Coupling Ni-based anodes for textile industry process stream electrooxidation with electrocatalytic CO2 reduction to formate in gas phase

Scaling up CO2 electroreduction to formate faces several challenges, including using chemicals as electrolytes and high energy demands. To address these issues, this study uses an industrial stream-specifically a caustic soda stream from the textile industry-as anolytes for the oxygen evolution reaction (OER). Using this approach, formate concentrations of 226 g L-1 and Faradaic efficiencies (FE) of 53 % are achieved at 200 mA cm-2, demonstrating the competitiveness of industrial streams compared to synthetic anolyte solutions. Various anode materials are tested to optimize OER kinetics under industrial conditions and reduce energy consumption. Ni foam exhibited promising results, achieving FEs of 78 % and 58 % at 90 and 200 mA cm-2, with energy consumption between 236 and 385 kWh kmol-1 , making it one of the most efficient options among commercially available materials. In addition, alternative materials, such as NiFeOx and NiZnFeOx particulate anodes, are synthesized to provide viable substitutes for commercial anodes that rely on scarce elements. These alternatives demonstrated similar formate concentrations, with FEs up to 74 % and reduced energy requirements compared to commercial NiO. The synthesized NiFe foam anode excelled in performance, with energy consumption below 210 and 380 kWh kmol-1 and an impressive formate production of 255 g L- 1 of formate achieving a 60 % FE at 200 mA cm- 2. Overall, this research demonstrates the feasibility of COQ electroreduction to formate using textile effluents under relevant conditions, representing a significant step toward making this process a competitive option for decarbonizing hard-to-abate industries.