Enhanced ORR Activity of MnO2 Nanoparticles through Direct Chemical Surface Attachment for Aluminum-Air Batteries
Authors: Washington Brian , Foister Shane , Griffith Colt , Goenaga Gabriel , Zawodzinski Thomas A. 
Published: December 2024

Manganese dioxide has garnered significant attention as a promising catalyst for the oxygen reduction reaction (ORR) in alkaline media due to its excellent catalytic activity, low cost, durability, and scalability. Despite its promising catalytic activity, MnO2 suffers from limitations such as low conductivity, particle dissolution, and diminished mass transport properties, particularly in high-throughput environments. Researchers typically couple MnO2 with high conductivity and high surface area materials such as conductive carbon black to overcome these challenges. However, this method still presents challenges, such as diminished catalyst-carbon interactions and the loss of catalytic active sites by the surrounding of larger carbon particles.

In this study, we present a two-step synthesis method, initially proposed for the application of MnO2 as supercapacitor materials1, for the improvement of MnO2 catalytic activity towards the ORR. This synthesis method was achieved using diazonium chemistry, which involves the direct chemical attachment of KJB carbon black with MnO2 via a phenyl group linkage site. This process was done so that the mass ratio of MnO2 and KJB was 50:50. The synthesized materials were characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive X-ray Spectroscopy (EDX) to confirm varying morphologies, particle sizes, and material compositions. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) were utilized to analyze the phases and crystallinities of the materials. Each characterization step was done before and after the chemical attachment process to ensure the modifications were performed.

The electrochemical activity of the materials was investigated using three-electrode cells to study the ORR activities and stabilities of the synthesized materials. Rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) data were employed to analyze kinetic current densities, the number of electrons transferred, and the hydrogen peroxide production rates. Furthermore, the catalyst materials were implemented into aluminum-air battery configurations where polarization curves, electrochemical impedance spectroscopy (EIS), and multistep chronoamperometry experiments were conducted to evaluate the performance of the modified MnO2 catalyst materials. Overall, implementing this process led to substantial increases in the catalytic activities morphologically dependent MnO2 particles towards the ORR and highlighted the significance of this research in advancing the understanding and application of MnO2 catalysts in energy conversion and storage technologies.

[1] Ramirez-Castro, C., Crosnier, O., Athouël, L., Retoux, R., Bélanger, D., & Brousse, T. (2015). Electrochemical Performance of Carbon/MnO 2 Nanocomposites Prepared via Molecular Bridging as Supercapacitor Electrode Materials. Journal of The Electrochemical Society, 162(5), A5179–A5184.