Gui Zhe, Gillette Eleanor, Duay Jonathon, Hu Junkai, Kim Nam, Lee Sang Bok
Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20740, USA.
Phys Chem Chem Phys. 2015 Jun 21;17(23):15173-80. doi: 10.1039/c5cp01814e.
A wide range of metal oxides have been studied as pseudocapitors, with the goal of achieving higher power than traditional batteries and higher energy than traditional capacitors. However, most metal oxides have relatively low conductivity, and the few exceptions, like RuO2, are prohibitively expensive. Mixed metal oxides provided an opportunity to incorporate small amounts of expensive materials to enhance the performance of a less expensive, poorer performing material. Here, by homogeneously co-depositing a small amount of energy dense and conductive RuO2 into MnO2 nanowires, we demonstrate an improvement in specific capacitance. Importantly, we also demonstrate that this improvement is not primarily provided by redox activity of RuO2, but rather by improvement of the composite conductivity. A series of RuO2-MnO2 composite nanowires with different RuO2 loading percentages have been synthesized by performing co-electrodeposition in a porous alumina template. The structure of these RuO2-MnO2 nanowires is characterized by TEM and SEM. EDS mapping shows that RuO2 is well distributed in MnO2 matrix nanowires. The chemical constituents and the phase of these composite nanowires are confirmed by X-ray photoelectron and Raman spectroscopy. The amount of RuO2 is controlled by varying the concentrations of RuCl3 and MnAc2 in the deposition solution. The precise masses of MnO2 and RuO2 are determined by ICP-AES elemental analysis. MnO2 nanowires with 6.70 wt% RuO2 demonstrate a specific capacitance of 302 F g(-1) at 20 mV s(-1), compared to 210 F g(-1) for pristine MnO2 nanowires. Investigation of the RuO2 loading amount effect was conducted by electrochemical impedance spectroscopy (EIS) and deconvolution of capacitances, using methods previously reported by both Dunn and Transsiti. The RuO2-MnO2 nanowires studied here demonstrate a simple, straighforward method to overcome the intrinsically poor conductivity of MnO2, and clarify the source of RuO2's contribution to the improved performance.
人们已经对多种金属氧化物作为赝电容器进行了研究，目的是实现比传统电池更高的功率以及比传统电容器更高的能量。然而，大多数金属氧化物的导电性相对较低，而少数例外情况，如RuO₂，价格高得令人望而却步。混合金属氧化物提供了一个机会，可以掺入少量昂贵材料来提高较便宜、性能较差材料的性能。在此，通过将少量能量密度高且导电的RuO₂均匀共沉积到MnO₂纳米线中，我们展示了比电容的提高。重要的是，我们还证明这种提高并非主要由RuO₂的氧化还原活性提供，而是由复合导电性的提高所致。通过在多孔氧化铝模板中进行共电沉积，合成了一系列具有不同RuO₂负载百分比的RuO₂-MnO₂复合纳米线。这些RuO₂-MnO₂纳米线的结构通过透射电子显微镜（TEM）和扫描电子显微镜（SEM）进行表征。能谱分析（EDS）映射表明RuO₂在MnO₂基体纳米线中分布良好。这些复合纳米线的化学成分和相通过X射线光电子能谱和拉曼光谱得到确认。通过改变沉积溶液中RuCl₃和MnAc₂的浓度来控制RuO₂的含量。MnO₂和RuO₂的精确质量通过电感耦合等离子体发射光谱（ICP-AES）元素分析确定。与原始MnO₂纳米线的210 F g⁻¹相比，含有6.70 wt% RuO₂的MnO₂纳米线在20 mV s⁻¹时表现出302 F g⁻¹的比电容。通过电化学阻抗谱（EIS）以及使用邓恩（Dunn）和特兰西蒂（Transsiti）之前报道的方法对电容进行去卷积，研究了RuO₂负载量的影响。本文研究的RuO₂-MnO₂纳米线展示了一种简单、直接的方法来克服MnO₂固有的低导电性，并阐明了RuO₂对性能改善的贡献来源。
