【作者】 李丹；

【导师】 倪红卫；

【作者基本信息】 武汉科技大学 ， 冶金工程， 2020， 硕士

【摘要】 氢气作为高效的二级能源载体,在氢冶金中可充当主要的还原剂和能量来源,是冶金绿色发展和“氢经济”的重要支柱;而电解水制氢可以利用电能作为分解水的动力,是当前能源体系中最有前景的氢气绿色制备技术之一。然而,优良的析氢反应(HER)催化电极——金属Pt,自然资源匮乏,价格昂贵,极大地限制了传统电解工艺的发展;而储量丰富的过渡金属催化电极,如用Ni,Fe等导电金属时,往往需要较高的过电位,致使产氢效率低、电能损耗大,使该技术应用范围受到了严重限制。此外,研究表明,由于反应路径不同,贵金属Pt在碱性电解液中催化HER时其反应动力学比在酸性电解液中慢至少两个数量级。本论文基于酸碱性介质中HER路径不同,设计了三种杂化催化剂用以推动整体HER的进行;所得双位点催化剂均展现出优于单一位点催化剂的析氢催化效果,证明了双位点设计的有效性,为工业催化剂的合理设计和应用提供了实验上和理论上的参考依据;杂化材料的设计和制备方法也将对电催化、超级电容器、金属—空气电池等电极材料的研究起到借鉴意义。本研究具体内容如下:(1)采用水热法在泡沫镍基底上制备了NiRu-LDH纳米薄膜,在用于析氧反应10 h后,发现其Ru物相发生一定程度地浸出,其转变为低结晶度的NiRu-OH,而这种低结晶度的Ni Ru-OH采用电化学的方法沉积Pt时,Pt的沉积速率是其他对比材料的数倍,经过材料表征认为Pt在Ni Ru-OH上以单原子形式分布,且与O或OH以共价键连接。所得杂化材料(Pt/Ni Ru-OH)在用作HER催化剂时,在碱性环境中10 mA cm-2电流密度下仅需要39 mV过电位。优异的性能可能来源于Pt活性位点和NiRu-OH活性位点两者的协同作用。(2)采用一步水热法将Ru团簇引入NiCo-LDH中,得到的杂化催化剂Ru-NiCo-LDH纳米薄膜用于碱性电解质中的HER。受益于Ni Co-LDH活性位点促进水的解离,Ru活性位点增强H的吸附,该杂化催化剂在碱性环境中催化HER时仅需要28 mV便可驱动10 mA cm-2的电流密度,且塔菲尔斜率只有42 mV dec-1。优异的性能来源于材料本身快速的电荷转移能力和合理的设计。此外,我们还发现原始材料中氧化态的Ru物相在HER后全部转化为金属态的Ru,进一步表明金属态的Ru更可能是H中间体吸附的活性位点。(3)针对在催化HER时MoS2基平面活性位点不足的问题,采用电化学的方法在水热制备的Mo S2纳米片表面沉积了Pt纳米颗粒并探讨了沉积的最佳条件。所得杂化催化剂(Pt-Mo S2)在酸性介质中相对于单一物相(MoS2和Pt颗粒)表现出更强的催化活性,在10 mA cm-2电流密度下需要87 mV的过电位。增强的催化性能应归因于杂化材料增加的活性位点数量和Mo S2增强的固有催化活性。更多还原

【Abstract】 As an economical and efficient secondary energy carrier,hydrogen can be used as the main reducing agent and energy source in hydrogen metallurgy,which is the important basis of green development of metallurgy and the"hydrogen economy".Electrolysis of water-splitting reaction,which can utilize the stable electricity driven from renewable energy（solar,wind,etc.）,is one of the most promising technology as a sustainable source of hydrogen.However,because the expensive price and scarce resources of Pt,which is the benchmark electrocatalyst toward hydrogen evolution reaction（HER）,the development of traditional electrolysis is greatly restricted.Meanwhile,the abundant transition metal catalyst,such as Ni and Fe,normally require high overpotential to boost HER,resulting in low efficiency and high power loss,which severely limits the large-scale application.Moreover,since the different reaction pathway,it has been reported that the state-of-the-art electrocatalyst（Pt）for hydrogen evolution reaction（HER）in acidic media,exhibits relatively sluggish kinetics in alkaline media,being at least two orders of magnitude slower than those in acidic media.In this context,this thesis demonstrates three hybrid electrocatalysts to boost HER.The design of various catalysts based on the different reaction steps in acidic or alkaline media and all these three catalyst have dual active site for HER.All as-resulted dual-site catalysts are better than the single-site catalysts towards HER,confirming the hybrid is more effective and these works will provide an experimental and theoretical basis for the rational design and application of industrial catalysts.The design and preparation of hybrid materials will also be beneficial to the investigation of electrode materials in electrocatalysis,supercapacitors and metal-air batteries.The main contents are as follows:（1）A functionalized Ni Ru-hydroxide（NiRu-OH）catalyst that acts as a capable candidate to immobilize highly dispersed single Pt atoms is described.We synthesize this catalyst by means of Ru leaching from a NiRu-layer double hydroxide（NiRu-LDH）under oxygen evolution reaction（OER）conditions.The hybrid catalyst shows extremely high HER activity,with an overpotential of 38 mV to drive a typical current density of 10 m A cm^-22 in alkaline media.We ascribe the excellent catalytic activity to the synergistic effect of the highly dispersed single Pt atoms and NiRu-OH in a dual-site alkaline HER mechanism.（2）A hybrid electrocatalyst consisting of Ru clusters trapped in NiCo-layered double hydroxide（NiCo-LDH）as the basis for an efficient hydrogen evolution reaction（HER）in alkaline media.Benefiting from the fast water dissociation kinetics on NiCo-LDH and favorable H recombination on Ru,the resultant Ru-Ni Co-LDH shows an extremely low HER overpotential of 28 mV at a current density of 10 mA cm^-22 with a small Tafel slope of 42 mV dec^-1.This superior catalytic activity can be ascribed to its high charge transfer ability and to the synergistic effect of the highly dispersed Ru and the Ni Co-LDH.Moreover,we also found that the oxidized Ru incorporated in NiCo-LDH was entirely reduced to Ru⁰ under hydrogen-evolution conditions,which suggests that Ru⁰ is the true catalytically active phase responsible for the outstanding HER performance.（3）In order to increase the active sites on the basal plane of Mo S2,a cyclic voltammetry（CV）cycling method was used to synthesize a catalyst comprising deposited Pt nanoparticles on MoS2 nanoflake stack structures on stainless steel mesh（SSM）.Compared with single materials（Mo S₂ or Pt particles）,the hybrid structure exhibits significantly enhanced hydrogen evolution reaction（HER）catalytic activity with an overpotentials of 87 mV at 10 mA cm^-2.The excellent HER performance should be attributed to the increase of active sites and improvement of intrinsic activity of MoS₂.更多还原