All Electrochemical Synthesis of Performic Acid Starting from CO$_2$ , O$_2$ , and H$_2$O

Driven by anthropogenic climate change, innovative approaches to defossilize the chemical industry are required. Herein, the first all-electrochemical feasibility study for the complete electrosynthesis of the strong oxidizer and effective disinfectant performic acid is presented. Its synthesis is achieved solely from CO$_2$, O$_2$, and H$_2$O in a two-step process. Initially, CO$_2$ is electrochemically reduced to formate employing Bi$_2$O$_3$-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%) are 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, O$_2$ is reduced to H$_2$O$_2$ and performic acid is directly formed in situ. As before, high H$_2$O$_2$ concentration (1.27 ± 0.06 mol L−1) and high Faradaic efficiency (85.3 ± 5.4%) are achieved. Furthermore, performic acid concentration suitable for disinfection is obtained (82 ± 11 mmol L$^{−1}$). In summary, this innovative feasibility study highlights the potential of combining electrochemical CO$_2$ reduction with H$_2$O$_2$ electrosynthesis, which could provide sustainable access to performic acid in the future.