Insights into surface microstructural engineering of Inconel 625 for enhanced oxygen evolution reaction performance

• Nitridation and anodic oxidation synergistically boost OER performance of Inconel 625. • Identical location SEM/EDS enable site-specific surface and microstructure tracking. • Nitridation enriches Ni/Fe at grain boundaries; uniform Cr surface depletion observed. • Anodic oxidation causes intergranular corrosion and Ni/Fe-rich cracks in fine grains. • Post-OER, Cr-oxide dominates cracks; Ni, Fe, Nb, and Mo are depleted. This study demonstrates the transformation of commercially produced Inconel 625, a Ni-based superalloy, into a high-performance oxygen evolution reaction (OER) anode material through sequential nitridation and anodic oxidation treatments. Nitridation at 750 °C enriches surface NiFe content at the grain boundaries and scratches while reducing Cr concentration. Subsequent anodic oxidation further aggressively restructures the surface, introducing micrometer-scale cracks through aggressive intergranular corrosion, where the regions with smaller grains exhibit enhanced porosity. Through these surface modifications, an 8:1 NiFe ratio is established as an active OER oxyhydroxide film. Nano-to-microscale morphological and compositional insights are revealed through an advanced electrochemical characterization approach, utilizing identical location (IL) electron microscopy techniques, including IL-scanning electron microscopy and IL-energy dispersive spectroscopy mappings, along with time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy and Fe and Ni K-edge X-ray absorption spectroscopy. The treated Inconel 625 exhibits a twofold increase in electrochemical surface area and outperforms both the untreated analog and iridium-based benchmark in OER performance. These findings establish Inconel 625 as a scalable and cost-effective material for alkaline water electrolyzers. Advanced surface engineering of complex alloys offers a promising route to address key electrocatalytic challenges and drive the hydrogen economy forward.