【作者】 万磊；

【导师】 邓意达；

【作者基本信息】 上海交通大学 ， 材料科学与工程， 2016， 硕士

【摘要】 Ni-P合金作为一种制氢反应（HER）的高效和廉价催化剂,近些年来引起了科学界的广泛关注。HER反应作为一种制备氢气的有效手段,在当今全球气候变暖和寻求新能源以代替化石燃料的背景下,十分值得进一步研究。在通电的条件下,Ni-P合金可以极大地减小HER反应所需的过电势。Ni-P纳米材料现在被认为是Pt催化剂的一种潜在的有效替代品。近期,Ni-P不仅被认为可以作为HER反应的催化剂,还能够作为水分解另一半反应制氧反应（OER）的催化剂。不过,尽管在近些年Ni-P合金研究上取得了不少进展,依然有许多基础问题没有解决。本文针最近对Ni-P纳米材料制备和HER催化的研究热点,在其制备工艺、表证手段和电化学性能上进行了一系列探索。通过镍的自催化还原性质和次亚磷酸钠作为还原剂分别制备了Ni-P蛋壳纳米粒子、Ni-P纳米球和酸碱浸泡处理的Ni-P球,并研究了各个反应参数对纳米粒子形成的影响。使用电化学工作站测试了Ni-P纳米粒子的HER催化性能,并讨论了制备工艺和热处理对电化学性能的影响。本文主要研究内容如下:（1）采用自催化还原原理成功制备了蛋壳结构的Ni-P纳米粒子、Ni-P纳米球和酸碱浸泡处理的Ni-P球。实验中采用硫酸镍为镍源,先制备出相应的前驱体,然后以次亚磷酸钠为还原剂、氯钯酸为形核剂还原出粒径在50¹00 nm之间对应的纳米粒子。对于酸碱浸泡处理的Ni-P球,还要进一步利用氨水、硫酸和盐酸的混酸进行表面处理。（2）使用热处理工艺对上述纳米材料进行热处理并采用一系列表征手段对上述纳米材料的制备方法、表面形貌、结构和元素组成进行分析。得到以下结论。1)对于制备蛋壳结构的Ni-P纳米粒子,使用80℃作为反应温度,利用十二烷基苯磺酸钠（SDBS）作为表面活性剂先得到稳定均一的Ni（OH）₂前驱体是制备的第一步。其后利用牺牲模板法得到蛋壳的形貌;2)制备Ni-P纳米球相对简单,利用现成的α-Ni（OH）₂纳米线作为前驱体,以90℃作为反应温度,但要缓慢加入还原剂,并伴随强烈搅拌使得材料均匀地生长成球状;3)酸碱浸泡处理后的Ni-P纳米球的形貌几乎不会改变,但是在碱液和酸液的作用后,体系的Ni元素百分比会上升,而P元素比例会略有上升。原有的非晶态的Ni-P合金会转化为Ni₁₂P₅和Ni₂P的混合物;4)热处理工艺对材料的表面形貌并不会造成太大影响,对体系中Ni元素和P元素的比值也不会造成太大影响,但会导致体系中原有的Ni-P相发生相变,转化为其他Ni-P相。5)由于反应在并非在密闭容器中进行,所以材料的表面会形成一定成分的氧化物。（3）Ni-P纳米球具有最佳的催化性能。其极化曲线中达到-100 mA/cm²电流密度对应的过电势为251 mV。相比之下,蛋壳Ni-P纳米粒子的催化性能相对较差。文中所制备的Ni-P合金都具有不错的稳定性。在酸性溶液中,尤其是经过热处理之后的样品具有较高的稳定性,其中8小时热处理之后的Ni-P纳米球在恒电势测试后,仍具有259 mA/cm²的电流密度。而在碱性溶液中测试时,样品一般要在很长一段测试时间以后方能达到较佳性能,这和材料表面除去氧化膜的过程有关。更多还原

【Abstract】 As a kind of highly effective and cost-effective catalyst for hydrogen evolution reaction（HER）,Ni-P alloys possessing nanostructure have attracted great attention from academia.HER–an efficient method for preparing hydrogen–is worth researching under the backdrop of global warming and the appeal for alternatives of fossil fuels.When the electric power is on,Ni-P alloys are expected to greatly lower the overpotenital required for HER.By far,Ni-P alloys have served as a potential alternative for Pt.Additionally,Ni-P alloys can not only serve as cataysts for HER,but can also be catalyst for other half-reaction of water-splitting–oxygen evolution reaction（OER）.Despite the progress made in research of Ni-P alloys,however,there still remains some basic questions unsolved.This thesis focuses on preparation of Ni-P nanomaterials,a research hotspot of HER catalysts and made a series of explorations of their preparation process,characterization and electrochemical properties.Capitalizing on nickel’s auto-catalytic property and sodium hypophosphite as reducing agent,a range of yolk-in-shell Ni-P nanoparticles and Ni-P nanospheres have been successfully prepared and the different reaction parameters leading to these morphologies have been studied.Electrochemical workstation was applied to test Ni-P alloys’catalytic properties and preparation process and heat treatment process,which are closely related with electrochemical properties,have also been discussed.The main content of this thesis is on the points below:（1）By taking advantage of the auto-catalytic property,a range of yolk-in-shell Ni-P nanoparticles,Ni-P nanospheres have been successfully prepared.The nickel sulfate was the nickel source and the corresponding precursor was prepared at first.Then nanoparticles of 50¹00 nm as mean size were prepared by taking sodium hypophosphite as reducing agent and palladium chloride as nucleate agent.For those acid-and alkali-soaked Ni-P nanospheres,an extra step was needed,which made use of ammonia water and a kind of acid comprised by chloric acid and sulfuric acid to rinse the nanospheres’surface.（2）A string of means of characterization were adopted to analyze the abovementioned nanomaterials’preparation method,surface morphology,microstructure and element ratio.Main conclusions of the means of characterization are:1)the first step to prepare yolk-in-shell nanoparticles was to obtain uniform and stable Ni-P nanoparticles which requires 80℃as reaction temperature and SDBS as surfactant.The next step was to get the yolk-in-shell surface morphology by the sacrificial template method;2)the method to prepare Ni-P solid nanospheres was comparatively easy.The reaction temperature was90℃,but this course should also be accompanied with strong stir,which would be helpful in making the materials grow into sphere-like form.3)surface morphology of the alkali-and acid-soaked Ni-P nanospheres will almost make no change;however,after this procedure of being soaked in alkali and acid,atomic percentage of nickel would decrease with a little increase of nickel.What’s more,the original amorphous Ni-P alloy phase would convert in to a mixture of Ni₁₂P₅ and Ni₂P phases.4)heat treatment procedure will not cast much influence on surface morphology of materials and the molar ratio of nickel to phosphorus,but will induce phase transformation of the primitive Ni-P phases to other corresponding phases.5)due to the fact that the chemical reaction did not happen in an airtight environment,there exists some amounts of oxides on materials’surface.（3）Among all the samples,the 8-hour-heat-treated Ni-P nanospheres bear the best catalytic properties.To achieve-100 mA/cm² output current density,only 251 mV overpotential is required.By contrast,the yolk-in-shell nanoparticles,despite their novel morphology which may be useful in other applications,have comparatively inferior catalytic property.Ni-P alloys prepared in this thesis all have favorable durability.Among them,the 8-hour annealed smaple is able to secure high current density（259 mA/cm²）after long-term stability tests.Additionally,samples tested in alkaline condition need a period of time to achieve their best catalytic property.This is concerned with the removal of the oxide film on the materials surface.更多还原