For metal–carbon shell catalysts of the hydrogen evolution reaction (HER), owing to the diversity of the inner metal phases and the adjustability of the outer carbon structure, the structure of the active sites is still puzzling. Here, with the guidance of density functional theory (DFT) calculations, verification of experimental results and operando X-ray absorption spectroscopy, we found that the multi-interfacial charge polarization around Mo atoms in MoP induced by S on MoS2 and N on adjacent NC layers in carbon defect locations of three phase interfaces could improve the adsorption/desorption behavior of H intermediates and accelerate the dissociative adsorption process of H2O molecules, which then exhibited distinct catalytic activities for the HER in both acidic (10.0 mA cm−2 at η = 120 mV) and alkaline media (10.0 mA cm−2 at η = 80 mV) and outstanding durability. This work offers atom-level insights into the active sites of metal–carbon shell catalysts, contributing to the rational design of efficient HER catalysts. Under the guidance of theoretical calculations, the present paper provides a new catalyst with novel inner metal cores of MoP nanoparticles (NPs) coupled with ultrafine MoS2 nanosheets encapsulated with NC shells. A combination of theoretical calculations and electrochemical analysis uncovers that the multi-interfacial charge polarization of MoP, MoS2 and NC in carbon defect locations could improve the HER performance in both acidic and alkaline media.
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