催化学报 ›› 2018, Vol. 39 ›› Issue (3): 534-541.DOI: 10.1016/S1872-2067(17)62973-5

• 论文 • 上一篇    下一篇

[Ag (H2O)(H3PW11O39)]3-修饰的TiO2阳极对水氧化的催化作用研究

李健生, 王蕾, 由万胜, 刘美英, 张澜萃, 桑晓静   

  1. 辽宁师范大学功能材料化学研究所, 辽宁大连 116029
  • 收稿日期:2017-09-30 修回日期:2017-11-09 出版日期:2018-03-18 发布日期:2018-03-10
  • 通讯作者: 由万胜, 刘美英
  • 基金资助:

    国家自然科学基金(21573099,21601077,21573100).

Catalytic effects of[Ag(H2O)(H3PW11O39)]3- on a TiO2 anode for water oxidation

Jiansheng Li, Lei Wang, Wansheng You, Meiying Liu, Lancui Zhang, Xiaojing Sang   

  1. Institute of Chemistry for Functionalized Materials, Liaoning Normal University, Dalian 116029, Liaoning, China
  • Received:2017-09-30 Revised:2017-11-09 Online:2018-03-18 Published:2018-03-10
  • Contact: 10.1016/S1872-2067(17)62973-5
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (21573099, 21601077, 21573100).

摘要:

高效的水氧化是实现大规模分解水制氢的瓶颈,开发稳定、经济、高效的水氧化催化剂是引人关注的.早在上世纪中期Ag+作为水氧化催化剂就有报道,但尚未见Ag+配合物作为分子基水氧化催化剂的报道.本课题组选择缺位多酸阴离子[H3PW11O39]3-作为配体,成功研制了银-多酸配合物[H3AgI(H2O)PW11O39]3-(AgPW11)分子基水氧化催化剂,发现其对使用S2O82-化学氧化水具有很好的催化作用,这主要归功于多酸配体在传输电子和质子的作用,对理解催化氧化水的机理有重要学术价值.
将分子基催化剂修饰到电极上是实现其电化学催化氧化水的必由之路.本文采用浸渍法将AgPW11修饰到TiO2电极上,成功制备了AgPW11-TiO2/ITO电极,并通过XRD,SEM,EDX技术对AgPW11-TiO2/ITO电极进行了表征.结果表明,AgPW11被成功负载到TiO2纳米粒子表面,它的引入使得TiO2电极表面的纳米粒子平均尺寸由10-40nm增加到15-60nm.在0.1mol L-1 Na2SO4电解质溶液中利用线性扫描伏安、计时电流和电化学阻抗技术研究了AgPW11-TiO2/ITO阳极催化氧化水的性能,结果发现,当施加偏压大于1.3 V vs. Ag/AgCl时,随电压升高,AgPW11-TiO2/ITO电极相比TiO2/ITO电极有更显著的氧化电流;当施加偏压在1.5V vs. Ag/AgCl时,AgPW11-TiO2/ITO电极氧化电流比TiO2/ITO电极和AgNO3-TiO2/ITO电极分别高出10倍和2.5倍,这归因于AgPW11-TiO2/ITO电极上电极-电解质界面具有更低的电荷转移阻抗,也说明多酸阴离子配体在催化过程中能够更好地传输电子和质子.在光照条件(100mW cm-2)下,AgPW11-TiO2/ITO电极有较高的阳极电流,但光电流并没有明显增加,这主要是由于修饰电极光生电子-空穴复合速率较快所致.AgPW11-TiO2/ITO阳极重复使用15次后,电流密度仍然高出TiO2/ITO电极3倍以上,表明AgPW11-TiO2复合电极稳定性较好.在0.1mol L-1磷酸缓冲溶液体系中研究了AgPW11在不同浓度、不同pH值和不同扫速下的循环伏安曲线.在1.1-1.6V vs. Ag/AgCl扫描范围和100mV s-1扫速条件下,在1.23和1.31V vs. Ag/AgCl处出现的一对氧化还原峰,归结为AgI/Ag的1e氧化还原过程.在1.0-1.4V vs.Ag/AgCl扫描范围内,随扫速由100增至900mV s-1,阴极还原峰电位负移而阳极氧化峰电位正移,导致峰-峰电位差△Ep增加,而且氧化峰电流与还原峰电流与扫速平方根呈线性关系,说明该电极氧化还原过程受扩散控制.对AgI/Ag的氧化还原过程,随着pH值由5.3增加到6.7,氧化还原峰电位负移,并且Epc与pH值呈现线性关系,斜率为-0.08882,根据能斯特方程S=2.303RTm/(αnF),推测转移的质子数为1.由此可知,AgPW11氧化是准可逆的、1电子和1质子转移过程.推测[H3AgI(H2O)PW11O39]3-氧化生成的[H2Ag(H2O)PW11O39]3-可能发生歧化反应,所生成[H3AgOPW11O39]3-进而氧化水放出氧气.

关键词: 水氧化, 电催化, 光电化学, 二氧化钛, 多金属氧酸盐, 银离子配合物

Abstract:

A[H3AgI(H2O)PW11O39]3--TiO2/ITO electrode was fabricated by immobilizing a molecular polyoxometalate-based water oxidation catalyst,[H3AgI(H2O)PW11O39]3- (AgPW11), on a TiO2 electrode. The resulting electrode was characterized by X-ray powder diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Linear sweep voltammetry, chronoamperometry, and electrochemical impedance measurements were performed in aqueous Na2SO4 solution (0.1 mol L-1). We found that a higher applied voltage led to better catalytic performance by AgPW11. The AgPW11-TiO2/ITO electrode gave currents respectively 10 and 2.5 times as high as those of the TiO2/ITO and AgNO3-TiO2/ITO electrodes at an applied voltage of 1.5 V vs Ag/AgCl. This result was attributed to the lower charge transfer resistance at the electrode-electrolyte interface for the AgPW11-TiO2/ITO electrode. Under illumination, the photocurrent was not obviously enhanced although the total anode current increased. The AgPW11-TiO2/ITO electrode was relatively stable. Cyclic voltammetry of AgPW11 was performed in phosphate buffer solution (0.1 mol L-1). We found that oxidation of AgPW11 was a quasi-reversible process related to one-electron and one-proton transfer. We deduced that disproportionation of the oxidized[H2Ag(H2O)PW11O39]3- might have occurred and the resulting[H3AgOPW11O39]3- oxidized water to O2.

Key words: Water oxidation, Electrocatalysis, Photoelectrochemistry, TiO2, Polyoxometalate, Ag+ complex