Controlling the Selectivity of Chlorine Evolution Reaction by IrTaOₓ/TiO₂ Heterojunction Anodes: Mechanism and Real Wastewater Treatment
Abstract
This study investigated the effects of varied loadings of TiO2 overlayers in heterojunction with conventional Ir0.7Ta0.3Ox (IrTaOx) anodes on chlorine evolution reaction (ClER) and real (waste)water treatment at circum-neutral pH. With an optimized design of IrTaOx/TiO2, elevated ClER selectivity was attained by more facile chemisorption of chloride ions to a thin TiO2 layer on IrTaOx. The current efficiency (CE) of ClER in galvanostatic electrolysis of 50 mM NaCl solutions (at 30 mA cm–2) was maximized to ∼80% by a heterojunction architecture with ∼605 μg cm–2 of IrTaOx and ∼265 μg cm–2 of TiO2 after specific rounds of drop casting. Further increases in loading resulted in escalated film-pore resistance or deterioration of ClER selectivity. The observed CE values were correlated with experimental descriptors, such as potential of zero charge and flat band potential, demonstrating that the weaker metal–oxygen bond strength on TiO2 could enhance the ClER selectivity compared to bare IrTaOx. We concluded that ClER primarily occurs on TiO2 near the junction owing to the nanoporous nature of the TiO2 layer, while IrTaOx serves as ohmic contact. The optimized IrTaOx/TiO2 anodes effectively improved the treatment of reverse osmosis concentrate, but phosphate ions in livestock wastewater caused adverse effects due to complexation on TiO2. The heterojunction architecture effectively tunes the surface charge density for selective generation of oxidants, which can facilitate electrochemical water treatment with reduced use of the precious metals.
Copyright and License
© 2024 American Chemical Society.
Acknowledgement
This work was supported by a National Research Foundation of Korea (NRF) grant funded by the government of the Republic of Korea (NRF-2022R1A2C4001228, NRF-2022M3H4A4086312, and 2022M3I3A1082499) and the Institutional Program of the Korea Institute of Science and Technology (KIST, grant number 2E33083).
Contributions
E.R. and J.S. contributed equally to this work.
Data Availability
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Estimated loadings and thickness for IrTaOx and TiO2; atomic composition measured by EDS; composition of target wastewater; additional SEM images; additional information for XPS analysis; Nyquist plot; EIS to measure EZC and EFB; cell voltage and control data in galvanostatic ClER experiments; variations of aqueous species and CE during real wastewater treatment (PDF)
Conflict of Interest
The authors declare no competing financial interest
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Additional details
- ISSN
- 2155-5435
- National Research Foundation of Korea
- NRF-2022R1A2C4001228
- National Research Foundation of Korea
- NRF-2022M3H4A4086312
- National Research Foundation of Korea
- 2022M3I3A1082499
- Korea Institute of Science and Technology
- 2E33083