Inside solid-liquid interfaces: Understanding the influence of the electrical double layer on alkaline hydrogen evolution reaction

In-depth understanding of alkaline hydrogen evolution reaction (HER) not only guides the design of catalysts, but also builds up strong foundation for CO₂/N₂ reduction reactions that both involves water molecules. In this review, we focused on electrical double layer (EDL) of the cathode where the electrochemical reaction takes place, and analyzed the role of main species in this region, i.e. water molecules, adsorbed H, adsorbed OH/OH⁻ and hydrogen gas bubbles. Through investigating these species inside EDL, the key problems are comprehensively covered, including Janus effect of interfacial water, whether or not H_ad is unique descriptor for alkaline HER, the influence of OH_ad on alkaline HER from the viewpoint of thermodynamics and kinetics, the effect of cations in electrolyte, as well as the importance of mass transfer at high current densities. Interactions between the interfacial species, as well as the dynamical changes of EDL during the electrocatalytic reaction are also summarized here. Lastly, an account of the methods for probing molecules/ions inside EDL to reveal the underlying mechanism of alkaline HER was presented.