Modulating Electronic Structure to Improve the Solar to Hydrogen Efficiency of Cobalt Nitride with Lattice Doping

Abstract

Development of state-of-the-art catalytic systems for highly efficient solar to hydrogen energy conversion is desirable but remains a challenge. In this work, transition metal (M = V, Mo, and W) doped cobalt nitride has been synthesized for solar to hydrogen energy conversion. Neutron diffraction results suggest that the composition of our as-prepared cobalt nitride is Co3.75N0.14, which contains many lattice defects. Neutron pair distribution function (PDF) analysis confirms the structural defects and lattice distortion in M-Co3.75N0.14. The M-doping is demonstrated to tune the electronic structure and properties of Co3.75N0.14 due to the formation of M–N bonds, which significantly improves charge carrier separation efficiency and the reaction kinetics. Density functional theory (DFT) calculations suggest that the d-band center of the doped cobalt nitrides exhibit downshifts compared to pure cobalt nitride. This is beneficial for the desorption of hydrogen atoms, promoting hydrogen evolution activity. The hydrogen evolution rate of the optimal V–Co3.75N0.14-Eosin-Y system reaches 21.21 μmol·mg–1·h–1, with quantum efficiency around 38% at 405 nm excitation wavelength. This remarkable value surpasses those reported for other hybrid photocatalysts.