We study the origin of enhanced PEC activity and stability from the chemical species changes by performing high-resolution XPS (HR-XPS) scanning on the photoanodes before and after the stability test of 20 h CA testing under constant bias of 1.09 V vs. RHE and 1 sun illumination (Fig. ). The HR-XPS spectra of Ni 2p consist of two spin-orbit doublets of Ni 2p 3/2 and Ni 2p 1/2 , and two satellite peaks (Fig. ).The deconvoluted peaks from Ni 2p 3/2 at 852.8 eV, 855.2 eV, 856.6 eV, 861.1 eV, and 862.9 eV correspond to Ni 0 , Ni 2+ , Ni 3+ , and two satellite peaks, respectively . Moreover, the sharp peak of metallic Ni 0 almost vanishes after the reaction (from 14.0% to 0.9%, Fig. ), indicating the conversion of NiFe alloy into oxidized species.