The highly efficient cathode of framework structural Fe₂O₃/Mn₂O₃ in passive direct methanol fuel cells

The development of power density and energy conversion efficiency of direct methanol fuel cells (DMFCs) is of great significance. This study presents a high-efficiency passive DMFC consisting of hetero-structured Fe₂O₃/Mn₂O₃ as the cathode catalyst, PtRu/C as the anode catalyst and polymer fiber membrane (PFM) as the electrolyte membrane. The peak power densities reached up to 60.6, 121.2 and 186.6 mW cm⁻² at 20, 50 and 70 °C, respectively, which was approximately 2.7 times greater than a normal cell composed of commercialized Nafion membrane and Pt/C cathode catalyst at 20 °C. Faradic efficiency of 85.1% and energy efficiency exceeding 42.2% were obtained. Herein, Fe₂O₃/Mn₂O₃ displays framework structure with edge lengths of 1 to 2 μm homogeneous micro-cubes. A synergistic effect between α-Fe₂O₃ and α-Mn₂O₃ matrix in Fe₂O₃/Mn₂O₃ significantly enhances its oxygen reduction reaction (ORR) catalyzed activity. α-Fe₂O₃ with abundant oxygen vacancies could store and release O₂ through the transformation of Fe³⁺/Fe²⁺ redox couple. The three-dimensional mesoporous channel structure of Fe₂O₃/Mn₂O₃ could act as effective mass transfer reactors, in which O₂ and electrolyte is uninhibited accessed to active sites. On the other hand, numerous heterogeneous interfaces can boost electron transfer efficiency, which is investigated using the electron transfer number, narrow band gap and lower charge transfer resistance. The output performance and the energy conversion efficiency of DMFCs is considerably improved through boosting oxygen and charge transfer capability in cathode. Overall, our result provides a promising strategy to fabricate high-efficient and cost-effective fuel cells for the enhanced power conversion.