Hierarchical 3D flower like cobalt hydroxide as an efficient bifunctional electrocatalyst for water splitting

Abstract

• Transition metal oxide/hydroxides grown on nickel foam (NF) by hydrothermal method. • Co(OH) 2 /NF showed higher OER activity with low overpotential of 230 mV@10 mA cm -2 . • MnO 2 /NF delivered better HER activity with an overpotential of 150 mV@10 mA cm -2 . • The Co(OH) 2 ||Co(OH) 2 electrolyzer demonstrated a cell voltage of 1.61 V@10 mA cm -2 . • The electrolyzer offered an excellent long-term stability of 80 hours@100 mA cm -2 . The development of cost-effective and extremely stable bifunctional electrocatalysts is highly challenging due to the sluggish kinetics of oxygen evolution reaction (OER) compared to hydrogen evolution reaction (HER). So finding a suitable electrocatalyst for the respective OER and HER activity is highly essential. The best OER and HER electrocatalyst demands enhanced kinetics with increased surface area, active sites, and lower charge transfer resistances at the interfaces. Hence, improving the efficiency of an electrocatalyst for bifunctional activity would be advantageous for OWS. Here, we have reported nickel hydroxide (Ni(OH) 2 ), manganese dioxide (MnO 2 ), and cobalt hydroxide (Co(OH) 2 ) self-supported transition metal oxide/hydroxides grown nickel foam (NF) substrate by simple hydrothermal method for overall water splitting (OWS) in alkaline medium. The Co(OH) 2 /NF show a low overpotential of 230 mV for OER, whereas MnO 2 /NF exhibits low overpotential of 150 mV for HER to accomplish a current density of 10 mA cm −2 . Though, MnO 2 exhibits low overpotential for HER, the current density is lower compared to Co(OH) 2 due to lower surface area and conductivity. The full electrolyzer constructed from Co(OH) 2 ||Co(OH) 2 show a lowest cell voltage of 1.61 V and with an anion exchange membrane H-cell delivers a cell voltage of 1.68 V at 10 mA cm −2 in 1M KOH. A long-term stability studies (80 hours) on Co(OH) 2 ||Co(OH) 2 demonstrate robustness of the prepared electrodes and confirms the superior bifunctional electrocatalytic activity to replace the expensive noble metals.