Transition metal tailored δ-MnO₂ with optimized charge compensation for enhanced hydrogen evolution

Layered manganese dioxide (δ-MnO₂) exhibits potential in the hydrogen evolution reaction (HER) due to its multivalent redox properties and high specific surface area. However, its poor intrinsic conductivity and insufficient active sites limit the electron transfer efficiency and adsorption/desorption of *H intermediates. Herein, we constructed an X-MO/NF (X = Ni, Cu, Zn) electrocatalytic system by in situ growth of δ-MnO₂ on the surface of nickel foam (NF) via a one-step hydrothermal method and introduction of transition metal atoms. It has been shown that the transition metals trigger the charge compensation mechanism by changing the O coordination environment, inducing the formation of oxygen vacancies and unsaturated Mn³⁺ sites in MnO₂ lattice, thus balancing the charge distribution and optimizing the electronic structure. Ni-MO/NF, Cu-MO/NF, and Zn-MO/NF exhibit low overpotentials of 145 mV, 131 mV, and 115 mV at 10 mA cm^-2 in 1 M KOH, respectively. Theoretical calculations confirmed that via Ni, Cu, and Zn doping, the hydrogen adsorption-free energy could be reduced and the surface reaction kinetics accelerated. Nevertheless, the diversity of their orbital contributions to the electronic structure of MnO₂ led to different redistributions of the electron cloud density, thus showing variation in the degree of enhancement of the catalytic performance. This work reveals the regulation rule of transition metal atoms on the coordination environment of δ-MnO₂, which provides a new perspective and theoretical guidance for optimizing the catalytic performance of transition metal oxides.