Tuning the Activity and Stability of CoCr-LDH by Forming a Heterostructure on Surface-Oxidized Nickel Foam for Enhanced Water-Splitting Performance.

ABSTRACT

The development of low-cost, efficient catalysts for electrocatalytic water splitting to generate green hydrogen is a hot topic among researchers. Herein, we have developed a highly efficient heterostructure of CoCr-LDH on NiO on nickel foam (NF) for the first time. The preparation strategy follows the simple annealing of a cleaned NF without using any Ni salt precursor, followed by the growth of CoCr-LDH nanosheets over the surface-oxidized NF. The CoCr-LDH/NiO/NF catalyst shows excellent electrocatalytic activity and stability toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in a 1 M KOH solution. For OER, only 253 mV and for HER, only 185 mV overpotentials are required to attain a 50 mA cm-2 current density. Also, the long-term stability of both the OER and HER for 60 h proves its robustness. The turnover frequency value for the OER increased 1.85 times after the heterostructure formation compared to bare CoCr-LDH. The calculated Faradaic efficiency values of 97.4 and 94.75% for the OER and HER revealed the high intrinsic activity of the heterostructure. Moreover, the heterostructure only needs 1.57 V of cell voltage when acting as both the anode and the cathode to achieve a 10 mA cm-2 current density. The long-term stability of 60 h for the total water-splitting process proves its excellent performance. Several systematic pre- and post-experiment characterizations prove its durable nature. These excellent OER and HER activities and stabilities are attributed to the surface-modified electronic structure and thin nanosheet-like surface morphology of the heterostructure. The thin, wide, and modified surface of the catalyst facilitates the diffusion of ions (reactants) and gas molecules (products) at the electrode/electrolyte interface. Furthermore, electron transfer from n-type CoCr-LDH to p-type NiO results in enhanced electronic conductivity. This study demonstates the effective design of a self-supported heterostructure with minimal synthetic steps to generate a bifunctional electrocatalyst for water splitting, contributing to the greater cause of green hydrogen economy.