Phosphorus-doped graphite felt allowing stabilized electrochemical interface and hierarchical pore structure for redox flow battery

The redox flow battery technology is of great potential for large-scale energy storage. However, its widespread application is suffering from the challenges of low energy efficiency and considerable performance degradation in the high-current cycles. Herein, we propose and develop a phosphorus-doped electrode with stabilized electrochemical interface and hierarchical pore structure for cost-effective flow batteries. Density functional theory calculation was first used to demonstrate the stability and activity of phosphorus-doped graphite surface. On basis of theoretical design, the phosphorus-doped graphite felt electrode was fabricated by a facial thermally treating method. Stabilized heteroatom-doped chemical surface with abundant phosphorus-containing functional groups (1.7%) was observed. Beyond that, the hierarchical pore structure from macro (~20 μm) to nanoscale (<200 nm) was formed synchronously, suggesting the enhanced reaction activity, stability and mass transport. In charge-discharge test, flow battery assembled with phosphorus-doped electrodes yielded a prominent energy efficiency of 81% at 200 mA cm⁻², 46% higher than battery with traditional electrodes. Even current densities up to 500 mA cm⁻², battery with phosphorus-doped electrodes still exhibits a workable energy efficiency of 64% while batteries with other electrodes cannot operate properly. Moreover, the superior durability of battery with phosphorus-doped electrodes was verified after 100-cycle charge-discharge test with nearly no-decay energy efficiencies. This work offers a promising way to develop stable and efficient flow batteries for the energy storage systems.