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Polymer electrolyte membrane fuel cells (PEMFCs) have attracted much attention as highly efficient, eco-friendly energy conversion devices. However, carbon-supported Pt (Pt/C) catalysts for PEMFCs still have several problems, such as low long-term stability, to be widely commercialized in fuel cell applications. To address the stability issues of Pt/C such as the dissolution, detachment, and agglomeration of Pt nanoparticles under harsh operating conditions, we design an interesting fabrication process to produce a highly active and durable Pt catalyst by introducing a robust carbon shell on the Pt surface. Furthermore, this approach provides insights into how to regulate the carbon shell layer for fuel cell applications. Through the application of an appropriate amount of H2 gas during heat treatment, the carbon shell pores, which are integral to the structure, can be systematically modulated to facilitate oxygen adsorption for the oxygen reduction reaction. Simultaneously, the carbon shell functions as a protective barrier, preventing catalyst degradation. In this regard, we investigate an in-depth analysis of the effects of critical parameters including H2 content and the flow rate of H2/N2 mixed gas during heat treatment to prepare better catalysts. [ABSTRACT FROM AUTHOR]

Ionic liquid modification for carbon-supported platinum (Pt/C) electrocatalysts to enhance their oxygen reduction reaction (ORR) activity has been well recognized. However, the research has only been reported on the low-Pt-loading Pt/C electrocatalysts, e.g., 20 wt%, while in practical applications, usually high-Pt-loading Pt/C electrocatalysts of 45–60 wt% are used. In this work, ionic liquid modification is systematically investigated for a Pt/C electrocatalyst with 60 wt% Pt loading for its ORR activity in the cathode in proton exchange membrane fuel cells (PEMFCs). Various adsorption amounts are studied on the catalyst surface. Different modification behavior is found. Mechanism exploration shows that the adsorption of ionic liquid mainly happens on the Pt electrocatalyst surface and in the micropores of the carbon support. The highest fuel cell power performance is achieved at an ionic liquid loading of 7 wt%, which is much higher than the 3 wt% reported for the low-Pt-loading Pt/C. [ABSTRACT FROM AUTHOR]

The efficiency and performance of proton exchange membrane fuel cells (PEMFCs) are primarily influenced by ORR electrocatalysts. In recent years, atomically dispersed metal–nitrogen–carbon (M-N-C) catalysts have gained significant attention due to their high active center density, high atomic utilization, and high activity. These catalysts are now considered the preferred alternative to traditional noble metal electrocatalysts. The unique properties of M-N-C catalysts are anticipated to enhance the energy conversion efficiency and lower the manufacturing cost of the entire system, thereby facilitating the commercialization and widespread application of fuel cell technology. This article initially delves into the origin of performance and degradation mechanisms of Fe-N-C catalysts from both experimental and theoretical perspectives. Building on this foundation, the focus shifts to strategies aimed at enhancing the activity and durability of atomically dispersed Fe-N-C catalysts. These strategies encompass the use of bimetallic atoms, atomic clusters, heteroatoms (B, S, and P), and morphology regulation to optimize catalytic active sites. This article concludes by detailing the current challenges and future prospects of atomically dispersed Fe-N-C catalysts. [ABSTRACT FROM AUTHOR]

Studying the ORR activity of platinum-based electrocatalysts is an urgent task in the development of materials for proton-exchange membrane fuel cells. The catalytic ink composition and the formation technique of a thin layer at the RDE play a significant role in studying ORR activity. The use of a polymer ionomer in the catalytic ink provides viscosity as well as proton conductivity. Nafion is widely used as an ionomer for research both at the RDE and in the MEA. The search for ionomers is a priority task in the development of the MEA components to replace Nafion. The study also considers the possibility of using the LF4-SK polymer as an alternative ionomer. The comparative results on the composition and techniques of applying the catalytic layer using LF4-SK and Nafion ionomers are presented, and the influence of the catalytic ink composition on the electrochemical characteristics of commercial platinum–carbon catalysts and a highly efficient platinum catalyst based on an N-doped carbon support is assessed. [ABSTRACT FROM AUTHOR]

Atomically dispersed Fe-N-C catalysts for the oxygen reduction reaction (ORR) have been synthesized with a template-free method using carbon xerogels (CXG) as a porous matrix. The porosity of the CXGs is easily tunable through slight variations in the synthesis procedure. In this work, CXGs are prepared by formaldehyde and resorcinol polymerization, modifying the pH during the process. Materials with a broad range of porous structures are obtained: from non-porous to micro-/meso-/macroporous materials. The porous properties of CXG have a direct effect on Fe-N-CXG activity against ORR in an acidic medium (0.5 M H2SO4). Macropores and wide mesopores are vital to favor the mass transport of reagents to the active sites available in the micropores, while narrower mesopores can generate additional tortuosity. The role of microporosity is investigated by comparing two Fe-N-C catalysts using the same CXG as the matrix but following a different Fe and N doping procedure. In one case, the carbonization of CXG occurs rapidly and simultaneously with Fe and N doping, whereas in the other case it proceeds slowly, under controlled conditions and before the doping process, resulting in the formation of more micropores and active sites and achieving higher activity in a three-electrode cell and a better durability during fuel cell measurements. This work proves the feasibility of the template-free method using CXG as a carbon matrix for Fe-N-C catalysts, with the novelty of the controlled porous properties of the carbon material and its effect on the catalytic activity of the Fe-N-C catalyst. Moreover, the results obtained highlight the importance of the carbon matrix's porous structure in influencing the activity of Fe-N-C catalysts against ORR. [ABSTRACT FROM AUTHOR]

An oxygen reduction reaction (ORR) is the key half reaction of proton exchange membrane fuel cells (PEMFCs), and is highly dependent on Pt-based nanocrystals as core electrocatalysts. Despite the exceptional ORR activity from adjusting the electronic structures of surface or near-surface atoms, several serious issues, including the corrosion of carbon supports, the preferential leaching of active metal elements, the instability of surface low-coordinated atoms and the sintering/agglomeration of nanocrystals, still exist, challenging the ORR durability of developed Pt-based ORR catalysts. From the point of view of the catalyst structure design, in this review, we summarized the state-of-the-art structural regulation strategies for improving the ORR durability of Pt-based catalysts. The current limitation of Pt-based binary catalysts for ORR electrocatalysis is firstly discussed, and the detailed strategies are further classified into the optimization of supports, metal-doped alloys, core/shell structures, intermetallics and high-entropy alloys, etc. The structure–performance relationship is detailedly explained, especially emphasizing the elimination of the above restrictions. Finally, the existing challenges and future research direction are further presented, aiming at practicing the PEMFC devices of the ultradurable Pt-based catalysts. [ABSTRACT FROM AUTHOR]

The use of platinum-free (Pt) cathode electrocatalysts for oxygen reduction reactions (ORRs) has been significantly studied over the past decade, improving slow reaction mechanisms. For many significant energy conversion and storage technologies, including fuel cells and metal–air batteries, the ORR is a crucial process. These have motivated the development of highly active and long-lasting platinum-free electrocatalysts, which cost less than proton exchange membrane fuel cells (PEMFCs). Researchers have identified a novel, non-precious carbon-based electrocatalyst material as the most effective substitute for platinum (Pt) electrocatalysts. Rich sources, outstanding electrical conductivity, adaptable molecular structures, and environmental compatibility are just a few of its benefits. Additionally, the increased surface area and the simplicity of regulating its structure can significantly improve the electrocatalyst's reactive sites and mass transport. Other benefits include the use of heteroatoms and single or multiple metal atoms, which are capable of acting as extremely effective ORR electrocatalysts. The rapid innovations in non-precious carbon-based nanomaterials in the ORR electrocatalyst field are the main topics of this review. As a result, this review provides an overview of the basic ORR reaction and the mechanism of the active sites in non-precious carbon-based electrocatalysts. Further analysis of the development, performance, and evaluation of these systems is provided in more detail. Furthermore, the significance of doping is highlighted and discussed, which shows how researchers can enhance the properties of electrocatalysts. Finally, this review discusses the existing challenges and expectations for the development of highly efficient and inexpensive electrocatalysts that are linked to crucial technologies in this expanding field. [ABSTRACT FROM AUTHOR]

The high cost and poor reliability of cathodic electrocatalysts for the oxygen reduction reaction (ORR), which requires significant amounts of expensive and scarce platinum, obstructs the broad applications of proton exchange membrane fuel cells (PEMFCs). The principles of ORR and the reasons for the poor stability of Pt-based catalysts are reviewed. Moreover, this paper discusses and categorizes the strategies for enhancing the stability of Pt-based catalysts in fuel cells. More importantly, it highlights the recent progress of Pt-based stability toward ORR, including surface-doping, intermetallic structures, 1D/2D structures, rational design of support, etc. Finally, for atomic-level in-depth information on ORR catalysts in fuel cells, potential perspectives are suggested, such as large-scale preparation, advanced interpretation techniques, and advanced simulation. This review aims to provide valuable insights into the fundamental science and technical engineering for practical Pt-based ORR electrocatalysts in fuel cells. [ABSTRACT FROM AUTHOR]

Sluggish oxygen reduction reaction (ORR) of electrodes is one of the main challenges in fuel cell systems. This study explored the kinetics of the ORR reaction mechanism, which enables us to understand clearly the electrochemical activity of the electrode. In this research, electrocatalysts were synthesized from platinum (Pt) catalyst with multi-walled carbon nanotubes (MWCNTs) coated by three polymers (polybenzimidazole (PBI), sulfonated tetrafluoroethylene (Nafion), and polytetrafluoroethylene (PTFE)) as the supporting materials by the polyol method while hexachloroplatinic acid (H2PtCl6) was used as a catalyst precursor. The oxygen reduction current of the synthesized electrocatalysts increased that endorsed by linear sweep voltammetry (LSV) curves while increasing the rotation rates of the disk electrode. Additionally, MWCNT-PBI-Pt was attributed to the maximum oxygen reduction current densities at −1.45 mA/cm2 while the minimum oxygen reduction current densities of MWCNT-Pt were obtained at −0.96 mAcm2. However, the ring current densities increased steadily from potential 0.6 V to 0.0 V due to their encounter with the hydrogen peroxide species generated by the oxygen reduction reactions. The kinetic limiting current densities (JK) increased gradually with the applied potential from 1.0 V to 0.0 V. It recommends that the ORR consists of a single step that refers to the first-order reaction. In addition, modified MWCNT-supported Pt electrocatalysts exhibited high electrochemically active surface areas (ECSA) at 24.31 m2/g of MWCNT-PBI-Pt, 22.48 m2/g of MWCNT-Nafion-Pt, and 20.85 m2/g of MWCNT-PTFE-Pt, compared to pristine MWCNT-Pt (17.66 m2/g). Therefore, it can be concluded that the additional ionomer phase conducting the ionic species to oxygen reduction in the catalyst layer could be favorable for the ORR reaction. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is an important challenge in the development and large-scale distribution of energy conversion devices, especially low-temperature proton exchange membrane (PEM) fuel cells. In order to speed up the ORR kinetics and improve fuel cell performance, iron-doped calcium titanate (CTFO) is proposed as a cocatalyst. Fundamental physical and chemical characterizations by means of X-ray diffraction, infrared spectroscopy, and morphological and thermal analyses for the understanding of the functional features of the proposed materials were carried out. Composite catalysts containing different amounts of CTFO additive with respect to platinum (i.e., Pt:CTFO 1:0.5 and 1:1 wt:wt) were studied using a rotating disk electrode (RDE). Fuel cell tests were performed at 80 °C under 30% and 80% relative humidity. The best Pt:CTFO composite catalyst was compared to a bare Pt/C and a Pt/C:CaTiO3−δ 1:1 catalyst, revealing superior performances of the latter at high relative humidity fuel cell operation, as a combined result of an optimized electrolyte-electrode interface and improved ORR kinetics due to the inorganic additive. [ABSTRACT FROM AUTHOR]

A number of nickel complexes of sodium pectate with varied Ni2+ content have been synthesized and characterized. The presence of the proton conductivity, the possibility of the formation of a dense spatial network of transition metals in these coordination biopolymers, and the immobilization of transition ions in the catalytic sites of this class of compounds make them promising for proton-exchange membrane fuel cells. It has been established that the catalytic system composed of a coordination biopolymer with 20% substitution of sodium ions for divalent nickel ions, Ni (20%)-NaPG, is the leading catalyst in the series of 5, 15, 20, 25, 35% substituted pectates. Among the possible reasons for the improvement in performance the larger specific surface area of this sample compared to the other studied materials and the narrowest distribution of the vertical size of metal arrays were registered. The highest activity during CV and proximity to four-electron transfer during the catalytic cycle have also been observed for this compound. [ABSTRACT FROM AUTHOR]

Proton exchange membrane (PEM) fuel cells using Pt-based materials as electrocatalysts have achieved a decent performance, represented by the launched Toyota Mirai vehicle. The ideal PEM fuel cells consume stored pure hydrogen and air. However, SO2, as a primary air contaminant, may be fed along with air at the cathode, leading to Pt site deactivation. Therefore, it is important to improve the SO2 tolerance of catalysts for the stability of the oxygen reduction reaction (ORR). In this work, we develop the Pt/C-TiO2 catalyst against SO2 poisoning during ORR. Impressively, the hybrid Pt/C-TiO2 catalyst with 20 mass % TiO2 shows the best ORR and anti-toxic performance: the kinetic current density of ORR is 20.5% higher and the degradation rate after poisoning is 50% lower than Pt/C. The interaction between Pt and TiO2 as well as the abundant hydroxyl groups on the surface of TiO2 are both revealed to account for the accelerated removal of poisonous SO2 on Pt surfaces. [ABSTRACT FROM AUTHOR]

Developing the optimized electrocatalysts with high Pt utilization as well as the outstanding performance for the oxygen reduction reaction (ORR) has raised great attention. Herein, the effects of the interlayer ZrC, HfC, or TiN and the multilayer Pt shell on the adsorption ability and the catalytic activity of the TiC@Pt core-shell structures are systemically investigated by density functional theory (DFT) calculations. For the sandwich structures, the presence of TiN significantly enhances the adsorption ability of the Pt shell, leading to the deterioration of the activity whilst the negligible influence of the ZrC and HfC insertion results the comparable performance with respect to TiC@Pt1ML. In addition, increasing the thickness of the Pt shell reduces the oxyphilic capacity and then mitigates the OH poisoning. From the free energy plots, the superior activity of TiC@Pt2ML is identified in comparison with 1ML and 3ML Pt shell. Herein, the improved activity with its high Pt atomic utilization makes the potential TiC@Pt2ML electrocatalyst for the future fuel cells. [ABSTRACT FROM AUTHOR]

Oxygen-depolarized cathodes are a novel concept to be used in chlor-alkali electrolysis in order to generate significant energy savings. In these porous gas diffusion electrodes, hydrophilic and catalytically active microsized silver grains and a hydrophobic polytetrafluoroethylene cobweb structure are combined to obtain the optimum amount of three-phase boundaries between the highly alkaline electrolyte and the oxygen gas phase to achieve high current densities. However, the direct correlation between specific electrode structure and electrochemical performance is difficult. In this work, we report on the successful design and adaptation of an in-operando cell for X-ray (micro-computed tomography, synchrotron) and neutron imaging of an operating oxygen-depolarized cathode under realistic operation conditions, enabling the investigation of the electrolyte invasion into, and distribution inside, the porous electrode for the first time. [ABSTRACT FROM AUTHOR]

In this paper, a numerical model of the kinetic Monte Carlo (KMC) method has been developed to study the oxygen reduction reaction (ORR) that occurs inside the cathode catalyst layer (CCL). Firstly, a 3-D model of the CCL that consists of Pt and carbon spheres is built using the sphere packing method; secondly, an efficient procedure of the proton-oxygen reaction process is developed and simulated. In the proton-oxygen reaction process, all of the continuous movements of protons and oxygen are considered. The maximum reaction distance is determined to be 8 Å. The input pressures of protons and oxygen are represented by the number of spheres of the species. The value of the current density is calculated based on the amount of reaction during the interval time. Indications are that the results of the present model match reasonably well with the published results. A new way to apply the KMC method in the proton exchange membrane fuel cell (PEMFC) research field is developed in this paper. [ABSTRACT FROM AUTHOR]