Energy Recovery\nfrom Hexavalent Chromium Reduction\nfor <i>In Situ</i> Electrocatalytic Hydrogen Peroxide Production

Recovering chemical energy embedded in pollutants is\nsignificant\nin achieving carbon-neutral industrial wastewater treatment. Considering\nthat industrial wastewater is usually treated in a decentralized manner, <i>in situ</i> utilization of chemical energy to achieve waste-to-treasure\nshould be given priority. Herein, the chemical energy released by\nthe electroreduction of Cr­(VI) was used to enhance on-site H<sub>2</sub>O<sub>2</sub> generation in a stacked flow-through electrochemical\nsystem. The driving force of water flow efficiently coupled O<sub>2</sub> evolution with 2-e O<sub>2</sub> reduction to facilitate\nH<sub>2</sub>O<sub>2</sub> generation by transporting anode-produced\nO<sub>2</sub> to the cathode. Meanwhile, the chemical energy released\nby Cr­(VI) promoted O<sub>2</sub> evolution and impeded H<sub>2</sub> evolution by regulating the electrode potentials, accounting for\nthe enhanced H<sub>2</sub>O<sub>2</sub> generation. The system could\ncompletely reduce 10–100 ppm of Cr­(VI), reaching the maximum\nH<sub>2</sub>O<sub>2</sub> concentration of 2.41 mM. In particular,\nthe H<sub>2</sub>O<sub>2</sub> concentrations in the Cr­(VI)-containing\nelectrolyte were 10.6–88.1% higher than those in the Cr­(VI)\nfree electrolyte at 1.8–2.5 V. A 24-day continuous experiment\ndemonstrated the high efficiency and stability of the system, achieving\na 100% reduction efficiency for 100 ppm of Cr­(VI) and producing ∼1.5\nmM H<sub>2</sub>O<sub>2</sub> at 1.8 V. This study presents a feasible\nstrategy for Cr­(VI) detoxification and synchronous on-site H<sub>2</sub>O<sub>2</sub> generation, providing a new perspective for innovative\nCr­(VI) wastewater treatment toward resource utilization.