Electrocatalytic arsenite oxidation in bicarbonate solutions combined with CO2 reduction to formate

• Published in: Applied catalysis. B, Environmental Environmental, 2020-05, Vol.265, p.118607, Article 118607
• Main Authors: Choi, Wonjung, Kim, Minju, Kim, Byeong-ju, Park, Yiseul, Han, Dong Suk, Hoffmann, Michael R., Park, Hyunwoong
• Format: Article
• Language: English
• Subjects: Arsenite; Bicarbonates; Bismuth; Carbon dioxide; Catalysts; Chlorides; Chlorine; Electrocatalysis; Electrochemistry; Electrodes; Hybrid systems; Iron; Nanoparticles; Oxidation; Photovoltaic cells; Photovoltaics; Redox reactions; Solar fuels; Titanium dioxide; Water treatment; Water-energy nexus
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2020.118607

[Display omitted] •Bicarbonate is a primary leaching agent of As(III) adsorbed on metal oxides in groundwater with CO2.•Nearly 100 % Faradaic efficiencies (FEs) for As(III) oxidation and CO2 reduction are obtained.•The addition of chloride significantly enhances the current while maintaining the FEs for both reactions.•The optimized n-TEC/Bi pair is coupled with a low-cost photovoltaic (PV) for off-grid processes.•The maximum FEs of ∼95 % are achieved for the production of both As(V) and formate. Sunlight-driven water-energy nexus technologies are receiving increasing attention. This study presents a hybrid electrochemical system that catalyzes the oxidation of As(III) to As(V) with a nanoparticulate TiO2 electrocatalyst (Ti/Ir1-xTaxOy/TiO2; denoted as an n-TEC) while simultaneously converting CO2 to formate on a Bi electrode in aqueous bicarbonate solutions at circum-neutral pH. Linear sweep voltammograms of n-TEC exhibit a specific As(III) oxidation peak (Ep,As), at which the Faradaic efficiency (FE) of As(V) production is ∼100 %. However, the application of a potential higher than the peak (E > Ep,As) leads to a significant decrease in the FE due to water oxidation. Upon the addition of chloride, the oxidation of water and chloride occur competitively, producing reactive chlorine species responsible for mediating the oxidation of As(III). The Bi electrodes synthesized via the electrodeposition of Bi3+ typically show high FEs of >80 % for formate production in bicarbonate solution purged with CO2. The addition of chloride significantly enhances the current while maintaining the FE. The n-TEC catalyst and Bi electrodes are paired in a single device equipped with a membrane, and significant effort is made to achieve the same FEs in both the anodic and cathodic reactions as in their half-reactions. Finally, the optimized n-TEC/Bi pair is coupled with a low-cost, commercially available photovoltaic (PV). Various technical factors that drive the overall reactions with the PV are considered, and maximum FEs of ∼95 % are achieved for the production of both As(V) and formate.