Operando Electro-Oxidation Reconstitution of a Newly Designed 2D Co(II)-MOF on Nickel Foam to Cobalt Oxyhydroxide Nanosheets towards Energy Sustainability: A Holy Grail in Electrocatalytic Water Splitting

The upsurging of cost-effective de novo electrocatalysts through the operando electro-oxidation approaches holds great promise for the scalable production of green energy in the pursuit of energy sustainability. This work introduces an operando electro-oxidation reconstitution strategy in producing a smart electrocatalyst, cobalt “oxyhydroxide” derived from a newly designed 2D cobalt(II) metal–organic framework (NBU-4) directly grown on nickel foam (NF), NBU-4/NF@CoOOH. The electrocatalyst, NBU-4/NF@CoOOH, exhibits an outstanding overpotential of 76 mV for the hydrogen evolution reaction and 336 mV for the oxygen evolution reaction to achieve a current density of 10 mA/cm² with remarkable Faradaic efficiencies of 97.1 and 93.4%, respectively, in 1 M aqueous KOH. Unveiling the bifunctionality of NBU-4/NF@CoOOH as the cathode and anode for overall water splitting in 1 M aqueous KOH, a low voltage of 1.65 V was needed to obtain 10 mA/cm² current density. Nonetheless, NBU-4/NF@CoOOH displayed excellent stability for 12 h as evidenced from the chronopotentiometry recorded at 10 mA/cm². The outstanding bifunctional electrocatalytic performance and stability of the electrocatalyst for 50 h is attributed to the unique 2D hexagonal nanosheet morphology of NBU-4/NF@CoOOH and the microporous structure with zigzag flow channels of NF, facilitating a faster kinetics through the Co³⁺ and Ni²⁺ dual sites synergism.