Probing the Co role in promoting the OER and Zn-air battery performance of NiFe-LDH: a combined experimental and theoretical study

NiFe layered double hydroxide (NiFe-LDH) is a cost-effective and active catalyst for the oxygen evolution reaction (OER), yet further promoting its OER performance is an ongoing challenge. Herein, we devised a facile strategy that can form two types of Co introduced NiFe-LDH catalysts, namely CoNiFe-LDH and Co@NiFe-LDH. Multiple techniques disclosed that a heterostructure is formed between Co(OH)(2) and NiFe-LDH for Co@NiFe-LDH, while electronic interactions between Co and NiFe atoms are observed for both samples. Notably, Co@NiFe-LDH exhibited markedly superior OER performance to the RuO2 benchmark in alkaline medium, manifested by a low overpotential of 253 mV at 10 mA cm(-2), an extremely small Tafel slope of 44 mV dec(-1), and the outperformed stability for long-time operation. Further, when employed as an air-cathode catalyst for rechargeable Zn-air batteries (ZABs), the Co@NiFe-LDH modified battery surpassed the Pt/C + RuO2 decorated one, evidenced by a larger power density, a bigger specific capacity, and a superior galvanostatic charge-discharge cycling stability for 90 h. Density functional theory (DFT) calculations revealed that the Fe site is the active center for the OER, and the formation of the heterostructure can increase the density of states of the active site near the Fermi level hence significantly enhancing the electrical conductivity, while also upshifting the d-band center of the Fe site to increase the adsorption capability of the *OOH intermediate, resulting in the energy barrier of the rate determining step being reduced eventually.