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Structurally ordered L10-PtM (M = Fe, Co, Ni, etc) intermetallic nanocrystals (iNCs), benefiting from the chemically ordered structure and higher stability, are one of the best electrocatalysts used for PEMFC. However, their practical development is greatly plagued by the challenge that high-temperature annealing (> 700 °C) has to be used for realizing disorder-order phase transition (DOPT) due to the high activation barrier (Ea), which always leads to severe particle sintering, morphology change, and makes it highly challenging for gram-scale preparation of desirable PtM iNCs. Here, we report a general low-melting-point metal induced bond strength weakening strategy to promote DOPT of PtM (M = Ni, Fe, Cu, Zn) alloy catalysts. We demonstrate that the introduction of Sn can reduce DOPT temperature to a record-low temperature (≤ 450 °C), which enables ten-gram-scale preparation of high-performance L10-PtM iNCs. X-ray spectroscopic studies, in-situ electron microscopy and theoretical calculations reveal that the Sn-facilitated DOPT mechanism at record-low temperature involves the weakened bond strength and reduced Ea via Sn doping, the formation and fast diffusion of low coordinated surface free atom, and subsequent L10 nucleation. Most importantly, the 15% Sn-doped L10-PtNi iNCs display outstanding performance in H2-air fuel cells with a high peak power density of 1.45 W cm-2 for Pt alloy catalysts and less than 25% activity loss after 30000 cycles at a quite low cathode Pt loading amount of 0.12 mg¬Pt cm-2, representing as one of the most efficient cathodic electrocatalyst for PEMFCs.

The commercialization of proton exchange membrane fuel cells (PEMFCs) relies on highly active and stable electrocatalysts for oxygen reduction reaction (ORR) in acid media. The most successful catalysts for this reaction are nanostructured Pt-alloy with a Pt-skin. The synthesis of ultrasmall and ordered L10 -PtCo nanoparticle ORR catalysts further doped with a few percent of metals (W, Ga, Zn) is reported. Compared to commercial Pt/C catalyst, the L10 -W-PtCo/C catalyst shows significant improvement in both initial activity and high-temperature stability. The L10 -W-PtCo/C catalyst achieves high activity and stability in the PEMFC after 50 000 voltage cycles at 80 °C, which is superior to the DOE 2020 targets. EXAFS analysis and density functional theory calculations reveal that W doping not only stabilizes the ordered intermetallic structure, but also tunes the Pt-Pt distances in such a way to optimize the binding energy between Pt and O intermediates on the surface.

Summary Well-defined metallic nanocrystals (NCs) have been explored as effective electrocatalysts for energy conversion and storage technologies (e.g., fuel cell or water splitting). It is commonly known that electrocatalytic performance can be enhanced by controlling composition, size, and surface morphology. In addition, precisely controlling the atomic arrangement inside NCs can improve performance, with their electronic structures being optimized via interfacial coupling. In this review, we summarize recent advances in atomic arrangement engineering approaches of metallic NCs. First, we introduce thermodynamic and kinetic principles to provide a basic understanding on atomic structure-property correlations. Then, several representative cases of atomic ordering and planar stacking engineering are highlighted for different electrocatalytic processes. Finally, perspectives on the roles of calculations, characterization, and practical applications are outlined.

The instinct scaling relations between the adsorption energies of key intermediates during OER lead to large overpotential for water/seawater splitting. Herein, we develop a new strategy to fabricate amorphous nickel-iron phosphides (NiFeP) with controllable morphologies as high-performance catalysts for overall seawater splitting. The ligand effect of P tunes the electronic states of the oxidized NiFe sites, thus breaks the scaling relations for OER and reduce the adsorption energy gap between HO* and HOO* from 3.08 eV to 2.62 eV. The NiFeP nanostructures exhibit extraordinarily low overpotentials of 129 mV for OER and 126 mV for HER at 100 mA cm−2 in simulated alkaline seawater, which outperform the best reported electrocatalysts. They could also be operated at 1.57 V with 100 mA cm−2 in a two-electrode electrolyzer and work for more than 500 h. Our work may provide a universal guidance for the design of highly active seawater splitting electrocatalysts.

The slow kinetics of oxygen reduction reaction (ORR) occurring at the cathode of a proton exchange membrane fuel cell require the presence of an electrocatalyst to reduce overpotential. MPt alloy nanocrystals (NCs) have been investigated over the last decade as efficient catalysts for ORR and recent studies have shown that structurally-ordered MPt NCs, i.e., intermetallic NCs (iNCs), are more active and exhibit enhanced stability compared with the corresponding randomly alloyed analogues. This mini-review highlights the recent progress in iNC catalyst development for ORR with emphasis on correlating the synthesis-structure-activity relationship. Perspectives and possible research directions to enhance MPt iNC catalytic performance are also proposed.

Pd is a catalyst for electrochemical CO2 reduction to CO but often disturbed by H2 and formate formation at low overpotentials due to its strong affinity to H atoms. Herein, guided by density functional theory (DFT) calculations, Bi-Pd single atom alloy (SAA) nanodendrites (NDs) with Bi atomically dispersed in Pd matrices have been developed for efficient CO2 reduction to CO. The Faradic efficiencies (FEs) of CO on the Bi6Pd94-SAA ND catalyst reach 90.5 % and 91.8 % in H-type and gas diffusion flow cells with overpotentials of only 290 and 200 mV, respectively, which are among the best of the reported Pd-based electrocatalysts. The greatly enhanced CO formation on the Bi6Pd94-SAA NDs can be attributed to the increased reaction barriers for H2 formation due to a lower H coverage resulted from Bi doping, and the decreased free energy for *COOH generation which is a key intermediate for CO production.