Intermetallic MnNi3 phase separated from nanoporous nickel as hydrogen evolution electrocatalyst in basic media

Abstract

It is acknowledged that hydrogen evolution reaction (HER) in basic media is mainly limited by H₂O molecule dissociation. To overcome this problem, in this study, intermetallic MnNi₃ phase separated from nanoporous (np) Ni was rapidly synthesized and proved to be a cost-effective HER catalyst. Interestingly, the as-prepared MnNi₃/np-Ni-9h has integrated and dense nanosheets, showing a huge surface area for electrocatalysis. It only demands HER overpotentials of 107, 234 and 337 mV to achieve current densities of 10, 50 and 100 mA cm⁻², respectively. It also possesses long-term durability for 650 h, indicating that the self-dissociated MnNi₃ phase is ultra-stable even under the action of violent H₂ bubbles. Furthermore, the MnNi₃/np-Ni-9h‖RuO₂ couple needs only 1.90 V to reach a high current density of 1 A cm⁻² at the industrial conditions (6 M KOH, 60 °C). Meanwhile, the simulated cell could steadily produce hydrogen for over 190 h with merely 6% voltage loss, reconfirming the superior catalytic activity and robustness of the MnNi₃/np-Ni-9h electrode. From a theoretical perspective, H₂O molecule is preferred to be adsorbed on the Mn site and subsequently is beneficial to be dissociated into *OH–*H co-adsorption. Correspondingly, the rate-determining step (RDS) of alkaline HER on MnNi₃ can be changed into the third step (*OH–*H → *H) and energy barrier can be reduced to 0.56 eV when *OH and *H are neither far nor near. This work offers a guide to facilely fabricate cost-effective HER catalysts that are suitable for industrial hydrogen production.