A Review on the Application of In-Situ Raman Spectroelectrochemistry to Understand the Mechanisms of Hydrogen Evolution Reaction

In our ever-growing society, enhanced energy security is needed now more than ever to mitigate large-scale climate change. One avenue for the renewable and sustainable energy transition is through electrochemical processes, such as water electrolysis, where hydrogen is produced through the hydrogen evolution reaction (HER). Currently, however, electrocatalysts for HER are either too costly or do not perform to industrial requirements. To mitigate this, a deeper understanding of the electrocatalytic system, including active site determination and structural reconfiguration, is needed. In-situ Raman spectroelectrochemistry is a powerful method in elucidating the mechanisms of electrocatalytic reactions in practical conditions due to its compatibility with electrolytes, small analysis spot size, high acquisition speed, and relative ease of spectral assignment. For the HER in particular, in-situ Raman spectroelectrochemistry can elucidate the active site location by providing a molecular fingerprint of adsorbed hydrogen onto a catalytic active site. In this Review, we provide an overview of the existing experimental works for HER using in-situ Raman spectroelectrochemistry. We discuss the application to existing electrocatalysts, such as the benchmark Pt-based materials and Pt-free alternatives, and we provide insights on the properties needed for a powerful, yet low-cost, HER electrocatalyst. We also discuss ways this method can be applied to further develop emerging electrocatalyst materials such as MXenes. Finally, we examine pertinent works specifically based on surface sensitive Raman techniques, such as surface enhanced Raman spectroscopy (SERS), which provide a revolutionary direction for future related works. Overall, this Review addresses the urgent need for applications of in-situ spectroelectrochemical methods to advance the discovery of catalysts for carbon-neutral energy.