Planar‐Coordination PdSe₂ Nanosheets as Highly Active Electrocatalyst for Hydrogen Evolution Reaction

Abstract The coordination environment is crucial for the activity of an electrocatalyst, which defines the interaction between the central and adjacent atoms. In traditional 2D MX 2 (M = Mo, W, etc., X = S, Se), M is usually coordinated with 6 X atoms in either trigonal prismatic (2H) or octahedral (1T) polyhedrons. With such a coordination configuration, only the edge X sites exhibit activity for hydrogen evolution reaction (HER). Here, a planar‐coordination transition metal chalcogenide, PdSe 2 is reported, as an efficient electrocatalyst for the HER in an alkaline electrolyte. By reducing the spatial polyhedron coordination to planar polygon coordination, the M sites in PdSe 2 can be efficiently activated to interact with the adsorptive intermediates. As a result, both Pd and Se atoms act as active sites for hydrogen evolution with neutral adsorption ability. With an overpotential of 138 mV at 10 mA cm −2 , this work advances the exploration of planar‐coordination HER electrocatalysts.