Creation of controllable cationic and anionic defects in tunnel manganese oxide nanowires for enhanced oxygen evolution reaction
Creation of controllable cationic and anionic defects in tunnel manganese oxide nanowires for enhanced oxygen evolution reaction
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DOI：
10.1016/j.poly.2019.06.050
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发表时间：
2019-10
期刊：
影响因子：
2.6
通讯作者：
P. West;Bryan W. Byles;E. Pomerantseva
中科院分区：
文献类型：
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作者：
P. West;Bryan W. Byles;E. Pomerantseva
高效析氧反应(OER)催化剂的开发对电解法生产氢气的环境和经济可行性至关重要。在这项工作中，两个简单的化学处理，酸浸和过渡金属掺杂，表明了改变低成本和环境友好的α-MnO2纳米线催化剂的化学和结构性能，从而提高了OER活性。X射线光电子能谱和X射线衍射分析表明，Co(NO3)2对α-MnO2纳米线进行熔盐处理后，Co2+离子进入了结构隧道。引入最低限度的钴(<；6 at.%)，在线性扫描伏安法测试中获得的最终电流密度增加了一倍以上。这一结果归因于钴掺杂样品中锰的平均氧化态的降低和塔菲尔斜率低于80 mV·dec−1。另一方面，酸浸被认为通过产生氧和锰空位来改变纳米线的形貌，暴露出更多的活性中心参与催化。原子吸收光谱和碘滴定相结合的表征方法表明，在与硝酸作用72小时后，氧空位增加了5.1%。当这些可控的缺陷形成方法串联应用时，掺钴样品的高活性与通过酸浸获得的暴露的活性中心的数量增加相结合，产生了一种高效的电催化剂，其OER活性是原始α-MnO2纳米线的3倍以上。我们的结果证明，可扩展和易于实施的方法，如酸浸和过渡金属掺杂，可以导致低成本无毒锰氧化物的OER活性增加三倍以上。该方法对其他材料体系用作OER电催化剂也有一定的借鉴意义。
The development of efficient oxygen evolution reaction (OER) catalysts is crucial to the environmental and economic feasibility of electrolysis for the production of hydrogen gas. In this work, two facile chemical treatments, acid leaching and transition metal doping, were shown to modify the chemical and structural properties of low cost and environmentally friendly α-MnO2nanowire catalysts resulting in increased OER activity. Through a combination of XPS and XRD analyses, it was shown that a molten salt treatment of α-MnO2nanowires with Co(NO3)2introduced Co2+ions into the structural tunnels. The introduction of minimal amounts of cobalt (<6 at. %) more than doubled ultimate current densities achieved in linear sweep voltammetry tests. This result was attributed to a reduction of the average oxidation state of manganese in Co-doped samples and a decrease in Tafel slope below 80 mV·dec−1. Acid leaching, on the other hand, is believed to modify nanowire topography through the creation of oxygen and manganese vacancies, exposing more active sites to participate in catalysis. A characterization approach combining atomic absorption spectroscopy and iodometric titration revealed a 5.1% increase in oxygen vacancies after 72 h of interaction with nitric acid. When these controllable defect formation approaches were applied in tandem, the high activity of the cobalt-doped samples was combined with the increased number of exposed active sites achieved through acid leaching producing a highly efficient electrocatalyst with more than a 3-fold increase in OER activity over pristine α-MnO2nanowires. Our results establish that scalable and easy-to-implement approaches, such as acid leaching and transition metal doping, can lead to more than a three-fold increase in OER activity of low-cost non-toxic manganese oxides. This methodology can be beneficial for other material systems used as OER electrocatalysts.