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In polymer electrolyte fuel cells, the oxygen reduction reaction (ORR) rate increases at high temperatures. Therefore, ORR catalysts must be designed for use at high temperatures and require evaluation. To address the problem of decreased dissolved oxygen concentrations in conventional channel flow double electrode (CFDE) systems, this study develops a CFDE system capable of electrochemical measurement at 120 °C that can evaluate the ORR activity of Pt-supported carbon (Pt/C) and carbon-based non-precious metal catalysts (NPMC). The ORR activity increased with an increasing reaction temperature, regardless of the catalyst, and the current density ratios at 120 °C and room temperature were estimated to be 2.4 and 5.4 for Pt/C and NPMC, respectively. This indicates that the NPMC ORR activity increased significantly with the increasing reaction temperature. This increased activation energy, which is approximately 2.3 times greater than that of Pt/C at the overpotential of 0.38 V, contributes to a significant increase in the ORR activity at higher temperatures. [Display omitted] • An improved channel flow double electrode system is developed. • Kinetic analysis of ORR up to 120 °C was performed by using the system. • The activation energy of NPMC is higher than Pt/C catalyst. • ORR activity of NPMC increased significantly with the increasing reaction temperature. [ABSTRACT FROM AUTHOR]

The warped graphene layer (WGL) has garnered attention as a potential alternative to Pt for oxygen reduction reaction (ORR) catalysts and as a platform for enhancing the activity of Pt or molecular catalysts through interactions. We propose an in-situ nano-templating method for the preparation and mass production of WGLs and demonstrate its efficiency. The in-situ nano-templating method facilitates the synthesis of materials with three-dimensional curvature by concurrently generating nanoparticles and carbonizing. The synthesized WGLs exhibited high ORR activity in acidic conditions. Although the ORR activity was not correlated with the surface area, it was strongly correlated with the curvature radius of the WGLs. This activity was considered to arise owing to the optimization of oxygen adsorption ΔG 0 with the decrease in the curvature radius of the WGLs; furthermore, the physicochemical characteristics of WGL possesses continuity of carbon layers and exhibit a Fermi level higher than the O 2 /H 2 O reduction potential. This report elucidates experimentally that WGLs contribute to ORR activity, suggesting the importance of incorporating WGLs in the development of non-precious metal catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

The activity of non-precious metal catalysts (NPMCs) has now reached a stage at which they can be considered as possible alternatives to Pt for some proton exchange membrane fuel cell (PEMFC) applications. However, despite significant efforts over the past 50 years on catalyst development, only limited studies have been performed on NPMC-based cathode catalyst layer (CCL) designs. In this work, an extensive ionomer study is performed to investigate the impact of ionomer equivalent weight on performance, which has uncovered two crucial findings. Firstly, it is demonstrated that beyond a critical CCL conductance, no further improvement in performance is observed. The procedure used to determine this critical conductance can be used by other researchers in this field to aid in their design of high performing NPMC-based CCLs. Secondly, it is shown that the stability of NPMC-based CCLs can be improved through the use of low equivalent weight ionomers. This represents a completely unexplored pathway for further stability improvements, and also provides new insights into the possible degradation mechanisms occurring in NPMC-based CCLs. These findings have broad implications on all future NPMC-based CCL designs. [ABSTRACT FROM AUTHOR]

A major hurdle to the widespread commercialization of proton exchange membrane fuel cells (PEMFCs) is the high loading of noble metal (Pt/Pt-alloy) catalyst at the cathode, which is necessary to facilitate the inherently sluggish oxygen reduction reaction (ORR). To eliminate the use of Pt/Pt-alloy catalysts at the cathode of PEMFCs and thus significantly reduce the cost, extensive research on non-precious metal catalysts (NPMCs) has been carried out over the past decade. Major advances in improving the ORR activity of NPMCs, particularly Fe- and Co-based NPMCs, have elevated these materials to a level at which they can start to be considered as potential alternatives to Pt/Pt-alloy catalysts. Unfortunately, the stability (performance loss following galvanostatic experiments) of these materials is currently unacceptably low and the durability (performance loss following voltage cycling) remains uncertain. The three primary mechanisms of instability are: (a) Leaching of the metal site, (b) Oxidative attack by H 2 O 2 , and (c) Protonation followed by possible anion adsorption of the active site. While (a) has largely been solved, further work is required to understand and prevent losses from (b) and/or (c). Thus, this review is focused on historical progress in (and possible future strategies for) improving the stability/durability of NPMCs. [ABSTRACT FROM AUTHOR]

A catalyst support can improve the catalytic activity of metal catalysts, and this phenomenon is well known as the support effect. The effective use of this support effect is considered important for improving catalytic activity. However, the factors affecting this phenomenon are complex. It is, therefore, important to understand the interaction between the support and metal catalyst as well as the surface characteristics of the support for elucidating this phenomenon. Carbon is a useful support material because of its high chemical and thermal stability and electroconductivity. Moreover, its surface properties can be controlled by doping the carbon structure with heteroatoms. In this study, the catalytic activity of metal particles supported on heteroatom-doped carbon materials was evaluated to investigate the support effect of the doped carbon. The catalytic activity of carbon-supported Ni particles in benzene hydrogenation was improved by introducing N and B into the carbon support. In particular, Ni supported on N-doped carbon showed a two-fold improvement in activity compared to that supported on undoped carbon. A compensation effect was confirmed for the catalytic activity of Ni particles. The results suggest that the introduction of heteroatoms into the carbon support changed the adsorption energy of the reactant on Ni, thereby improving the Ni catalytic activity. [Display omitted] • A catalyst support can improve the catalytic activity of metal catalysts. • Ni on B- and N-doped carbons has better activity than Ni on undoped carbon. • Heteroatoms on carbon change the energy of reactant adsorption onto Ni. • A compensation effect was confirmed for the activity of Ni on doped carbon. [ABSTRACT FROM AUTHOR]