电解水过程ZnO电极表面氢物种行为的表征.pdf

ARTICLEBehavior Characterization of Hydrogen Species on ZnO Electrode during Elec-trolytic Reduction of WaterLufengYuan,WangyangLi,GuangyuanXu,MengqiWan,ZhenZhang*Key Laboratory of Surface and Interface Chemistry and Energy Catalysis of Anhui Higher Education Insti-tutes,and Department of Chemical Physics,University of Science and Technology of China,Hefei 230026,China(Dated:Received on June 17,2022;Accepted on July 27,2022)The behavior of hydrogenproduction on ZnO elec-trode during the electrolyt-ic reduction of water was in-vestigated by cyclic voltam-metry(CV)and cathodepolarization experimentscombined with in situ Ra-man and photolumines-cence spectroscopy.CV ex-periments indicate that hy-drogen species prefers to diffuse into the ZnO bulk at negative potentials and occupies oxygenvacancies and interstitial sites.Meanwhile,the H2O reduction is self-enhanced during theelectroreduction process,as evidenced by the trace crossing of the CV curves and thechronoamperometric experiment.The influence of the H species on the ZnO electrode duringthe electrocatalytic processes was characterized by the in situ Raman and photoluminescencespectroscopies.These results help us to understand the hydrogen-related catalytic or electro-catalytic processes on ZnO surfaces.Key words:Electrocatalysis,ZnO,Water reduction,Interstitial hydrogenI.INTRODUCTIONZinc oxide(ZnO)is a semiconductor material with adirect band gap of 3.37 eV as well as a large excitonbinding energy of 60 meV at room temperature 1,2.Due to its excellent properties including high electronmobility,good thermal stability,earth abundance andlow cost,ZnO has a wide application prospect in thefields of catalysis 3,conductive films 4,solar cells 5,gas sensors 6,photodetectors 7,and luminescent de-vices 8.The defects,such as oxygen vacancy(VO),intersti-tial Zn(Zni),Zn vacancy(VZn),and even hydrogenspecies,can significantly affect the electrical and opti-cal properties of ZnO 911.Hydrogen is an almostubiquitous impurity in ZnO.The interaction betweenhydrogen and ZnO plays important roles in energy con-version reactions,such as syngas conversion reaction orhydrogen evolution reaction(HER)3,1214.As earlyas the 1950s,Thomas et al.have observed that the elec-trical conductivity of ZnO crystals increased after hy-drogen diffusion 15.In addition,density functionaltheory calculations by van de Walle and Janotti 16,17have predicted that hydrogen can act as a shallowdonor,which is possibly related to the n-type behaviorof ZnO.So far,three kinds of hydrogen states have beensuggested in ZnO crystals 18:(i)the interstitial H *Author to whom correspondence should be addressed.E-mail:CHINESE JOURNAL OF CHEMICAL PHYSICSVOLUME 36,NUMBER 3JUNE 27,2023DOI:10.1063/1674-0068/cjcp2206100313 2023 Chinese Physical Society(Hi),which is bound to the lattice oxygen 16;(ii)thehydrogen attached to defects,such as hydrogen at theoxygen vacancy(HO)10,1922;(iii)the loose hydro-gen as interstitial H2 in the lattice of ZnO 23,but thiskind of hydrogen is uncommon.In most of the published works,hydrogen is general-ly introduced into ZnO films by exposing to H2 atmo-sphere,hydrogen plasma treatment,or hydrogen ionimplantation at high H2 pressure and high tempera-tures.The electrochemical doping of hydrogen into ZnOprovides a simple strategy without requiring stringentexperimental conditions.For example,ek andLuket et al.18,24 reported that hydrogen was elec-trochemically introduced into single ZnO crystals.Windisch et al.21 reported that hydrogen diffused in-to ZnO during electrochemical polarization in aqueoussolution at 25 C.However,the behavior of hydrogenspecies on ZnO electrode during electrochemical treat-ment has not been well clarified.In this work,we intro-duced hydrogen species into ZnO by cathodic reductionand investigated the behavior of hydrogen species onZnO electrode during the electrolytic reduction of wa-ter.II.EXPERIMENTSA.Preparation of ZnO electrodeThe ZnO electrodes were prepared by the doctorblade technique on the fluorine-doped tin oxide(FTO)conducting glass(size:10 mm20 mm2.2 mm,Shen-zhen Rigorous Technology Co.,Ltd.).The FTO glasswas cleaned by acetone,ethanol,and deionized water insequence and dried in air.0.4 g ZnO powder(Sinopharm Chemical Reagent Co.Ltd.,99.99%)wasground and mixed with 0.83 mL ethanol under vigorousstirring to prepare the ZnO slurry.Then 0.01 mL of theabove prepared ZnO slurry was uniformly coated on theFTO.The electrode was dried and annealed at 673 Kfor 60 min at a heating rate of 2 K/min in air.B.Electrochemical measurementsAll electrochemical measurements were performed atroom temperature in 0.5 mol/L Na2SO4 aqueous elec-trolyte with a computer-controlled CHI 660E potentio-stat(CH Instruments).A standard three-electrode cellwith the ZnO/FTO sample as the working electrode,aPt electrode as the counter electrode,and a Ag/AgClelectrode as the reference electrode were used in theelectrochemical studies.All measured potentials(E(Ag/AgCl)were converted to r