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Vol. 17 (2025)

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

https://doi.org/10.1007/s40820-024-01542-x
Sukhwa Hong
Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790−784, Korea
Jiseon Kim
Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790−784, Korea
Jaebeom Park
Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790−784, Korea
Sunmi Im
Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790−784, Korea
Michael R. Hoffmann
Linde Laboratory, California Institute of Technology, Pasadena, CA 91125, USA
Kangwoo Cho
Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790−784, Korea

Corresponding Author: Kangwoo Cho

kwcho1982@postech.ac.kr

Nano-Micro Letters, Vol. 17 (2025), Article Number: 51

Abstract

Wastewater electrolysis cells (WECs) for decentralized wastewater treatment/reuse coupled with H2 production can reduce the carbon footprint associated with transportation of water, waste, and energy carrier. This study reports Ir-doped NiFe2O4 (NFI, ~ 5 at% Ir) spinel layer with TiO2 overlayer (NFI/TiO2), 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/TiO2 marks superior activity and selectivity for chlorine evolution reaction, outperforming the benchmark IrO2. Robust operation in near-neutral pH was confirmed. Electroanalyses including operando X-ray absorption spectroscopy unveiled crucial roles of TiO2 which serves both as the primary site for Cl− chemisorption and a protective layer for NFI as an ohmic contact. Galvanostatic electrolysis of NH4+-laden synthetic wastewater demonstrated that NFI/TiO2 not only achieves quasi-stoichiometric NH4+-to-N2 conversion, but also enhances H2 generation efficiency with minimal competing reactions such as reduction of dissolved oxygen and reactive chlorine. The scaled-up WEC with NFI/TiO2 was demonstrated for electrolysis of toilet wastewater.


Highlights:
1 Ir-doped NiFe2O4 (NFI) spinel with TiO2 heterojunction overlayer brought about outstanding chlorine evolution reaction in circumneutral pH.
2 Electroanalyses including operando X-ray absorption spectroscopy uncovered the active role of TiO2 for Cl− chemisorption.
3 NFI/TiO2 anode boosted both NH4+-to-N2 conversion and H2 generation in wastewater, and the practical applicability was confirmed with scaled-up anodes and real wastewater.

Keywords

Wastewater electrolysis cell Ir-doped NiFe2O4 Reactive chlorine species Decentralized H2 production On-site wastewater treatment
Hong, Sukhwa, Jiseon Kim, Jaebeom Park, Sunmi Im, Michael R. Hoffmann, and Kangwoo Cho. 2024. “Scalable Ir-Doped NiFe2O4/TiO2 Heterojunction Anode for Decentralized Saline Wastewater Treatment and H2 Production”. Nano-Micro Letters 17 (October):51. https://doi.org/10.1007/s40820-024-01542-x.
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