Scalable Ir-Doped NiFe2O4/TiO2 Heterojunction Anode for Decentralized Saline Wastewater Treatment and H2 Production

Abstract Wastewater electrolysis cells (WECs) for decentralized wastewater treatment/reuse coupled with H 2 production can reduce the carbon footprint associated with transportation of water, waste, and energy carrier. This study reports Ir-doped NiFe 2 O 4 (NFI, ~ 5 at% Ir) spinel layer with TiO 2 overlayer (NFI/TiO 2 ), as a scalable heterojunction anode for direct electrolysis of wastewater with circumneutral pH in a single-compartment cell. In dilute (0.1 M) NaCl solutions, the NFI/TiO 2 marks superior activity and selectivity for chlorine evolution reaction, outperforming the benchmark IrO 2 . Robust operation in near-neutral pH was confirmed. Electroanalyses including operando X-ray absorption spectroscopy unveiled crucial roles of TiO 2 which serves both as the primary site for Cl − chemisorption and a protective layer for NFI as an ohmic contact. Galvanostatic electrolysis of NH 4 + -laden synthetic wastewater demonstrated that NFI/TiO 2 not only achieves quasi-stoichiometric NH 4 + -to-N 2 conversion, but also enhances H 2 generation efficiency with minimal competing reactions such as reduction of dissolved oxygen and reactive chlorine. The scaled-up WEC with NFI/TiO 2 was demonstrated for electrolysis of toilet wastewater.