Microwave-assisted synthesis of P-doped and O-rich graphitic carbon catalyst for vanadium redox flow batteries

P-doped, O-rich graphitic carbon (POGC) was synthesized via an environmentally friendly, cost effective microwave (MW)-assisted treatment using a phytic acid precursor. The treatment facilitated the formation of coral-like clusters and barrel-like graphitic structures; the P-doped graphitic structures and P–C bonds increased with the increasing irradiation time. The irradiation process increased the graphitization degree of the P-doped structure, resulting in high catalytic activity toward vanadium ion redox reactions (VIRRs), as well as improved electrical conductivity. The optimal treatment time (60 s) for POGC (POGC-60) was determined by evaluating the cyclic voltammetry curves of VIRR using POGC. POGC-60 exhibited the highest peak current densities in the anolyte and catholyte, approximately three times higher than that of the control electrode. Additionally, POGC-60 significantly reduced the charge-transfer resistance, indicating a decrease in the overpotential of VIRR. Similar improvements (increased peak current densities, reduced potential differences, and reduced charge-transfer resistance) were observed when POGC was combined with commercial graphite felt (GF) electrodes, GF/POGC. The vanadium redox flow batteries (VRFBs) utilizing the GF/POGC electrodes demonstrated enhanced efficiencies and discharge capacities (even at high current densities), as well as exceptional long-cycle stability. These findings highlight MW irradiation as a commercially feasible option for achieving the facile manufacture of cost effective, outstanding, environmentally friendly catalysts for VRFBs.