Ni-Fe Oxides/TiO 2 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 Ni 0.33 Fe 0.67 O y /TiO 2 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 -1 ) were comparable to benchmarking Ir 7 Ta 3 O y /TiO 2 at 30 mA cm -2 in 50 mM NaCl solutions with near-neutral pH. Correlations of ClER CE of variable Ni x Fe 1- x O y /TiO 2 ( x : 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 2 to be the active ClER center. The underlying Ni 0.33 Fe 0.67 O y , characterized as biphasic NiFe 2 O 4 and NiO, effectively lowered the O binding energy of TiO 2 by electronic interaction across the junction. The OER activity of Ni 0.33 Fe 0.67 O y superior to the other Fe-doped Ni oxides suggested that the conductive OER intermediates generated on Ni 0.33 Fe 0.67 O y could also facilitate the ClER as an ohmic contact. Stability tests and NH 4 + degradation in synthetic and real wastewater confirmed the feasibility of Ni 0.33 Fe 0.67 O y /TiO 2 heterojunction anode for mediated water treatments in mild pH.