Abstract
Nickel/Nickel oxide (Ni/NiO) nanosheets heterostructure is a cheap and active catalyst for hydrogen evolution reaction (HER) in alkaline electrolytes. However, the reason for this activity is still under debate. Herein in-situ Raman electrochemistry has been established as a method to probe interfacial intermediates and correlate the performance of various nickel catalysts (Ni, NiO, and Ni/NiO nanosheets) during HER. In-situ Raman spectroscopy demonstrated that Ni/NiO nanosheet heterostructure maintained β-Ni(OH)2 species initially, which may contribute to the superior initial HER activity. Ni/NiO nanosheets lost β-Ni(OH)2 species by preserving a high cathodic overpotential (-0.4 V vs. RHE) for 2000 sec. The results confirmed the importance of Ni metal sites in addition to NiO sites and maintaining hydroxide species for superior and durable HER activity. These results can be utilized to design an efficient and durable catalyst for alkaline electrolyzers for the sustainable production of hydrogen.