Compositionally Tuned Trimetallic Thiospinel Catalysts for Enhanced Electrosynthesis of Hydrogen Peroxide and Built-In Hydroxyl Radical Generation

Abstract

On-site electrochemical production of hydrogen peroxide (H2O2), an oxidant and disinfectant with growing demand, could be realized through the selective two-electron oxygen reduction reaction (2e– ORR), but the widespread adoption of this method depends on robust and efficient electrocatalysts. Current catalysts have been limited by cost or toxicity and lack well-defined structures that can facilitate systematic tuning of activity and selectivity. Here, we demonstrate a series of CuCo2–xNixS4 (0 ≤ x ≤ 1.2) thiospinel catalysts for 2e– ORR with variable compositions that can be synthesized via hydrothermal conversion. Rotating ring disk electrode measurements show that these catalysts have high selectivity for 2e– ORR (>60%) and that their activity can be improved by increasing the nickel content without compromising selectivity. An acid treatment step is critical prior to employing the optimized CuCo0.8Ni1.2S4 catalyst for bulk electrosynthesis of H2O2 in 0.05 M H2SO4 solution. Various structural analyses, including synchrotron X-ray spectroscopy, confirm that the catalysts retain the spinel structure after acid treatment and H2O2 electrosynthesis. The acid treatment likely leaches the soluble copper species from the as-synthesized catalysts that would catalyze an electro-Fenton process to consume H2O2, generate hydroxyl radicals, and therefore prevent the accumulation of H2O2. This work demonstrates a general strategy for systematic tuning of metal compound catalysts for practical H2O2 electrosynthesis and facile generation of hydroxyl radicals.