Mechanistic Claims in Oxygen Evolution Electrocatalysis for Water Splitting: Evidence, Ambiguity, and Best-Practice Interpretation

Mechanistic interpretation in transition metal electrocatalysts for water splitting, particularly for the oxygen evolution reaction (OER), remains challenging despite major advances in operando spectroscopy, isotope labelling, and electrochemical analysis. Mechanistic claims are frequently supported by incomplete or overinterpreted evidence, leading to persistent ambiguity in active site identification, rate-limiting step assignment, and pathway discrimination. This review adopts a claim-centric framework that organises experimental approaches around the specific mechanistic assertions they aim to support, rather than cataloguing catalyst classes or performance metrics, and formalises this perspective as a decision-guided framework for mechanistic validation. We critically assess how techniques such as isotope labelling, operando spectroscopy, and electrokinetic analysis can and cannot substantiate claims related to adsorbate-versus lattice-oxygen-mediated pathways, reconstruction-defined active phases, and dynamic surface behaviour. Application of this framework to common mechanistic archetypes in OER electrocatalysis shows that surface reconstruction and condition-dependent pathway switching limit static mechanistic assignments, and that single-technique interpretations are rarely definitive. By clarifying the minimum evidentiary standards required for common mechanistic claims, this review aims to promote more rigorous, transparent, and falsifiable mechanistic analysis, supporting durable progress beyond descriptor-driven correlations and isolated performance benchmarks.