Crystalline Form Controlled Synthesis of MnO₂ Nanoarrays for Electrocatalytic Oxygen Evolution Performance

Two kinds of MnO2 nanoarrays, including alpha-MnO2 nanowires and delta-MnO2 nanosheets, were synthesized on carbon fiber paper (CFP) via the one-step hydrothermal method by changing the temperature and the addition of sulfuric acid, respectively. Moreover, the oxygen evolution reaction (OER) properties for the MnO2 nanoarrays were studied. The results showed that the performance of alpha-MnO2 nanowires outperformed delta-MnO2 nanosheets in alkaline medium and the overpotential of alpha-MnO2 was 444 mV under 10 mA.cm(-2) current density (the overpotential of delta-MnO2 was 522 mV). According to the analysis of X-ray photoelectron spectroscopy, the higher content of Mn3+ and more abundant oxygen vacancies on the surface are the reasons for the higher catalytic activity of alpha-MnO2 nanowires.