Paired Electrosynthesis: Concurrent Production of V 3.5+ Electrolyte for Vanadium Redox Flow Battery and p‐Chlorobenzaldehyde in a Flow Microreactor

This work addresses the preparation of V 3.5+ electrolyte for vanadium redox flow batteries (VRFBs) by proposing an efficient paired electrosynthesis strategy, combining it with the synthesis of the high‐value‐added chemical p‐chlorobenzaldehyde (PCAD). Traditional methods for preparing V 3.5+ electrolyte suffer from issues like impurity introducing and low energy utilizing, while the hydrogen reduction reaction at the cathode in PCAD synthesis has low value. To solve these problems, this work designed and constructed a paired electrosynthesis system based on an electrochemical microchannel reactor: precisely reducing VOSO 4 to V 3.5+ electrolyte at the cathode, while simultaneously electro‐oxidizing Mn 2+ to Mn 3+ at the anode, which subsequently oxidizing p‐chlorotoluene (PCT) to synthesize PCAD. The effects of current density, sulfuric acid concentration, and reactant ratio on reaction efficiency were systematically investigated. Results show that the total vanadium valence state of the cathodically prepared V 3.5+ electrolyte stabilized at 3.50 ± 0.02, the yield of anodically synthesized PCAD was 35.51%, the total current efficiency of the paired electrosynthesis system reached 178.8%, and the system demonstrated good repeatability and stability. This study provides a new approach for the green and efficient preparation of VRFB electrolytes and the electrosynthesis of high‐value chemicals.