Tuning the d-band center of NiC2O4 with Nb2O5 to optimize the Volmer step for hydrazine oxidation-assisted hydrogen production

Abstract

Replacing the thermodynamically unfavorable oxygen evolution reaction (OER) with the low theoretical potential (−0.33 V) and safe by-product (N₂/H₂O) hydrazine oxidation reaction (HzOR) is an energy-saving way for hydrogen production. Nevertheless, the complexity of bifunctionality increases the difficulty of catalyst design. In this work, a hybrid of NiC₂O₄ and Nb₂O₅ is synthesized on nickel foam via a two-step low temperature reaction using Ni₃S₂ as a sacrificial template, named SNiC₂O₄–Nb₂O₅/NF. The experimental and theoretical calculation results illustrate that electrons are transferred from Ni to Nb, thus regulating the electronic structure of Ni. In the hybrid, Nb₂O₅ can effectively adsorb and split H₂O, as well as downshift the d-band center of SNiC₂O₄, thereby optimizing the Volmer step. SNiC₂O₄–Nb₂O₅/NF achieves the properties for the hydrogen evolution reaction (HER: η₂₀ = 155 mV) and the oxygen evolution reaction (OER: η₂₀ = 293 mV). The addition of hydrazine to an alkaline electrolyte can decrease the cell voltage by 1.41 V when the current density is 20 mA cm⁻², and achieve a high-speed hydrogen yield driven by an AA battery. This work puts forward an idea for the rational design of environmentally friendly and effective hybrid catalysts.