理论模型在贮氢合金研究与发展中的应用（稀有金属材料与工程论文）

理论模型在贮氢合金研究与发展中的应用（稀有金属材料与工程论文） 第36卷xx在第11期l1月稀有金属材料与工程RARE METALMATERIA【S ANDENGn EERINGVo136No11NovemberxxApplication ofTheoretical M odel in Research andDevelopm entof HydrogenStorage AlloyDong Xiaoping，-，Ln Fanxiu，Zhang Yanghuan，Quan Baiyun，Wang Xinlin(1University ofScience andTechnology Beijing，Bei jing100083，China)(2Central Iron and SteelResearch Institute，Bei jing100081，China)(3Science andTechnology University of Inner Mongolia，Baotou014010，China)AbstractThe research of theoretical model inhydrogen storage alloy waspresented inthis paperThe relationsbetween electronic structure and stability of the hydride，thermodynamic investigationand electrode reaction mechanismwere summarizedin detailApplying the theoretical modelseffectively inthe researchof hydrogen storage alloyswill greatlyaelerate theprogress ofresearch andindustrialization inthis areaKey wordshydrogen storage alloy；electronic structure；thermodynamics；electrodereaction；model CLCnumberTG139Document codeAArticle1002-185X (xx)11-1881-05l Intr0ducti0n Hydrogenstorage alloyas negativeelectrode of the NiM Hbattery is a keymaterial for the developmentof NiM HbatteryA vastamount ofexperiences as well asexperim entaldata havebeen aumulatedthrough research and developmentf orover40yearsResearchers alreadyestablished sometheoretical modelto describe structure andproperty of hydrogen storage alloy,and put forward thecorresponding formula_lJA scientifictheoretical model can provideguidance f o roptimizing bothpositions andperfor m ances inthe practicalproduction of the alloys，and areference f or theresearch jnthjs area2Application ofElectronic StructureModelThe alloyshaving samestr ucture differobviously fromeach otherin theirperf o rmances of hydrogen absorptiondesorptionIn order to disclosethese differencesChen et al appliedquantummechanical SCFXo-SW methodto theresearchof the electronic str ucturesof RENi5(RE=La，Ce，Pr，Nd)alloysThe results showed thatclosedshell5s and5p。 electrons ininner REatom couplewith outershell electronsof theother elements，and thecoupling influencesgreatly thestr uctu ralvalence bondsandstability of theRENi(RE=La，Ce，Pr，Nd)alloys，for m ing amore relaxedand stablef ramework whichcan absorbhydrogen atomsThe studyalso revealedthat Fermilevel Ef is relatedt0hydrogenation plateau，ie，the smallerthe Ferm ilevel El,the lowerthe pressure of the hydrogenation plateau，the easierf o rthehydrogen atomto enterinto interstitialposition and，as aconsequence，the morestable the hydride beesThe substitutionof Pr and Ndf or La wouldreduce Ef and weakenthe anisotropyof LaNi alloyConsequently,the bondingforces among atoms werereinforced alongver ticalto latticeaxis cand weakenedalong thec axis，which mightslightly afect thehydrogenation proper tyof the alloyM ali et al_jJ calculated the electronicstr ucturesof NdNi4Jl(M=Nd，Cr，Mn，Fe，Co，Cu，Ni)by SCFXnSW method，and establishedthe relationsbetween electronand ahydrogenation proper tyof the alloyBecause Cr and Cuare liableto loseelectrons pared withNithe Fermilevel Ef of theNdNi4Cr and NdNi4Cu alloyswere lessthan those of theN dNi4M nandNdNi4Co alloys，respectively，while thepressure of thehydrogen absorption plateauof theNdNi4Cr，NdNi4Cu alloyswere higherthan thoseOf NdNiaM nandNdNi4Co alloysTheref o re，it wasbelieved thatEfandcharge numberstransfe redwas relatedto the stability of hydrideYakim aet alE，J investigated the relationsbetween the stability of the alloyand bindingforces among atoms Receiveddataxx1215Founf ionItemSupposed byNational NaturalScience Foundationsof Chinar50642033)；Key TechnologiesR&D Programof Inner Mongolia (xx0205)and collegescientific researchproject ofinnermongolia(nj05064)biographydong xiaoping，candidate forphd，school of mater ialscience andengineer ing，university ofscience andtechnology beijing，beijing100083，p rchina,tel0086-10-62184609，e-maildxp03161631882稀有金属材料与工程第36卷in octahedronstructurestru cture of the hydridefor lani5alloy，the crystalwas the same asthat of the originalalloythe bindingforce betweenla atom and ni atom wasstrengthened，and that of among ni atoms weakenedin octalqledral interstice，which reducedthe stability of the hydride；and sodid thehyd rides of the tife，zrm n2alloysfor m g2ni alloy,cr ystal stru cture of its hvdridechanged fromits originalf o rll af ter absorbinghyd rogen，and t hestabilityoft hehydride was controlledby bindingforces ofm-m g and hhoweverthe bindingforce ofh playedan importantrole inthe stabilityof them g2nih4，and sodid v-based hyd r ogenstorage alloyguoin et al。 ，calculated the electronicstructureof theLaNi4朋(M=Ni，Cu，Mn，AI)and theirhydride byusing t he self-consistentcharge discretevariational Xdmethod(sD、LXd)(The atomcluster modelis shownin Fig1(a1，and analyzed the inf luence of electronicstructure onhyd r ogen absorptionpropertyThe obtainedresultsshowed that thestabilityof LaN MH6hyd ridewascorrelated to the charget ransferof hydrogen atomThe reductionof chargenumber enteringinto H l swould decreasethestabilityofhyd rideThe greaterthe bondingf orce betweenthe4f orbit ofLa atom and4p orbitof Ni (1)，thestronger theirbonding capabilityThe3d orbitof Nif31f ormedan nonstable chemicalbond with4f electronorbitofLa atom along c axis resulting in fracture after hydrogenabsor ption，which mightcause pulverization after repeating hydrogenabsor p tiondesor ptionIn LaNisH6hydride，H atom was not bond with Laatom，but Ni4p electronformed covalentbond withHls electronorbit throughdelocalization，but the covalentbond wasrather weakand was favorable forreleasing hyd r ogen atomLin et al obtainedthesameresults forLaNi5alloy byusing first-principles DVMmethodIn addition，delocalization bondingalso ou red betweenNi andLa atoms，but hydr ogenatom weakenedthe bondingf orceThe expansion of latticevolume ofthe alloyled toan outwardmotion f orLaatomalonga axis，and theexpansion alonga axiswas more than that of alongcaxisbecause H atomwasnotbondwithLaatomFor Mg2NiH4hyd ridethe atomcluster modelis shownin Fig1(b)】，the highreleasing hydrogentemperature forM g2Ni alloy was ascribedto strongbonding function between Hatomand Ni atomIt can be seenfrom thedistance amongatoms in M g2NiH4hydridethat thedistance between H andNi atomswas shorter than that ofbetweenHand M gatoms，and the bonding lengthbetween M gandNi atoms forMg2NiH4hydride waslonger thanthat betweenMgandNiatomsf or Mg2Ni alloytThis showed that theHatomwas moreinclined toapproach Niatom；and thebondingintensit yofMgNi bondwas decreasedand sodid theproperty ofabsorbingreleasing hyd rogenOn theot herhand，23positions insix latticepositions aroundNiatomwere randomlyoupied byhydrogen atoms，resultingincer tain distor tionof intersticea roundNiatomAs aconsequence，lattice expansionouredcausing anisotropy after hydrogenabsor ption，which mightbe the reasonf orpulverizationafter hydrogenabsor ptionaswellas f or theproperty degradationLONi (1)Ni (2)0Ni (3)Ni OMgH OLa OH(a)LaNisH6(b)Mg2NiH4Fig1Cluster model applied inthe calculation3Application ofTheoretical Model inTherm odynamics and Dynamics Recently,som emodels havebeen developedto auratelyand effectivelyinvestigate thethermody-namicsanddynamics ofthe alloyelect rodesFang et alt【I1presented semiempirical mathematicm odelto pre-dict the generating enthalpy,P-C-T curveand hysteresis of AB2type hydrogen storage alloyIts generating enthalpyH wasexpressed bythe followingrelations AH=-R107l04_42710(+22510-I24110(ea)1 (1)where Ris gasconstant，8314JmolK；is squareof electronegativity difference；is squareof atom size andea iselect ron densityThe authorst udiedthehysteresis ofthe Zr(Fe075Cr025)2hydrogen storagealloyIts expressiveequation wasas followsRTlnP尸d=772l03_1816T+5665CLcm)-，0OI6T(C-Ur n) (2)where Pa is hydrogenabsor ption plateau pressure，Paishydrogenabsor ptionplateau pressure，C is hydrogen contentand Cmishydrogencontent ofplateau pressurem iddlevalue inp-CT curveIt canbe derivedfrom equation (2)that thehysteresisofthe alloyis afunction oftemperat ureand absorption contentduring thehydrogenabsorptionj them iedemamodel for heatformation is a main第11期dong xiaopinget alapplication oftheoretical model inresearchand developmentofhydrogen storagealloy1883result ofalloying theoryrecently l2】based onthis model，zheng qu al】investigated theeffects ofchemical patibleforce，atom size，electron densityfactors on the energyofthe alloythe authorsobtained anoptimum regression equation byapplying thefull regressionanalysis methodto thegathered experimentaldatathe optimumregressionequationcanbeestablished as follows ah=一98277611033(axf-2390l+5397l(ea)23009459 (3)Table1Comparison betweencalculated andexperimental valuesofH forhydrides ofMg2Nia Mx alloys Aording to equation (3)，the enthalpyvariation ofhvdrO2enizatiOn reactionwas calculatedfor Mgbased alloyand paredwith experimentresult inthe table1It canbe derivedfrom thetablel that there isno majordifference betweenthe calculatedvalue and the experimentalresultAordingtohydrogen releasingplateaupressureofthe TiFe M(M=Co，Zr，Mn，V，Cr，A1)system alloysWu et al_】41established mathematicmodel forstandard mole enthalpy ofdehvdro2enization reactionby stepwiseregression methodThe standardmoleenthalpyis calculatedas follows=一334981-332511l0。 r+854202l0+280458(e (4)The estimatedvalue isin goodaord withthat ofexperiment bythis mode1Luo et al，】calculatedthe generating enthalpies of binary alloy systemLaNiM andternar yalloy systemLaNi5-x坛(M=Co，Mn，Al，Cr，Fe，Cu)For binaryalloy systemthe calculationresults matchedwell withthoseofexperiment inthe rangewhere ismore than70For ternaryalloysystem，the generatingenthalpiesofLaNi5Mxalloysincreased slightlywith the addition ofM n，Co，Cr，Fe and Cu elements，respectively,and theeffects ofadding Mn，CrandFe on thegeneratingenthalpies wasmorethanthatofadding CoandCuelementsBut theaddition ofAl elementobviously decreasedthegeneratingenthalpy ofthe alloyIt canbe derivedfrom literatureI7,18】and theabovementioned resultsthat electrOne2ativitV，electron density，atom sizefactors slightlyinfluencegeneratingenthalpyH ofthehydrideThe sequenceof theseparameterscontribution toH iselectron densityelectrone-gativityatomsizeTherefore，the energyvariation ofthe hvdro2enization mainlyarises f rom thevariation ofFermi energy,chemical patibleenergy andelastic strainenergy factorsM linOvaet al】predicted theeffect ofalloy elementonthe amount of hydrogen storage，hydrogen releasing temperature andpressure inMgbased alloyby adoptingartif icialnerve workmode1The resultsshowed that theadditionof otheralloy elementsexcept A1element decreasedtheamount of hydrogenstorage for Mgbased alloy，and theamountof hydrogenstorage increased withincrease ofAl contentYi，Ce，Si elementslowered hydrogenreleasingtemperatureofthe alloy，enhanced hydrogenreleasing pressure，but theeffect forLi，A1elements isreverseOn thebasis ofspherical coreshrink model，Cui et alt20investigatedthediffusion of hydrogen atom inMg，Ni alloy,the resultsshowedthatdiffusion coef-f icientofhydrogen atom ind phasewas largerthanthatofhydrogenatominphase hydride，because whenthe alloy electrode wascharged，the formationof phasehydride delayedthe transmissionofhydrogen，impeding alloys furtherhydrOgenizatiOn，and leadingto itsinplete chargestateAs aresult，there wasa ratherlow electrochemicalcapacity inMg2NialloyBy DV-Xd Molecular orbitalmethodYukawa et al【,221studied theinteraction mechanismofhydrogenabsorption elementsA(La，Yi，Mg)and catalyticelements B(Ni，Fe)In thecase ofcoexistence ofA and B elements，hydrogenatomandBelement adsorbedeach othermore tightly4ApplicationofTheoretical ModelinProcess ofAlloy ElectrodeReaction Thehigh electrochemicalperformances ofthe alloyslink directlywith theirpractical usesThe establishmentof theoreticalmodel willaelerate mechanismresearch for the alloy electrodereactionZhu et alt Janalyzedthe maximum discharge capacity ofthe AB5type1。 (ninti)5alloys(where aisarandom binationof twooftheelements ofla，ce，prandnd)the resultsshowedthat the maximumdischarge capacity ofthe alloywascorrelated with4fl884稀有金属材料与工程第36卷electron densityn4e are(where n4e areis theratio ofits total4felectron numberof rareearth elementand itsatom number)as shownin fig2it canbe seenf romfig2thatthecurve of dischargecapacit y forthe alloyof ne4fnare fig2relation betweenthe maximumdischarge capacitycmax andthe4f electronioncentration ne4fhare thesame n4elnare ina sideis similar to thatofn4e areva riation，and thereisamaximum anda minimumwhen n4eln areis10and20，respectivelyzhang et al utilizedthe activationcha racteristicfactor8and capacit y decayfactor ato describethe intrinsicattribution ofhydrogenstoragealloythe larger the8value，the easierthe alloyis toget activated；the larger thea value，the largerthecapacitydecay ofthealloythis resultwas validatedwell inthe experimentof acti-vation andchargingdischa rgingfortheti026zr007v021一m n01ni033cro03，tio26zr007v019m n0ini033cro05alloysm eanwhile，an electrochemical modelfor ti-mnbased hydrogenstoragealloywas alsoputforwa rdbecause theoxidation andcorrosion aresimultaneous onthe surfaceofthealloy,which isdi fi cultforanalysis，the authorsdevised threehypothesizes inordertosimplify themodel andthe derivationprocedure，these hyp o-theses areasfollows (1)at onepart ofthealloysurface abad oxidationtakes place，while theother surfaceis highlyco roded； (2)once theoxide film forms，hydro-genatomcan onlypass through thecor rosionarea； (3)charge currentdensit yis equaltothatofdischa rgeOn thebasis ofthese hypotheses，authors gavethe expres-sionofcycling stability curve C一c一爿J)n-1一rr (5)I C?l一一+f_L丧j一It canbe madeout fromfor mula (5)thatthecapacityofthealloyis relatedto thefollowing parameters，iethemaximumcapacityofthealloy C巾“，temperature bindingenergy Ecbetween alloyand hydrogenatom，chargecu rentI。 charge timet，alloy mass m，activation frequency no，oxidation zoneklkl+k2，co rosionzone I+，average corosion velocity,thevariation dimen-sional constantcoe fi cientG，L，a nd proportioncoe fi-cient andso onXu】et alsimulated polarization curve ofalloyelectrodeaording toelectrochemical basicpr incipleOn thehypotheses thatother parameterswere constant，the authorslooked intothee fects of temperature，exchange cu rent，di fusioncoe fi cient，and energy transmission coe fi cient onpola rizationper formanceofthealloyT heincreaseoftemperaturedecreased pola-rization perfor manceofthealloyAs the temperatureincreased，polarization over-potential wasenha nced atthe inva riable polarizationcu rent，while thepolarization curent decreasedattheinvariable over-potentia1The polarizationperformance wasobviously improvedas theexchange curent increased，and polar izationcurrent increasedat invariablepolar izationpotentia1The feature oftheefectoflimit curent ondi fu sionpolari-zation wasasfollowsThe Polarization decreasedwi也the increaseof limitcurentThe energytransmission coeficientinf luencedboth diffusiona nd electrochemical processesAfter energytransmissioncoeficient deviatedfrom05，electrochemical polarization，a nd concentrationdi ferencepola rizationsdeter ioratedobvi-oussly,andthelinear areaofelectrochemical polari-zation reduced，which producedbad efect tomeasRre exchangecurentby linearmethod5Sum mary GreataRention hasbeen paidtothetheoretical research inthis area，but theresearch isstill inits primarystage，and lackof profoundlysystemic st udyVa rioustheoretical modelspresent somechallenges inresearchandapplication；therefore，theoreticalmodelstudyofhydrogenstoragealloyis oneof promising，brand-new research emphasisT hetheoreticalmodelcanbeused toinvestigate systemicallythe mechanismof elementsfunction，their synergisticaction andthe influence ofstruct ureonthepropertyofthealloy,optimize theponent ofthealloy,and gainchampion propertyforhydrogenstoragemateria1References【1】Yukawa Het a1Computational Materials Science，1999，1429l【2】Chen Ling(陈宁)et a1Chinese ScienceBulletin(科学通报)【J，1995，40 (24)2234【3】ma li(马丽)et a1journal ofthe chineserare earths昱ilg一11dongxiaoping etalapplication oftheoreticalmodelinresearchanddevelopment ofhydrogenstoragealloy1885society(国稀土学报)j，2000，18 (1)4