Synergistically engineered B- and P-doped graphite felts as tailored asymmetric electrodes for aqueous quinone-based redox flow batteries

Aqueous organic redox flow batteries (AORFBs) have emerged as a novel type of large-scale, long-duration energy storage technology, garnering significant attention due to their resource and cost benefits. However, the electrode reaction kinetics of various electroactive substances differ fundamentally. Consequently, it is essential to design electrode materials that are tailored to specific organic electroactive substances to enhance the performance of AORFBs even further. This study investigates the composition and structural characteristics of various heteroatom-doped graphite felt (GF) electrode materials and their electrochemical reactivity towards the positive benzoquinone disulfonic acid (BQDSH₂) and negative anthraquinone sulfonic acid (AQSH) electrolytes. Several patterns and insights are deduced. Among pristine graphene (GF) and five heteroatom-doped graphenes (N, O, P, B, S), B-doped GF and P-doped GF exhibit the best electrochemical activity for BQDSH₂ and AQSH, respectively. Density functional theory has confirmed that electrodes with different properties exhibit distinct characteristic reactivities towards various electroactive substances. The effectiveness of designing the positive and negative electrodes separately to enhance the performance of AORFBs is further verified through kinetic tests and the assembly of asymmetric batteries. By conducting targeted design for the positive and negative electrodes, the energy efficiency and utilization rate of the all-quinone AORFBs has increased by 18% and 10%, and the power density has risen by nearly 43%. All these results have verified the effectiveness and necessity of the targeted design of electrode materials in improving the performance of AORFBs.