The comparative electrochemical behaviour of both α- and β-nanorods of manganese dioxide (MnO₂) and microparticles of predominantly β-phase manganese dioxide is investigated at pHs close to neutral. In order to understand the observed voltammetric behaviour of all three materials the mechanisms of electrodeposition of MnO₂ onto a graphite electrode surface from a solution of Mn(II) at pH 3–7 is also reported. It is proposed that two competing mechanistic pathways operate, both invoking MnOOH as an intermediate species, which are an ECE or a DISP process, respectively. At low pH values (<pH 3) the mechanism likely proceeds via a DISP mechanism whereas at high pHs (pH ∼ 7) the mechanism proceeds predominantly as an ECE process with the diffusion of protons out of the MnOOH intermediate being the likely rate determining step.

The α- and β-MnO₂nanorods display a ca. 30 mV difference in the observed reduction potentials corresponding to a ca. 3 kJ mol⁻¹ difference in the Gibb’s energy between the two phases. There is also an observable difference in the reduction potential of the β-nanorods and β-microparticles, which probably reflects the differing surface or structural energies of the two materials. Finally the electrocatalytic performance of the three MnO₂ materials with respect to the analytical determination of hydrogen peroxide is investigated. Both phases of the MnO₂nanorods exhibited a lower limit of detection (5.0 ± 2.5 μM based on 3σ) and greater sensitivity towards H₂O₂ than the MnO₂ microparticles, likely attributed to an increased surface area.