物理化学学报 >> 2021, Vol. 37 >> Issue (11): 2007067.doi: 10.3866/PKU.WHXB202007067

所属专题: 能源与材料化学

通讯 上一篇    下一篇

石墨烯膜质子传输巨大光效应的微观机理

关黎明1, 郭北斗1,2, 贾鑫蕊1,2, 谢关才1,2, 宫建茹1,2,*()   

  1. 1 国家纳米科学中心,中国科学院纳米系统与多级次重点实验室,中国科学院纳米科学卓越创新中心,北京 100190
    2 中国科学院大学,北京 100049
  • 收稿日期:2020-07-25 录用日期:2020-09-07 发布日期:2020-09-11
  • 通讯作者: 宫建茹 E-mail:gongjr@nanoctr.cn
  • 作者简介:第一联系人:

    These authors contributed equally to this work.

  • 基金资助:
    中科院战略重点研究项目(XDB36030000);国家自然科学基金项目(21422303);国家自然科学基金项目(21573049);国家自然科学基金项目(21872043);国家重点研发项目(2016YFA0201600);北京自然科学基金项目(2142036);中国科学院青年创新促进会及中国科学院“一带一路”专项资助

Microscopic Mechanism on Giant Photoeffect in Proton Transport Through Graphene Membranes

Liming Guan1, Beidou Guo1,2, Xinrui Jia1,2, Guancai Xie1,2, Jian Ru Gong1,2,*()   

  1. 1 Chinese Academy of Sciences (CAS) Center for Excellence in Nanoscience, CAS Key Laboratory of Nanosystem and Hierarchy Fabrication, National Center for Nanoscience and Technology, Beijing 100190, China
    2 University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2020-07-25 Accepted:2020-09-07 Published:2020-09-11
  • Contact: Jian Ru Gong E-mail:gongjr@nanoctr.cn
  • About author:Jian Ru Gong, Email: gongjr@nanoctr.cn; Tel.: +86-10-82545649
  • Supported by:
    the Strategic Priority Research Program of CAS(XDB36030000);the National Natural Science Foundation of China(21422303);the National Natural Science Foundation of China(21573049);the National Natural Science Foundation of China(21872043);the National Basic Research Plan, China(2016YFA0201600);the Beijing Natural Science Foundation, China(2142036);the Youth Innovation Promotion Association and the Special Program of "One Belt One Road" of CAS

摘要:

单层石墨烯已被证明对质子是可渗透的,而对其它原子和分子不可渗透,这一特性在燃料电池和氢同位素分离等方面具有潜在的应用。Geim等人报道了催化活化石墨烯膜质子传输的巨大光效应。其实验表明,光照和具有催化活性金属纳米颗粒的协同作用在这种光效应中起关键作用。Geim等人认为巨大光效应是由金属纳米颗粒和石墨烯之间产生的局部光电压引起的。局部光电压将质子和电子传送至金属纳米颗粒以产生氢气,同时将空穴排斥使之远离。但是,根据静电场理论,这种解释并不能令人信服,并且在他们的工作中也没有此效应的微观机理分析。我们在此文中提出了一种该现象背后的确切微观机制。对于具有半金属性质的石墨烯,光激发的大多数热电子会在皮秒时间内驰豫到较低的能态,而发生化学反应所需的时间一般为纳秒范围。因此,在单一石墨烯的情况下,入射光激发的热电子在与透过石墨烯的质子反应之前就已驰豫到较低的能态。当用金属粒子修饰石墨烯时,由功函数不同引起的电子转移会导致界面偶极子的形成。当金属为可与石墨烯具有相互强烈作用的Pt、Pd、Ni等时,就会形成局部偶极子。质子将被俘获在局部偶极子的负极周围,而电子则被俘获在正极附近。在光照射后,被俘获的电子会被激发到具有更高能级的亚稳激发态。处于高活化能的亚稳激发态的自由电子具有更长的寿命,使得它有更充分的时间与透过石墨烯的质子发生化学反应。对光照情况下高能电子的浓度的计算结果显示,光照越强时被激发到激发态的电子越多。根据本文的分析,质子通过催化活化石墨烯膜的巨大光效应归因于较长寿命的热载流子和快速的质子传输速率。因为这一反应的活化能没有变化,所以金属催化剂是通过增加反应物之间成功碰撞的次数来增大反应速率,从而产生显著的光效应。该工作可能揭示了催化剂在提高光(电)催化反应效率方面的一种新微观机制。

关键词: 石墨烯, 质子传输, 偶极, 热电子, 氢气

Abstract:

Graphene monolayers are permeable to thermal protons and impermeable to other atoms and molecules, exhibiting their potential applications in fuel cell technologies and hydrogen isotope separation. Furthermore, the giant photoeffect in proton transport through catalytically activated graphene membranes was reported by Geim et al. Their experiment showed that the synergy between illumination and the catalytically active metal plays a key role in this photoeffect. Geim et al. suggested that the local photovoltage created between metal nanoparticles and graphene could funnel protons and electrons toward the metal nanoparticles for the production of hydrogen, while repelling holes away from them, causing the giant photoeffect. However, based on static electric field theory, this explanation is not convincing and the work lacks an analysis on the microscopic mechanism of this effect. Herein, we provide the exact microscopic mechanism behind this phenomenon. In semi-metal pristine graphene, most photon excited hot electrons relax to lower energy states within a timescale of 10−12 s, while the typical timescale of a chemical reaction is 10−6 s. Thus, hot electrons excited by incident photons relax to lower energy states before reacting with protons through the graphene. When graphene is decorated with metal, electron transfer between the graphene and the metal, induced by different work functions, would result in the formation of interface dipoles. When using metals such as Pt, Pd, Ni, etc., which can strongly interact with graphene, local dipoles form. Protons are trapped around the negative poles of the local dipoles, while electrons are around the positive poles. Upon illumination, the electrons are excited to metastable excited states with higher energy levels. Due to the energy barriers around them, the free electrons in the metastable excited states will have a relatively longer lifetime, which facilitates the production of hydrogen through their effective reaction with protons that permeated through the graphene. The concentration of high-energy electrons under illumination was estimated, and the results showed that more electrons are energized to the excited state with strong illumination. According to the analysis, the giant photoeffect in proton transport through the catalytically activated graphene membrane is attributed to long-lived hot electrons and a fast proton transport rate. Since there is no change in the activation energy of the reaction, the metal catalyst increases the rate of the reaction by increasing the number of successful collisions between the reactants to produce the significant photoeffect. This might lead to a new microscopic mechanism that clarifies the role of the catalyst in improving the efficiency of photo(electro)catalytic reactions.

Key words: Graphene, Proton transport, Dipole, Hot electron, Hydrogen

MSC2000: 

  • O649