Uniformly electrodeposited α-MnO₂ film on super-aligned electrospun carbon nanofibers for a bifunctional catalyst design in oxygen reduction reaction

Highlights: •A constant low-current (45 μA) electrodeposition technique for 4 h is used to form a uniform Na+ induced α-MnO2 film. •The as-prepared MnO2/ECNFs-glassy carbon catalyst system exhibits a 3.84-electron pathway near the theoretical limit. •Homogeneous surface coverage successfully allows hydrogen peroxide to be effectively confined. •A 4-electron pathway mechanism is proposed in this study. -- Abstract: Metal oxide/carbonaceous nanomaterials are promising candidates for the oxygen reduction in energy converting systems. However, inhomogeneous surface coverage allows hydrogen peroxide to escape into the bulk solution due to unstable metal or metal oxide/carbonaceous nanomaterial synthesis, which limits their performance in fuel cells. Here, we show that the above problems can be mitigated through a stable low-current electrodeposition of MnO₂ on super-aligned electrospun carbon nanofibers (ECNFs). The key to our approach is coupling a self-designed four steel poles collector for aligned ECNFs and a constant low-current (45 μA) electrodeposition technique for 4 h to form a uniform Na⁺ induced α-MnO₂ film. By using the cyclic voltammetry to proceed the electrocatalytic oxygen reduction reaction (ORR), the bifunctional catalysts show a 3.84-electron pathway due to the rapid decomposition of hydrogen peroxide by the uniform α-MnO2 film and ending with formation of water. This research may enable a practical catalyst with a large number of cycling of oxygen reduction/regeneration to reduce the risk of the fuel cell degradation and an effective confinement of oxygen and hydrogen peroxide in the catalyst matrix to maximize the energy output of the fuel cell.