All Electrochemical Synthesis of Performic Acid Starting from CO2, O2 and H2O.

Driven by anthropogenic climate change, innovative approaches to defossilise the chemical industry are required. With this study, the first all-electrochemical feasibility study for the complete electrosynthesis of the strong oxidiser and effective disinfectant performic acid is presented. Its synthesis was achieved solely from CO2, O2 and H2O in a two-step process. Initially, CO2 is electrochemically reduced to formate employing Bi2O3 based gas diffusion electrodes in a phosphate buffered electrolyte. Thereby, high formate concentration (500.7 ± 0.6 mmol L-1) and high Faradaic efficiency (86.3 ± 0.3%) were achieved at technically relevant current density (150 mA cm-2). Subsequently, the formate acts as (storable) feed electrolyte for the second electrolysis step. Employing carbon based gas diffusion electrodes, O2 is reduced to H2O2 and performic acid is directly formed in-situ. As before, high H2O2 concentration (1.27 ± 0.06 mol L-1) and high Faradaic efficiency (85.3 ± 5.4%) were achieved. Furthermore, performic acid concentration suitable for disinfection was obtained (82 ± 11 mmol L-1). In summary, this innovative feasibility study highlights the potential of combining electrochemical CO2 reduction with H2O2 electrosynthesis, which could provide sustainable access to performic acid in the future.