from [51]. Copyright 2019, Elsevier).
Figure 4. LSV curves at different electrode rotation rates of (a) C/FeMnO3 and (b) GO/FeMnO3 in O2-saturated neutral PBS (scan rate:10 mVs−1), with Koutecky–Levich plots obtained at ~0.6 V as an inset; (c) polarization and power density (PD) curves of MFCs assembled with C/FeMnO3, GO/FeMnO3 and Pt/C cathodes fed with 1 mgL−1 sodium acetate in neutral PBS; (d) voltage cycles under 1 kΩ external resistance as a function of time. (Reprinted with permission from [51]. Copyright 2019, Elsevier).
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Figure 5. (a) The fabrication process of CaFexZn(1-x)O3 catalysts; (b) electron transfer number and H2O2 yield of CaFe0.7Zn0.3O3; (c) simulated operation of MFCs; (d) output voltage of CaFe0.7Zn0.3O3 and Pt/C; (e) polarization curves; (f) power density of CaFe0.7Zn0.3O3 and Pt/C. (Reprinted with permission from [52]. Copyright 2021, Elsevier).
Figure 5. (a) The fabrication process of CaFexZn(1-x)O3 catalysts; (b) electron transfer number and H2O2 yield of CaFe0.7Zn0.3O3; (c) simulated operation of MFCs; (d) output voltage of CaFe0.7Zn0.3O3 and Pt/C; (e) polarization curves; (f) power density of CaFe0.7Zn0.3O3 and Pt/C. (Reprinted with permission from [52]. Copyright 2021, Elsevier).
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Figure 6. (a) Pictorial representation of ORR pathway on LaCo0.5Mn0.5O3; (b) a column/bar diagram of the obtained results of the MFC with La-based perovskite catalyst in comparison with bare and Pt-coated carbon cloth cathode; (c) polarization curves; (d) power density curves of different electrodes. (Reprinted with permission from [5]. Copyright 2020, Springer, Open Access).
Figure 6. (a) Pictorial representation of ORR pathway on LaCo0.5Mn0.5O3; (b) a column/bar diagram of the obtained results of the MFC with La-based perovskite catalyst in comparison with bare and Pt-coated carbon cloth cathode; (c) polarization curves; (d) power density curves of different electrodes. (Reprinted with permission from [5]. Copyright 2020, Springer, Open Access).
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Figure 7. (a) Line sweep voltammograms; (b) MFC polarization; (c) Tafel plots; (d) curves with the three-air cathodes (50 mmol L−1 PBS and T = 30 °C) of LCCF/C, Pt/C and C cathodes. (Reprinted with permission from [53]. Copyright 2012, Wiley Online Library).
Figure 7. (a) Line sweep voltammograms; (b) MFC polarization; (c) Tafel plots; (d) curves with the three-air cathodes (50 mmol L−1 PBS and T = 30 °C) of LCCF/C, Pt/C and C cathodes. (Reprinted with permission from [53]. Copyright 2012, Wiley Online Library).
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Figure 8. (a) Cyclic voltammograms; (b) LSV of Co/Al2O3–rGO at different wt% concentrations in a mixed bacterial culture, scan rate 10 mv/s; (c) polarization curve and power density curve of cathode catalysts at different Co wt%. (Reprinted with permission from [1]. Copyright 2017, Elsevier).
Figure 8. (a) Cyclic voltammograms; (b) LSV of Co/Al2O3–rGO at different wt% concentrations in a mixed bacterial culture, scan rate 10 mv/s; (c) polarization curve and power density curve of cathode catalysts at different Co wt%. (Reprinted with permission from [1]. Copyright 2017, Elsevier).
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Figure 9. (a) Cyclic voltammetry; (b) linear sweep voltammogram, BaMnO3 (black curve) BaMnO3@ 5% C (red curve) in O2 saturated 0.1 M KOH solution, commercial Pt/C (blue curve); (c) electron transfer rate; (d) LSV in N2 saturated 0.1 KOH solution. (Reprinted with permission from [54]. Copyright 2015, Elsevier).
Figure 9. (a) Cyclic voltammetry; (b) linear sweep voltammogram, BaMnO3 (black curve) BaMnO3@ 5% C (red curve) in O2 saturated 0.1 M KOH solution, commercial Pt/C (blue curve); (c) electron transfer rate; (d) LSV in N2 saturated 0.1 KOH solution. (Reprinted with permission from [54]. Copyright 2015, Elsevier).
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Table
Table 1. The kinetic data of Pt and the various perovskite-type oxides used in MFCs.
Table 1. The kinetic data of Pt and the various perovskite-type oxides used in MFCs.
ORR CatalystMatrixMax. Power DensityRef. ElectrodeOnset PotentialHalf-Wave PotentialNumber of Electrons Transferred Current DensityReference
PlatinumCarbon783 mWm−2Ag/AgCl0.158 V−0.193 V3.94.83 mAcm−2[52]
CaFeZnO3Carbon Cloth892 mWm−2Ag/AgCl0.194 V−0.219 V3.945.46 mAcm−2[52]
LaMnO3Carbon Cloth14 mWm−2Ag/AgCl--3.41.1 mAcm−2[5]
FeMnO3Graphene Oxide166 mWm−2Ag/AgCl-−0.22 V3.63.8 mAcm−2[51]
FeMnO3Carbon460 mWm−2Ag/AgCl-−0.30 V3.64.2 mAcm−2[51]
LaCaCoFeO3Carbon405 mWm−2Ag/AgCl----[53]
LaSrCoO3Carbon104 mWm−2Ag/AgCl----[55]
CoAl2O3Graphene Oxide548 mWm−2Ag/AgCl0.13 V−0.15 V-1.79 mAcm−2[1]
BaMnO3Carbon790 mWm−2Ag/AgCl0.19 V−0.36 V3.44.84 mAcm−2[54]
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Nandikes, G.; Gouse Peera, S.; Singh, L. Perovskite-Based Nanocomposite Electrocatalysts: An Alternative to Platinum ORR Catalyst in Microbial Fuel Cell Cathodes. Energies 2022, 15, 272. https://doi.org/10.3390/en15010272

AMA Style

Nandikes G, Gouse Peera S, Singh L. Perovskite-Based Nanocomposite Electrocatalysts: An Alternative to Platinum ORR Catalyst in Microbial Fuel Cell Cathodes. Energies. 2022; 15(1):272. https://doi.org/10.3390/en15010272

Chicago/Turabian Style

Nandikes, Gopa, Shaik Gouse Peera, and Lakhveer Singh. 2022. "Perovskite-Based Nanocomposite Electrocatalysts: An Alternative to Platinum ORR Catalyst in Microbial Fuel Cell Cathodes" Energies 15, no. 1: 272. https://doi.org/10.3390/en15010272

APA Style

Nandikes, G., Gouse Peera, S., & Singh, L. (2022). Perovskite-Based Nanocomposite Electrocatalysts: An Alternative to Platinum ORR Catalyst in Microbial Fuel Cell Cathodes. Energies, 15(1), 272. https://doi.org/10.3390/en15010272

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