Electro-synthesis of pure aqueous H2O2 on nitrogen-doped carbon in a solid electrolyte flow cell without using anion exchange membrane

[Display omitted] •A PTFE-ionomer layer replaces standard AEM for better performance.•A redesigned cell without involving AEM delivers an industrial-relevant current.•On-site electrosynthesis of pure, concentrated H2O2 in the solid electrolyte flow cell.•A tweaked catalyst microenvironment maximizes ORR and suppresses HER.•Simple N-doped-C catalyst showed exclusive H2O2 selectivity in all pH media. The two-electron oxygen reduction reaction (2e-ORR) generates on-site hydrogen peroxide (H2O2) more sustainably than the industrial anthraquinone process. Pure aqueous H2O2 electrosynthesis is the most desirable approach, as it is ready-to-use and pH-adjustable. Recently an innovative dual membrane-based solid-electrolyte flow cell (SE-FCAEM/CEM) was reported [Science, 2019, 366, 226-231], in which the anode and cathode “sandwiched” the cation-exchange-membrane (CEM) and anion-exchange-membrane (AEM), separated by a solid-electrolyte, thus allowing H+ and HO2– ions to recombine to form pure H2O2 in deionized (DI)-water stream. One key research needs to effectively deploy this flow cell is to address the stability and engineering difficulties of using an AEM, creating significant drawbacks in cell performance and lifespan. Here, we report a modified SE-FC without involving AEM (SE-FCAEM-FREE) to achieve better performance of H2O2 electrosynthesis. To validate SE-FCAEM-FREE for industrial-relevant production rates, we first developed a nitrogen-doped-carbon catalyst (N-C) with varied nitrogen-to-carbon ratios. Among all samples, the catalyst N-C(2:3) contains high carbon and a proper nitrogen precursor that boosted its activity, resulting in excellent half-cell performance with faradaic efficiency (FE) above 90% at different pH-electrolytes. Secondly, we optimized the catalyst microenvironment by applying a PTFE layer. The Layered-PTFE (5 wt.%) arrangement suppresses hydrogen evolution reaction (HER) and exhibits a high 2e-ORR activity with high current density of 389 mA cm−2 (about 6.53 mmol cm-2h−1) at 90% FEH2O2 without degradation for a 50-hour durability test.