Techniques to Enhance Electrocatalyst Performance in Hydrogen Fuel Cells

The hydrogen oxidation reaction (HOR) is the anodic reaction of hydrogenoxygen fuel cells, which plays a decisive role in the whole-device performance. However, inexpensive crude hydrogen inevitably contains carbon monoxide (CO) impurities, and even the state-of-the-art platinum (Pt) electrocatalysts can suffer an obvious activity decrease due to the poisoning of active sites, seriously hindering the efficiency of fuel cells. Developing electrocatalysts with promoted CO tolerance necessitates the elucidation of the HOR mechanism and deep understanding of the intrinsic nature of fuel cell poisoning. To date, weakening CO adsorption or accelerating its oxidation could improve the CO tolerance of the catalyst, so it is critical to seek much more effective strategies. Based on the study of the reaction mechanism, this Review summarizes the latest progress of HOR electrocatalysts with high stability and high activity against CO poisoning from two typical theories: hydrogen binding energy theory and bifunctional theory. The strategies for enhancing the CO tolerance of catalysts are gather... Read More

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During the transition from conventional energy sources to sustainable alternatives, the role of energy storage and conversion is pivotal. Unitized regenerative fuel cells (URFCs) have attracted significant attention as promising energy storage and conversion devices owing to their ability to operate in both fuel cell (FC) and electrolyser (EL) modes within a compact single cell. They possess several advantages, including high power density, high specific energy density, light-weight design, low-cost production, high efficiency, long lifespan, and near-zero environmental impact. The development of efficient and durable bifunctional electrocatalysts is essential for the practical implementation and outstanding performance of URFCs. In URFCs, oxygen holds greater significance than hydrogen because its electrochemical reactions at the interface between the electrolyte and the electrode tend to be slow and intricate, primarily due to the pronounced irreversibility of oxygen-related processes. This chapter begins with a brief introduction to various types of FCs, setting the context for th... Read More

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As a clean energy conversion technology, hydrogen fuel cell has great development prospect in the field of sustainable energy. Scientists have been working on the design and optimization of hydrogen fuel cells to make the efficiency and performance higher. This article introduces the main directions and methods of designing and optimizing hydrogen fuel cells. First, the design of hydrogen fuel cell mainly depends on the which catalyst materials you choose and catalyst active sites. For example, precious metal catalysts, transition metal catalysts, and catalysts of nanostructured materials all make a huge impact on battery performance. Improving the activity and stability of catalyst and reducing the cost is one of the key points of this design. In addition, optimizing of the electrolyte film to improve the efficiency and battery life is also key. By taking the above factors into consideration and using advanced materials and technologies, hydrogen fuel cells can achieve high efficiency, high performance, and long life, and promote their commercial application.

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Searching for highly efficient and economical electrocatalysts for alkaline hydrogen oxidation reaction (HOR) is crucial for the development of alkaline polymer membrane fuel cells. Here, we report a valid strategy to active pyrite-type RuS

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Abstract Fuel cell technology, as a new way of energy conversion, is widely used in various fields. At present, the electrocatalyst, as one of the key components of the electrochemical reaction of fuel cells, still suffers from the problems of high cost, low activity and poor stability. Excellent fuel cell electrocatalysts must have excellent catalytic activity, antipoisoning ability, electrical conductivity and stability. Metal oxides with corrosion resistance, electrochemical stability and strong metal support interaction effects have been intensively studied. The influence of the synthesis method on the catalytic performance is also crucial. In this review, the importance of fuel cells and their catalysts is introduced. The characteristics of catalysts with three metal oxides, titanium dioxide, cerium dioxide and tungsten oxide, as supports, preparation methods and applications in different fuel cells are reviewed. The synthesis of metal oxide supported catalysts by impregnation, precipitation and hydrothermal methods is described. Finally, the research on metal oxide supported c... Read More

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ConspectusWith the increasing concerns about the energy and environmental crisis, hydrogen, with the high energy density and cleanliness, has been widely regarded as one ideal energy carrier for adjusting the fossil fuel dependent energy system. In this context, extensive studies are focused on improving the efficiency of the sustainable hydrogen production, storage, and utilization coupled with the renewable energy. And it can be realized in electrolysis cells and fuel cell devices. Several electrochemical reactions are involved, such as water splitting (hydrogen/oxygen evolution: HER/OER) for hydrogen production, electroreduction of nitrogen/nitrate, and carbon dioxide to NH3 and HCOOH (NRR, NO3RR, CO2RR) for hydrogen storage, and oxygen reduction reaction (ORR) for hydrogen utilization. However, the achieved efficiency of the hydrogen energy conversion is still unsatisfactory due to these intrinsically sluggish electrochemical reactions, which has spawned a revival of research interests in developing the electrocatalysts with high activity, selectivity, and durability. Therefore, ... Read More

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With much enhanced fuel flexibility to overcome the shortcomings of hydrogen production and storage, high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are still facing challenges of activity loss of oxygen reduction electrocatalyst under the working circumstance of phosphoric acid (PA) electrolyte. Dissolution and leaching of metal component of PtM (M = Cu, Co, Ni) electrocatalysts is one of the key factors that degrade their initial resistance toward PA and hinder the accessing of activity and durability simultaneously. Here, we report an ultradurable PtRhCu@Pt/C electrocatalyst with a high mass activity of 0.90 A mg1Pt, which only decreased by 14.4% after 30K ADT cycles in the half-cell and reaches the DOE at 2025 target (<30 mV at 0.8 A cm2) with 27 mV voltage loss at 0.8 A cm2 in the single-cell. After adding 0.1 M PA into the electrolyte, the half-wave potential of PtRhCu@Pt/C is negatively shifted by only 52 mV, much lower than that of commercial Pt/C (90 mV). Moreover, the HT-PEMFC assembled by this catalyst delivers a preeminent peak power density of ... Read More

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Hydrogen, characterized by its carbon-neutral attributes and high energy density, is gaining momentum as a promising energy source. Platinum group metal (PGM) catalysts have emerged as pivotal components in water electrolysis and fuel cell technologies. However, their constrained availability and high cost impede the advancement of energy conversion systems. To address these challenges, various strategies have been explored within the realm of PGM catalysts. Particularly noteworthy are catalysts that exhibit an overlayer structure, offering exceptional catalyst utilization efficiency, bimetallic synergies, and strain-induced enhancements. Self-terminated electrodeposition (SED) stands out as a technique that enables precise atomic layer electrodeposition within an aqueous electrolyte environment. It allows meticulous control of metal loading quantities and surface coverage while operating at low temperatures and without the need for vacuum conditions. Catalysts with tailored properties achieved through SED exhibit distinct electrochemical reactivity compared to bulk catalysts, showca... Read More

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This chapter describes the theoretical aspects and main characteristics of fuel cells and electrolyzers, a technological field in constant evolution. Hydrogen can be produced through the electrolysis of water to be stored and subsequently supplied to a fuel cell to obtain electrical energy and water as products. The biggest obstacle for these devices is their cost since they are not yet able to compete economically with more traditional energy technologies. The progress of proton exchange membrane (PEM) fuel cell and PEM electrolyzers is complex and requires significant research on the materials of electrodes (specifically on those were take place the oxygen reduction reaction and the oxygen evolution reaction) membranes and the overall components of both cells. Nevertheless, the development and commercialization of this equipment at market price would give a huge boost to hydrogen systems. Great technical advances have been achieved due to the great effort of researchers in the need to reduce the load of catalysts, enhance the catalytic performance, and improve their components to r... Read More

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Fuel cells are one of the prioritized energy conversion technologies with highly focused research and development. For the whole fuel cell commercial realization on the market, fuel cells must be very affordable. This realization calls for critical developments in addressing the technical hindrance such as the overall fuel cell cost, electrocatalysts stability, and durability. A step towards fuel cell commercialization means well-defined architectural electrocatalysts designs that fully enhance the oxygen reduction reaction and fuel oxidation reaction. The currently pursued electrocatalyst has drawbacks. These include poisoning from methanol and ethanol cross-over, sluggish anodic and cathodic kinetics, air, fuel management, stability, and durability management. This chapter aims to elucidate how the mentioned challenges affect the electrocatalytic activity of the electrocatalysts and expound on some approaches to mitigate the challenges, enhancing adaptability as fuel cells electrocatalysts.

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Abstract In light of the intensifying global energy crisis and the mounting demand for environmental protection, it is of vital importance to develop advanced hydrogen energy conversion systems. Electrolysis cells for hydrogen production and fuel cell devices for hydrogen utilization are indispensable in hydrogen energy conversion. As one of the electrolysis cells, water splitting involves two electrochemical reactions, hydrogen evolution reaction and oxygen evolution reaction. And oxygen reduction reaction coupled with hydrogen oxidation reaction, represent the core electrocatalytic reactions in fuel cell devices. However, the inherent complexity and the lack of a clear understanding of the structureperformance relationship of these electrocatalytic reactions, have posed significant challenges to the advancement of research in this field. In this work, the recent development in revealing the mechanism of electrocatalytic reactions in hydrogen energy conversion systems is reviewed, including in situ characterization and theoretical calculation. First, the working principles and appl... Read More

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<h2>Summary</h2> Hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) are both two-electron processes that culminate in the formation or consumption of gaseous hydrogen in an electrolyzer or a fuel cell, respectively. Unitized regenerative proton exchange membrane fuel cells merge these two functionalities into one device, allowing to switch between the two modes of operation. This prompts the quest for efficient bifunctional electrode materials catalyzing the HER and HOR with reasonable reaction rates at low overpotentials. In the present study using a data-driven framework, we identify a general criterion for efficient bifunctional performance in the hydrogen electrocatalysis, which refers to a change in the reaction mechanism when switching from cathodic to anodic working conditions. The obtained insight can be used in future studies based on density functional theory to pave the design of efficient HER and HOR catalysts by a dedicated consideration of the kinetics in the analysis of reaction mechanisms.

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The general principles in terms of reactivity and stability to design efficient electrocatalysts for the alkaline hydrogen oxidation reaction are reviewed. The performance of catalysts in anion-exchange membrane fuel cells is further discussed.

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Hydrogen fuel cells, which produce electrical energy and only water as a byproduct, are evaluated for their use in eco-friendly technology. However, there are challenges with using abundant precious metal catalysts for electrodes, particularly regarding hydrogen gas crossover and managing the moisture of the polymer electrolyte membrane. To overcome these challenges, a mediated fuel-cell (MedFC) system, in which hydrogen fuel cells are combined with a redox-flow battery using an oxidationreduction reaction of an electrolyte, has been recently developed. In a MedFC system, the reduced ions of redox-active materials generated by the oxidation of hydrogen in a packed-bed reactor are fed to the fuel cell electrode as a mediator. In this study, 2,5-dihydroxy1,4-benzoquinone (DHBQ) was used as a anode mediator to operate MedFCs under alkaline conditions. DHBQ and hydrogen were injected with an upward flow into the packed-bed reactor to reduce DHBQ via a chemical reaction. On the anode side of the fuel cell, DHBQ oxidized and transferred the electrons to the cathode. By contrast, an oxygen... Read More

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Research focusing on catalyst layers is critical for enhancing the performance and durability of proton exchange membrane fuel cells.

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Abstract Anion exchange membrane fuel cells (AEMFCs) have been hailed as a promising hydrogen energy technology due to high energy conversion efficiency, zero carbon emission and the potential independence on scare and expensive noble metal electrocatalysts. A variety of platinum group metal (PGM)free catalysts has been developed with superior catalytic performance to noble metal benchmarks toward cathodic oxygen reduction reactions (ORR). However, PGM electrocatalysts still dominate the anodic catalyst research because the kinetics of hydrogen oxidation reaction (HOR) are two or three orders of magnitude slower than in that acidic media. Therefore, it is urgently desirable to improve noble metal utilization efficiency and/or develop highperformance PGMfree electrocatalysts for HOR, thus promoting the realworld implementation of AEMFCs. In this review, the current research progress of electrocatalysts for HOR in alkaline media is summarized. We start with the discussion on the current HOR reaction mechanisms and existing controversies. Then, methodologies to improve the HOR perfo... Read More

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Development of highly active, stable, and economic electrocatalyst for sustainable hydrogen (H2) production is crucial in the water electrolysis. In this work, a very effective and affordable electrocatalyst for hydrogen...

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The development of efficient electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) is pivotal for advancing cleaner and sustainable fuel production technologies.

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There is a need for flexible and efficient storage facilities so that the integration of renewable energies and thus the energy transition can succeed. Intermediate storage of energy in the form of hydrogen by electrolysers and effective reconversion to electricity by fuel cells is a possibility. The unitized regenerative fuel cell (URFC) is a single-unit device that combines an electrolyser and a fuel cell, which makes the system costs much cheaper compared to two separate devices. Currently, the focus of URFC research, similar to proton exchange membrane (PEM) electrolysers, is on the development of new catalysts and electrodes with the aim of reducing costs through manufacturing and design optimization [1,2]. In this context, equally important is the increase of electrochemical activity on the oxygen side since oxygen evolution (OER) and oxygen reduction (ORR) are the speed-determining steps comparatively to their counter reactions on the hydrogen side. Due to high potentials and the corrosive oxygen atmosphere, there are additional requirements for electrode stability on the oxyg... Read More

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Proton exchange membrane fuel cell converts hydrogen and oxygen into electricity with zero emission. The high cost and low durability of Pt-based electrocatalysts for oxygen reduction reaction hinder its wide applications. The development of non-precious metal electrocatalysts also reaches the bottleneck because of the low activity and durability. Here we rationally design a hybrid electrocatalyst consisting of atomically dispersed Pt and Fe single atoms and Pt-Fe alloy nanoparticles. The Pt mass activity of the hybrid catalyst is 3.7 times higher than that of commercial Pt/C in a fuel cell. More importantly, the fuel cell with an ultra-low Pt loading in the cathode (0.015 mg Pt cm -2 ) shows excellent durability, with 97 % activity retention after 100,000 cycles and no noticeable current drop at 0.6 V for over 200 h. These results highlight the importance of the synergistic effects among active sites in hybrid electrocatalysts and provide an alternative way to design more active and durable low-Pt electrocatalysts for electrochemical devices.

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The recent development in electrocatalysts for the hydrogen oxidation reaction (HOR) attracted significant attention. In this sense, this chapter provides a fundamental understanding of the state-of-the-art PGM and non-PGM-based electrocatalysts for the HOR in alkaline conditions. Moreover, a strong focus has been made on the strategies to overcome the slow kinetics of the HOR to commercialize anion-exchange membrane fuel cells.

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Electrocatalysis is the fundamental principle behind the fuel cell's operation. The voltage, as well as the current, produced mainly depends on the mechanism of the electrocatalytic reaction taking place on the metal nanoparticle catalyst. Various dynamics processes on the catalyst surface, especially the adsorption and desorption of different adsorbates such as oxidant/reductant molecules or any intermediate molecules or atomic species, need to be probed under real fuel cell operating conditions to understand the electrocatalytic mechanism. In addition, structural changes, such as particle growth, particle dissolution, and dealloying, need to be probed and correlated with associated experimental conditions to envisage operating protocols that enhance the durability of the fuel cell. X-ray absorption spectroscopy ( XAS ) is the most commonly used characterization technique to investigate fuel cell catalysts under operando conditions. This chapter gives an overview of various operando XAS measurements carried out to address various fundamental questions related to fuel cell electrocat... Read More

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Hydrogen enables energy pathways across applications and sectors in an increasingly interconnected energy system, helping deep decarbonization, economic growth, and jobs creation. Electrochemical Energy Conversion Devices produce "green" H2 from water: electrolyzers. H2 is used to produce "green" electricity through fuel cells. There is a need of catalysts to enhance reactions kinetics at the electrodes.

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It has been challenging over the past three decades to find viable energy alternatives with higher efficiency and lower cost to beat the non-friendly and commercially dominant hydrocarbon energy sources. Hydrogen is deemed to be one of the most prominent candidates, as a green fuel. Hydrogen can be generated in abundance from water splitting. Utilization of hydrogen in fuel cells, with no doubt, produces no harmful gases. Nevertheless, the two parts of the technology: hydrogen production and reduction are cumbersome. Both processes rely on kinetically sluggish electrocatalytic reactions. Enormous research efforts have been spent, with thousands of studies presented in literature, despite the technology left with a dim light shed on from commercial and practical point of views. Many materials-related challenges are hindering the flourishing of green hydrogen technology, where poor catalyst durability is a major challenge, despite being made from very expensive elements (e.g., Ir, ru or Pt). Therefore, gigantic effort of research has been devoted to find inexpensive alternatives. Trans... Read More

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One bottleneck hampering the widespread use of fuel cell vehicles, in particular of proton exchange membrane fuel cells (PEMFCs), is the high cost of the cathode where the oxygen reduction reaction (ORR) occurs, due to the current need of precious metals to catalyze this reaction. Electrochemists tackle this issue in the short/medium term by developing catalysts with improved utilization or efficiency of platinum, and in the longer term, by developing catalysts based on Earth-abundant elements. Considerable progress has been achieved in the initial performance of Metal-nitrogen-carbon (Metal-N-C) catalysts for the ORR, especially with Fe-N-C materials. However, until now, this high performance cannot be maintained for a sufficiently long time in an operating PEMFC. The identification and mitigation of the degradation mechanisms of Metal-N-C electrocatalysts in the acidic environment of PEMFCs has therefore become an important research topic. Here, we review recent advances in the understanding of the degradation mechanisms of Metal-N-C electrocatalysts, including the recently identif... Read More

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Hydrogen has the potential to be one of the solutions that can address environmental pollution and greenhouse emissions from traditional fossil fuels. However, high costs hinder its large-scale commercialization, particularly for enabling devices such as proton exchange membrane fuel cells (PEMFCs). The precious metal Pt is indispensable in boosting the oxygen reduction reaction (ORR) in cathode electrocatalysts from the most crucial component, i.e., the membrane electrode assembly (MEA). MEAs account for a considerable amount of the entire cost of PEMFCs. To address these bottlenecks, researchers either increase Pt utilization efficiency or produce MEAs with enhanced performance but less Pt. Only a few reviews that explain the approaches are available. This review summarizes advances in designing nanocatalysts and optimizing the catalyst layer structure to achieve low-Pt loading MEAs. Different strategies and their corresponding effectiveness, e.g., performance in half-cells or MEA, are summarized and compared. Finally, future directions are discussed and proposed, aiming at afforda... Read More

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Fuel cell is a kind of power generation device that directly converts chemical energy in fuels and oxidants into electricity (with no Carnot cycle and high energy conversion). The birth and development of fuel cells are based on multiple disciplines of electrochemistry, electrocatalysis, electrode process kinetics, material science, and chemical process. Both the anode and cathode of fuel cells need to contain a certain amount of electrocatalyst to accelerate the electrochemical reaction on the electrodes. In this chapter, the basic structure, energy storage mechanism, electrode material (especially the oxygen reduction reaction electrocatalyst), and application prospects of fuel cells are briefly reviewed.

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Hydrogen energy is an important energy carrier, which is an ideal choice to meet energy demand and reduce harmful gas emissions. The green recycling of hydrogen energy depends on water electrolysis and hydrogen fuel cells, which involves hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER). The activity of HER/HOR in alkaline electrolyte, however, exhibits a significantly lower magnitude (2-3 orders) compared to that observed in an acidic medium, which hinders the development of alkaline water electrolysis and alkaline membrane fuel cells. Therefore, comprehending the characteristics of HOR/HER activity in alkaline electrolytes and elucidating its underlying mechanism is a prerequisite for the design of advanced electrocatalysts. Based on this background, this review will briefly summarize the explanations and controversies about the basic HOR mechanism, including bifunctional mechanism and hydrogen binding energy theory. Moreover, the crucial affecting factors of the HOR kinetics, such as d-band center theory, interfacial water recombination, alkali metal cations ... Read More

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Abstract Hydrogen fuel cell technology is gaining significant attention as a promising alternative for decarbonizing automotive vehicles. At the heart of hydrogen fuel cell technology is the electrode, composed of catalysts, supports, binders, and pores, which facilitates the halfcell reactions and often governs the efficiency of fuel cells. Over the last decade, scientists have made great strides in discovering catalyst, support, and binder materials featuring unique nanostructures and compositions that significantly enhance the efficiency of those devices. While innovations must continue, we must not overlook how these materials are put together to form an electrode and how it impacts the overall efficiency. This perspective article discusses the urgent need for developing alternative electrodes for designing next generation hydrogen fuel cells.

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Hydrogen oxidation reaction (HOR) is an important semicell reaction in the renewable energy conversion technology such as fuel cells. However, due to the slow reaction rate, the development of highly active catalysts remains a major challenge in alkaline fuel cells. Based on fundamental understanding of the sluggish kinetics toward the reaction mechanism in alkaline electrolytes, noble and nonnoble metal catalysts and their regulation strategies including geometry, composition, atomdoping, oxyphilic site and substrate engineerings are analyzed and summarized in this review to seek for the possible breakthrough toward HOR catalytic performance enhancement. Eventually, challenges and opportunities faced by alkaline HOR, and potential future research trends are proposed. This review not only deepens the understanding of the hydrogen electrocatalysis mechanism, but also provides guidelines for the rational design of advanced HOR catalysts.

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<h2>Summary</h2> The ambition to achieve high-performance proton exchange membrane fuel cells (PEMFCs) with a low Pt loading has been a driving force for researchers to develop active and durable electrocatalysts and electrodes for oxygen reduction reactions. While progress has been made in reducing material costs and improving electrocatalyst activity over the past decades, there remains a significant need for breakthroughs in durability enhancement to enable large-scale commercialization. This review aims to provide a comprehensive overview of recent advancements in durability enhancements of PEMFCs, along with the design of durable electrocatalysts and electrodes. The strategies for achieving durability improvements are categorized into three key aspects: active sites, support materials, and electrode design. Furthermore, research insights and suggestions for accelerating the optimization process of low Pt loading PEMFCs are provided.

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The transition from a carbon-centered economy to an era of renewable energy has led to global attention on hydrogen energy, ultimately leading to the development of fuel cells using hydrogen as a fuel. In response to global demand, overall fuel cell technology has grown remarkably over the past few years; yet, commercialization remains sluggish owing to cost. As the cathode of a proton exchange membrane fuel cell (PEMFC), which is the most commercialized fuel cell, is markedly dependent on platinum (Pt), anion exchange membrane fuel cells (AEMFCs), which can utilize non-precious materials as cathode catalysts, have emerged as a promising alternative. Earth-abundant metals are used as cathode catalysts, and metal-free materials are used to achieve comparable performance to Pt. Compared to the single-cell performance of Pt catalysts, a gap still exists; however, the applicability of non-noble metals has been extensively evaluated. If catalyst development is accompanied by efficient electrode structure design, a significant part of the cost problem can be overcome. AEMFCs have advantage... Read More

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Polymer electrolyte fuel cells (PEFCs) are a key device for the hydrogen economy. In PEFCs, the oxygen reduction reaction (ORR) occurs at the cathode, and its electrocatalytic activity is known to govern the PEFC performance. In practical PEFCs, electrocatalysts based on platinum group metals (PGMs) are used for the ORR. Since PGMs are expensive, non-PGM electrocatalysts showing high ORR activity and product selectivity with almost no by-product of H2O2 in acidic media should be developed for the widespread applications of PEFCs. In this article, recent research progresses in non-PGM-based electrocatalysts for the ORR inspired by the active sites of metalloenzymes are discussed.

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Abstract Hydrogen production from water electrolysis plays an important role for the development of hydrogenbased energy sources. Developing efficient electrocatalysts is crucial for accelerating the reaction kinetics and achieving largescale water electrolysis. Despite the significant advancements in electrocatalysts for the hydrogen evolution reaction (HER) achieved over the past few decades, there remains a lack of comprehensive discussion on the indepth mechanism for the enhanced activity, particularly with regard to the active intermediates. Recently, with the development of stateoftheart characterization methods and theoretical computation, optimizing interaction between reaction intermediates and corresponding active sites has been demonstrated as an effective strategy to enhance the intrinsic catalytic activity. Herein, the recent advances in the electrocatalysts design guided by active intermediates of HER are presented. Emphasis is focused on the discussion of key intermediates that determine HER activity and the strategies to tune the interaction between active sites... Read More

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Developing hydrogen economy significantly relies on water electrolyzers and fuel cells, where electrocatalysts towards the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) play pivotal roles. For generating unusual catalyst species and preventing detrimental catalyst degradations, manipulating catalyst reconstructions is gaining intensive interest. This work reviews current understandings and modulations of reconstructions of representative OER/ORR electrocatalysts for water electrolyzers and fuel cells, covering platinum group metal- (PGM) based and PGM-free ones. By rigorously discussing the most recent progress, we distinguished catalyst reconstruction from self-optimization or electrochemical activation, and emphasized that (engineered) reconstruction does not necessarily yield improved catalytic performance. More importantly, we highlighted the strategy of rationally designing the physicochemical properties of catalysts and managing the electrochemical conditions to achieve superior control of catalyst reconstructions. Through discussing the advances, challeng... Read More

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Hydrogen oxidation reactions in hydroxide exchange membrane fuel cells have slow kinetics. Switching from platinum group metal (PGM) electrocatalysts to those that are PGM-free is a challenging task as the latter are prone to oxidation. Now, stable and active nickelmolybdenumniobium catalysts are introduced for this type of fuel cell.

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The need to replace conventional sources of energy has driven the development of fuel cell technology. The polymer electrolyte membrane fuel cells (PEMFCs) show high performance and are important power sources for hydrogen fuel cell vehicles due to the fact that the cells can operate at relatively low temperatures (50 - 90 o C) , has high energy efficiency and only emits water as a byproduct. Furthermore, the direct methanol fuel cell emerge as an important technology for the green energy transition with the use methanol fuel. The most important electrocatalyst for the fuel cells is platinum and efforts are made to enhance its performance and reduce its requirement by alloying with other metals. Therefore, novel approaches are required to develop electrocatalysts for the oxygen reduction reaction (ORR) and methanol oxidation using reduced amounts of Pt for use at PEMFC cathodes with high electrocatalytic activity. Investigation of alloying Pt with transition metals (Ni, Co, Fe) has demonstrated increased electrocatalytic activity and is attributed to changes in the Pt-Pt atomic inter... Read More

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A constellation of technologies has been researched with an eye toward enabling a hydrogen economy. Within the research fields of hydrogen production, storage, and utilization in fuel cells, various classes of materials have been developed that target higher efficiencies and utility. This Review examines recent progress in these research fields from the years 2011-2021, exploring the most commonly occurring concepts and the materials directions important to each field. Particular attention has been given to catalyst materials that enable the green production of hydrogen from water, chemical and physical storage systems, and materials used in technical capacities within fuel cells. The quantification of publication and materials trends provides a picture of the current state of development within each node of the hydrogen economy.

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Hydrogen technologies such as low-temperature fuel cells are, besides batteries, the most promising technologies for mobility and transport applications. Currently, Proton Exchange Membrane Fuel Cells (PEMFCs) are, in terms of low-temperature fuel cells, the state-of-the-art technology achieving high power densities and reasonable stabilities. With the recent development and increasing availability of stable and performant hydroxide conductive ionomers, Anion Exchange Membrane Fuel Cells (AEMFCs) have gained increasing interest in recent years as they combine the advantages of PEMFCs, like low-temperature operation and high-power density with the low component costs of alkaline fuel cells. 1,2 Especially the possibility of replacing the expensive Pt-based electrocatalysts used in PEMFCs with cheaper electrocatalysts like nickel-based materials for the anode and iron-based materials for the cathode could significantly decrease the fuel cell costs. 1,3,4 Although the oxygen reduction reaction (ORR) at the cathode is favored in alkaline media compared to acidic media, the ORR is still a... Read More

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Backgrounds: In pursuit of sustainable development, a fuel cell become a key device that can convert chemical energy in hydrogen and oxygen into electrical energy. In this field, the sluggish reaction kinetics of the oxygen reduction reaction (ORR) on cathode side of fuel cell has been a key issue hindering largescale applications. Although many efforts have been devoted to the development of efficient electrocatalysts for ORR, platinum (Pt)based catalysts remain the most efficient electrocatalysts owing to their high intrinsic activity. However, their reservescarcity and low stability limit their widespread use. Strategy: Therefore, it is highly desirable to develop electrocatalysts with high catalytic activities and stability as well. Among various strategies, metal chalcogenides have led to remarkable electrochemical performances beyond those of pure metals. Also, they have unique characteristics such as multiple crystal phases (e.g., 1H, 2H, 1T, and 1T); the phase of 1H and 2H correspond to semiconductor, whereas the 1T and distorted 1T are metallic phases. Generally, the me... Read More

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This book discusses electrocatalysis and electrocatalysts for energy, water electrolysis, water treatment, CO2 conversion, and green chemistry. It reviews various electrocatalysts and their properties and electrochemical performances. The first section of the book covers topics in direct alcohol fuel cells including Pt-based electrocatalysts as non-carbon electrode support materials and the development of electrocatalysts for direct methanol fuel cells. The second section of the book covers various topics in electrocatalysis and electrocatalysts for a cleaner environment, including electrocatalysts for the conversion of CO2 to valuable products and SYNGAS, electrocatalysts for water electrolysis, and much more.

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The fabrication of economic electrocatalysts having high hydrogen evolution reaction ability and durability is one of the major challenges of hydrogen-based technologies. For the development of hydrogen fuel cell technology, it is equally crucial to have an easy way to produce hydrogen as a source of fuel. Metal-organic frameworks (MOFs)-driven materials are considered among the most promising electrocatalysts for hydrogen generation among the available economic electrocatalysts, including single-atom electrocatalysts, metal oxides, phosphides, sulfides, and so on. This is because of their chemically adjustable and well-defined architecture and pore size with high intrinsic electrical conductivity. This work discusses successful manufacturing techniques for MOF-based electrocatalysts, recent advances in their usage for hydrogen generation, and prospects for MOF engineering for hydrogen generation.

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Abstract Proton exchange membrane fuel cells convert hydrogen and oxygen into electricity without emissions. The high cost and low durability of Pt-based electrocatalysts for the oxygen reduction reaction hinder their wide application, and the development of non-precious metal electrocatalysts is limited by their low performance. Here we design a hybrid electrocatalyst that consists of atomically dispersed Pt and Fe single atoms and PtFe alloy nanoparticles. Its Pt mass activity is 3.7 times higher than that of commercial Pt/C in a fuel cell. More importantly, the fuel cell with a low Pt loading in the cathode (0.015 mg Pt cm 2 ) shows an excellent durability, with a 97% activity retention after 100,000 cycles and no noticeable current drop at 0.6 V for over 200 hours. These results highlight the importance of the synergistic effects among active sites in hybrid electrocatalysts and provide an alternative way to design more active and durable low-Pt electrocatalysts for electrochemical devices.

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Chapter 24 Hydrogen Energy Recovery H 2 - Based Fuel Cells Nada Zamel, Nada ZamelSearch for more papers by this authorUlf Groos, Ulf GroosSearch for more papers by this author Nada Zamel, Nada ZamelSearch for more papers by this authorUlf Groos, Ulf GroosSearch for more papers by this author Book Editor(s):Andreas Hauer, Andreas Hauer ZAE-Bayern, Garching, GermanySearch for more papers by this author First published: 25 April 2022 https://doi.org/10.1002/9781119239390.ch24Citations: 1 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Abstract The Hydrogen economy is a crucial part in the future energy mix. In order to complete the circle in this economy, the recovery and use of H 2 becomes crucial. In this chapter, we introduce various H 2 -based fuel cells discussing their electrochemical reactions, advantages and disadvantages as well as their application fields. Based on market shares, the focus of the chapter is put on polymer electrolyte membrane fuel cells. The discussion put for... Read More

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Hydrogen energy-based electrochemical energy conversion technologies offer the promise of enabling a transition of the global energy landscape from fossil fuels to renewable energy. Here, we present a comprehensive review of the fundamentals of electrocatalysis in alkaline media and applications in alkaline-based energy technologies, particularly alkaline fuel cells and water electrolyzers. Anion exchange (alkaline) membrane fuel cells (AEMFCs) enable the use of nonprecious electrocatalysts for the sluggish oxygen reduction reaction (ORR), relative to proton exchange membrane fuel cells (PEMFCs), which require Pt-based electrocatalysts. However, the hydrogen oxidation reaction (HOR) kinetics is significantly slower in alkaline media than in acidic media. Understanding these phenomena requires applying theoretical and experimental methods to unravel molecular-level thermodynamics and kinetics of hydrogen and oxygen electrocatalysis and, particularly, the proton-coupled electron transfer (PCET) process that takes place in a proton-deficient alkaline media. Extensive electrochemical and... Read More

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With the price-competitiveness of solar and wind power, hydrogen technologies may be game changers for a cleaner, defossilized, and sustainable energy future. H2 can indeed be produced in electrolyzers from water, stored for long periods, and converted back into power, on demand, in fuel cells. The feasibility of the latter process critically depends on the discovery of cheap and efficient catalysts able to replace platinum group metals at the anode and cathode of fuel cells. Bioinspiration can be key for designing such alternative catalysts. Here we show that a novel class of iron-based catalysts inspired from the active site of [FeFe]-hydrogenase behave as unprecedented bidirectional electrocatalysts for interconverting H2 and protons efficiently under near-neutral aqueous conditions. Such bioinspired catalysts have been implemented at the anode of a functional membrane-less H2/O2 fuel cell device.

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As the center of fuel cells, electrocatalysts play a crucial role in determining the conversion efficiency from chemical energy to electrical energy.

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The hydrogen fuel cell is a quiet and clean energy conversion technology that offers a sustainable and carbon-free alternative to the combustion of fossil fuels. A major advantage of this technology is that when pure hydrogen is used as the fuel, the only products are water, heat, and electricity. The oxygen reduction reaction (ORR) occurs at the cathode in a hydrogen fuel cell, but its slow kinetics have a detrimental effect on efficiency. Therefore, the use of electrocatalytic materials is required to achieve reasonable reaction rates. Platinum provides the best electrocatalytic performance but is expensive, scarce, and in demand from many industries. As such, alternatives with less platinum or platinum-free must be developed. Electrocatalytic materials must also withstand harsh operating conditions and be producible on a large scale if the widespread practical application of fuel cell technology is to be realized. Since the ORR occurs at the surface of electrocatalytic materials, nanostructured materials offer better activities than their bulk counterparts due to their increased s... Read More

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The development of low-cost electrocatalysts with high oxygen reduction reaction (ORR) activity and durability is one of the key requirements for the commercialization of fuel cells technologies. Additionally, a facile hydrogen production as fuel using electrocatalysts is equally important for the development of hydrogen fuel cells technology. Among available low-cost electrocatalysts such as single atoms electrocatalysts, metal oxides, phosphides and sulfides, MN4-type molecular catalysts etc., the metal-organic frameworks (MOFs)-based materials is found to be one of the potential electrocatalysts for ORR and hydrogen production. Because of their several merits such as (1) well-defined architecture with exact location of active sites and structure-activity relationships, (2) chemically adjustable and well-defined pore-size architecture, (3) suitably incorporation of redox-active moieties in MOFs to initiate the charge transfer to improve the intrinsic electrical conductivity, and (4) well-characterized reaction pathways. In this chapter, we highlighted the (1) engineering and effect... Read More

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Abstract Carbon dioxide generated by the combustion of fossil fuels exacerbates global environmental problems and hydrogen produced by renewable energy is a viable alternative in the continuous transition to sustainable and ecoconscience development. Electrocatalysts are vital to electrocatalytic reactions and plasma surface modification is one of the promising techniques to modify nanoscale electrocatalysts for water splitting. Up to now, a comprehensive review on the latest developments, challenges, and opportunities of plasmatailored defective electrocatalysts for water electrolysis and hydrogen fuel cells is lacking. This paper systematically summarizes the current status of hydrogen production and fuel cell technologies, plasma principles and advantages, plasmatailored defective electrocatalysts from the perspective of water splitting and fuel cell applications, advanced characterization of defects, relationship between materials structure and catalytic activity of electrocatalysts, and finally challenges, opportunities, and future roadmap of plasma technologies. This review ... Read More

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