物理化学学报2021，Vol.37Issue(11)：12-18,7.DOI:10.3866/PKU.WHXB202007067
石墨烯膜质子传输巨大光效应的微观机理
Microscopic Mechanism on Giant Photoeffect in Proton Transport Through Graphene Membranes
摘要
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.关键词
石墨烯/质子传输/偶极/热电子/氢气Key words
Graphene/Proton transport/Dipole/Hot electron/Hydrogen分类
化学化工引用本文复制引用
关黎明,郭北斗,贾鑫蕊,谢关才,宫建茹..石墨烯膜质子传输巨大光效应的微观机理[J].物理化学学报,2021,37(11):12-18,7.基金项目
The project was supported by the Strategic Priority Research Program of CAS(XDB36030000),the National Natural Science Foundation of China(21422303,21573049,21872043),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.中科院战略重点研究项目(XDB36030000),国家自然科学基金项目(21422303,21573049,21872043),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 （XDB36030000）
