Cerium-doping and nitridation effects on nickel-based metal organic frameworks for alkaline water oxidation

Abstract

In the quest for a green energy future, renewable energy-driven hydrogen production via alkaline water electrolyzers leads toward a sustainable human society. However, the complementary oxygen evolution reaction (OER) in alkaline water electrolysis limits the overall electrolyzer efficiency since it requires complex, multi-step electron transfer. This work introduces a synthetic strategy that translates a less-conductive Ce-doped nickel metal–organic framework (MOF) into a conductive precatalyst (i.e., a Ce-doped nickel nitride and carbon-based composite) through nitrogen incorporation. Nitrogen incorporation leads to the formation of a nitride phase, and a carbon-based material phase, while the Ce³⁺ species leads to the formation of pseudo-tetrahedral geometries at Ni sites, which enhances OER kinetics, as indicated by a Tafel slope of 83.6 mV dec⁻¹. Nitridation led to an approximately 50× improvement in OER activity relative to the parent MOFs. Moreover, cerium doping and nitridation produced a synergistic effect, with Ce_0.03Ni_0.97-NMOF achieving a faradaic efficiency of 100% and maintaining stable operation for 24 hours at a current density of 10 mA cm⁻², exhibiting even higher activity after prolonged testing.