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Mesoporous α-MoO3–x combined with poly(diallyldimethylammonium chloride)–functionalized reduced graphene oxide (PDDA–rGO) is introduced as an inexpensive and efficient oxygen reduction reaction (ORR) catalyst. The mesoporous catalysts are wrapped by conductive rGO sheets via an electrostatic interaction induced by a PDDA polyelectrolyte. The thermal interaction of PDDA with MoO3 efficiently reduces the metal oxide to MoO3–x at 400–600 °C, creating a surface oxygen vacancy. Through a combination of density functional theory and experiments, the role of the surface oxygen vacancy sites in the ORR activity of MoO3–x is identified. For the first time, all the energy barriers against ORR are calculated at each step for MoO3 with no oxygen vacancies and MoO3–x with surface oxygen vacancies. It is shown that the presence of an Mo4+‐vO•• oxygen vacancy site on the surface significantly reduces the energy barriers against ORR in the reaction pathways. An overpotential of 0.86 V (vs a reversible hydrogen electrode)...

The presence of oxygen vacancy sites fundamentally affects physical and chemical properties of materials. In this study, a dipole-containing interaction between poly(diallyldimethylammonium chloride) PDDA and α-MoO3 is found to enable high-concentrations of surface oxygen vacancies. Thermal annealing under Ar resulted in negligible reduction of MoO3 to MoO3–x with x = 0.03 at 600 °C. In contrast, we show that the thermochemical reaction with PDDA polyelectrolyte under Ar can significantly reduce MoO3 to MoO3–x with x = 0.36 (MoO2.64) at 600 °C. Thermal annealing under H2 gas enhanced the substoichiometry of MoO3–x from x = 0.62 to 0.98 by using PDDA at the same conditions. Density functional theory calculations, supported by experimental analysis, suggest that the vacancy sites are created through absorption of terminal site oxygen (Ot) upon decomposition of the N–C bond in the pentagonal ring of PDDA during the thermal treatment. Ot atoms are absorbed as ionic O– and neutral O2–, creating Mo5+-vO· and Mo...

Metal oxides have been widely studied in recent years to replace commercial graphite anodes in lithium ion batteries. Among the metal oxides, manganese oxide has a high theoretical capacity, low cost, and is environmentally friendly. However, many MnO materials have shown limited reaction reversibility and poor conversion kinetics. To understand why, in this paper we investigate the mechanism, kinetics, and reversibility for the solid-state conversion reaction of MnO with Li+. We definitively show, for the first time, that during repeated reaction cycles, multiple reaction pathways occur that lead not only to the reformation of MnO but also higher oxidation-state Mn3O4—which when combined with the poor intrinsic electronic conductivity of both manganese oxide species results in a rapid loss in the amount of charge that can be stored in these materials. Learning this, the approach in this study was to use cobalt doping to concomitantly stabilize the redox behavior of manganese (allowing for the gradual tra...

Hollow spherical structures of ternary bismuth molybdenum oxide doped with samarium (Bi2–xSmxMoO6) were successfully synthesized via development of a Pluronic P123 (PEO20-PPO70-PEO20)-assisted solvothermal technique. Density functional theory calculations have been performed to improve our understanding of the effects of Sm doping on the electronic band structure, density of states, and band gap of the material. The calculations for 0 ≤ x ≤ 0.3 revealed a considerably flattened conduction band minimum near the Γ point, suggesting that the material can be considered to possess a quasi-direct band gap. In contrast, for x = 0.5, the conduction band minimum is deflected toward the U point, making it a distinctly indirect band gap material. The effects of a hollow structure as well as Sm substitution on the absorbance and fluorescence properties of the materials produced increased emission intensities at low Sm concentrations (x = 0.1 and 0.3), with x = 0.1 displaying a peak photoluminescence intensity 13.2 ti...

Metal oxide compounds are a promising category of materials for the Li-ion battery anode due to their high theoretical capacity and natural abundance, although acceptable capacity retention and cycle life has not yet been achieved. In this work, we significantly improve the cycle life of manganese oxide through simultaneous cobalt doping and impregnation with a low 10% mass loading of carbon nanotubes (CNTs). The MnO/CNT anode was able to retain its capacity of ca. 550 mAh/g over 300 cycles at 400 mA/g. To the best of our knowledge, this is among the best cycle life data reported for any MnO/CNT based anode. The composite also shows excellent rate capability, still supplying 400 mAh/g at a current rate of 1600 mA/g.

MnO is an electrically insulating material which limits its usefulness in lithium ion batteries. We demonstrate that the electrochemical performance of MnO can be greatly improved by using oxygen-functional groups created on the outer walls of multiwalled carbon nanotubes (MWCNTs) as nucleation sites for metal oxide nanoparticles. Based on the mass of the active material used in the preparation of electrodes, the composite conversion-reaction anode material Mn1-x Co x O/MWCNT with x = 0.2 exhibited the highest reversible specific capacity, 790 and 553 mAhg-1 at current densities of 40 and 1600 mAg-1, respectively. This is 3.1 times higher than that of MnO/MWCNT at a charge rate of 1600 mAg-1. Phase segregation in the [Formula: see text] nanoparticles was not observed for x ≤ 0.15. Capacity retention in x = 0, 0.2, and 1 electrodes showed that the corresponding specific capacities were stabilized at 478, 709 and 602 mAhg-1 respectively, after 55 cycles at a current density of 400 mAg-1. As both MnO and CoO exhibit similar theoretical capacities and MnO/MWCNT and CoO/MWCNT anodes both exhibit lower performance than Mn0.8Co0.2O/MWCNT, the improved performance of the [Formula: see text] alloy likely arises from beneficial synergistic interactions in the bimetallic system.