Pyridylamine templated borate-derived Co nanoparticles anchored on N-doped carbon for enhanced oxygen reduction reaction in Al–air batteries

Abstract

The design and synthesis of non-precious metal catalysts with high oxygen reduction reaction (ORR) activity are crucial for replacing Pt/C catalysts. Herein, two templated borates have been successfully synthesized via a solvothermal method: [Co(DPA)₂][B₁₀O₁₃(OH)₆] (1, DPA = 2,2′-dipicolylamine) and [Co(2-AMP)₃][B₅O₆(OH)₄]₂ (2, 2-AMP = 2-(aminomethyl)pyridine). Pyrolysis of these borates produced Co nanoparticles anchored on N-doped carbon, with the resulting multiple N species collectively enhancing the electrocatalytic activity. As a result, the half-wave potentials (E_1/2) of 1 pyrolyzed at 750 °C (Co1/750) and 2 pyrolyzed at 600 °C (Co2/600) are 0.84 V and 0.82 V, respectively, approaching that of commercial Pt/C (0.86 V). When applied in liquid Al–air batteries (AABs), Co1/750 delivers a high peak power density, reaching 191 mW cm⁻², which is significantly higher than that of Pt/C at 132 mW cm⁻² and the majority of currently reported catalysts. In the quasi-solid-state Al–air battery (SAAB), the cell assembled with Co1/750 exhibits an open-circuit voltage (OCV) of 1.588 V and demonstrates stable discharge for over 16 hours at 1 mA cm⁻². This study represents the first application of borate-derived catalysts in AABs, thus demonstrating their significant applicability in practical energy conversion devices.