Enhanced ORR Activity of Modified Recycled Graphite-Based Anode Materials.

Addressing the kinetic limitations of the oxygen reduction reaction (ORR) is essential for improving the efficiency of electrochemical energy-conversion devices such as fuel cells and metal-air batteries. Here, we demonstrate a circular-economy-oriented upcycling strategy for transforming end-of-life lithium-ion battery graphite anodes into metal-free ORR catalysts through oxidative activation and targeted molecular functionalization. Spent graphite anode material was activated by using H2SO4/HNO3 mixtures to increase defect density and surface reactivity, followed by surface functionalization with BPDI-OH-Cl, NDI-alendronic acid (NDI-ALEN), and NDI-aspartic acid (NDI-ASP). Acid activation significantly enhanced apparent ORR activity, yielding the highest half-wave potential (0.782 V for the 8 M acid-treated material), attributed to increased defect density and improved electrolyte accessibility. Subsequent molecular functionalization selectively modulated ORR behavior by introducing heteroatom-containing surface species, with NDI-ASP functionalization enhancing kinetic current density and charge-transfer characteristics relative to acid-treated graphite, although the half-wave potential remained slightly lower. XPS and SEM/EDX analyses confirm surface-confined incorporation of nitrogen- and phosphorus-containing molecular species following functionalization. These findings demonstrate that recycled graphite can serve as a chemically tunable, metal-free ORR catalyst platform, where defect generation governs apparent activity while molecular functionalization modulates kinetic behavior and effective electron-transfer characteristics, supporting circular-economy strategies for sustainable electrochemical energy conversion.