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Preparation and Modification of Cathode Materials for Amorphous/Nanocrystalline Ni-Mo Alloys by Electrodeposition

Author: LiNing
Tutor: GaoChengHui
School: Fuzhou University
Course: Materials Science
Keywords: Ni-Mo coating Amorphous/nanocrystalline Rareearth(La,Ce) Nano-particles ZrO2 HER
CLC: TQ116.2
Type: PhD thesis
Year: 2010
Downloads: 28
Quote: 0
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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-Mo23.16electrode 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-Mo25.03-La0.92electrode is about30mV lower than that of amorphous/nanocrystalline Ni-Mo23.16electrode 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-Mo22.68/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-Mo25.03-La0.92and Ni-Mo18.68alloys are inferior to theamorphous Ni-Mo37wt.%alloy. Heat treatment at lower temperature can help improve the electrode catalytic activity of hydrogen evolution.

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