LAUSR

Water splitting driven by renewable energy represents a sustainable way to store clean energy. However, its efficiency is limited by the kinetically sluggish oxygen evolution reaction (OER), calling for highly active catalysts to accelerate the reaction rate. Herein, NiO is reduced by cellulose through a hydrothermal method to obtain the highly active OER catalysts. The obtained cellulose‐partially‐reduced‐NiO (CL‐prNiO) shows a hybrid structure, composed of 3.6 wt.% face‐centered cubic (fcc) Ni and 96.4 wt.% rock salt structured NiO with highly disordered interface. The CL‐prNiO delivers a current density of 10 mA cm−2 with an overpotential of 288 mV, which is comparable to the commercial RuO2 and outperforms many of the recently reported Ni‐NiO based OER catalysts. As benefited from the hybrid and disordered structure, CL‐prNiO shows great ability of converting Ni2+ to Ni3+ at a potential prior to the OER onset. The in situ generated Ni3+ species can activate the lattice oxygen in the unreduced NiO of CL‐prNiO, significantly boosting the OER activity.