• • In situ XAS-XRD and TEM studies reveal that OER catalysts undergo surface restructuring, with lattice oxygen participation (LOM) and oxide pathway mechanism (OPM) occurring at overpotentials as low as 250 mV, directly impacting catalyst stability and efficiency.
• • Operando characterization of Fe-doped Ni oxides shows dynamic Fe site evolution, with Fe content modulating OER activity by up to 30% at current densities of 10 mA/cm², critical for optimizing earth-abundant catalysts.
• • Sulphur-oxygen exchange in metal sulphides prior to OER is observed, with complete conversion to (oxy)hydroxides occurring within 5 minutes at 1.5 V vs. RHE, determining the true active phase and influencing long-term durability.
• • Facet-dependent restructuring on nickel (oxy)hydroxides enhances OER activity by 2.5-fold on (100) facets compared to (111), as measured by turnover frequency (TOF) at 300 mV overpotential, guiding morphology-controlled catalyst synthesis.