催化学报 ›› 2020, Vol. 41 ›› Issue (8): 1161-1167.DOI: 10.1016/S1872-2067(20)63543-4

• 快讯 • 上一篇    下一篇

通过拉伸应变调节Ru@RuO2核壳纳米球中Ru(IV)的电荷密度并应用于酸性环境电解水产氧

闻益智, 杨韬, 程传祺, 赵雪茹, 刘恩佐, 杨静   

  1. 天津大学材料科学与工程学院新能源材料研究所, 先进陶瓷与加工技术教育部重点实验室, 天津 300072
  • 收稿日期:2019-11-11 修回日期:2019-12-11 出版日期:2020-08-18 发布日期:2020-08-08
  • 通讯作者: 杨静
  • 基金资助:
    国家自然科学基金(51572188,51822106).

Engineering Ru(IV) charge density in Ru@RuO2 core-shell electrocatalyst via tensile strain for efficient oxygen evolution in acidic media

Yizhi Wen, Tao Yang, Chuanqi Cheng, Xueru Zhao, Enzuo Liu, Jing Yang   

  1. Institute of New-Energy Materials, Key Laboratory of Advanced Ceramics and Machining Technology of Ministry of Education, School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China
  • Received:2019-11-11 Revised:2019-12-11 Online:2020-08-18 Published:2020-08-08
  • Supported by:
    This work was supported by the National Natural Science Foundation of China (51572188, 51822106).

摘要: 水作为一种储量巨大且可循环利用的资源,可以被电解槽电化学分解为清洁的氢能和化学品氧气,从而实现环境友好的能源循环.与碱性电解槽相比,质子交换膜(PEM)电解槽具有明显优势,例如更高的电流密度、更高的电压效率、更低的欧姆损耗和更少的不利反应,使其成为生产氢能和氧气的最有希望的装置.作为电化学水分解的半反应之一,氧析出反应(OER)过程是一个四电子和四质子耦合的多步电化学反应,与双电子转移的氢析出发应(HER)相比,需要更高的能量来补偿缓慢的动力学过程.PEM电解槽中高的阳极电势和苛刻的腐蚀环境为阳极电催化剂设定了更高的选择标准,同时由于缺乏高活性和高稳定性的阳极电催化剂,限制了PEM电解槽的广泛应用.在这种条件下,适用的阳极电催化剂主要局限于钌(Ru)和铱(Ir)及其衍生物,因为其固有的电子结构使之具有较高的催化活性.然而,由于Ir的低地球丰度和高成本,人们更希望开发RuO2基电催化剂.遗憾的是,商业RuO2电催化剂在酸性介质中的OER过电位仍然过高,稳定性也比在碱性介质中低得多,无法满足实际应用的要求.此外,从实用角度出发,研究者始终希望提高贵金属Ru基电催化剂的本征活性以减少实际应用所需的催化剂量.因此,迫切需要改性RuO2基电催化剂以提升其在酸性介质中的析氧反应催化活性.
迄今,研究已经证实活性中间体*OOH的形成是酸性介质中OER的速率决定步骤(RDS),但是RuO2基催化剂中Ru4+活性位点对活性中间体*OOH的吸附过强,导致商用RuO2具有约300mV的过电势(10mA cm-2).为了减弱*OOH在Ru4+活性位点上的吸附能并降低RDS能垒,研究人员做了大量的试验来调节Ru4+活性位点的电子结构,包括杂原子掺杂和制备Ru基固溶体.应变效应也是调整合金催化剂电子结构的有效策略.在RuO2中利用应变来调节Ru4+活性位点的电子结构进而增强其在酸性介质中的OER催化活性是一种简便的手段,但是形成稳定的应变而不引入任何杂原子仍然是一个巨大的挑战.
本文首次在不掺杂任何杂原子的情况下,采用一步激光辐照法合成了高效的Ru@RuO2-L电催化剂,利用Ru@RuO2核壳纳米颗粒RuO2壳层的拉伸应变,有效调节了Ru4+的电荷密度,其本征活性显著增强,酸性水氧化的过电位大大降低,远远低于商用RuO2催化剂.X射线精细吸收结构(XAFS)显示Ru-O键中存在6%的拉伸应变,X射线光电子能谱(XPS)和电子能量损失谱(EELS)表明Ru4+的价态明显增加.Ru@RuO2-L催化剂在酸性电解液中表现出191mV的极低过电位(10mA cm-2),这是迄今为止报道的不借助杂原子修饰的高效Ru基电催化剂的最低值,其面积比活性和质量比活性分别比商用RuO2催化剂高4倍和18倍.当使用Ru@RuO2-L作为阳极催化剂在酸性电解液中进行整体水分解时,双电极系统只需要1.45V的极低的外加电压使系统达到10mA cm-2电流密度.酸性析氧活性的大幅度提高归因于由拉伸应变引起的Ru4+电荷密度的降低,从而削弱了*OOH在RuX+(4 < X < 5)活性位点上的吸附能.

关键词: 拉伸应变, 核壳结构, 钌氧化物, 电荷密度, 析氧反应, 酸性介质

Abstract: The design of efficient Ru-based electrocatalysts with high intrinsic activities for acidic water oxidation is highly desirable and challenging for water splitting in proton exchange membrane electrolyzers. Here, for the first time, we engineer the charge density of Ru(IV) by creating tensile strains in the RuO2 shell of Ru@RuO2 core-shell nanoparticles, viz. Ru@RuO2-L. High-resolution spectroscopic characterizations confirm the presence of av. 6% tensile strain in Ru-O bonds, which results in an effective reduction of the Ru(IV) charge density. The resultant RuX+ (4 < X < 5) active sites greatly accelerate the oxygen evolution reaction (OER) in an acidic electrolyte, leading to a remarkably low overpotential of 191 mV at 10 mA cm-2. These values are lower than those for the benchmark RuO2 catalyst and are also among the lowest for efficient Ru-based electrocatalysts reported thus far. The specific activity and mass activity are also greatly enhanced 4.2-fold and 17.7-fold compared to those of RuO2, respectively. The acidic OER activity improvement is ascribed to the lowered adsorption energy of *OOH, owing to the reduced charge density of Ru(IV), and the rapid charge transport owing to the Ru core. Ru@RuO2-L also demonstrates high feasibility as the anode catalyst for the overall water splitting in acidic media.

Key words: Tensile strain, Core-shell structure, Ruthenium oxide, Charge density, Oxygen evolution reaction, Acidic media