Consequences of overtones in Raman spectra for assigning nickel anode surface structures as NiO 2 during alkaline electrolysis

Nature Catalysis, Published online: 11 September 2026; doi:10.1038/s41929-026-01613-9 Ni(OH)2 catalysts are commonly assumed to oxidize to NiOOH under water oxidation conditions. Now in situ surface-enhanced Raman spectroscopy and DFT calculations reveal that the catalytically active surface at relevant potentials is terminated by NiO2 as bands once assigned to superoxides instead arise from NiO2 overtone and combination modes.