Carbon nanofiber-based catalysts derived from polyacrylonitrile for efficient oxygen reduction in alkaline and neutral Zn-air batteries

Carbon-based catalysts hold great promise as the oxygen reduction catalyst in fuel cell applications. However, enhancing the catalytic performance of carbon-based catalysts through a facile way is still challenging. Here, we show that an efficient carbon nanofiber-based catalyst for the oxygen reduction in both alkaline and neutral electrolytes can be fabricated using polyacrylonitrile as the precursor through an electrospinning-preoxidation-oxidation-carbonization approach. Particularly, we demonstrate that H₂O₂ used in the oxidation step is an important additive for improving the catalytic activity. When our optimum carbon nanofiber-based catalyst is applied in Zn-air batteries with alkaline and neutral electrolytes, the catalyst exhibits improved performance compared to the benchmark Pt/C catalyst, yielding an increase of ∼24% and ∼52% in maximum power density, respectively. The superior catalytic performance of the optimum catalyst can be ascribed to the increased electrochemical active surface area brought by the H₂O₂ treatment. Further investigations indicate that the H₂O₂ treatment can induce alterations in the local structure of the carbon-based catalyst, well expose the active sites towards oxygenated species, and thus facilitate the oxygen reduction reaction. This study may provide insights into the fabrication of carbon-based metal-free catalysts and promote the practical application of carbon-based catalysts in fuel cells in the future.