In situ infrared, Raman and X-ray spectroscopy for the mechanistic understanding of hydrogen evolution reaction

Hydrogen production by water reduction reactions has received considerable attention because hydrogen is considered a clean-energy carrier, key for a sustainable energy future. Computational methods have been widely used to study the reaction mechanism of the hydrogen evolution reaction (HER), but the calculation results need to be supported by experimental results and direct evidence to confirm the mechanistic insights. In this review, we discuss the fundamental principles of the in situ spectroscopic strategy and a theoretical model for a mechanistic understanding of the HER. In addition, we investigate recent studies by in situ Fourier transform infrared (FTIR), Raman spectroscopy, and X-ray absorption spectroscopy (XAS) and cover new findings that occur at the catalyst–electrolyte interface during HER. These spectroscopic strategies provide practical ways to elucidate catalyst phase, reaction intermediate, catalyst-electrolyte interface, intermediate binding energy, metal valency state, and coordination environment during HER.