In Situ and Operando Characterization Techniques for In‐Depth Understanding of Hybrid Water Electrolysis

Abstract Hybrid water electrolysis provides an energy‐efficient route for hydrogen production by replacing the oxygen evolution reaction (OER) with oxidation of small organic or biomass‐derived substrates, lowering cell voltages and enabling co‐production of value‐added chemicals. However, competition with OER, transient intermediates, and dynamic catalyst transformations complicates mechanistic understanding. Conventional ex situ techniques cannot capture these short‐lived processes, whereas in situ and operando characterization techniques provide real‐time insights into reaction pathways, active phases, and degradation mechanisms. This review highlights recent advances in applying these techniques to uncover catalyst dynamics in hybrid electrolysis. How such mechanistic insights are guiding the rational design of catalysts toward improved efficiency, selectivity, and durability is emphasized. Finally, opportunities for developing next‐generation electrolyzers powered by renewable energy for sustainable hydrogen and chemical production are discussed.