Aqueous Vanadium–Cadmium Redox Flow Batteries: Pioneering High‐Efficiency Energy Storage

The escalating demand for efficient and sustainable energy storage solutions has intensified research in redox flow battery technology, with vanadium redox flow batteries (VRFBs) standing out due to their superior cyclic stability and electrochemical performance. However, VRFBs are constrained by a low open‐circuit potential (OCP) and high material procurement costs. This study introduces a novel vanadium–cadmium redox flow battery (VCRFB), utilizing vanadium (V ⁴⁺ /V ⁵⁺ ) as the catholyte and cadmium (Cd ²⁺ /Cd) as the anolyte solutions. The VCRFB demonstrates a theoretical OCP of 1.4 V and a stable operational potential of 1.65 V despite the use of aqueous solutions, with a peak discharge current >20 mA and a nominal discharge voltage of 1.422 V for 2.5 M concentration. Furthermore, UV–vis spectroscopy confirmed the crossover of vanadium ions into the anolyte solution, which was mitigated using a premixed electrolyte approach. This strategy significantly enhanced the coulombic efficiency of VCRFB, achieving a coulombic efficiency >85% during the long‐term performance evaluation. These findings demonstrate that the VCRFB offers a scalable alternative for energy storage with peak Coulombic efficiency (>95%), although its voltage efficiency (∼30%) requires further optimisation. The mixed electrolyte approach reduce the costs for electrolyte purification while enhancing stability and Coulombic efficiency.