Oxygen-Deficient Ruthenium Oxide for Selective Oxygen Evolution in Additive-Free Brine Electrolysis

Here, low-crystalline ruthenium oxide (S-RuOx) with abundant oxygen vacancies was synthesized, after which its activity and selectivity toward oxygen evolution reaction (OER) in additive-free brine solution were compared with those of commercial ruthenium(IV) dioxide (C-RuO2), a benchmark catalyst for OER in an alkaline electrolyte. S-RuOx delivered a current density of 10 mA cm(-2) at a significantly low overpotential (465 mV) in a 0.5 M NaCl solution without requiring an alkali. The estimated Faradaic efficiency toward chloride oxidation reaction (COR), FE(COR), was 2%, and exceptional OER was achieved without generating chlorine oxide species. This sharply contrasts the fact that C-RuO2 required an overpotential of 525 mV to generate 10 mA cm(-2), where the FE(COR) was 59%. The activity and selectivity toward OER decreased after reducing the oxygen vacancies by sintering S-RuOx at different temperatures. S-RuOx continued to generate 10 mA cm(-2) in 0.5 M NaCl solution for >= 60 h while maintaining the increasing potential at <30 mV. However, FE(COR) increased from a few percent for 20 h to 34% probably because of an irreversible decrease in vacancies. Notably, the addition of an alkali or a buffer could only enhance OER. (c) 2024 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. This is an open accessarticle distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY,http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI:10.1149/1945-7111/ad86ed]