Ni-Fe Oxides/TiO Heterojunction Anodes for Reactive Chlorine Generation and Mediated Water Treatment.

Reactive chlorine-mediated electrochemical water treatment necessitates selective chlorine evolution reaction (ClER) versus parallel oxygen evolution reaction (OER) in mild pH (7-10), with minimal deployments of precious electrocatalysts. This study reports NiFeO/TiO heterojunction anode prepared by a straightforward sol-gel coating with thermal decomposition at 425 °C. The ClER current efficiency (CE, 70%) and energy efficiency (2.3 mmol W h) were comparable to benchmarking IrTaO/TiO at 30 mA cm in 50 mM NaCl solutions with near-neutral pH. Correlations of ClER CE of variable NiFeO/TiO (: 0.33, 0.8-1) with the flat-band potential and p-band center, as experimental descriptors for surface charge density, nominated the outer TiO to be the active ClER center. The underlying NiFeO, characterized as biphasic NiFeO and NiO, effectively lowered the O binding energy of TiO by electronic interaction across the junction. The OER activity of NiFeO superior to the other Fe-doped Ni oxides suggested that the conductive OER intermediates generated on NiFeO could also facilitate the ClER as an ohmic contact. Stability tests and NH degradation in synthetic and real wastewater confirmed the feasibility of NiFeO/TiO heterojunction anode for mediated water treatments in mild pH.