High-power density turbostratic carbon nano-onion functionalized carbon paper electrodes for vanadium flow batteries

The growing integration of intermittent renewable energy calls for versatile stationary energy storage solutions. Short-term storage stabilizes the electric grid, while long-term storage optimizes non-programmable energy utilization. Redox flow batteries (RFB) are well-suited for stationary storage, offering unique features like power-energy decoupling, a predicted lifespan of over 20 years, and fire safety. However, their high cost hinders widespread adoption. State-of-the-art carbon felt electrodes face high resistance and pressure drop, while thinner carbon paper electrodes reduce ohmic losses and allow higher flow rates but are limited by low active area, affecting their overall performance. This paper introduces high power density hierarchical mesoporous nanostructured electrodes (HMNE) for RFBs, targeting cost reduction: indeed, increasing the power density of the battery allows to reduce the total active area and number of cells, decreasing the quantity of material required in terms of electrodes, membrane, bipolar plates and current collectors. HMNEs incorporate turbostratic carbon nano onions (TCNO) within a mesoporous assembly on commercial carbon paper. Produced via a proprietary NanoJeD nanoparticle source and annealed at 1000 °C, the HMNE's structural attributes are linked to electrochemical performance. The optimized HMNE achieves a current density of 400 mA cm −2 , 80.9 % energy efficiency, and 70 % electrolyte utilization in a VRFB test cell. With a low 0.004 % efficiency loss over 1000 cycles, this study highlights the potential of nanoscale-engineered RFB electrodes for enhanced performance and cost-effective power solutions. • Synthesis of hierarchical mesoporous nanostructured electrode (HMNE) is performed. • The building block of the HMNE are defects rich turbostratic carbon nano onion. • Overpotentials significantly decrease for positive and negative electrode in VRFBs. • At 400 mA cm −2 voltage and energy efficiency are 82.9 % and 80.7 % respectively. • Excellent stability is demonstrated for 1000 cycles at 300 mA cm −2 .