微波辅助合成非晶态钴掺杂磷酸镍电化学储能电极材料.pdf

第40卷第4期2023年7月新疆大学学报（自然科学版）（中英文）Journal of Xinjiang University(Natural Science Edition in Chinese and English)Vol.40,No.4Jul.,2023Microwave Assisted Synthesis of Amorphous CobaltDoped Nickel Phosphate as Electrode Materials forElectrochemical Energy StorageXIAO Zhenyuan,MA Ruining,LI Yuanyuan,PENG Xiao,CHEN Xin,CHAI Hui(State Key Laboratory of Chemistry and Utilization of Carbon Based Energy Resources,Key Laboratory of Advanced FunctionalMaterials,School of Chemistry,Xinjiang University,Urumqi Xinjiang 830017,China)Abstract:Heteroatom doping has been regarded as an effective route to tune the electronic structure of electrode materialsto achieve enhanced capacitive performance and cycling stability.Herein,cobalt doped nickel phosphate equipped with 3Dflower-like microstructure was successfully obtained by a facile microwave assisted method with follow-up thermal treatment.Subsequently,it was assembled into an asymmetric supercapacitor(ASC)with good electrochemical performance.Interestingly,benefitting from the synergistic and structural effects of cobalt and nickel during calcination,the agglomerated nanoparticlesgradually transform into microscopic flower-like structure with uniform size.Then,a battery-type electrode based on the cobaltdoped nickel phosphate was fabricated and exhibited an excellent specific capacity of 1 214 Fg1at the current density of 1 Ag1due to the increased OHadsorption energy given by the synergistic effect between Ni and Co.Its noted that an outstandingcapacitance retention was delivered(83.9%maintained after 3 000 cycles at 1 Ag1).Furthermore,ASC assembled with thecobalt doped nickel phosphate as the positive electrode and rGO as the negative electrode demonstrates a high energy density of26.25 Whkg1at a power density of 750 Wkg1and outstanding cycling stability.Our results suggest that the design of cobaltdoped nickel phosphate 3D flower-like microstructure owns great prospect for application to hybrid supercapacitor.Key words:Co2+doping;nickel phosphate;microwave assisted synthesis;flower-like microstructure;cycling stabilityDOI：10.13568/ki.651094.651316.2022.05.08.0002CLC number：O646Document Code：AArticle ID：2096-7675(2023)04-0433-011引文格式：萧桢源,马瑞宁,李媛媛,彭筱,陈新,柴卉.微波辅助合成非晶态钴掺杂磷酸镍电化学储能电极材料J.新疆大学学报(自然科学版)(中英文),2023,40(4):433-443.英文引文格式：XIAO Zhenyuan,MA Ruining,LI Yuanyuan,PENG Xiao,CHEN Xin,CHAI Hui.Microwave assisted synthesisof amorphous cobalt doped nickel phosphate as electrode materials for electrochemical energy storageJ.Journal of XinjiangUniversity(Natural Science Edition in Chinese and English),2023,40(4):433-443.微波辅助合成非晶态钴掺杂磷酸镍电化学储能电极材料萧桢源，马瑞宁，李媛媛，彭 筱，陈 新，柴 卉(新疆大学 化学学院 省部共建碳基能源资源化学与利用国家重点实验室 先进功能材料重点实验室，新疆 乌鲁木齐830017)摘要：杂原子掺杂被认为是调节电极材料电子结构以提高电容性能和循环稳定性的有效途径，采用微波辅助的方法，通过后续热处理，成功获得了具有 3D 花状结构的钴掺杂磷酸镍 随后，将其组装成了具有良好电化学性能的非对称超级电容器（ASC）得益于钴和镍在煅烧过程中的协同作用和结构效应，团聚的纳米颗粒逐渐转变为粒径均匀的微观花状结构 作为电极材料在电流密度为 1 Ag1时，由于 Ni 和 Co 之间的协同作用增加了 OH吸附能，所制备材料的比容量达到了 1 214 Fg1 电化学测试进一步表明，在 1 Ag1下循环 3 000 次后，电极的电容保持率达到了 83.9%以钴掺杂磷酸镍为正极、还原氧化石墨烯为负极组装的超电器件在功率密度为 750 Wkg1的情况下，能量密度为 26.25Whkg1，循环稳定性良好 这也表明所设计钴掺杂磷酸镍 3D 花状微结构在混合超级电容器中具有一定的应用前景关键词：Co2+掺杂；磷酸镍；微波辅助合成；花状微结构；循环稳定 Received Date：2022-05-08Foundation Item：This work was supported by the Scientific Research Program of the Higher Education Institution of Xinjiang Uygur AutonomousRegion of China“Construction and electrochemical performance of carbon material/transition metal compounds composite”(XJEDU2019I008).Biography：XIAO Zhenyuan(1996-),male,master student,research fields:supercapacitors,E-mail: Corresponding author：CHAI Hui(1978-),female,doctor,professor,research fields:nano functional materials(especially the design and application ofenergy environment and electrochemical related materials),E-mail:.434Journal of Xinjiang University(Natural Science Edition in Chinese and English)20230IntroductionTo alleviate the energy consumption and environmental pollution,remarkable efforts have been devoted into the designand synthesis of electrode materials for sustainable energy systems12.Supercapacitors,as one of the electrochemical energystorage devices,have attracted great attention for their diverse advantages such as high-power density,outstanding cyclicstability and low cost35.Furthermore,since the electrode material exerts a tremendous influence on the electrochemical property of energystorage devices,the exploitation and research of active materials has become the focus issue67.Various materials havebeen explored as the active materials,for instance,the metal oxides(RuO2,MnO2and Co3O4)810hydroxides(Ni(OH)2,Co(OH)2)1112,sulfides(MoS2,NiCo2S4)1314and phosphides(Ni2P,Co2P)1516show up promising electrochemical per-formances.Among those candidates,transition metal phosphates such as nickel phosphate,cobalt phosphate and nickelpyrophosphates,cobalt pyrophosphates et al.,have been regarded as fascinating electrode materials for supercapacitors dueto their low cost,wide electrochemical window and environmental friendliness,and then attracted the attention of numerousresearchers17.Han et al.synthesized Co3(PO4)28H2O/NF via a hydrothermal method,with a specific capacitance of 1 578.7Fg1at an applied current of 5 mAcm2and remain 72.8%of its initial specific capacitance after 1 000 cycles18.Wang etal.prepared flower-like amorphous cobalt hydrogen phosphate(ACHP)by hydrothermal approach and the ACHP displays aspecific capacitance(411.2 Fg1at 1 Ag1)as well as excellent rate capability(remained capacitance retention of 82.0%at 10Ag1)7.Despite their excellent performance,transition metal phosphate still needs to make more breakthroughs in findingsimpler and more efficient synthesize methods to enhance their cyclic stability and specific capacitance simultaneously.Microwave assisted technique,among many synthesis methods,has attracted much attention in preparing materialswith unique microstructure and properties due to its various advantages such as energy-efficient,environmental-friendly andcontrollable composition1922.In this work,the simple and very efficient microwave assisted approach for the preparationof cobalt doped nickel phosphate precursors was demonstrated,through which different Ni-Co compositions by adjustingthe ratios of Ni and Co controllably were fabricated.The amorphous cobalt doped nickel phosphates were obtained bycalcining the precursors in air at different temperature.Its noted that the amorphous phases or poor crystallinity may exhibitunique physical and chemical properties due to their disordered structures,mechanical/electric isotropy,and defect-richcharacteristics2324.Generally,materials with amorphous phases produce higher capacitance than that of correspondingcrystallized materials tested as supercapacitor electrode.Furthermore,the strain and stress within amorphous materials areisotropic during charging/discharging,beneficial to the long-term electrochemical stability25.As for our work,the as-synthesized amorphous Ni-Co-450 delivers an outstanding specific capacitance of 1 214 Fg1at 1 Ag1and a remarkable cyclic stability of 83.9%after 3 000 cycles.The excellent electrochemical performance wasattributed to the advantageous structural and chemical compositional design of Co2+doped nickel phosphate that led toimproved electrical conductivity,facile electron/mass transport,and desirable OHadsorption capability.Furthermore,theoptimized cobalt doped nickel phosphate(Ni-Co-450)acted as positive electrode was employed to assemble hybrid asymmet-ric supercapacitors device with rGO served as a negative electrode.The device possessed good energy-storage characteristics,including an energy density of 26.25 Whkg1at a power density of 750 Wkg1,and a cycling stability of 80%after 1 000cycles as well as a voltage window of 01.5 V.The results suggest that the transition metal phosphate prepared by facilemethods can serve as a promising candidate electrode material.1Experimental Section1.1Preparation of Flower-Like Microstructure Co-Doped Nickel PhosphateAll reagents in the experiments were analytical grade and used without further purification.First,1.5 mmol of Ni(NO3)26H2O and 1 mmol Co(CH3COO)24H2O were firstly dissolved in 10 mL deionized water(DIW).5 mmol NaHCO3was dis-solved in 20 mL DIW and added dropwise to above solution with continuous stirring for 10 min.Then 2.5 mmol NH4H2PO4was dissolved in another 5 mL DIW and mixed with the above solutions.After 10 min continuous stirring,the as-obtainedsolution was transferred into a 100 mL round-bottom flask and maintained in a microwave apparatus at 80 W,50for 60min,with magnetic stirring and refluxing.After cooling to room temperature naturally,the resultant precipitates were filtratedand rinsed by DIW and ethanol,and subsequently dried at 60for 12 h in air to obtain the products.Different samplesNo.4XIAO Zhenyuan,et al:Microwave Assisted Synthesis of Amorphous Cobalt Doped Nickel Phosphate as Electrode Materials435were fabricated by adjusting the proportion of Co and Ni.These target samples were named as Ni1xCoxprecursors(x isranging from 0.2 to 0.8,e.g.,the Ni0.8Co0.2,Ni0.6Co0.4,Ni0.5Co0.5,Ni0.4Co0.6and Ni0.2Co0.8,representing the products preparedat Ni2+/Co2+ratio of 41,32,11,23 and 14,respectively).Then,the selected Ni0.6Co0.4precursor was annealedin air at temperatures of 350,450,550,650and 750for 30 min.The calcinated products were namedNi-Co phosphates(Ni0.6Co0.4phosphates)and marked with Ni-Co-350,Ni-Co-450,Ni-Co-550,Ni-Co-650 and Ni-Co-750separately.1.2Synthesis of Reduced Graphene Oxide(rGO)In a typical procedure,graphene oxide(GO)was prepared by a modified Hummers method26.The reduced grapheneoxide(rGO)was obtained by reduction of graphene oxide with glycine.100 mg of glycine was gradually added to 36 mLof GO(2 mgmL1)solution with vigorous stirring for 2 h,then the as-obtained suspension was put in a 50 mL teflon-linedstainless-steel autoclave and maintained at 160for 6 h in an oven.The final product(rGO)was obtained by filtering andfreeze-drying for further use.1.3CharacterizationThe crystal structures of the obtained materials were analyzed by X-ray diffraction(XRD Bruker D8,=1.540 6)withCuKradiation.Thesurfacemorphologyofsynthesizedmaterialswascarriedoutusingscanningelectronmicroscopy(SEM,S-4800,Japan).The microstructure and compositional elements were further studied by transmission electron microscopy(TEM,JEM-2100F,Japan)equipped with an electron dispersive spectroscopy(EDS).The X-ray photoelectron spectroscopy(XPS)analyseswereobservedinanESCALAB250XielectronspectrometerusingAlKradiation.Themicrowaveapparatuswas MARS-5,CEM,Discover of USA.1.4Electrochemical MeasurementTo prepare the working electrodes,the active substance,acetylene black and polytetrafluoroethylene(PTFE)binderwere mixed with a weight ratio of 751510 to obtain a homogeneous slurry.Then the slurry was coated and pressedonto a nickel foam(1 cm1 cm)current collector.After drying in air at 60for 12 h,the nickel foam was pressed to bea thin foil at a pressure of 10 MPa.The actual mass loading of active substance in the working electrode was around 3.0mg.The electrochemical performance of the electrodes was then investigated on an electrochemical work station(CHI760E)using a traditional three-electrode system.The nickel foam supported active material was used as the working electrode and aHg/HgO electrode and a platinum foil counter were chosen as reference and counter electrodes with 2.0 mol/L KOH solutionas electrolyte.Electrochemical impedance spectroscopy(EIS)measure at a frequency ranging from 0.1 Hz to 100 kHz.Thespecific capacitance(Cs,Fg1)and specific capacity(C,Cg1)was calculated based on the discharging profiles of GCDusing the formulas(1)and(2).Cs=ItVm(1)C=Itm(2)The discharge current density was expressed with I(A),m(g)corresponds the mass loading of active material withinthe electrode,t(s)represent the discharge time,V(V)represent the discharge potential range.The asymmetric supercapacitor was constituted by Ni-Co phosphates as the positive electrode and reduced grapheneoxide(rGO)as the negative electrode in a 2 mol/L KOH solution using a two-electrode configuration for supercapacitordevice.The mass loading for each electrode was confirmed on the basis of charge balance by the following the formulas(35).Q+=Q(3)Q=CsmV(4)m+m=CsVCs+V(5)Cs(Fg1)represent the specific capacitance,m(g)corresponds mass loading of electrode,V(V)represent the potentialwindowintheprocessofdischarge.Energydensity,E(Whkg1)andpowerdensity,P(Wkg1)ofasymmetricsupercapacitorwere confirmed by the formulas(67).E=CsV27.2(6)436Journal of Xinjiang University(Natural Science Edition in Chinese and English)2023P=E3 600V2(7)Where Cs(Fg1)represent the specific capacitance,V(V)signify voltage window,t(s)corresponds the discharge time.2Results and DiscussionThe patterns with a Ni/Co molar ratio of 32 before calcination have a number of peaks that can be well-indexed toNi3(PO4)28H2O sample(JCPDS PDF No.46-1338)25,and no diffraction peak related to cobalt is monitored in Fig 1(a).Based on the reports concerning the preparation of Ni-based and Co-based phosphate compounds,it can be induced thatthe Ni-rich phosphates are more prone to form hydrates than Co-rich phosphates because Co2+is considerably more stablethan Ni2+10,27.Fig 1(b)shows the XRD patterns of the calcinated products,the Ni0.6Co0.4precursors appear sharp diffractionpeaks.However,after calcinating at 350for 2 h as shown in Ni-Co-350,the sharp diffraction peaks disappears and exhibitsan amorphous phase,and the amorphous phase is still existed as the calcination temperature increases to 450.With thecalcination temperature increasing to 750,the diffraction peak of cobalt appears and well crystallized Co2+doped nickelphosphate can be obtained.Fig 1XRD patterns of(a)samples with different molar ratio of Co2+/Ni2+obtained and(b)Ni0.6Co0.4precursors werecalcinated at different temperaturesThe SEM images show structural information of the samples displayed in Fig 2.And Fig 2(b)demonstrates that thesample calcinated at 350has a flower-like structure for the first time.Raising the temperature makes the Ni2+becomestable from amorphous cobalt doped nickel phosphate.After calcination at 450,the regulation of the flower-like structureis improved,which can be illustrated in SEM images in Fig 2(cd).As demonstrated in Fig 2(d)(calcinating at 450),these flower-like structures are assembled of numerous sheets interweaving with each other and present an average size of23m,indicating that the synergistic effect and structure effect of cobalt and nickel.It has been found that the co-existenceof cobalt and nickel can significantly improve the electrochemical properties of the materials.Because Co2+can optimizethe electro structure and efficiently reduce the resistance due to the rapid of electron transfer,and Ni2+can give a hightheoretical capacitance.Each microflower has a uniform shape which would support easy electrolyte ion diffusion,control ofthe volume expansion/shrinkage during charge/discharge cycling,and encourage fast electro