Impact of the crystal phase and 3d-valence conversion on the capacitive performance of one-dimensional MoO2, MoO3, and Magneli-phase Mo4O11 nanorod-based pseudocapacitors

One-dimensional nanorods of MoO2, MoO3 and Magneli-phase Mo4O11 were effortlessly prepared using the hot-filament metal oxide vapor deposition technique. Long straight and uniform nanorods were grown on indiumtin-oxide (ITO) thin film coated glass substrates. Thermal reduction and oxidation were then used to process 1D Magneli-phase Mo4O11 nanorods synthesized at 1000, 1050, 1100, 1150, and 1200 degrees C into 1D MoO2 and MoO3 nanorods, respectively. The nanorods prepared at higher synthesis temperatures were thinner and longer. The 1D Magneli-phase Mo4O11 nanorods consisted of various combinations of two orthorhombic (alpha ) and monoclinic (eta) crystals and varying mixtures of Mo4+, Mo5+ and Mo6+ (3d(5/2) and 3d(3/2)) cations. The 1D MoO2 nanorods were comprised of only monoclinic (eta) crystals and various complex mixtures of Mo4+, Mo5+ and Mo6+ (3d(5/2) and 3d(3/2)) cations. The 1D MoO3 nanorods contained only orthorhombic (alpha) crystals and varying mixtures of Mo5+ and Mo6+ (3d(5/2) and 3d(3/2)) cations. Comparison of the crystal phases and 3d valences showed that the MoO2 nanorods supplied more oxidation states than the Mo4O11 or MoO3 nanorods. According to the results of cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) measurements, and electrochemical impedance (EI) spectroscopy, the capacitive performance of the MoO2 nanorod-based pseudocapacitor was much better than that of the MoO3 and Magneli-phase Mo4O11 nanorod-based pseudocapacitors. The crystal phases and 3d-valence conversions clearly had a tremendous impact on the capacitive behaviors of the MoO2, MoO3, and Magneli-phase Mo4O11 nanorod-based pseudocapacitors.