Next Article in Journal
A Multi-Temporal Analysis on the Dynamics of the Impact of Land Use and Land Cover on NO2 and CO Emissions in Argentina for Sustainable Environmental Management
Previous Article in Journal
Determinants of Long-Term Water and Energy Conservation Behavior: An Integrated Review
Previous Article in Special Issue
Electrospun Microstructured Biopolymer Fibers Containing the Self-Assembled Boc–Phe–Ile Dipeptide: Dielectric and Energy Harvesting Properties
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Sustainability
Volume 16
Issue 11
10.3390/su16114398
sustainability-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Practice of Ecological Aesthetics in Green Production of Bimetallic Carbide Catalyst for Oxygen Reduction Reaction: Integrating Technological Development with Ecological Protection

by
Meiping Zhang
1,*,
Kailun Wang
2 and
Zaoxue Yan
2,*
1
College of Humanities, Yangzhou University, Yangzhou 225012, China
2
School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China
*
Authors to whom correspondence should be addressed.
Sustainability 2024, 16(11), 4398; https://doi.org/10.3390/su16114398
Submission received: 21 April 2024 / Revised: 15 May 2024 / Accepted: 21 May 2024 / Published: 23 May 2024
(This article belongs to the Special Issue Advanced Energy Materials for Sustainability)
Browse Figures
Versions Notes

Abstract

:
This work summarizes the disciplinary connotation of ecological aesthetics, discusses the social and philosophical background of the origination of ecological aesthetics, and applies ecological aesthetics to the research on the production processes of catalytic materials. It is found that compared with conventional chemical processes, catalytic materials synthesized using green chemical processes that conform to ecological aesthetics have advantages in raw material cost, energy consumption, environmental protection, operational complexity, and product performance. Based on this, it is proposed that, as green chemical processes develop to a certain extent, they will unify anthropocentrism and ecocentrism, and meet both human needs and ecological protection requirements. The mentioned green chemical processes adopt biomass lotus leaf stems as a carbon source to produce non-noble metal bimetallic carbide (C19Cr7Mo24)-based catalysts for oxygen reduction reaction (ORR). Its initial half-wave potential (E1/2) for catalyzing ORR in an alkaline medium is 0.903 V, the E1/2 retention rate after 50,000 cycles is 98.9%, and its peak power density in H2/O2 fuel cell reaches 1.47 W cm−2, making it one of the most active non-noble metal catalysts for ORR reported so far; its stability is unparalleled.

Graphical Abstract

1. Introduction

Oxygen reduction reaction (ORR) plays an irreplaceable role in electrochemical energy devices, such as fuel cells and zinc-air batteries. ORR involves multi-step proton-coupled electron transfer, which has slow kinetics and greatly affects the overall efficiency of the energy conversion. Pt is the most adopted catalytic active ingredient for ORR, but its application is limited by the scarcity of resources and insufficient stability. One solution is to use inexpensive non-noble metal catalysts. The currently studied non-noble metal catalysts include heteroatom-doped carbon [1], single (or multiple) metal atom catalysts [2], and heteroatom-doped transition metal compounds [3,4]. The activities of the reported top-level non-noble metal catalysts have exceeded that of commercial Pt/C.
However, most of the non-noble metal catalysts still suffer from low activity and insufficient stability. To obtain non-noble metal components with a high intrinsic activity and a high intrinsic stability is of significance. Bimetallic carbide-based catalysts (such as Co6Mo6C2, Co3W3C, and Fe2MoC) have reported excellent activity, electron-donating performance, and stability in both acidic and alkaline media for ORR [5,6,7]. The doping of heteroatoms (such as N) can alter the electronic structure of the active center, further enhancing their activity [8,9,10]. As the synthesis temperature increases (above 1300 °C), metal carbides could transform into more stable crystals and have more favor for electron donation [6], exhibiting a much higher activity; more importantly, their stability is extremely high.
In addition, as people attach increasing importance to environmental protection and sustainable development concepts, they are becoming more conscious of adopting green methods to obtain catalytic materials in both research and production [11,12,13,14,15]. Typically, we investigated the literature on the research of biomass-based catalysts in the field of fuel cell cathode materials in recent years and found that the enthusiasm for green chemical processes is generally on the rise (Figure 1). Obviously, the concept of sustainable development or ecological aesthetics has penetrated into scientific research and design.
In fact, humans are always subject to certain philosophical ideas in their production and scientific research processes. Since the Industrial Revolution in Britain, the world’s political and economic development has been rapid. For a long time, people’s definition of the world has been anthropocentric [16,17]. Human activities have greatly damaged the natural ecosystem. In order to save the ecological environment, the international community began to reflect on modern industrial civilization since the 1960s. The “ecocentrism” viewpoint, which is opposite to anthropocentrism, was popular for a while, emphasizing the absolute value of nature. Obviously, both anthropocentrism and ecocentrism are not feasible at present. In the contemporary era when commercialism and internationalism are prevalent, the sustainability of development has become one of the topics discussed in the industrial community [18]. With the relatively complete development of ecology, aesthetics has also shown a trend of aesthetic ecologicalization by combining with ecology. Ecological aesthetics has emerged with the reflection on modern ecological crises. It introduces an ecological perspective into aesthetics, emphasizing that human aesthetic activity should be implemented from an ecological perspective.
People nowadays have become accustomed to using ecological aesthetics to handle the relationship between humans and nature, and between human development and ecological protection; people have also realized that both anthropocentrism and ecocentrism are not feasible. However, in practice, people always waver between the positions of anthropocentrism and ecocentrism, which are opposing and contradictory. For example, if new technologies being developed cause pollution, people would limit the development in order to avoid pollution. Currently, the activity of the reported ORR catalyst obtained using green chemical processes is still far inferior to the top-level noble metal-based catalysts, and even inferior to the non-noble metal catalysts synthesized using conventional chemical processes [19,20]. It seems that the ecological aesthetics ideology has a hindering effect on the rapid progress of technology, that is, the ecological aesthetics ideology seems to be more inclined towards “ecocentrism”. So, how to coordinate anthropocentrism and ecocentrism in practice? Can the two be perfectly unified? If catalytic materials with higher activity and stability are obtained using green processes, it will not only promote significant progress in the commercialization of fuel cells, but also provide a valuable example for demonstrating the significance of practicing ecological aesthetics in technological progress.
In response to this issue, we conducted research on catalysts for the fuel cell cathode catalyst. Here, the bimetallic carbide (C19Cr7Mo24)-based catalyst using both ion exchange resin (through conventional chemical processes) and the lotus leaf stem (through green chemical processes) as carbon sources were synthesized. The effects of the conventional chemical processes and green chemical processes on production costs, energy consumption, environmental protection, operational complexity, and catalytic performance were compared. It was found that the green chemical processes showed advantages in all the above aspects. To our knowledge, the catalyst obtained using green processes was highly active for the ORR reported so far, and its stability was unparalleled (Figure 2 and Table 1).
Up to now, there have been no reports on ecological aesthetics research in the energy material field. This paper firstly discusses the ecological aesthetics theory as a guiding ideology for the green production of catalytic materials; secondly, it compares the advantages of green chemical processes over conventional chemical processes in various aspects; finally, it concludes that green chemical processes can not only better meet human needs, but also protect the ecological environment. Therefore, we believe that with the ultimate development of green chemical processes, anthropocentrism and ecocentrism will no longer be in opposition, and may even be perfectly unified. This work will not only provide example support for ecological aesthetics research, but also provide a reference for the preparation of efficient nano-catalysts through green processes.

2. Ecological Aesthetics Theory

This part discusses the connotation, social background, philosophical background, and ethical foundation of ecological aesthetics. The theoretical basis for the origin of ecological aesthetics can be found in the Supplementary Materials.

2.1. The Proposal and Connotation of Ecological Aesthetics

In 1866, the German naturalist E. Haeckel proposed the term “ecology” in Genelle Morphologie der Organismen [36]. In 1869, he defined “ecology” as the science of studying the interdependence between organisms (including humans) and their living environment [37]. Introducing ecological concepts into aesthetics; interpreting aesthetic activities and experiences through ecological values; reflecting on traditional human aesthetic concepts; and re-exploring the multiple aesthetic relationships between humans and nature, humans and society, and humans and themselves; thus moving towards a free-life realm of harmony between humans and nature, is ecological aesthetics.
After the age of G. W. F. Hegel (1770–1831, Germany), aesthetics has mainly focused on art, hence aesthetics is also known as the philosophy of art. The origination of ecological aesthetics is a breakthrough of this traditional aesthetics; however, it does not mean that ecological aesthetics only focuses on nature, because nature cannot be solely an aesthetic object, human participation is necessary.
Ecological aesthetics includes ecological beauty and ecological value; however, traditional aesthetics usually overlook ecological values. Expanding the scope of aesthetics research to the aesthetic relationship between humans and the entire natural world greatly expands the perspective of aesthetics research. In practice, ecological aesthetics is a new type of aesthetics approach and view aimed at responding to global ecological crises. Based on ecological ethics, ecological aesthetics uses ecological knowledge to stimulate imagination and emotions, overcoming human aesthetic preferences. Ecological aesthetics is committed to correcting the misleading view of anthropocentrism in the traditional aesthetics theory from an ecological holism perspective. It takes the entire ecosystem, including all natural things and humans, as the object of observation, and studies the aesthetic issues within it. Under this concept, things that are usually perceived as lacking aesthetic characteristics, such as wetlands, swamps, and other primitive natural objects, also enter people’s aesthetic vision. When the viewer appreciates one thing, they also appreciate other things in the living environment. Traditional aesthetics usually focuses on subjective sensations, such as pleasure and cultivation, while ecological aesthetics emphasizes the importance of ethical consciousness, believing that ecological aesthetics cannot be discussed without ecological ethical consciousness.
In 1972, Joseph W. Meeker published a paper titled Notes Toward an Ecological Esthetic, and the term “ecological aesthetics” officially emerged [38]. Until today, ecological aesthetics remains a hot topic among international scholars.

2.2. The Background of Ecological Aesthetics

2.2.1. Social Background

The origination and development of a subject are closely related to the social, economic, ideological, and even lifestyle changes of its era, fundamentally driven by the need to solve practical problems. The Industrial Revolution in the 18th century brought about the rapid development of productivity. With the birth and expansion of industrial civilization, anthropocentrism clearly dominates the ideology of human society. Anthropocentrism regards nature as a resource that humans can endlessly utilize. After World War II, technological progress and the unprecedented improvement of human ability to influence nature resulted in increasingly severe damage to the environment, making it difficult to curb environmental degradation. Hence, ecological theories, such as land aesthetics and deep ecology, have emerged in the West, thoroughly reflecting and deeply criticizing the traditional concept of the opposition between humans and nature since the 1960s. These theories all share a common orientation that opposes anthropocentrism and calls for a holistic perspective on the relationship between humans and nature. Ecological aesthetics thus emerged with the development of these theories. In short, ecological aesthetics is a subject that emerged during the transition from industrial civilization to ecological civilization in the mid-20th century. It is a reflection and answer from an aesthetic perspective on how to construct an ideal relationship between humans and nature, humans and society, and humans and themselves.

2.2.2. Philosophical Background

In 1750, the German philosopher Baumgarten defined aesthetics as a subject that studies human perceptual understanding [39]. In 1790, the German philosopher Kant pointed out in his Critique of Judgment that aesthetic appreciation ability is an important component of human psychological function and a symbol of the establishment of human subjectivity [40]. In 1835, Hegel’s Aesthetics, the culmination of German classical aesthetics, focused on exploring the corresponding object of perceptual cognitive ability-art [41]. In Hegel’s view, artistic beauty is higher than natural beauty, and aesthetics is equated with artistic philosophy. The German classical aesthetics since the Baumgarten era have established two fundamental characteristics for modern aesthetics, one is the human-centered aesthetic model, and the other is to focus on art. Although this kind of aesthetics has an important historical significance, its tendency towards anthropocentrism, which disregards nature, clearly does not meet the value requirements of the ecological ethics era. The concept of anthropocentrism emerged during the Industrial Revolution in the 18th century. Before the Industrial Revolution, the level of social productivity was low, and people were superstitious and worshipped nature. After the Industrial Revolution, productivity developed rapidly, and humans held an absolute dominant position in nature, leading to “anthropocentrism” represented by “technologism” and “rationalism”. The typical examples include the view of the British scientist Francis Bacon that “knowledge is power” and the view of the French philosopher René Descartes that “I think, therefore I am”. Anthropocentrism has greatly promoted human civilization and the progress of history. However, the industrialization process guided by anthropocentrism has caused serious environmental pollution and local ecological disasters, directly threatening human survival.
The origination of ecological aesthetics, therefore, is inevitable in philosophy. In 1966, the French philosopher Michel Foucault declared the end of “anthropocentrism” and declared that humans will enter into a new philosophical era [42]. The philosophical foundation of ecological aesthetics is ecological holism, which is a correction and transcendence of anthropocentrism. Ecological holism holds that all species and non-living organisms, such as air, water, and soil on Earth, form an inseparable organic unit. The entire Earth is a complete ecosystem, and humans cannot surpass other species, being only a part of all things. The awareness of this correlation is the core connotation of ecological holism.

2.3. The Ethical Contradictions in the Development of Ecological Aesthetics

Since the outbreak of the third technological revolution in the mid-20th century, the depth and breadth of human practice have been greatly expanded, creating unprecedented material wealth. However, people are not always able to make reasonable use of new technologies, so ecological problems are not only unresolved in contemporary times, but also more serious. Human beings have to reflect on the relationship between humans and nature from both a value and a moral perspective. There have been two viewpoints on how to reconcile the contradiction between humans and nature, which are anthropocentrism and ecocentrism.
The so-called anthropocentrism advocates putting human interests first in the interaction between humans and nature, and everything should start and end with human interests. Although anthropocentrism also emphasizes the unity of humanity and nature, it views this unity as a human domination over nature, and nature is subject to the human will. Anthropocentrism believes that nature can only show value in the process of serving human purposes. Guided by anthropocentrism, humans protect the natural environment in order to meet their own survival and development needs, and do not harbor moral care and an emotional identification with nature. Anthropocentrism constantly reinforces humanity’s sense of superiority over nature, viewing it as an object that can be conquered and ruled at will. Anthropocentrism inevitably leads to the indiscriminate exploitation of nature, exacerbating contradictions and conflicts between humans and nature.
Ecocentrism believes that anthropocentrism is the source of ecological destruction and environmental pollution. It believes that humans should establish an ethical value system and corresponding development concept based on natural ecology. Ecocentrism holds that animals themselves possess emotional and innate rights, and that living beings possess intrinsic value. It believes that the value status of nature is higher than that of humanity, emphasizing the rights and intrinsic values of nature. Therefore, ecocentrism opposes the anthropocentrism that prioritizes human interests over nature. However, ecocentrism has gone to another extreme. Ecocentrism attempts to bridge the divide between humans and nature, but the result is either “human transformation into biology” or “the disappearance of humans”.
It can be seen that neither anthropocentrism nor ecocentrism can truly establish an equal and friendly relationship between humans and nature, nor can they truly achieve harmony between humans and nature and the sustainable development of human society. Both anthropocentrism and ecocentrism are one-sided. Therefore, it is necessary to go beyond the limitations of anthropocentrism and ecocentrism and establish an ecological holism ethics that integrates humans and nature, which is equal, friendly, and harmonious. Only when humans are integrated with nature—caring for nature means caring for oneself, caring for oneself means caring for nature—will protecting nature become the responsibility that humans actively undertake. Marx holds that the coordination between humans and nature can only be truly achieved through the bidirectional movement of the “humanization of nature” and the “naturalization of humans” [43]. There should be coexistence, co-prosperity, and coordinated development between humans and nature. On one hand, humans can start with their goals and needs, fully exert their subjective initiative, occupy, and enjoy nature. On the other hand, humans cannot conquer and dominate nature as they please; human activities cannot violate objective natural laws, and their utilization and transformation of nature cannot exceed the limits of self-regulation of natural ecosystems. Only by simultaneously considering these two aspects can the relationship between humans and nature be harmonious.

2.4. Practical Application of Ecological Aesthetics

The value of the ecological aesthetics theory lies in not only its speculative value but also in its guiding significance for practice. The two are in a mutually guiding and promoting relationship. With people actively exploring sustainable development based on ecological aesthetics, ecological aesthetics has infiltrated into the fields of humanities, social sciences, and natural sciences. Ecological aesthetics has been widely reflected in literary creations, such as novels, dramas, and poetry, as well as in the planning and design of architecture, the environment, cities, and gardens. Ecological aesthetics has also been integrated into various disciplines, such as physics, chemistry, biology, and medicine, overcoming the neglect of harmony between humans and the environment. For example, López-McAlest et al. conducted research on cements from the perspectives of aesthetics and sustainability [44]. Ecological aesthetics has long been applied to industry processes, which are sustainable industry processes developed in response to the deepening ecological crisis of conventional industry, including ecological industry and green industry. However, so far, there are few reports on the practical application of ecological aesthetics in industrial production and research processes, especially in specific processes or products. The in-depth practice of ecological aesthetics in green chemical processes will undoubtedly enrich people’s understanding of ecological aesthetics. The following shows the detailed practice of ecological aesthetics in the production of energy materials.

3. Materials and Methods

N-doped bimetallic carbide C19Cr7Mo24 with carbonized resin as the matrix (N/C19Cr7Mo24/RC) was synthesized using ion-exchange resin as the carbon source through a conventional chemical process. N-doped C19Cr7Mo24 with carbonized lotus leaf stem as the matrix (N/C19Cr7Mo24/LC) was synthesized using lotus leaf stem as the carbon source through a green chemical process. The physical, chemical, and electrochemical characterizations are shown in the Supplementary Materials.

3.1. Synthesis of the N/C19Cr7Mo24/RC

Typically, 10 g of macroporous weakly alkaline anion exchange resin (D314, Tianjin Xinyue Huamei Environmental Protection Technology Co., Ltd., Tianjin, China) was added to 200 mL 0.044 mol L−1 ammonium molybdate ((NH4)6Mo7O24, AR, Chemical Reagent Factory of Hefei University of Technology, Hefei, China) solution and magnetically stirred for 4 h. Then, the solid sample was isolated and added to 200 mL 0.090 mol L−1 potassium chromate (K2CrO4, AR, 99.5%, Langfang Pengcai Fine Chemical Co., Ltd., Langfang, China) solution and magnetically stirred for 4 h. The solid was collected, dried at 100 °C for 4 h, and heated with N2 (99.999%, Zhenjiang Zhongpu Specialty Gases Co., Ltd., Zhenjiang, China) protection at a heating rate of 5 °C min−1 from room temperature to 1300 °C and kept at 1300 °C for 1 h. After cooling to an ambient temperature, the sample was milled, dispersed into 2 mol L−1 HCl (AR, Xiangfan Shunsheng Fine Chemical Co., Ltd., Xiangfan, China), magnetically stirred for 10 h, washed to neutral using deionized water, and dried at 100 °C for 4 h. The solid was heated again in NH3 (99.999%, Zhenjiang Zhongpu Specialty Gases Co., Ltd., Zhenjiang, China) at a heating rate of 5 °C min−1 from room temperature to 700 °C and kept at 700 °C for 2 h. After cooling to an ambient temperature, the sample was collected and defined as N/C19Cr7Mo24/RC. The TD results (Figure S1a, Supplementary Materials) showed that the C19Cr7Mo24 content in the N/C19Cr7Mo24/RC was 55.7 wt.%.

3.2. Synthesis of the N/C19Cr7Mo24/LC

Ten g of cleaned and dried lotus leaf stem (collected on the campus of Yangzhou University) was cut into small pieces, added to 200 mL 0.044 mol L−1 ammonium molybdate solution, and magnetically stirred for 4 h. The sample was collected, added to 200 mL 0.090 mol L−1 potassium chromate solution, and magnetically stirred for 4 h. The sample was collected again and dried at 100 °C for 4 h, heated at a heating rate of 5 °C min−1 from room temperature to 800 °C under N2 protection, and kept at 800 °C for 1 h. Then the temperature was reduced to 700 °C and N2 was replaced with NH3 and kept for 2 h. After cooling to an ambient temperature under N2 protection, the sample was washed with deionized water (200 mL) seven times to remove the impurities. The solid was finally dried at 100 °C for 8 h and was defined as N/C19Cr7Mo24/LC. The TD results (Figure S1b, Supplementary Materials) showed that the C19Cr7Mo24 content in the N/C19Cr7Mo24/LC was 54.2 wt.%.

4. Results and Discussion

4.1. Analysis of Physical Characterizations

4.1.1. Crystal Formation Mechanism

Figure S2 (XRD patterns) shows that both the N/C19Cr7Mo24/RC and the N/C19Cr7Mo24/LC were composed of the C19Cr7Mo24 compound and carbon (or graphite); N dopants were not detected, indicating that they were uniformly embedded in the carbon matrix. Figure 3a displays the XRD patterns during the carbonization process for the N/C19Cr7Mo24/RC. At a relatively low temperature of 800 °C, there were monometallic carbides (Cr23C6 and Mo2C) and oxides (Cr2O3 and MoO3). At a high temperature of 1200 °C, all the oxides were transformed into carbides, and the bimetallic carbide C19Cr7Mo24 appeared. At a very high temperature of 1300 °C, there was only C19Cr7Mo24; meanwhile, a sharp graphite peak C (002) appeared, indicating the formation of a graphite matrix, being consistent with the Raman result (Figure S3, Supplementary Materials). As a comparison, Figure 3b displays the XRD patterns during the carbonization process for the N/C19Cr7Mo24/LC. At a low temperature of 700 °C, there were monometallic carbides (Cr3C2 and Mo2C). At a relative high temperature of 800 °C, there was only C19Cr7Mo24. It showed that the lotus leaf stem as a carbon source more favored the formation of the C19Cr7Mo24 compound (at 800 °C) than the ion-exchange resin as a carbon source (at 1200–1300 °C), which greatly reduced the energy consumption. It can be seen that the half-peak-width for the N/C19Cr7Mo24/LC was wider than that of the N/C19Cr7Mo24/RC, meaning that the C19Cr7Mo24 particle size in the N/C19Cr7Mo24/LC was smaller. That is to say, the lotus leaf stem favored dispersing the carbide precursors, which was very beneficial for the full utilization of both the C19Cr7Mo24 components and the precursor materials. However, the N/C19Cr7Mo24/LC synthesized at a relative low temperature (800 °C) showed no sharp graphite peak, indicating an amorphous carbon matrix, consistent with its Raman result (Figure S3), which might lead to poor stability in electrochemical catalysis.

4.1.2. Morphology and Pore Structure

Figure 4a,b display the SEM images of the N/C19Cr7Mo24/RC and the N/C19Cr7Mo24/LC. The N/C19Cr7Mo24/RC showed big blocks (after milling); however, the N/C19Cr7Mo24/LC showed uniform and small particles (without the milling process). It was found that the N/C19Cr7Mo24/RC was too hard and dense to be broken and milled; while the N/C19Cr7Mo24/LC was very soft and loose and could be easily crushed. Figure 4c,d show the TEM images. The N/C19Cr7Mo24/LC obviously had smaller C19Cr7Mo24 particles (~3 nm in diameter) than that of the N/C19Cr7Mo24/RC (~20 nm in diameter), which was consistent with the XRD results (Figure 3). The small particles of both the N/C19Cr7Mo24/LC (SEM result) and the C19Cr7Mo24 (TEM result) favored full utilization of active components when used as a catalyst.
Figure 5 displays the N2 adsorption–desorption isotherms and the corresponding pore size distributions. Table 2 summarizes the data. They show that the N/C19Cr7Mo24/LC had a high specific surface area, a high pore volume, and a large average pore diameter; the N/C19Cr7Mo24/RC had a much lower specific surface area and a small average pore diameter. The results indicated that the N/C19Cr7Mo24/LC would be more favorable to exposing active sites and mass transportation, favoring catalysis.

4.2. ORR Activity and Stability

The different pore size, specific surface area, particle size, and graphitization degree significantly affected the catalytic activity and stability. Figure 6a displays the linear sweeping voltammetry (LSV) curves for ORR with Pt/C (40 wt.% Pt, Johnson Matthey) being compared. The half-wave potential (E1/2 vs. RHE) is usually adopted to compare the activities, which was 0.903 V for the N/C19Cr7Mo24/LC, 0.871 V for the N/C19Cr7Mo24/RC, and 0.862 V for the Pt/C, respectively. The N/C19Cr7Mo24/RC had slightly higher ORR activity than the Pt/C, yet the N/C19Cr7Mo24/LC had much higher ORR activity than both the N/C19Cr7Mo24/RC and the Pt/C. The Tafel curves in Figure 6b show that the slope of the N/C19Cr7Mo24/LC was the lowest (37.0 mV dec−1). The lowest slope means the fastest kinetics, corresponding to the highest catalytic activity. The Cyclic voltammetry (CV) curves without electrode rotation (Figure 6c) displayed similar results; therein, the N/C19Cr7Mo24/LC showed a high double layer capacitance, being consistent with its high specific surface area. Figure 6d shows that the C19Cr7Mo24/RC without the N dopant had no ORR activity, yet the C19Cr7Mo24/LC had a slight ORR peak, which was due to the lotus leaf stem itself containing a small amount of N (see Figure S4 for the EDS pattern, Supplementary Materials). In addition, Figure S5 (Supplementary Materials) shows that both the N-doped lotus leaf stem carbon (N-LC, without C19Cr7Mo24) and the C19Cr7Mo24/LC (without N dopant) had low or no ORR activity, meaning that the synergistic effect between N (or N-LC) and C19Cr7Mo24 accounted for the above excellent ORR activity.
The catalytic stability for ORR was characterized through carrying on many cycles of CV (Supplementary Materials). Figure 7 shows that both the N/C19Cr7Mo24/RC and the N/C19Cr7Mo24/LC had excellent catalytic stability, which were much better than that of the Pt/C. Therein, the N/C19Cr7Mo24/RC was slightly better than the N/C19Cr7Mo24/LC in stability, which was due to the fact that the N/C19Cr7Mo24/RC has a graphite matrix (XRD and Raman results) is more electrochemically stable. Nevertheless, even the lowest activity value of the N/C19Cr7Mo24/LC was much higher than the highest activity value of the N/C19Cr7Mo24/RC (see the green dotted lines in Figure 7d), indicating that N/C19Cr7Mo24/LC had many significant advantages in practical application.

4.3. Electron Transfer Number, Resistance to Methanol and CO

The electron transfer numbers on the N/C19Cr7Mo24/RC and the N/C19Cr7Mo24/LC were calculated as 3.91–3.97, and 3.93–3.98, respectively, at potential range of 0.4~0.9 V, according to the Koutecky–Levich equation (Figure S6, Supplementary Materials), which meant that the 4-electron process dominated ORR on both the electrodes.
In addition, both the N/C19Cr7Mo24/RC and the N/C19Cr7Mo24/LC showed excellent resistance to methanol and CO (Figure S7, Supplementary Materials).

4.4. H2/O2 Fuel Cell Characterization

The synthesized materials were used as cathode materials for the fuel cell testing system (Figure 8). The N/C19Cr7Mo24/RC and the N/C19Cr7Mo24/LC displayed peak power densities (PPD) of 1.09 W cm−2 and 1.24 W cm−2, which were 1.08 and 1.23 times the PPD of the Pt/C (1.01 W cm−2), respectively (Figure 8a). Figure 8b displays that the PPD of the N/C19Cr7Mo24/RC enhanced from 0.61 to 1.09 W cm−2 as its loading is added from 0.5 to 1.0 mg cm−2 (Figure S8a, Supplementary Materials), due to the increased active sites. As its loading was further added to 2.0 mg cm−2, the PPD remained almost unchanged. However, Figure 8c displays that when the loading of the N/C19Cr7Mo24/LC increased from 0.5 to 1.0 and 2.0 mg cm−2, the PPD continuously increased from 0.67 to 1.24 and 1.47 W cm−2. Only when the loading increased to 3.0 mg cm−2, the PPD did not increase significantly (Figure S8a). The N/C19Cr7Mo24/LC improved the pore structure (Figure 5), favoring mass transportation, making it more capable of large loadings. Significantly, as the loadings reached 3 mg cm−2, the N/C19Cr7Mo24/LC was well protected from being affected by detachment and corrosion for a longer time.
The durability of the N/C19Cr7Mo24/RC and the N/C19Cr7Mo24/LC was also characterized on the fuel cell testing system. Figure 8d,e and Figure S8b (Supplementary Materials) show that, after 25,000 and 50,000 cycles, the N/C19Cr7Mo24/RC maintained, respectively, 97.5% and 95.2% of its initial PPD; the N/C19Cr7Mo24/LC maintained, respectively, 96.9% and 94.1% of its initial PPD. However, within 6000 cycles, the Pt/C maintained merely 90.0% of its initial PPD (Figures S8b and S9, Supplementary Materials). Figure 8f prove the excellent stability of the N/C19Cr7Mo24/RC and the N/C19Cr7Mo24/LC catalysts.

4.5. Mechanism of ORR Activity and Stability

The reported PDF calculations explained that the C atom adjacent to the N atom formed a positive charge center, which was easy to adsorb O2 molecules; while the N atom formed a negative charge center, which was easy to provide electrons to O2, thus promoting ORR [45]. The XPS results (Figures S10 and S11) indicated that the N/C19Cr7Mo24/RC formed both stronger positive and negative charge centers due to the electron transfer of a higher extent, compared with the N-doped carbonized resin (N-RC); while the N/C19Cr7Mo24/LC further enhanced this degree of electron transfer, thus more promoting ORR. In addition, the excellent pore structure and smaller particle size of the N/C19Cr7Mo24/LC facilitated the mass transportation and exposure of active sites, accounting for the highest activity.
As for the excellent stability, firstly, it was related to the intrinsic stability of the bimetallic carbide C19Cr7Mo24; secondly, the high degree of electron transfer mentioned above implied an increase in the mutual binding forces between the components, which improved stability.

4.6. Summary

Table 3 summarizes the preparation process, structure, and performance of the N/C19Cr7Mo24/RC and N/C19Cr7Mo24/LC. Compared with the N/C19Cr7Mo24/RC, the N/C19Cr7Mo24/LC synthesized using green chemical processes had significant advantages in terms of environmental friendliness, operation simplicity, energy saving, structure, and activity. The stability of the N/C19Cr7Mo24/RC was slightly higher than that of the N/C19Cr7Mo24/LC. However, the initial activity of N/C19Cr7Mo24/LC was much higher, and it maintained higher activity than the N/C19Cr7Mo24/RC during long-term operation. The results demonstrated that green chemical processes can completely surpass conventional chemical processes, achieving an all-win situation in terms of environmental protection, performance, and cost. In future work, the activity could be further enhanced through dispersing C19Cr7Mo24 into smaller particles and improving the pore structure of the carbon matrix; the stability could be further enhanced through increasing the graphitization degree of the carbon matrix and increasing the crystallinity of the C19Cr7Mo24.

5. Conclusions

Ecological aesthetics has emerged in the process of the human response to ecological crises, and continuously developed in the process of solving various practical engineering problems. This work combines ecological aesthetics with energy material research. Ecological aesthetics was adopted to guide the research on the green production of energy materials. Correspondingly, the green production process research for energy materials provides examples and ideas for ecological aesthetics. The combined research helps to deeply understand the concept of ecological aesthetics and green chemical processes. In the example of green production research, bimetallic carbide C19Cr7Mo24 with a particle size of about 3 nm has been synthesized using lotus leaf stem as the carbon source at a relative low temperature of 800 °C. After N doping, the N/C19Cr7Mo24/LC composite with a high specific surface area and porous structure was obtained. Compared with the N/C19Cr7Mo24/RC that was synthesized using conventional chemical processes, the N/C19Cr7Mo24/LC has many advantages, such as a lower synthesis temperature, less use of chemicals, a simpler preparation process, a superior pore structure, a higher catalytic activity, more environmental friendliness, and a lower energy consumption. It was demonstrated that the advance of science and technology that conforms to ecological aesthetics can meet human needs without damaging the environment and may even simultaneously meet the requirements of both anthropocentrism and ecocentrism.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/su16114398/s1, Methods for physical characterization, Electrochemical characterization, and H2/O2 fuel cell characterization; K–L (Koutecky–Levich) equation; Discussion on TG analysis; Discussion on EDS analysis; Discussion on anti-methanol and anti-CO performance; Discussion on XPS data; Theoretical Basis for the Origin of Ecological Aesthetics; Figure S1: TG plot of the N/C19Cr7Mo24/RC (a) and N/C19Cr7Mo24/LC (b) in air, insets are the XRD patterns of the residual; Figure S2: XRD patterns of the N/C19Cr7Mo24/RC and N/C19Cr7Mo24/LC; the peak position and relative intensity of the C19Cr7Mo24 (PDF#29-0451) are also plotted; Figure S3: Raman spectroscopy curves of the N/C19Cr7Mo24/RC and N/C19Cr7Mo24/LC; Figure S4: EDS patterns of the LC (lotus-leaf-stem carbon) before and after washing by deionized water; Figure S5: LSV curves on the C19Cr7Mo24/LC, Pt/C and N-LC (N-doped carbonized lotus leaf stem); the electrode rotation speed is 1600 rpm; the scan rate is 10 mV s−1. 0.1 mol L−1 KOH solution with O2-saturation is used as electrolyte; Figure S6: Polarization plots on (a1) C19Cr7Mo24/RC and (a2) C19Cr7Mo24/LC in O2-saturated 0.1 mol L−1 KOH solution at the electrode rotation speed of 100–3600 rpm and scan rate of 10 mVs−1; the Koutecky–Levich plots at different potentials on (b1) C19Cr7Mo24/RC and (b2) C19Cr7Mo24/LC; Figure S7: Chronoamperometric plots at 0.80 V on various electrodes in O2-saturated 0.1 mol L−1 KOH solution. (a) Methanol was added, (b) O2 was replaced with N2 or CO; Figure S8: PPD histograms (a) versus catalyst loading and (b) versus cycle of polarization; Figure S9: Durability curves of polarization and power density on H2/O2 fuel cell, Pt/C is used as cathodic catalyst; Figure S10: (a) XPS spectra of the N/C19Cr7Mo24/RC and N/C19Cr7Mo24/LC. N 1s spectra of (b) N-RC, (c) N/C19Cr7Mo24/RC, and (d) N/C19Cr7Mo24/LC. Mo 3d spectra of (e) N/C19Cr7Mo24/RC and (f) N/C19Cr7Mo24/LC. Cr 2p spectra of (g) N/C19Cr7Mo24/RC and (h) N/C19Cr7Mo24/LC; Figure S11: XPS binding energy and peak area percentage of (a1,a2) N 1s, (b1,b2) Mo 3d5/2, and (c1,c2) Cr2p3/2 for the N/C19Cr7Mo24/RC and N/C19Cr7Mo24/LC. The data are summarized in Figure S10.

Author Contributions

Conceptualization, M.Z. and Z.Y.; methodology, M.Z., K.W. and Z.Y.; validation, M.Z., K.W. and Z.Y.; investigation, M.Z., K.W. and Z.Y.; resources, Z.Y.; writing—original draft, M.Z. and K.W.; writing—review and editing, Z.Y.; supervision, Z.Y.; project administration, Z.Y. 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

The data presented in this study are available on request from the corresponding author.

Acknowledgments

The authors are grateful to Tianqian Yan for the support of the lotus leaf stem.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Liu, Z.F.; Ye, D.D.; Zhu, X.; Wang, S.L.; Zou, Y.N.; Lan, L.H.; Chen, R.; Yang, Y.; Liao, Q. ZIF-67-Derived Co Nanoparticles Embedded in N-Doped Porous Carbon Composite Interconnected by MWCNTs as Highly Efficient ORR Electrocatalysts for a Flexible Direct Formate Fuel Cell. Chem. Eng. J. 2022, 432, 134192. [Google Scholar] [CrossRef]
  2. Barrio, J.; Pedersen, A.; Feng, J.; Sarma, S.C.; Wang, M.; Li, A.Y.; Yadegari, H.; Luo, H.; Ryan, M.P.; Titirici, M.M.; et al. Metal coordination in C2N-like materials towards dual atom catalysts for oxygen reduction. J. Mater. Chem. A 2022, 10, 6023–6030. [Google Scholar] [CrossRef] [PubMed]
  3. Tong, Y.; Chen, P.; Zhou, T.; Xu, K.; Chu, W.; Wu, C.; Xie, Y. A Bifunctional Hybrid Electrocatalyst for Oxygen Reduction and Evolution: Cobalt Oxide Nanoparticles Strongly Coupled to B, N-Decorated Graphene. Angew. Chem. Int. Ed. 2017, 56, 7121–7125. [Google Scholar] [CrossRef] [PubMed]
  4. Huo, L.; Lv, M.H.; Li, M.J.; Ni, X.; Guan, J.Y.; Liu, J.; Mei, S.X.; Yang, Y.Q.; Zhu, M.M.; Feng, Q.C.; et al. Amorphous MnO2 Lamellae Encapsulated Covalent Triazine Polymer-Derived Multi-Heteroatoms-Doped Carbon for ORR/OER Bifunctional Electrocatalysis. Adv. Mater. 2024, 36, 2312868. [Google Scholar] [CrossRef] [PubMed]
  5. Ma, X.; Meng, H.; Cai, M.; Shen, P.K. Bimetallic Carbide Nanocomposite Enhanced Pt Catalyst with High Activity and Stability for the Oxygen Reduction Reaction. J. Am. Chem. Soc. 2012, 134, 1954–1957. [Google Scholar] [CrossRef]
  6. Yan, Z.; Zhang, M.; Xie, J.; Shen, P.K. An ultrastable bimetallic carbide as Platinum Electrocatalyst Support for Highly Active Oxygen Reduction Reaction. J. Power Sources 2015, 295, 156–161. [Google Scholar] [CrossRef]
  7. Li, Z.; Ji, S.; Pollet, B.G.; Shen, P.K. A Co3W3C Promoted Pd Catalyst Exhibiting Competitive Performance over Pt/C Catalysts towards the Oxygen Reduction Reaction. Chem. Commun. 2014, 50, 566–568. [Google Scholar] [CrossRef] [PubMed]
  8. Feng, X.; Bo, X.; Guo, L. An Advanced Hollow Bimetallic Carbide/Nitrogen-Doped Carbon Nanotube for Efficient Catalysis of Oxygen Reduction and Hydrogen Evolution and Oxygen Evolution Reaction. J. Colloid Interface Sci. 2020, 575, 69–77. [Google Scholar] [CrossRef] [PubMed]
  9. Yan, Z.; Zhang, Y.; Jiang, Z.; Jiang, D.; Wei, W.; Hu, Z. Nitrogen-Doped Bimetallic Carbide-Graphite Composite as Highly Active and Extremely Stable Electrocatalyst for Oxygen Reduction Reaction in Alkaline Media. Adv. Funct. Mater. 2022, 32, 2204031. [Google Scholar] [CrossRef]
  10. Yan, Z.; Cui, J.; Jiang, D.; Xie, J.; Zhang, M.; Wei, W.; Zhao, X. Nitrogen- and fluorine-doped bimetallic carbide as active and stable oxygen reduction reaction electrocatalyst. J. Colloid Interface Sci. 2024, 660, 345–355. [Google Scholar] [CrossRef]
  11. Wu, Y.; Chen, Y.; Wang, H.; Wang, C.; Wang, A.; Zhao, S.; Li, X.; Sun, D.; Jiang, J. Efficient ORR Electrocatalytic Activity of Peanut Shell-Based Graphitic Carbon Microstructures. J. Mater. Chem. A 2018, 6, 12018–12028. [Google Scholar] [CrossRef]
  12. Sekhon, S.S.; Kaur, P.; Park, J.S. From Coconut Shell Biomass to Oxygen Reduction Reaction Catalyst: Tuning Porosity and Nitrogen Doping. Renew. Sustain. Energ. Rev. 2021, 147, 111173. [Google Scholar] [CrossRef]
  13. Hao, Y.; Zhang, X.; Yang, Q.; Chen, K.; Guo, J.; Zhou, D.; Feng, L.; Slanina, Z. Highly Porous Defective Carbons Derived from Seaweed Biomass as Efficient Electrocatalysts for Oxygen Reduction in Both Alkaline and Acidic Media. Carbon 2018, 137, 93–103. [Google Scholar] [CrossRef]
  14. Li, Y.; Qu, Y.; Liu, C.; Cui, J.; Xu, K.; Li, Y.; Shen, H.; Lu, Z.; Pan, H.; Xu, T.; et al. Processing Agricultural Cornstalks toward High-Efficient Stable Bifunctional ORR/OER Electrocatalysts. Adv. Sustain. Syst. 2022, 6, 2100343. [Google Scholar] [CrossRef]
  15. Zhang, M.; Zhang, Y.; Cui, J.; Zhang, Z.; Yan, Z. Biomass-Based Oxygen Reduction Reaction Catalysts from the Perspective of Ecological Aesthetics—Duckweed Has more Advantages than Soybean. Sustainability 2022, 14, 9087. [Google Scholar] [CrossRef]
  16. Boothroyd, D. Futural Dispatches on Responsibility for the Earth, or, ‘What on Earth Is Ethical Responsibility? Humanities 2022, 11, 18. [Google Scholar] [CrossRef]
  17. Ganoulis, J. The Dialectics of Nature–Human Conflicts for Sustainable Water Security. Sustainability 2024, 16, 3055. [Google Scholar] [CrossRef]
  18. Li, X.; Wei, F.M. What Confucian Eco-Ethics Can Teach Us about Solving the Dilemma of Interpreting the Concept of Sustainability. Religions 2023, 14, 1216. [Google Scholar] [CrossRef]
  19. Chen, G.; Yang, X.; Xie, Z.; Zhao, F.; Zhou, Z.; Yuan, Q. Hollow PtCu Octahedral Nanoalloys: Efficient Bifunctional Electrocatalysts towards Oxygen Reduction Reaction and Methanol Oxidation Reaction by Regulating Near-Surface Composition. J. Colloid Interface Sci. 2020, 562, 244–251. [Google Scholar] [CrossRef]
  20. Wu, X.; Ni, C.; Man, J.; Shen, X.; Cui, S.; Chen, X. A Strategy to Promote the ORR Electrocatalytic Activity by the Novel Engineering Bunched Three-Dimensional Pd-Cu Alloy Aerogel. Chem. Eng. J. 2023, 454, 140293. [Google Scholar] [CrossRef]
  21. Han, J.; Bao, H.; Wang, J.Q.; Zheng, L.; Sun, S.; Wang, Z.L.; Sun, C. 3D N-Doped Ordered Mesoporous Carbon Supported Single-Atom Fe-N-C Catalysts with Superior Performance for Oxygen Reduction Reaction and Zinc-Air Battery. Appl. Catal. B Environ. 2021, 280, 119411. [Google Scholar] [CrossRef]
  22. Wang, Q.; Yang, Y.; Sun, F.; Chen, G.; Wang, J.; Peng, L.; Chen, W.T.; Shang, L.; Zhao, J.; Waterhouse, D.S.; et al. Molten NaCl-Assisted Synthesis of Porous Fe-N-C Electrocatalysts with a High Density of Catalytically Accessible FeN4 Active Sites and Outstanding Oxygen Reduction Reaction Performance. Adv. Energy Mater. 2021, 11, 2100219. [Google Scholar] [CrossRef]
  23. Ha, Y.; Fei, B.; Yan, X.; Xu, H.; Chen, Z.; Shi, L.; Fu, M.; Xu, W.; Wu, R. Atomically Dispersed Co-Pyridinic N-C for Superior Oxygen Reduction Reaction. Adv. Energy Mater. 2020, 10, 2002592. [Google Scholar] [CrossRef]
  24. Qu, X.; Han, Y.; Chen, Y.; Lin, J.; Li, G.; Yang, J.; Jiang, Y.; Sun, S. Stepwise Pyrolysis Treatment as an Efficient Strategy to Enhance the Stability Performance of Fe-Nx/C Electrocatalyst towards Oxygen Reduction Reaction and Proton Exchange Membrane Fuel Cell. Appl. Catal. B Environ. 2021, 295, 120311. [Google Scholar] [CrossRef]
  25. He, Y.; Shi, Q.; Shan, W.; Li, X.; Kropf, A.J.; Wegener, E.C.; Wright, J.; Karakalos, S.; Su, D.; Cullen, D.A.; et al. Dynamically Unveiling Metal-Nitrogen Coordination during Thermal Activation to Design High-Efficient Atomically Dispersed CoN4 Active Sites. Angew. Chem. Int. Ed. 2021, 60, 9516–9526. [Google Scholar] [CrossRef] [PubMed]
  26. Zeng, R.; Yang, Y.; Feng, X.R.; Li, H.Q.; Gibbs, L.M.; DiSalvo, F.J.; Abruña, H.D. Nonnoble Transition Metal Nitrides as Efficient Oxygen Reduction Electrocatalysts for Alkaline Fuel Cells. Sci. Adv. 2022, 8, 1584. [Google Scholar] [CrossRef] [PubMed]
  27. Hu, K.; Wang, X.; Hu, Y.X.; Hu, H.L.; Lin, X.R.; Reddy, K.M.; Luo, M.; Qiu, H.J.; Lin, X. Simultaneous Improvement of Oxygen Reduction and Catalyst Anchoring via Multiple Dopants on Mesoporous Carbon Frameworks for Flexible Al-Air Batteries. ACS Nano 2022, 16, 19165–19173. [Google Scholar] [CrossRef] [PubMed]
  28. Wang, R.; Yang, H.; Lu, N.; Lei, S.; Jia, D.; Wang, Z.; Liu, Z.; Wu, X.; Zheng, H.; Ali, S.; et al. Precise Identification of Active Sites of a High Bifunctional Performance 3D Co/N-C Catalyst in Zinc-Air Batteries. Chem. Eng. J. 2022, 433, 134500. [Google Scholar] [CrossRef]
  29. Li, L.; Wen, Y.; Han, G.; Liu, Y.; Song, Y.; Zhang, W.; Sun, J.; Du, L.; Kong, F.; Ma, Y.; et al. Tailoring the Stability of Fe-N-C via Pyridinic Nitrogen for Acid Oxygen Reduction Reaction. Chem. Eng. J. 2022, 437, 135320. [Google Scholar] [CrossRef]
  30. Fu, X.; Zhang, L.; Zhu, X.; Zhu, S.; Min, Y.; Xu, Q.; Li, Q. Trace Mn-Doped on Highly Dispersed Fe/Mn-SNC Ultrathin Carbon Nanosheets for Efficient Oxygen Reduction Reaction. Appl. Surf. Sci. 2023, 613, 156087. [Google Scholar] [CrossRef]
  31. Jiang, H.; Ai, J.; Li, Z.; Guo, Y.; Shao, T.; Wang, K.; Zheng, C.; Xu, X.; Wang, B.; Zhou, Z.; et al. Regulation of Graphitized Pore Structure Adjacent to Atomic FeN4 Sites with Pyrolyzing Rate for Highly Active Oxygen Reduction Reaction Electrocatalysts. Appl. Surf. Sci. 2023, 614, 156076. [Google Scholar] [CrossRef]
  32. Cao, M.; Liu, Y.; Sun, K.; Li, H.; Lin, X.; Zhang, P.; Zhou, L.; Wang, A.; Mehdi, S.; Wu, X.; et al. Coupling Fe3C Nanoparticles and N-Doping on Wood-Derived Carbon to Construct Reversible Cathode for Zn-Air Batteries. Small 2022, 18, 2202014. [Google Scholar] [CrossRef] [PubMed]
  33. Men, X.; Tang, R.; Yang, H.; Wang, M.; Sun, H.; Liang, S.; Liu, Z.; Lu, G. Bio-Inspired Micro-Reactor Mimicking Multi-Ridged Mitochondrial Intimae for Efficient Oxygen Reduction. Appl. Surf. Sci. 2023, 610, 155469. [Google Scholar] [CrossRef]
  34. Liu, B.; Yuan, B.; Wang, C.; You, S.; Liu, J.; Meng, X.; Xu, X.; Cai, Z.; Xie, J.; Zou, J. Highly-Dispersed NiFe Alloys In-Situ Anchored on Outer Surface of Co, N co-Doped Carbon Nanotubes with Enhanced Stability for Oxygen Electrocatalysis. J. Colloid Interface Sci. 2023, 635, 208–220. [Google Scholar] [CrossRef] [PubMed]
  35. Guo, Y.; Yin, H.; Cheng, F.; Li, M.; Zhang, S.; Wu, D.; Wang, K.; Wu, Y.; Yang, B.; Zhang, J.N. Altering Ligand Microenvironment of Atomically Dispersed CrN4 by Axial Ligand Sulfur for Enhanced Oxygen Reduction Reaction in Alkaline and Acidic Medium. Small 2023, 19, 2206861. [Google Scholar] [CrossRef]
  36. Lin, X.L. Thoreau, Haeckel and Invention of the Word “Ecology”. Sci. Cult. Rev. 2013, 10, 18–28. [Google Scholar]
  37. Haeckel, E. Uber Entwicklungsgang Und Aufgabe Der Zoologie. Jenaische Z. Med. Naturwiss 1870, 5, 353–370. [Google Scholar]
  38. Joseph, W.M. Notes toward an Ecological Esthetic. Can. Fict. Mag. 1972, 2, 4–15. [Google Scholar]
  39. Zhu, G.Q. History of Western Aesthetics (Volume 1); People’s Literature Publishing House: Beijing, China, 1963; Available online: https://baike.baidu.com/item/%E8%A5%BF%E6%96%B9%E7%BE%8E%E5%AD%A6%E5%8F%B2%EF%BC%88%E4%B8%8A%E5%8D%B7%EF%BC%89/57348047?fr=ge_ala (accessed on 10 January 2024). (In Chinese)
  40. Kant. Critique of Judgment (Volume 1); Commercial Press: Beijing, China, 2009; Available online: https://baike.baidu.com/item/%E5%88%A4%E6%96%AD%E5%8A%9B%E6%89%B9%E5%88%A4/1545759?fr=ge_ala (accessed on 10 March 2024). (In Chinese)
  41. Hegel. Aesthetics (Volume 1); Commercial Press: Beijing, China, 1979; Available online: https://baike.baidu.com/item/%E7%BE%8E%E5%AD%A6/2234028?fromModule=lemma_search-box (accessed on 11 March 2024). (In Chinese)
  42. Foucault, M. Words and Objects: Archaeology of Humanities and Sciences; Shanghai Sanlian Bookstore: Shanghai, China, 2001; Available online: https://baike.baidu.com/item/%E8%AF%8D%E4%B8%8E%E7%89%A9%20%3A%20%E4%BA%BA%E6%96%87%E7%A7%91%E5%AD%A6%E8%80%83%E5%8F%A4%E5%AD%A6?fromModule=lemma_search-box (accessed on 2 March 2024). (In Chinese)
  43. Marx, K. Economic and Philosophic Manuscripts of 1844; People’s Publishing House: Beijing, China, 2018; Available online: https://baike.baidu.com/item/1844%E5%B9%B4%E7%BB%8F%E6%B5%8E%E5%AD%A6%E5%93%B2%E5%AD%A6%E6%89%8B%E7%A8%BF/62455318?fromModule=search-result_lemma-recommend (accessed on 15 April 2024). (In Chinese)
  44. López-Malest, A.; Gabor, M.R.; Panait, M.; Brezoi, A.; Veres, C. Green Innovation for Carbon Footprint Reduction in Construction Industry. Buildings 2024, 14, 374. [Google Scholar] [CrossRef]
  45. Jo, W.K.; Moru, S.; Lee, D.E.; Tonda, S. Cobalt- and Iron-Coordinated Graphitic Carbon Nitride on Reduced Graphene Oxide: A Nonnoble Bimetallic M–Nx–C Analogue Electrocatalyst for Efficient Oxygen Reduction Reaction in Acidic Media. Appl. Surf. Sci. 2020, 531, 147367. [Google Scholar] [CrossRef]
Sustainability 16 04398 g001
Figure 1. Statistics on the number of papers on biomass-based ORR catalysts published in the recent 6 years (search for the following words in Abstract: biomass, oxygen reduction reaction).
Figure 1. Statistics on the number of papers on biomass-based ORR catalysts published in the recent 6 years (search for the following words in Abstract: biomass, oxygen reduction reaction).
Sustainability 16 04398 g001
Sustainability 16 04398 g002
Figure 2. Comparison of ORR activity and stability between the N/C19Cr7Mo24/RC, the N/C19Cr7Mo24/LC (this work; using conventional processes for the N/C19Cr7Mo24/RC and green chemical processes for the N/C19Cr7Mo24/LC, respectively) and the excellent non-noble metal catalysts reported in the recent 4 years (data sources are in Table 1). E1/2 means half-wave potential; CV means cyclic voltammetry.
Figure 2. Comparison of ORR activity and stability between the N/C19Cr7Mo24/RC, the N/C19Cr7Mo24/LC (this work; using conventional processes for the N/C19Cr7Mo24/RC and green chemical processes for the N/C19Cr7Mo24/LC, respectively) and the excellent non-noble metal catalysts reported in the recent 4 years (data sources are in Table 1). E1/2 means half-wave potential; CV means cyclic voltammetry.
Sustainability 16 04398 g002
Sustainability 16 04398 g003
Figure 3. (a) XRD patterns during the carbonization process for the N/C19Cr7Mo24/RC at 800 °C, 1200 °C, and 1300 °C, respectively. (b) XRD patterns during the carbonization process for the N/C19Cr7Mo24/LC at 700 °C and 800 °C, respectively. The carbonization time at the specified temperature was each kept for 1 h.
Figure 3. (a) XRD patterns during the carbonization process for the N/C19Cr7Mo24/RC at 800 °C, 1200 °C, and 1300 °C, respectively. (b) XRD patterns during the carbonization process for the N/C19Cr7Mo24/LC at 700 °C and 800 °C, respectively. The carbonization time at the specified temperature was each kept for 1 h.
Sustainability 16 04398 g003
Sustainability 16 04398 g004
Figure 4. SEM images of the N/C19Cr7Mo24/RC (a) and the N/C19Cr7Mo24/LC (b). TEM images of the N/C19Cr7Mo24/RC (c) and the N/C19Cr7Mo24/LC (d).
Figure 4. SEM images of the N/C19Cr7Mo24/RC (a) and the N/C19Cr7Mo24/LC (b). TEM images of the N/C19Cr7Mo24/RC (c) and the N/C19Cr7Mo24/LC (d).
Sustainability 16 04398 g004
Sustainability 16 04398 g005
Figure 5. (a) N2 adsorption-desorption isotherms and (b) pore size distributions of the N/C19Cr7Mo24/RC and the N/C19Cr7Mo24/LC.
Figure 5. (a) N2 adsorption-desorption isotherms and (b) pore size distributions of the N/C19Cr7Mo24/RC and the N/C19Cr7Mo24/LC.
Sustainability 16 04398 g005
Sustainability 16 04398 g006
Figure 6. (a) LSV (linear sweeping voltammetry) curves on the N/C19Cr7Mo24/RC, the N/C19Cr7Mo24/LC, and the Pt/C, at a scan rate of 10 mV s−1, with an electrode rotation speed of 1600 rpm. (b) Tafel curves obtained from (a). (c) CV curves on the N/C19Cr7Mo24/RC, the N/C19Cr7Mo24/LC, and the Pt/C, (d) CV curves on the C19Cr7Mo24/RC and the C19Cr7Mo24/LC, at a scan rate of 50 mV s−1. The electrolyte was 0.1 mol L−1 KOH solution with O2 saturation.
Figure 6. (a) LSV (linear sweeping voltammetry) curves on the N/C19Cr7Mo24/RC, the N/C19Cr7Mo24/LC, and the Pt/C, at a scan rate of 10 mV s−1, with an electrode rotation speed of 1600 rpm. (b) Tafel curves obtained from (a). (c) CV curves on the N/C19Cr7Mo24/RC, the N/C19Cr7Mo24/LC, and the Pt/C, (d) CV curves on the C19Cr7Mo24/RC and the C19Cr7Mo24/LC, at a scan rate of 50 mV s−1. The electrolyte was 0.1 mol L−1 KOH solution with O2 saturation.
Sustainability 16 04398 g006
Sustainability 16 04398 g007
Figure 7. LSV curves during the stability characterization on (a) the N/C19Cr7Mo24/RC, (b) the N/C19Cr7Mo24/LC, and (c) the Pt/C, with an electrode rotation speed of 1600 rpm, at a scan rate of 10 mV s−1. (d) E1/2 of LSV curve vs. number of CV cycle; the green dotted lines refer to the lowest activity of the N/C19Cr7Mo24/LC and the highest activity of the N/C19Cr7Mo24/RC. The electrolyte was an O2-saturated 0.1 mol L−1 KOH solution.
Figure 7. LSV curves during the stability characterization on (a) the N/C19Cr7Mo24/RC, (b) the N/C19Cr7Mo24/LC, and (c) the Pt/C, with an electrode rotation speed of 1600 rpm, at a scan rate of 10 mV s−1. (d) E1/2 of LSV curve vs. number of CV cycle; the green dotted lines refer to the lowest activity of the N/C19Cr7Mo24/LC and the highest activity of the N/C19Cr7Mo24/RC. The electrolyte was an O2-saturated 0.1 mol L−1 KOH solution.
Sustainability 16 04398 g007
Sustainability 16 04398 g008
Figure 8. H2/O2 fuel cell polarization and power density curves: (a) N/C19Cr7Mo24/RC and N/C19Cr7Mo24/LC as cathodes; (b) N/C19Cr7Mo24/RC as a cathode at various loadings; (c) N/C19Cr7Mo24/LC as a cathode at various loadings; (d) N/C19Cr7Mo24/RC as a cathode at various cycles; (e) N/C19Cr7Mo24/LC as a cathode at various cycles. The arrows point to the left or right vertical axis corresponding to the curves; (f) The durability curves at 0.7 V in MEA. The relative humidity (RH), back pressure, operating temperature, and catalyst loadings are displayed in the figures.
Figure 8. H2/O2 fuel cell polarization and power density curves: (a) N/C19Cr7Mo24/RC and N/C19Cr7Mo24/LC as cathodes; (b) N/C19Cr7Mo24/RC as a cathode at various loadings; (c) N/C19Cr7Mo24/LC as a cathode at various loadings; (d) N/C19Cr7Mo24/RC as a cathode at various cycles; (e) N/C19Cr7Mo24/LC as a cathode at various cycles. The arrows point to the left or right vertical axis corresponding to the curves; (f) The durability curves at 0.7 V in MEA. The relative humidity (RH), back pressure, operating temperature, and catalyst loadings are displayed in the figures.
Sustainability 16 04398 g008
Table 1. Cyclic voltammetry (CV) cycles and corresponding half-wave potential (E1/2 vs. RHE) changes of ORR catalyzed by non-noble catalysts.
Table 1. Cyclic voltammetry (CV) cycles and corresponding half-wave potential (E1/2 vs. RHE) changes of ORR catalyzed by non-noble catalysts.
Sample NameE1/2
(Initial → End)		Aging CV CyclesElectrolyteCatalyst LoadingRef.
Fe-N-C/N-OMC0.93 → 0.925 V50000.1 M KOH-[21]
Fe/NC-NaCl0.832 → 0.81 V20,0000.1 M HClO41200 µgcat·cm−2[22]
Co-pyridinic N-C0.87 → 0.86 V50000.1 M KOH250 µgcat·cm−2[23]
Fe-NX/C-NC9000.815 → 0.762 V30,0000.1 M HClO4800 µgcat·cm−2[24]
Co-N-C0.83 → 0.795 V30,0000.5 M H2SO40.6 mgcat·cm−2[25]
Co3N/C0.862 → 0.848 V10,0001 M KOH1.8 mgcat·cm−2[26]
MnS/NS-C0.91 → 0.90 V50000.1 M KOH0.4 mgcat·cm−2[27]
3D Co/N-C0.84 → 0.815 V50000.1 M KOH0.25 mgcat·cm−2[28]
Fe-pyridinic N-C0.824 → 0.804 V20,0000.1 M HClO4800 μgcat·cm−2[29]
Fe/Mn-SNC0.92 → 0.915 V10,0000.1 M KOH580 μgcat·cm−2[30]
Fe-N4@GPC0.891 → 0.88 V50000.1 M KOH2 μgcat·cm−2[31]
Fe3C@NPW0.87 → 0.86 V50000.1 M KOH557 μgcat·cm−2[32]
Fe/N-HRCS0.88 → 0.871 V50000.1 M KOH278 μgcat·cm−2[33]
NiFe/Co-N@CNT0.87 → 0.86 V50000.1 M KOH1.322 mgcat·cm−2[34]
Cr/N/C-9500.773 → 0.758 V20,0000.1 M HClO40.6 mgcat·cm−2[35]
N/C19Cr7Mo24/RC0.871 → 0.866 V50,0000.1 M KOH50 μgcat·cm−2this work
N/C19Cr7Mo24/LC0.903 → 0.893 V50,0000.1 M KOH50 μgcat·cm−2this work
Table 2. Pore and surface parameters of the N/C19Cr7Mo24/RC and the N/C19Cr7Mo24/LC.
Table 2. Pore and surface parameters of the N/C19Cr7Mo24/RC and the N/C19Cr7Mo24/LC.
SampleTotal Area (m2 g−1)Microspore Area (m2 g−1)Total Pore Volume (cm3 g−1)Microspore Volume (cm3 g−1)Average Pore Diameter (nm)
N/C19Cr7Mo24/RC173590.10.022.0
N/C19Cr7Mo24/LC4981190.90.0510.2
Table 3. Preparation process and performance comparison of the N/C19Cr7Mo24/RC and N/C19Cr7Mo24/LC.
Table 3. Preparation process and performance comparison of the N/C19Cr7Mo24/RC and N/C19Cr7Mo24/LC.
SampleN/C19Cr7Mo24/RCN/C19Cr7Mo24/LC
Carbon sourceChemical product (ion-exchange resin)Biomass (lotus leaf stem)
Carbonization temperature1200–1300 °C800 °C
N-doping temperature700 °C700 °C
Need to mill product?YesNo
Emiss oil and gas?YesNo
Impurity removal reagentHCl + H2OH2O
Specific surface area173 m2 g−1498 m2 g−1
Average pore diameter2.0 nm10.2 nm
C19Cr7Mo24 diameter~20 nm~3 nm
Initial activity (E1/2)0.871 V0.903 V
Activity at the 50,000th cycle (E1/2)0.866 V0.893 V
Stability (E1/2 retention rate after 50,000 CV cycles)99.40%98.90%
Fuel cell PPD1.13 W cm−2 at 2 mg cm−21.47 W cm−2 at 2 mg cm−2
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Zhang, M.; Wang, K.; Yan, Z. Practice of Ecological Aesthetics in Green Production of Bimetallic Carbide Catalyst for Oxygen Reduction Reaction: Integrating Technological Development with Ecological Protection. Sustainability 2024, 16, 4398. https://doi.org/10.3390/su16114398

AMA Style

Zhang M, Wang K, Yan Z. Practice of Ecological Aesthetics in Green Production of Bimetallic Carbide Catalyst for Oxygen Reduction Reaction: Integrating Technological Development with Ecological Protection. Sustainability. 2024; 16(11):4398. https://doi.org/10.3390/su16114398

Chicago/Turabian Style

Zhang, Meiping, Kailun Wang, and Zaoxue Yan. 2024. "Practice of Ecological Aesthetics in Green Production of Bimetallic Carbide Catalyst for Oxygen Reduction Reaction: Integrating Technological Development with Ecological Protection" Sustainability 16, no. 11: 4398. https://doi.org/10.3390/su16114398

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop