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 securityis needednow more than ever to mitigate large-scale climate change. One avenuefor the renewable and sustainable energy transition is through electrochemicalprocesses, such as water electrolysis, where hydrogen is producedthrough 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 understandingof the electrocatalytic system, including active site determinationand structural reconfiguration, is needed. In-situ Raman spectroelectrochemistryis a powerful method in elucidating the mechanisms of electrocatalyticreactions in practical conditions due to its compatibility with electrolytes,small analysis spot size, high acquisition speed, and relative easeof spectral assignment. For the HER in particular, in-situ Raman spectroelectrochemistrycan elucidate the active site location by providing a molecular fingerprintof adsorbed hydrogen onto a catalytic active site. In this Review,we provide an overview of the existing experimental works for HERusing in-situ Raman spectroelectrochemistry. We discuss the applicationto existing electrocatalysts, such as the benchmark Pt-based materialsand Pt-free alternatives, and we provide insights on the propertiesneeded for a powerful, yet low-cost, HER electrocatalyst. We alsodiscuss ways this method can be applied to further develop emergingelectrocatalyst materials such as MXenes. Finally, we examine pertinentworks specifically based on surface sensitive Raman techniques, suchas surface enhanced Raman spectroscopy (SERS), which provide a revolutionarydirection for future related works. Overall, this Review addressesthe urgent need for applications of in-situ spectroelectrochemicalmethods to advance the discovery of catalysts for carbon-neutral energy.