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.