MOF Derived Nonstoichiometric NixCo3−xO4−y Nanocage for Superior Electrocatalytic Oxygen Evolution

Nonstoichiometric NixCo3−xO4−y 3D nanocages are fabricated through metal–organic framework template route and their electrocatalytic oxygen evolution reaction (OER) characteristics have been investigated. Substitution of Ni in Co3O4 spinel structure improves the intrinsic catalytic activity. Enhanced OER activity stems from the presence of nonstoichiometry and low coordination metal sites, which lower the OH− adsorption energy and improve the conductivity of the catalysts. OER activity is tuned by varying Ni to Co ratio and the best activity is observed for NiCo‐1, having Ni/Co = 1. This is reflected in a lower overpotential (η) of 320 mV at a current density of 10 mA cm−2 and a lowest Tafel slope of 53 mV dec−1. The turnover frequency value (1.37 × 10−2 s−1) and lower apparent activation energy (35.5 ± 3 kJ mol−1) at η = 350 mV further support the superior intrinsic activity of NiCo‐1. The synergetic effect of porosity, nonstoichiometry, and rich redox centers results in enhancement of the OER activity of NixCo3−xO4−y 3D nanocage. Present work provides a simple strategy to design a low‐cost and efficient electrocatalyst which can be combined with photoelectrode to realize superior solar to hydrogen conversion devices. The nonhomogeneous surface charge distribution and high electrochemical surface area of nonstoichiometric NixCo3–xO4–y three dimensional nanocages results in improved electrocatalytic oxygen evolution activity compared to Co3O4. This is due to the synergetic effect of porosity, nonstoichiometry and rich redox centers in NixCo3−xO4−y The efficient catalytic activity for NixCo3−xO4−y is supported by higher turnover frequency and lower apparent activation energy.