Imidazole coordination lowers Ni-FeNbO4 surface energy for water oxidation

It is crucial to rationally design catalysts with high activity and strong stability for electrolytic water oxygen evolution reaction (OER). Here, Ni-FeNbO 4 @NC microspheres were successfully synthesized as OER catalysts by interface optimization and Ni-doping. To address FeNbO 4 problems such as easy agglomeration, low catalytic activity and poor electrical conductivity, the catalyst was incorporated in N p-orbital of imidazole and metals (Ni and Fe) empty d-orbitals to form coordination compound, thus avoiding oxides direct contact and effectively improving dispersion. Moreover, Ni-doping provides additional catalytic active sites, good current impact resistance and large intrinsic conductivity for Ni-FeNbO 4 @NC. Besides, under high-temperature carbonization, the Ni-FeNbO 4 surface imidazole evolves into N-containing carbon layer, which enhances overall electrical conductivity to reduces ohmic overpotential. According to density functional theory calculations (DFT), Ni-doping lowers Gibbs free energy of OER decisive rate step, and enlarges reaction kinetics. From in-situ Fourier Transform infrared spectroscopy (FTIR) and in-situ differential electrochemical mass spectrometry (DEMS), Ni-FeNbO 4 @NC displays multiple types of catalytic active sites (Ni∗, and C-N∗) and efficient oxygen production efficiency. Under the synergistic effect of interface optimization and Ni-doping, Ni-FeNbO 4 @NC exhibits good catalytic activity in OER (low overpotential: 286 mV@10 mA cm −2 , small Tafel slope: 56.7 mV dec −1 , 50 h long stability).