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

[Display omitted] •Alkaline HER from the view of electrical double layer (EDL) was first reviewed.•The effects of EDL on the alkaline HER were comprehensively summaried.•Methods for probing EDL were highlighted for guiding practical uses. 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 Had is unique descriptor for alkaline HER, the influence of OHad 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.