Electrolyte effects at solid–liquid interfaces in electrocatalysis: From fundamentals to electrolyte engineering

The universality and atomic-level structure of solid-liquid interfaces critically govern functionality across chemical, biological, and geological systems. In electrocatalysis, this interfacial structure dictates reaction thermodynamics and kinetics. However, fundamental understanding of structure-property relationships and their correlation with preferential reaction pathways remains incomplete. While conventional models emphasize adsorbate-surface covalent bonding and long-range electrode-electrolyte electrostatic interactions, emerging evidence highlights the significant impact of noncovalent adsorbate-electrolyte interactions on the electrical double layer (EDL) structure and electrocatalytic kinetics. Critically, both electrode and electrolyte co-determine catalytic performance. Despite advances in catalyst design, the electrolyte's role in modulating the local interfacial environment is inadequately understood, hindering optimization of activity, selectivity, and stability. Elucidating interfacial electrolyte effects is thus paramount, equaling the importance of intrinsic catalyst properties. This review commences by evaluating established and emerging theoretical frameworks describing the electrochemical solid-liquid interphase. Progressing to mechanistic insights, we decipher the role of electrolyte composition—specifically cation/anion speciation, concentration, and pH—in modulating the activity, stability and selectivity of core electrocatalytic reactions. Critical assessment follows of state-of-the-art <em>operando </em>spectroscopic and scattering methodologies for resolving the dynamic evolution of buried interfaces. We conclude by delineating fundamental knowledge gaps and strategic research trajectories for electrolyte engineering to advance electrocatalytic microenvironments.