Flatband-enabled catalysis of alkaline hydrogen evolution on kagome CoSn

Flatband materials offer a unique platform for catalysis due to their intrinsically localized electronic states and high density of states near the Fermi level. Here, we investigate the kagome intermetallic compound CoSn as a representative flatband catalyst for the hydrogen evolution reaction (HER) under alkaline conditions. First-principles calculations reveal that the CoSn(001) surface retains flatband features originating from Co dyz and dxz orbitals, which enhance hydrogen adsorption and facilitate water dissociation. Compared to elemental Co, CoSn exhibits significantly improved intrinsic activity, as confirmed by both theoretical analysis and experimental measurements. To further optimize catalytic performance, surface doping with 3d transition metals (X@CoSn, X = Ti, V, Cr, Mn, Fe, Ni) was employed. Among the dopants tested, Cr achieves the most favorable balance of HER energetics, exhibiting reduced water dissociation barriers and suitable adsorption strengths. A strong correlation between the dopant-modulated flatband center and OH* binding energy is established, demonstrating that flatband tuning directly governs surface reactivity. These findings highlight flatband engineering as an effective strategy for designing high-performance electrocatalysts.