Synergistic amorphous <scp> IrO _<i>x</i> </scp> and crystalline <scp> RuO ₂ </scp> nanodomains for efficient acidic oxygen evolution reaction

Abstract Breaking the activity‐stability trade‐off in acidic oxygen evolution reaction (OER) is pivotal for realizing industrial‐grade proton exchange membrane water electrolyzers (PEMWEs). Herein, we report amorphous/crystalline Ru 0.3 Ir 0.7 O x nanorods (a/c‐Ru 0.3 Ir 0.7 O x NRs) synthesized via ion exchange and thermal annealing. The a/c‐Ru 0.3 Ir 0.7 O x NRs showed a 229 mV overpotential at 10 mA/cm 2 . In PEMWEs, the catalyst achieved cell voltages of 1.56 and 1.77 V at 1.0 and 3.0 A/cm 2 , respectively, and demonstrated stable operation for 350 h at 1.0 A/cm 2 , outperforming most previous reports. Characterization reveals RuO 2 in crystalline microdomains and IrO ₓ in amorphous regions. In situ studies clearly showed that the OER on a/c‐Ru 0.3 Ir 0.7 O x NRs proceeds via a hybrid mechanism combining lattice oxygen oxidation (LOM) and adsorbate evolution mechanism (AEM), avoiding the disadvantages of the exclusive LOM and AEM pathways in amorphous (a‐Ru 0.3 Ir 0.7 O x NRs) and crystalline (c‐Ru 0.3 Ir 0.7 O x NRs) counterparts and facilitating practical PEMWE application.