吡啶—胺五配位钴、镍、铜配合物的水相电催化还原产氢性质研究

发布时间：2018-03-30 09:33

  本文选题：制氢　切入点：电解水　出处：《大连理工大学》2015年博士论文

【摘要】：气候变暖和全球能源危机迫使科学家寻找新的可再生能源,如风能、太阳能。但是这些新能源在时间和空间上分布不均,这就要求我们开发新技术来解决能源的储存和利用问题。利用新能源发电产生的电力,实现水裂解产生氢气,将电能转化为化学燃料是发展新能源系统的有效方法之一。铂是在酸性水溶液中催化活性最高的电化学产氢催化剂,电能转化效率最高。但是,铂是贵金属,全球储量低,价格昂贵。商业化的氢电解装置迫切的需要用非贵金属催化剂来替代铂。因此,开发能在水相中工作的高效、稳定、低价、低过电势的基于非贵金属的催化剂是实现电能向氢能的高效率、低成本转化的关键科学问题之一论文首先设计合成了四种含有三吡啶-二叔胺结构的氮五配位钴配合物[(Ll)CoNCCH3]2+(Al) (L1=N-benzyl-N,N',N'-tris(2-pyridylmethyl)ethylenediamine)/ [(Ll)CoOH2]2+(A2)、[(L2)CoNCCH3]2+(B1) (L2=N-benzyl-N,N',N'-tris(2-pyridylmethyl) propylenediamine)和 [(L2)CoOH2]2+(B2),并对其进行了结构表征。循环伏安和极谱电化学研究表明,配体桥连基团由乙二胺到丙二胺的细微变化对钴配合物的电化学性质有明显影响。研究发现,在四个钴配合物中带有乙二胺桥连配体的钴配合物A2在中性水溶液中-1.25 V应用电势下电化学产氢效率(TOF)为860 mol H2 (mol cat)-1 h-1 (cm2 Hg)-1,并且经过60 h的控制电势电解水反应电流无明显衰减。为了进一步研究配体对配合物催化性质的影响,通过改变五配位配体中的叔胺氮和吡啶氮比例合成了单核镍配合物[(L3)NiR]2+(L3=1,1-di(2-pyridinyl)-N,N-bis (2-pyridinylmethyl)methanamine)(C1, R=CH3CN; C2, R=H2O)、[(Ll)NiR]2+(D1, R = CH3CN;D2, R=H2O)和[(L4)NiL]2+(L4=N,N'-dibenzyl-N-(2-(benzyl(2-pyridinylmethyl)amino)ethyl)-N-(2-pyridinylmethyl)-ethane-1,2-diamine) (El, R=CH3CN; E2, R=H2O),并进行了结构表征。电化学研究表明,配合物C1-E1在THF中的NiⅡ/NiⅠ还原电势随着叔胺N比例的增加明显的向正电势方向移动,而对更负的第二个还原过程影响不大。这些Ni单核配合物(C2-E2)都能在中性水溶液中实现电催化产氢,但相同电势下催化活性明显不同。D2是催化活性和稳定性最好的催化剂。在-1.25 V电势下,D2在中性磷酸缓冲溶液中的TOF值为1650 mol H2 (mol cat)-1 h-1(cm2 Hg)-1,是相同结构钴配合物A2的两倍,是其他已报道的多氮配位非贵金属分子催化剂的3-37倍(应用电势为-1.30--1.40 V)。设计合成了含有胺—吡啶五配位的铜配合物[(L1)Cu]2+(G).该配合物在pH 2.5的缓冲溶液中电催化产氢速率常数(Kobs)为10000 s-1,过电势为420 mV。以G为催化剂,在pH 2.5的缓冲溶液中,-0.90 V下电解2h的催化转化数(TON)为1.4×104mol H2(mol cat)-1 cm-2,法拉第效率96%,对应的TOF值为2.0 mol H2 (mol cat)-1 s-1 cm-2。光谱电化学研究表明,该铜配合物催化质子还原产氢经历两个质子耦合电子转移过程：第一步质子化发生在配体上,第二步质子化发生在金属铜上生成[(LlH)CuⅡ(H)]2+,然后释放出一分子氢气,催化剂回到起始的CuⅡ状态。研究中发现,当以铂片为对电极,以玻璃碳为工作电极在酸性水溶液中对铜配合物G进行电解时,能够在工作电极表面发生电沉积生成活性沉积膜Cu-CuxO-Pt-1。这种铂掺杂的铜纳米催化剂在中性水溶液中表现出比铂片和Pt/C还要好的催化活性；该沉积膜的Tafel斜率为44mV dec-1,交换电流密度为1.601 mA cm-2,电催化产氢起始过电势≤10 mV,催化电流密度达到20 mA cm-2所需的过电势为45 mV,催化电流密度达到500mA cm-2所需的过电势为370 mV。Cu-CuxO-Pt-1在中性水溶液中的催化活性可以与铂在0.5 M H2SO4中的催化活性相媲美,基于铂的质量活性是CuPt电极在强酸水溶液中催化活性的11倍。中性水溶液中,Cu-CuxO-Pt-1电极在200 mV过电势下能够保持～190mAcm-2催化电流密度100小时内无衰减。
[Abstract]:Global warming and energy crisis forced scientists to search for new and renewable energy, such as wind energy, solar energy. But these new energy in time and space distribution is uneven, which requires us to develop new technology to solve the energy storage and utilization. The use of new energy power generating electricity, water will produce hydrogen cracking. Electric energy is converted into chemical fuel is one of the effective methods for the development of new energy systems. Platinum is in acidic solution, the highest catalytic activity for hydrogen production of electrochemical catalyst, power conversion efficiency is the highest. However, platinum precious metals, the world's reserves is low, the price is expensive. The hydrogen electrolysis device commercialization of the urgent need for non noble instead of platinum metal catalysts. Therefore, development can work in water efficient, stable, low-cost, low overpotential catalyst of non noble metal based on electrical energy into hydrogen energy conversion efficiency, low cost One of the key scientific problem is firstly designed four kinds of pyridine containing three di TERT amine structure n five ligand cobalt complexes [(Ll) CoNCCH3]2+ synthesis (Al) (L1=N-benzyl-N, N', N'-tris (2-pyridylmethyl) ethylenediamine) / (Ll) CoOH2]2+ (A2), [(L2) CoNCCH3]2+ (B1) (L2=N-benzyl-N, N', N'-tris (2-pyridylmethyl) propylenediamine) and [(L2) CoOH2]2+ (B2), and it was characterized by cyclic voltammetry and polarography. Electrochemical studies showed that the ligand bridging group by ethylenediamine to slight changes in C two amines have obvious effects on the electrochemical properties of cobalt complexes. The study found that in four with Ethylenediamine bridged cobalt cobalt complexes A2 in neutral aqueous solution of -1.25 V application potential in electrochemical hydrogen production efficiency (TOF) of 860 mol H2 (mol cat) -1 H-1 (cm2 Hg -1), and through the controlled potential electrolysis water reaction current of 60 h of ignorance Significant attenuation. In order to further study the influence on catalytic properties of ligand coordination, by changing the five ligand in the tertiary amine nitrogen and pyridine nitrogen proportion of synthesis of mononuclear nickel complex [(L3) NiR]2+ (L3=1,1-di (2-pyridinyl) -N, N-bis (2-pyridinylmethyl) methanamine) (C1, R=CH3CN; C2, R=H2O), [(Ll) NiR]2+ (D1, R = CH3CN; D2, R=H2O) and [(L4) NiL]2+ (L4=N, N'-dibenzyl-N- (2- (benzyl (2-pyridinylmethyl) amino) ethyl) -N- (2-pyridinylmethyl) -ethane-1,2-diamine (El), R=CH3CN; E2, R, =H2O) and characterized. The electrochemical study shows that Ni /Ni I, II complexes of C1-E1 in THF with the reduction potential of tertiary amine N ratio significantly increased to the positive potential direction, while the second reduction process has little effect on the more negative. These Ni complexes (C2-E2) can realize the electrocatalytic hydrogen production in neutral aqueous solution, but the same catalytic potential live 鎬ф槑鏄句笉鍚，

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