Low-platinum (Pt) alloy catalysts hold promising application in oxygen reduction reaction (ORR) electrocatalysis of proton-exchange-membrane fuel cells (PEMFCs). Although significant progress has been made to boost the kinetic ORR mass activity at low current densities in liquid half-cells, little attention was paid to the performance of Pt-based catalysts in realistic PEMFCs particularly at high current densities for high power density, which remains poorly understood. In this paper, we show that, regardless of the kinetic mass activity at the low current density region, the high current density performance of the low-Pt alloy catalysts is dominantly controlled by the total Pt surface area, particularly in low-Pt-loading H₂–air PEMFCs. To this end, we propose two different strategies to boost the specific Pt surface area, the post-15-nm dealloyed nanoporous architecture and the sub-5-nm solid core–shell nanoparticles (NPs) through fluidic-bed synthesis, both of which bring in comparably high mass activity and high Pt surface area for large-current-density performance. At medium current density, the dealloyed porous NPs provide substantially higher H₂–air PEMFC performance compared to solid core–shell catalysts, despite their similar mass activity in liquid half-cells. Scanning transmission electron microscopy images combined with electron energy loss spectroscopic imaging evidence a previously unreported “semi-immersed nanoporous-Pt/ionomer” structure in contrast to a “fully-immersed core–shell-Pt/ionomer” structure, thus favoring O₂ transport and improving the fuel cell performance. Our results provide new insights into the role of Pt nanostructures in concurrently optimizing the mass activity, Pt surface area and Pt/Nafion interface for high power density fuel cells.

The low intrinsic activity of Fe/N/C oxygen catalysts restricts their commercial application in the fuel cells technique; herein, we demonstrated the interface engineering of plasmonic induced Fe/N/C-F catalyst with primarily enhanced oxygen reduction performance for fuel cells applications. The strong interaction between F and Fe-N₄ active sites modifies the catalyst interfacial properties as revealed by X-ray absorption structure spectrum and density functional theory calculations, which changes the electronic structure of Fe-N active site resulting from more atoms around the active site participating in the reaction as well as super-hydrophobicity from C–F covalent bond. The hybrid contribution from active sites and carbon support is proposed to optimize the three-phase microenvironment efficiently in the catalysis electrode, thereby facilitating efficient oxygen reduction performance. High catalytic performance for oxygen reduction and fuel cells practical application catalyzed by Fe/N/C-F catalyst is thus verified, which offers a novel catalyst system for fuel cells technique.

Developing alternative oxygen reduction reaction (ORR) catalysts to replace precious Pt-based metals with abundant materials is the key challenge of commercial application of fuel cells. Owing to their various compositions and tunable electronic properties, transition metal dichalcogenides (TMDs) have the great potential to realize high-efficiency catalysts for ORR. Here, various 3R-phase dichalcogenides of group VB and VIB transition metals (MX₂, M = Nb, Ta, Mo, W; X = S, Se, Te) are investigated for ORR catalysts by using density functional theory calculations. The computed over-potentials of group VB TMDs are much less than those of group VIB TMDs. For group VB TMDs, a volcano-type plot of ORR catalytic activity is established on the adsorption energies of *OH, and NbS₂ and TaTe₂ exhibit best ORR activity with an over-potential of 0.54 V. To achieve even better activity, strain engineering is performed to tune ORR catalytic activity, and the minimum over-potential of 0.43 V can be realized. We further demonstrate that the shift of p orbital center of surface chalcogen elements under strain is responsible for tuning the catalytic activity of TMDs.