Energy Recovery from Hexavalent Chromium Reduction for Electrocatalytic Hydrogen Peroxide Production.

Recovering chemical energy embedded in pollutants is significant in achieving carbon-neutral industrial wastewater treatment. Considering that industrial wastewater is usually treated in a decentralized manner, utilization of chemical energy to achieve waste-to-treasure should be given priority. Herein, the chemical energy released by the electroreduction of Cr(VI) was used to enhance on-site HO generation in a stacked flow-through electrochemical system. The driving force of water flow efficiently coupled O evolution with 2-e O reduction to facilitate HO generation by transporting anode-produced O to the cathode. Meanwhile, the chemical energy released by Cr(VI) promoted O evolution and impeded H evolution by regulating the electrode potentials, accounting for the enhanced HO generation. The system could completely reduce 10-100 ppm of Cr(VI), reaching the maximum HO concentration of 2.41 mM. In particular, the HO concentrations in the Cr(VI)-containing electrolyte were 10.6-88.1% higher than those in the Cr(VI) free electrolyte at 1.8-2.5 V. A 24-day continuous experiment demonstrated the high efficiency and stability of the system, achieving a 100% reduction efficiency for 100 ppm of Cr(VI) and producing ∼1.5 mM HO at 1.8 V. This study presents a feasible strategy for Cr(VI) detoxification and synchronous on-site HO generation, providing a new perspective for innovative Cr(VI) wastewater treatment toward resource utilization.