Fabrication of Ni₂O₂(OH)/CNTs-based electrocatalyst for efficient bifunctional electrocatalytic water splitting

Exploring the cost-effective and earth-abundant electrocatalyst for efficient bifunctional activity is very challenging these days. The main reason is very slow OER (oxygen evolution reaction) kinetics as compared with HER (hydrogen evolution reaction). An electrocatalyst with enhanced kinetics towards OER and HER is highly required, which may be attributed to a larger surface area, an increased number of active sites, and lower charge transfer resistance. In this paper, we have reported a very efficient bifunctional Ni₂O₂(OH)/CNTs electrocatalyst by a facile ultrasonication route followed by annealing for OER/HER performance in an alkaline solution. The Ni₂O₂(OH)/CNTs electrocatalyst exhibits a lower overpotential of 228 mV and 270 mV during OER to accomplish a current density of 40 and 100 mAcm⁻² while it requires a 368 mV and 418 mV overpotential during HER to achieve a current density of 40 and 100 mAcm⁻². The prepared Ni₂O₂(OH)/CNTs electrocatalyst has a lesser Tafel slope (132 mVdec⁻¹; OER, 115 mVdec⁻¹; HER) as compared to Ni₂O₂(OH) (239 mVdec⁻¹; OER, 124 mVdec⁻¹, HER). Ni₂O₂(OH)/CNTs exhibit reduced charge resistance, enhanced electrochemical active surface area, greater carrier concentration, and a higher exchange current density, which confirms its superior bifunctional electrocatalytic activity. This work provides an economical and affordable means to prepare superior, efficient bifunctional electrocatalysts for widespread commercial applications.