α-MnO₂ Nanowires/Graphene Composites with High Electrocatalytic Activity for Mg-Air Fuel Cell

Highlights: • α-MnO₂ NWs/graphene was synthesized and studied in Mg-air fuel cell. • The performance of α-MnO₂ NWs/graphene is close to the Pt/C. • The ORR mechanism involves a one-step, quasi-4-electron pathway. • A large area (5 cm*5 cm) cathode was prepared and tested in a full cell. - Abstract: This paper reports the preparation of α-MnO₂ NWs/graphene composites as the cathode catalyst for magnesium-air fuel cell and its excellent electrochemistry performance. The composites are synthesized by self-assembly of α-MnO₂ nan α-MnO₂ NWs/graphene was synthesized and studied in Mg-air fuel cell. α-MnO₂ NWs/graphene was synthesized and studied in Mg-air fuel cell. owires (NWs) on the surface of graphene via a simple hydrothermal method. The α-MnO₂ NWs/graphene composites showed a higher electrochemical activity than the commercial MnO₂. The oxygen reduction peak of the α-MnO₂ NWs/graphene composites catalyst is tested in a 0.1 M KOH solution at −0.252 V, which is more positive than the commercial MnO₂ (−0.287 V). The ORR limit current density for 28% α-MnO2 NWs/graphene composite is approximately 2.74 mA/cm², which is similar to that of the 20% Pt/C(2.79 mA/cm²) in the same conditions. Based on the Koutecky–Levich plot, the ORR mechanism of the composite involves a one-step, quasi-4-electron pathway. In addition, magnesium-air fuel cell with α-MnO₂ NWs/graphene as catalyst possesses higher current density (140 mA/cm²) and power density (96 mW/cm²) compared to the commercial MnO₂. This study proves that the cost-effective α-MnO₂ NWs/graphene with higher power generation ability make it possible for the substitute of the noble metals catalyst in the Mg-air fuel cell.