Solid-aqueous interfaces and their associated phenomena (adsorption, nucleation, corrosion, catalysis, etc.) are ubiquitous in a multitude of chemical systems linking various sub-fields of chemical science. In the realm of heterogeneous catalysis, where an emphasis has been historically placed on chemical transformations at solid-gas interfaces, our molecular understanding of the structures of catalyst-liquid interfaces and the kinetics and mechanisms of the catalytic reactions unfortunately lags behind the development of catalysts and processes in the liquid phase. Heterogeneously catalyzed hydrogenation and oxidation reactions at metal-aqueous interfaces are among the most important processes in the current chemical industry and in a constant pursuit of a greener and more sustainable future, and they also bear significant relevance for the functioning of biological entities. Molecular-level insights into these reactions, however, are often concealed due to the complexity of the dynamic solid-aqueous interfaces. Accordingly, the primary goal of this review is to summarize recent advances in the fundamental understanding of these interfacial chemical processes, particularly spotlighting research in the last decade on dissecting chemical and mechanistic origins of water effects in the catalytic systems. Specifically, we describe a selection of water-engendered effects on the kinetic behaviors and mechanistic consequences for several prototypical metal-catalyzed hydrogenation and oxidation reactions, and critically assess the general and specific roles of water molecules (as solvent or additive) as well as those of the neutral and ionic moieties (particularly H+ and OH-) that are dissolved and solvated in water or equilibrated with the functionalities at the catalyst surfaces. We also show growing evidence that has endorsed close mechanistic connections between thermo- and electrocatalytically enabled redox chemistry at the interfaces, which point to promising strategies of integrating the two historically separated fields. While doing so, systematic approaches combining rigorous reaction tests, kinetic and isotopic probes, advanced characterization techniques and theoretical methods are highlighted. Altogether, the discussed examples underscore the paramount importance of hydrogen-bonding interactions, ionization of covalently bonded surface moieties, heterolytic bond activations and proton-coupled electron transfer as the main factors underlying the uniqueness of water-mediated interfacial redox chemistries and their associated solvation effects.
