三维碳纳米纤维负载过渡金属及其氧化物复合电催化剂用于高效氧析出

发布时间：2018-08-15 18:37

【摘要】：电化学催化水分解制氢技术,为间歇性能源如风能、太阳能以及其他可再生能源大规模转换为氢能提供了一种途径。然而,由于氧析出反应的迟滞性,该反应过程的综合效率受到很大影响,亟待开发出高效的电催化剂来加速其反应速率,进而提高能源转换效率。目前,被公认性能最优的氧析出催化剂是金属Ru和Ir的氧化物,但其昂贵的价格及稀缺性制约了其大规模应用。作为贵金属催化剂的替代品,过渡金属氧化物因其丰富的储量以及较高的理论活性近年来得到了广泛研究。目前,这类催化剂均通过滴涂或者旋涂的方法在二维基底上制成薄膜,虽然其性能得到了一定提高,但需要通过进一步优化结构及机械性能来提高其催化活性和稳定性。因此,本文以细菌纤维素衍生的碳纳米纤维为载体,通过简单的方法制备了几种具有多孔网络结构的三维碳纳米纤维负载过渡金属及其氧化物的复合物催化剂,并对其形貌结构及物质组成进行了表征,最后对其催化氧析出的性能进行了研究。以细菌纤维素为模版,通过热沉淀法在其三维多孔网络结构的纳米纤维上负载氢氧化钴纳米片,随后通过高温裂解得到细菌纤维素衍生的碳纳米纤维@钴复合物,该复合物不仅保留了先进的多孔网络结构,而且还具有高比表面积以及良好的机械性能。将该复合物直接作为三维电极,对其催化氧析出性能进行了测试。测试结果表明:其具有较低的起始电位(0.458 V(vs.Ag/AgCl)),在0.1 M KOH溶液中,电流密度达到10mA/cm2时,过电位为476 mV,表现出了较高的催化活性。通过长达11小时的恒压(0.5 V(vs.Ag/AgCl))稳定性测试后,其电流密度仍然保持70%,证明了其具有良好的稳定性。在氧析出反应中,三维多孔结构不仅有利于电解液以及氧气的高速传质,而且碳纳米纤维网络的导电性能有利于电子的高速转移,这些特性的协同作用使该材料具有优异的电催化性能。此外,以细菌纤维素衍生的碳纳米纤维为载体,通过水热法直接负载镍钴双氢氧化物纳米片得到碳纳米纤维-镍钴双氢氧化物复合物,该材料具有良好的三维多层多孔结构以及巨大的比表面积,使其在催化氧析出反应中具有良好的质量传递以及较多的活性位点。通过催化氧析出性能测试表明,该三维复合物催化剂同样表现出了非常优异的催化活性以及出色的稳定性。在此基础上,以细菌纤维素为基底,通过“模版沉淀—裂解法”制备了其他几种碳纳米纤维负载过渡金属复合物,并对其进行了物理表征及催化氧析出性能研究。
[Abstract]:Electrochemical catalytic water decomposition to produce hydrogen provides a way for large-scale conversion of intermittent energy such as wind, solar and other renewable energy to hydrogen energy. However, due to the hysteresis of the oxygen precipitation reaction, the comprehensive efficiency of the reaction process is greatly affected. It is urgent to develop an efficient electrocatalyst to accelerate the reaction rate and improve the energy conversion efficiency. At present, the oxides of metal Ru and ir are the best catalysts for oxygen precipitation, but their large scale application is restricted by their high price and scarcity. As a substitute for noble metal catalysts, transition metal oxides have been widely studied in recent years because of their rich reserves and high theoretical activity. At present, these catalysts are prepared on two-dimensional substrates by trickling or spin-coating. Although their properties have been improved to some extent, the catalytic activity and stability need to be improved through further optimization of structure and mechanical properties. Therefore, in this paper, several kinds of complex catalysts with porous network structure supported on transition metals and their oxides were prepared by using the carbon nanofibers derived from bacterial cellulose as the carrier. Its morphology, structure and composition were characterized. Finally, the catalytic properties of oxygen precipitation were studied. Using bacterial cellulose as template, cobalt hydroxide nanoparticles were loaded on the nanofibers with three dimensional porous network by thermal precipitation method, and then the carbon nanofibers / cobalt complexes derived from bacterial cellulose were obtained by pyrolysis at high temperature. The composite not only retains the advanced porous network structure, but also has high specific surface area and good mechanical properties. The complex was directly used as a three-dimensional electrode and its catalytic oxygen precipitation performance was tested. The results show that it has a lower initial potential (0.458 V (vs.Ag/AgCl), in 0. 1 M KOH solution) and an overpotential of 476 MV when the current density reaches 10mA/cm2, which shows high catalytic activity. After 11 hours of constant voltage (0. 5 V (vs.Ag/AgCl) stability test, its current density remains 70. It is proved that it has good stability. In the oxygen precipitation reaction, the three-dimensional porous structure is not only conducive to the high speed mass transfer of electrolyte and oxygen, but also the conductive property of carbon nanofiber network is favorable to the high-speed transfer of electrons. The synergistic effect of these properties makes the material have excellent electrocatalytic performance. In addition, carbon nanofibers derived from bacterial cellulose were directly loaded with nickel-cobalt double hydroxide nanochips by hydrothermal method to obtain carbon nanofibers and nickel-cobalt double hydroxide complexes. The material has a good three-dimensional multilayer porous structure and a large specific surface area, which makes it have good mass transfer and more active sites in the catalytic oxygen precipitation reaction. The results of catalytic oxygen precipitation test showed that the three dimensional complex catalyst also showed excellent catalytic activity and excellent stability. On this basis, several other carbon nanofiber supported transition metal complexes were prepared by "template precipitation-pyrolysis" method, and their physical characterization and catalytic properties of oxygen precipitation were studied.
【学位授予单位】：北京理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O643.36;TQ116.2

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