Currently, Pt-based electrocatalysts are adopted in the practical proton exchange membrane fuel cell (PEMFC), which converts the energy stored in hydrogen and oxygen into electrical power. However, the broad implementation of the PEMFC, like replacing the internal combustion engine in present automobile fleet, sets a requirement for less Pt loading compared to current devices. In principle, the requirement needs the Pt-based catalyst to be more active and stable. Two main strategies, engineering electronic (d-band) structure (including controlling surface facet, tuning surface composition, and engineering surface strain) and optimizing reactant adsorption sites are discussed and categorized based on the fundamental working principle. In addition, general routes for improving the electrochemical surface area, which improves activity normalized by the unit mass of precious group metal/platinum group metal, and stability of the electrocatalyst are also discussed. Furthermore, the recent progress of This article is protected by copyright. All rights reserved. 2full fuel cell tests of novel electrocatalysts is summarized. It is suggested that a better understanding of the reactant/intermediate adsorption, electron transfer, and desorption occurring at the electrolyte-electrode interface is necessary to fully comprehend these electrified surface reactions; and standardized MEA testing protocols should be practiced, and data with full parameters detailed, for reliable evaluation of catalyst functions in devices.

Pt-based alloy nanocrystals have shown great success in oxygen reduction electrocatalysis owing to their unique surface and electronic structures. However, they suffer from severe stability issues due to the dissolution of non-noble metal elements, leading to the "trade-off " between activity and stability. In this work, targeting the stability issue of a Pt x Cu y -based alloy, Pt 2 CuW 0.25 ternary alloy nanoparticles are synthesized by thermal reduction strategy based on wet-chemical method using W(CO) 6 as a reductant. Apart from the competitive activity, the obtained Pt 2 CuW 0.25 /C shows remarkable stability, whereby the area specific activity and mass activity maintain 89.5% and 95.9% of the initial values, respectively, after 30 000 cycles of accelerated polarization between 0.6 and 1.1 V (vs reversible hydrogen electrode). By using vacancy formation energy of surface Pt as the descriptor, it is found that the enhanced stability of Pt 2 CuW 0.25 /C originates mainly from the stronger bonding between W and Pt/Cu atoms, acting as an "adhesive" to stabilize the atoms from dissolution, which is further verified by chemical stability experiments. This work demonstrates a rational design strategy for ternary alloy nano-electrocatalyst that has high thermodynamic stability while maintaining high activity by employing high-melting-point metal.

Dual-metal single-atom catalysts (DACs), featuring high atomic utilization efficiency, excellent selectivity, and stability originating from the atomically dispersed nature, have emerged as a new frontier in heterogeneous electrocatalysis due to the synergistic effect between diversified metal active sites in promoting their catalytic activity. In this review, the recent progress and development on the syntheses, characterizations, theoretical uniqueness, and applications for various catalytic reactions and devices (oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, CO 2 reduction reaction, N 2 reduction reaction, proton exchange membrane fuel cells) are summarized and reviewed. Specifically, the synergistic effect between the two metal centers and electronic structures of catalysts is systematically discussed. Moreover, the future challenges and prospects in developing practical DACs are proposed as a possible direction for further investigation.

Co-based single-atom-catalyst has been discovered as a possible candidate for the oxygen evolution reaction (OER), whereby further improvements in performance with only Co metal sites are still challenging with limited...