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Water electrolysis using proton exchange membrane technology offers an ideal process for green hydrogen production, but widespread deployment is inhibited by insufficient catalyst activity, stability and affordability. Iridium-based oxides provide the best overall performance for acidic water oxidation, the limiting reaction for this process, but further improvements are impeded by poor understanding of the restructured active catalyst surface that forms under reaction conditions. Here we present a combination of X-ray and electron scattering data that reveals direct evidence for three paracrystalline structural motifs at the restructured surfaces of highly active catalysts (including rutile IrO2 and perovskite SrIrO3) that have previously been described as amorphous. These insights enable the design of a paracrystalline IrOx catalyst that is independent of the bulk crystalline support and maintains higher activity, longer stability and more effective use of iridium to promote the production of green hydrogen.