Fabrication and performance optimization of cobalt/nitrogen co-doped carbon-based electrocatalyst

Abstract:

Noble metal-based electrocatalysts are the key materials to promote the technical development of fuel cells and metal-air batteries. However, the single catalytic function towards oxygen reduction/oxygen evolution and the prohibitive cost restrict their extensive application. Therefore, it is of great significance to develop non-noble metal-based bi-functional electrocatalysts with low-cost and high-efficiency. In this study, taking core-shell metal organic frameworks (MOFs) as precursors, cobalt/nitrogen co-doped carbon-based electrocatalyst (Co/Co₃O₄@NGC) was fabricated using high-temperature calcination technology, with a core-shell structure, high catalytic activity, and high conductivity. Results show that the calcination temperature was the key factor affecting the micro-nano structure, physicochemical composition, and catalytic activity of the electrocatalyst. The optimal temperature of calcination was 900 ℃. The fabricated electrocatalyst (Co/Co₃O₄@NGC-900) had a clear core-shell structure and 3D-dodecahedron morphology with Co/Co₃O₄ nanoparticles and Co-N_x sites on its micro-surface. In addition, Co/Co₃O₄@NGC-900 inherently combined the synergistic effects of both multiple active ingredients (e.g., active Co/Co₃O₄ nanoparticles, Co-N_x, and N dopants) and highly graphitized carbon substrates, and thus exhibited efficient oxygen reduction performance (ORR, onset potential of 0.89 V, half-wave potential of 0.82 V, Tafel slope of 58.1 mV/dec, and charge transfer resistance of 26.6 Ω) and oxygen evolution performance (OER, overpotential of 410 mV, Tafel slope of 132 mV/dec, and charge transfer resistance of 24.5 Ω). Therefore, Co/Co₃O₄@NGC-900 exerted electrocatalytic performance comparable to that of typical noble metal-based electrocatalysts (e.g., Pt/C, RuO₂/C), and achieved significant reduction of catalyst fabrication cost on the premise of ensuring its high-efficient electrocatalytic activity, providing theoretical and technical support for the fabrication and application of innovative MOFs derived electrocatalytic materials.