(190i) Direct Electrosynthesis of Pure Aqueous H2O2 Solutions with High Production Rates Based on Carbon Catalysts Using a Solid Electrolyte

Hydrogen peroxide (H₂O₂) is a crucial chemical with a wide range of applications in civil and industrial fields. It is currently produced from the industrial energy- and waste-intensive anthraquinone process. Its centralized feature also makes it rely heavily on the storage and transportation of H₂O₂, which is unstable and hazardous. Electrocatalytic oxygen reduction reaction (ORR) to H₂O₂ provides an alternative to realize green and delocalized production, with the only inputs from renewable electricity, water and air. However, this route still faces two challenges: 1) lack of catalysts which selectively drive the 2e^- ORR towards H₂O₂ (instead of H₂O); 2) generated H₂O₂ are typically in mix with solutes in traditional electrolyzers, which necessitates complicated separation processes to recover pure H₂O₂ solutions for applications.

To make the electrochemical route more reliable in the future scaling-up, we reported a direct and continuous production of pure H₂O₂ solutions for the first time, through rational design of both catalyst and reactor. Here, we report a direct electrosynthesis strategy that delivers separate water (H₂O) and oxygen (O₂) streams to an anode and cathode separated by a porous solid electrolyte, wherein the electrochemically generated H⁺ and HO₂^– recombine to form pure aqueous H₂O₂ solutions with different concentrations. By optimizing a functionalized carbon black catalyst, we achieved over 90% selectivity for pure H₂O₂ at current densities up to 200 mA cm^-2, which represents a H₂O₂ productivity of 3.4 millimoles per square centimeter per hour.

To further improve the activity and lower the overpotential at high current densities for industrial-level applications, we introduced boron-doped carbon catalyst which can achieve better activity under industrial-relevant current densities (saving over 200 mV overpotential at up to 300 mA cm^-2) compared to the state-of-the-art oxidize carbon catalyst while maintaining a high selectivity (up to 90%). By incorporating the boron-doped carbon catalyst into our solid electrolyte cell setup, we achieved high partial H₂O₂ current densities (400 mA cm^-2) with high selectivities (up to 95%), which represents a H₂O₂ productivity of 7.36 millimoles per square centimeter per hour. The setup can also undergo 200-hour stability test without degradation, making it a good candidate to be further improved in the aspect of potential scaling-up for electrochemical H₂O₂ production in industrial level with long-lasting performance.