【作者】 李凝；

【导师】 高诚辉；

【作者基本信息】 福州大学 ， 材料学， 2010， 博士

【摘要】 电解水制氢是制氢技术中最具应用前景的一种技术。目前工业使用的Fe、Ni电极电能消耗居高不下，降低阴极的析氢过电位迫在眉睫，Ni-Mo合金因其催化活性好成为研究的热点。但从实际应用考虑，Ni-Mo合金的活性还有待提高，稳定性也是其应用的关键制约因素。本文从成分、结构和复合三方面着手提高其电催化活性和稳定性。在碱性镀液中成功制备了非晶/纳米晶混合结构Ni-Mo合金，系统研究了制备工艺、组元含量以及非晶与纳米晶结构的比例对其电化学活性的影响，首次向Ni-Mo合金镀液中分别添加稀土La、Ce元素卤化物，以及在镀液中添加ZrO₂纳米颗粒进行复合镀，研制开发了非晶/纳米晶Ni-Mo-La、Ni-Mo-Ce和Ni-Mo/ZrO₂合金电极，具有很好的电化学活性和较好的电解稳定性。以碱式碳酸镍为镍的主盐，在弱碱性条件下进行电镀。首先研究电镀镀液组成及主要工艺参数对电沉积非晶/纳米晶Ni-Mo合金的镀层结构、成分及其析氢性能的影响。当钼酸盐浓度在0.04⁰.1mol·L^-1时，镀层钼原子含量在21.0²6.0at.%之间，镀层为非晶态含量大于60wt.%的混晶结构，具有较高的析氢催化活性。在80℃、7mol·L^-1NaOH溶液中，D为100mA·cm^-2时，非晶/纳米晶Ni-Mo_23.16合金电极的析氢过电位比纳米Ni电极降低约400mV，同时比Ni-Mo-Fe、Ni-Mo-Co、Ni-S、Ni-P合金电极的析氢电位分别降低约85mV、95mV、140mV和195mV。在此基础上添加稀土卤化物，获得了非晶/纳米晶Ni-Mo-La、Ni-Mo-Ce合金电极。当稀土La、Ce加入量分别为1.6g·L^-1、2.0g·L^-1时，镀层具有最佳的物理化学性能，良好的耐蚀性能和析氢催化活性。80℃高温条件下的碱性溶液中，非晶/纳米晶Ni-Mo_25.03-La_0.92合金电极的析氢过电位比非晶/纳米晶Ni-Mo_23.16合金电极进一步降低了约30mV。稀土元素的引入不仅促进了非晶态的形成和比表面积的增加，同时提高了合金电极的析氢催化活性。Ni-Mo、Ni-Mo-RE（La,Ce）合金的结构形态与Mo、RE元素还原过程中的价态有关，其还原过程为多步还原过程。混晶结构合金具有储氢材料的特性，其电解析氢过程包含吸氢-储氢-脱附的过程。ZrO₂纳米颗粒改性的复合镀层Ni-Mo_22.68/ZrO₂，室温条件电解时仍具有较好的析氢催化活性良好的耐腐蚀性能。模拟工业条件下的电解实验表明，混晶结构合金具有较好的电化学稳定性和析氢催化活性。Ni-Mo合金电极失效的原因与Mo元素的溶出有关，稀土La和纳米颗粒ZrO₂的存在阻止了Mo的溶出。非晶/纳米晶Ni-Mo_25.03-La_0.92、Ni-Mo_18.68合金的热分析表明，两种合金的结构稳定性同比非晶态Ni-Mo₃₇wt.%合金有所降低，较低温度下的热处理有利于提高合金电极的析氢催化活性。更多还原

【Abstract】 Water electrolysis is one of the most efective techniques to produce hydrogen. Butthe high energy consumption restricts its large-scale application due to high hydrogenevolution reaction （h.e.r.） overpotential caused by ferrous or nickel electrodes, whichare widely used in industry. Therefore, it is urgent to get more active electrodes forh.e.r. in alkaline media. Ni-Mo alloy is considered as a very suitable one in view ofhigh electrochemical activity, high stability and low cost. The activity and stability ofNi-Mo alloy are the key constraints for its applications, so that the composition,microstructure and complex modification Ni-Mo alloys have been studied in thisarticle. The amorphous/nanocrystalline Ni-Mo alloys were successfully obtained in analkaline bath, and the effectes of the preparation process, composition and theproportion of amorphous or nanocrystalline phase on the electrochemical activitywere also discussed in this paper. In order to improve its activity and stability further,lanthanum, cerium and nano-particles ZrO₂were added into the electrodepositionplating to prepare amorphous/nanocrystalline Ni-Mo-La, Ni-Mo-Ce and Ni-Mo/ZrO₂electrodes, respectively, which are based on systematical study of electrodepositingamorphous/nanocrystalline Ni-Mo coatings. And the results showed that they all havea good electrochemical activity and a better electrolysis stability.The electrodeposition is controlled in weak alkaline solution with additional nickelcarbonate as the main salt. The amorphous/nanocrystalline Ni-Mo coatings areobtained by electrodeposition on low carbon steel sheet. The effects ofelectrodeposition parameters on the deposites microstructure and electrochemicalcatalysis activity are investigated. The results showed that the deoxidized Mo contentis about21.0²6.0at.%with molybdate concentration0.04⁰.1mol·L^-1in solution,while the microstructure is composed of more than60wt.%amorphous phase andother nanocrystalline phase with the best electrochemical catalytic activity. The resultsof the electrochemical parameters effect and h.e. properties showed that theamorphous/nanocrystalline Ni-Mo alloy had a better h.e. performance. The cathode electrode hydrogen evolution patterns aquired by linear sweep voltammetry （LSV） at80℃,7mol·L^-1NaOH solution show that, when D=100mA·cm^-2, the h.e.overpotential of Ni-Mo_23.16electrode is about400mV lower than that of nano-Nielectrode, about85mV,95mV,140mV and195mV lower than that of Ni-Mo-Fe,Ni-Mo-Co, Ni-S, Ni-P electrodes, respectively.The Ni-Mo-La and Ni-Mo-Ce alloys were obtained with lanthanum halide andcerium halide solution added into Ni-Mo bath plating, respectively. The morphologyof surface particles gradually transform from spherical particles into sand-like,meticulous and flat particles. When the concentration of lanthanum and cerium isabout1.6g·L^-1,2.0g·L^-1respectivly, the deoposites can obtain the best physical andchemical properties, the better corrosion resistance and higher electrocatalyticperformance. The h.e. overpotential of amorphous/nanocrystalline Ni-Mo_25.03-La_0.92electrode is about30mV lower than that of amorphous/nanocrystalline Ni-Mo_23.16electrode in alkaline solution electrolysis when80℃, D=100mA·cm^-2. The additionof rare earth not only promote the amorphous formation but aslo increase the surfacearea, while the electrode catalytic activity of hydrogen evolution is increased. Thestructural form of the Ni-Mo and Ni-Mo-RE （La, Ce） alloys have greatly beeneffected by the Mo, RE valence state, and so for a multi-step deoxidization. Theamorphous/nanocrystalline Ni-Mo alloy electrolysis has a characteristic ofcomplex-hydrogen evolution process. Meanwhile, the amorphous/nanocrystallineNi-Mo-La alloy has a certain capacity of storing hydrogen, and its h.e.r. is in anadsorption hydrogen-hydrogen storage-desorption hydrogen process. The h.e.performance of Ni-Mo_22.68/ZrO₂co-electrode modified with nano-particles ZrO₂has abetter catalytic activity and corrosion resistance at room temperature, alkaline solutionelectrlysis.Electrolysis experiments under industrial conditions showed that theamorphous/nanocrystalline alloys have a good electrochemical stability and bettercatalytic activity of hydrogen evolution. The electrolysis experiments results showedthe weakness of Ni-Mo alloy eletrodes during eletrolysis process is related to themolybdenum dissolution. The existence of La and nano-ZrO₂particles can prevent theMo dissolution and keep the h.e. performances better. Crystallization dynamics fromdifferential scanning calorimetry （DSC） showed that the microstructure stability of theamorphous/nanocrystalline Ni-Mo_25.03-La_0.92and Ni-Mo_18.68alloys are inferior to theamorphous Ni-Mo₃₇wt.%alloy. Heat treatment at lower temperature can help improve the electrode catalytic activity of hydrogen evolution.更多还原