Oxygen reduction reaction (ORR) catalysts with applications in fuel cells and metal-air batteries can be tailored to overcome the slow kinetics and to reduce overpotentials of the reaction. In this work, a series of amorphous manganese dioxides are synthesised via a chemical redox synthesis method. Synthesis parameters including molar ratio, the order of adding sequence of reactants, pH, and temperature are found to affect the catalyst’s physical and chemical properties such as morphology, lattice hydration, active surface area, and surface properties. The samples are characterised by SEM, BET, XPS and XRD as well as cyclic voltammetry, rotating disc electrode, and gas diffusion electrode measurements. The results indicated that an optimal catalyst sample can be synthesized by reduction of KMnO4 with Mn(CH3COO)2 in MnO4 −/Mn2+ molar ratio of 2.67 by addition of KMnO4 into Mn(CH3COO)2 at pH 12, 295K. The gas diffusion electrode coated with amorphous manganese dioxide catalyst ink in 10:10:2wt% of MnO2:XC-72R:PTFE with a loading of 2mgcm−2, was shown to support current densities up to 100mAcm−2 with improved performance.