Zhang Wu, Li Haizeng, Firby Curtis J, Al-Hussein Mohamed, Elezzabi Abdulhakem Y
Department of Civil and Environmental Engineering , University of Alberta , Edmonton , Alberta T6G 1H9 , Canada.
Ultrafast Optics and Nanophotonics Laboratory, Department of Electrical and Computer Engineering , University of Alberta , Edmonton , Alberta T6G 2V4 , Canada.
ACS Appl Mater Interfaces. 2019 Jun 5;11(22):20378-20385. doi: 10.1021/acsami.9b04386. Epub 2019 May 24.
Molybdenum oxides have been widely studied in recent years, owing to their electrochromic properties, electrocatalytic activities for hydrogen evolution reactions (HERs) and excellent energy storage performance. These characteristics strongly depend on the valence states of Mo in the oxides such as IV, V, and VI, which can be efficiently altered through oxygen deficiencies within the oxides. Here, we present a colloidal electrodeposition method to introduce oxygen vacancies in such Mo oxide films. We prepared uniform MoO films and investigated their electrochemical characteristics under different valence states IV, V, and VI. In this paper, we demonstrate that MoO films, where Mo in valence states IV and V, can be used for high-performance supercapacitor electrodes. Due to their high conductivity, they exhibit an areal capacitance of 89 mF cm at 1 mA cm and negligible capacitance loss within 600 cycles. Additionally, we demonstrate that, in a complementary electrochromic device configuration, the introduction of an MoO counter electrode remarkably lowers the activation potential of WO from -2 to -0.5 V and achieves a fully bleached state at 0.5 V. These properties make the MoO film an ideal counter electrode to store ions for an electrochromic device. Furthermore, MoO films, where Mo in the valence states V and VI, are obtained by annealing the electrodeposited MoO film under 200 °C for 24 h. Such films exhibit an excellent catalytic for the HER with an overpotential of 201 mV. Furthermore, we show that MoO films, where Mo at its highest oxidation state (VI), can be obtained via annealing the MoO film at 300 °C for 6 h, and the resulting films exhibit battery characteristics. Our research provides a new and facile strategy to fabricate substoichiometric molybdenum oxide nanofilms and reveals the effect of different valences on the electrochemical performance of molybdenum oxide films, which opens new doorways for future research in the electrochemical applications of transition metal oxides.
近年来，氧化钼因其电致变色特性、析氢反应（HERs）的电催化活性以及优异的储能性能而受到广泛研究。这些特性很大程度上取决于氧化物中钼的价态，如IV、V和VI价态，而这些价态可通过氧化物中的氧缺陷有效地改变。在此，我们提出一种胶体电沉积方法，用于在这种氧化钼薄膜中引入氧空位。我们制备了均匀的MoO薄膜，并研究了它们在不同价态IV、V和VI下的电化学特性。在本文中，我们证明，价态为IV和V的MoO薄膜可用于高性能超级电容器电极。由于其高导电性，它们在1 mA cm下表现出89 mF cm的面积电容，并且在600次循环内电容损失可忽略不计。此外，我们证明，在互补电致变色器件配置中，引入MoO对电极可显著降低WO的激活电位，从-2 V降至-0.5 V，并在0.5 V时实现完全漂白状态。这些特性使MoO薄膜成为电致变色器件中存储离子的理想对电极。此外，价态为V和VI的MoO薄膜是通过在200°C下对电沉积的MoO薄膜进行24小时退火获得的。这种薄膜对HER表现出优异的催化性能，过电位为201 mV。此外，我们表明，通过在300°C下对MoO薄膜进行6小时退火可获得处于最高氧化态（VI）的MoO薄膜，所得薄膜表现出电池特性。我们的研究提供了一种制备亚化学计量氧化钼纳米薄膜的新颖且简便的策略，并揭示了不同价态对氧化钼薄膜电化学性能的影响，这为过渡金属氧化物电化学应用的未来研究打开了新的大门。
