Symmetry Evolution Induced 2D Pt Single Atom Catalyst with High Density for Alkaline Hydrogen Oxidation.

The performance of single-atom catalysts is greatly influenced by the chemical environment surrounding the central atom. Here, a salt-assisted method is employed to transform the tetrahedral coordination structure of zeolitic imidazolate frameworks - 8 (ZIF-8) into a planar square coordination structure without altering the ligands. During the subsequent carbonization process, concurrent with the evaporation of zinc atoms, the structure of the nitrogen and carbon carriers (NC carriers) undergoes a transition from five-membered rings to six-membered rings to preserve the 2D structure. This transition results in the generation of additional defect sites on the 2D-NC substrates. Hence, the Pt single-atom catalysts with planar square coordination symmetries can be precisely prepared via electrodeposition (denoted as 2D-Pt SAC). The Pt loading of 2D-Pt SAC is 0.49 ± 0.03 µg cm -2 , higher than that of 3D-Pt SAC (0.37 ± 0.04 µg cm -2 ). In the context of the hydrogen oxidation reaction electrocatalysis, under an overpotential of 50 mV, these single-atom catalysts with 2D coordination exhibit mass activities of 2396 A g Pt -1 (32 times higher than commercial Pt/C catalyst, 2 times higher than 3D-PtNC).