Investigation of nickel iron layered double hydroxide for water oxidation in different pH electrolytes

Nickel iron layered double hydroxide (NiFe LDH) is one of the best oxygen evolution reaction (OER) catalysts in alkaline electrolytes. However, it performs poorly in neutral electrolytes, and the detailed mechanism is still unclear. Herein, we introduce electrochemical measurements, operando surface enhanced Raman spectroscopy and operando 57Fe Mössbauer spectroscopy to elucidate the mechanism of NiFe LDH for OER process in different pH electrolytes. Our results show that even though there exist Ni3+ and Fe4+ species, the NiFe LDH based electrocatalysts still show worse OER performance in neutral electrolytes than in alkaline conditions. Combining the electrochemical measurements with spectroscopic investigations, we demonstrated that the rate-determining step (RDS) of OER on NiFe LDH based electrocatalysts is from *O to *OOH in alkaline medium while *OH formation is the RDS in neutral conditions. Our work provides new insights into elucidating the OER mechanism in different pH electrolytes.