N-rGO-supported α-MnO₂ composites as efficient oxygen reduction reaction catalyst in aluminum-air battery

MnO₂ is one of the most common catalyst materials for oxygen reduction reaction (ORR) in alkaline media due to their high electrocatalytic activity, environmental friendliness, low cost, and abundant earth reserves. However, MnO₂, as an ORR catalyst, suffered from poor conductivity, poor rate performance, and rapid capacity deterioration. Herein, a novel N-doped reduced graphene-supported α-MnO₂ (α-MnO₂/N-rGO) composite was designed by using highly conductive N-doped reduced graphene oxide (N-rGO) as a good carrier for MnO₂ nanorods to obtain superior ORR performance. The prepared α-MnO₂/N-rGO composites were systematically characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), specific surface area measurement (BET), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy (Raman). The experimental results shows that the rod-like MnO₂ is evenly dispersed on the N-rGO sheet after the hydrothermal process. In the ORR process, α-MnO₂/N-rGO exhibits excellent catalytic activity and stability (onset potential of 0.918 V, half-wave potential of 0.784 V, electron transfer number of 3.45, current attenuation rate of 2.16%·h⁻¹), which are significantly improved compared with single N-rGO and α-MnO₂. The characterization results further confirms that the covalent coupling between the well-dispersed N-rGO and α-MnO₂ jointly promotes the effective improvement of the catalytic activity and stability of the α-MnO₂/N-rGO catalyst. In addition, the α-MnO₂/N-rGO catalyst displays excellent electrochemical properties (energy density of 1230.7 mW·h·g⁻¹-Al, power density of 135.8 mW·cm⁻²) and mechanical properties (current retention of >96% after 5000 bending) in aluminum-air battery. In conclusion, the introduction of N-rGO to adjust the electronic and chemical states of MnO₂ and establish covalent interface between the N-rGO and α-MnO₂ can provide an effective strategy for the development of efficient and stable manganese dioxide-based ORR catalysts.