Electrode–Polyoxometalate Interactions: Adsorption-Driven Control of Redox Properties in Polyoxometalates

Polyoxometalates (POMs) are redox-active metal–oxide clusters with well-defined electron transfer properties that make them promising candidates for electrocatalysis and energy conversion. Examples include dinitrogen reduction to ammonia, carbon dioxide reduction to carbon monoxide and cathodic oxygenation of alkanes with dioxygen. While the intrinsic redox behavior of POMs has been extensively studied, the role of interfacial interactions at electrode surfaces remains poorly understood. Herein, the electron transfer kinetics of Keggin-type POMs is investigated, using rotating disk electrode voltammetry to systematically decouple mass transport from interfacial kinetics. Both the redox thermodynamics and kinetics are demonstrated that are sensitive to structural variables, including the identity of the heteroatom (X = Al³⁺, Si⁴⁺, P⁵⁺) and the nature of the addenda metal (Mo vs. W) in plenary compounds, and the substitution with first-row transition metals (Cu²⁺, Ni²⁺, Fe³⁺). Cu-substituted analogs exhibit quasireversible, multielectron behavior marked by electrodeposition at more negative potentials and higher charge transfer coefficients (α), while Fe and Ni substitutions preserve diffusion-limited kinetics. Using rotating disk electrode–linear sweep voltammetry analysis, this study provides a mechanistic basis for the rational tuning of POM and enables clear differentiation between competing interfacial processes.