Electrocatalyst is the key in developing electrochemical energy conversion and storage, and in green chemistry of electrosynthesis using electrons as reagents. The activity, selectivity and stability of electrocatalysts depend strongly on both their bulk and surface structures. Therefore, the rational design and control-synthesis of electrocatalysts are the central subject, and mainly focused on the structure-catalytic functionality of nanomaterials, since practical electrocatalysts often consist of nanosized particles substrated on conductive support. The bulk structure of nanoparticles could be tuned by changing their chemical nature and composition, while tuning their surface structure is more difficult, especially the high catalytic activity corresponding to high surface energy that leads to disappear thermodynamically the nanoparticles during their growth. We have devoted, in recent years, to the structure design and controlled synthesis of electrocatalysts of metal/alloy nanocrystals of high surface energy, and non-precious metal electrocatalysts as well.

(1) Tuning the surface atomic arrangement of well-defined metal nanocatalysts. Well-defined Pt, Pd, Rh and Cu nanocrystals enclosed by high-index facets have been successfully obtained by developing electrochemically shape-controlled synthesis, such as tetrahexahedral nanocrystals (THH NCs) enclosed with {hk0} high-index facets, trapezohedral nanocrystals (TPH NCs) with {hkk} high-index facets, triambic icosahedral nanocrystals (TIH NCs) with {hhl} high-index facets and hexoctahedral Pt NCs (HOH NCs) with {hkl} facets. As the high-index facets contain a high density of active centers, these NCs of high surface energy exhibit much higher electrocatalytic activity than commercial catalysts for small organic fuel oxidation reactions.

(2) Tuning the electronic structure of Pt- and Pd-based nanocatalysts. The electronic structure of NCs catalysts has been tuned either by surface decoration using foreign adatoms, or through alloying Pt and Pd with other metals. Different adatoms such as Bi, Ru and Au were used to decorate the THH Pt NCs, and both THH and TPH Pt-based alloy nanocatalysts were prepared by electrochemically shape-controlled method. The THH and TPH alloy NCs preserve the high-index facets while hold a synergy of electronic effect that enhances further the electrocatalytic activity.

(3) Synthesis of non-precious metal electrocatalysts with high ORR activity. Fe/N/C is a promising electrocatalyst for oxygen reduction reaction (ORR). By well-screening the precursors, optimizing the synthetic procedures and surface decoration, the resulted Fe/N/C exhibits high activity and stability in both acid and alkaline conditions. The results demonstrated that the Fe/N/C-SCN catalysts in a proton exchange membrane fuel cell (PEMFC) can output a maximum power density of 1.03 W/cm², and by using 2-aminothiazole as precursor the synthesized S-doped Fe/N/C catalyst with graphene nanosheets can yield a peak power density of 164 mW/cm² in an anion exchange membrane fuel cell (AEMFC).

Acknowledgements. The studies were supported by NSFC (21621091, 21573183)

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