Streamlined V 3.5+ Electrolyte Production by Leveraging Chemical and Catalytic Reductions

Vanadium redox flow batteries are constrained by the high cost of producing V 3.5+ electrolyte, which conventionally relies on oxalic‐acid–driven reduction from V 5.0+ to V 4.0+ followed by electrolysis from V 4.0+ to V 3.5+ . While Pt/C catalysis can replace the costly electrolysis step, the sluggish V 5.0+ V 4.0+ reduction remains the key bottleneck to streamlining electrolyte production and improving its economics. Here, we show that extending the catalytic process to the rate‐determining V 4.1+ V 4.0+ transition shortens the electrolyte production time by 67% and eliminates problematic residual oxalic acid. Our analysis reveals that the catalyst suffers from carbon corrosion and Ostwald ripening at high vanadium oxidation states, whereas these effects are negligible below V 4.3+ , ensuring stable catalyst performance under the extended catalytic process. This extended catalytic process for V 3.5+ electrolyte production can operate at least 2 500 cycles without notable loss in the observed rate constant, as shown by accelerated lifetime testing.