Polyoxometalates for redox chemistry

Molecular metal oxides, commonly referred to as polyoxometalates (POMs), are anionic metal–oxo clusters of early, high-valent transition metals that combine atomically defined active sites with reversible multi-electron redox activity. Over the past decade, redox-active POMs have emerged as molecular analogues of solid-state metal oxides and as key components in sustainable energy and catalysis technologies. Their applications span from photocatalysis and electrocatalysis to electrochemical energy storage, redox-mediated electrosynthesis and thermal catalysis. In this Primer, we outline how redox-active POMs are selected, synthesized, characterized and integrated into functional systems. We describe best practices for correlating cluster composition and structure with target functionality, for combining complementary experimental and theoretical approaches to elucidate electronic structure and reactivity, and for assessing cluster speciation and stability under operating conditions. Emphasis is placed on distinguishing genuine molecular reactivity from decomposition-derived but still reactive metal-oxide phases. We further discuss reproducibility, data deposition and the experimental controls needed for rigorous mechanistic interpretation. ... mehrFinally, we identify the principal limitations of current methods and highlight that atomic-level structural understanding, operando insights and theoretical property predictions are the central drivers towards rational design of POM-based systems for next-generation energy and catalysis technologies.