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金属腐蚀_燃料电池(天津大学)

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金属腐蚀_燃料电池(天津大学) 1 11 Atkins E 25.6(a)Atkins E 25.6(a) zz By SI regulations, the chemical reaction in case By SI regulations, the chemical reaction in case can note as:can note as: 2C+3D2C+3D--2A2A--B=0, where B=0, where vvAA==--2, 2, vvBB==--1, 1, vvCC=2, =2, vvDD=3=3 zz The r...
金属腐蚀_燃料电池(天津大学)
1 11 Atkins E 25.6(a)Atkins E 25.6(a) zz By SI regulations, the chemical reaction in case By SI regulations, the chemical reaction in case can note as:can note as: 2C+3D2C+3D--2A2A--B=0, where B=0, where vvAA==--2, 2, vvBB==--1, 1, vvCC=2, =2, vvDD=3=3 zz The rate of formation in case isThe rate of formation in case is zz That means the rate of formation / consumption That means the rate of formation / consumption for each participant:for each participant: zz consumptionconsumption A:1.0 mol LA:1.0 mol L--11 ss--11 ; B:0.5 mol L; B:0.5 mol L--11 ss--11 ;; formationformation D:1.5 mol LD:1.5 mol L--11 ss--11 ; ; rate of reaction 0.5 mol Lrate of reaction 0.5 mol L--11 ss--11 1 1 1 1 [ ] [ ] 1 [ ] 1 [ ] 2 2 3 [ ]: 1.0 i i dcd d A d B d C d D dt v dt dt dt dt dt d Cin case mol L s dt ξ − − −= = = − = = = 22 Atkins E 25.6(b)Atkins E 25.6(b) zz By SI regulations, the chemical reaction in case By SI regulations, the chemical reaction in case can note as:can note as: C+2DC+2D--AA--3B=0, where 3B=0, where vvAA==--1, 1, vvBB==--3, 3, vvCC=1, =1, vvDD=2=2 zz The rate of formation in case isThe rate of formation in case is zz That means the rate of formation / consumption That means the rate of formation / consumption for each participant:for each participant: zz Consumption A:0.333 mol LConsumption A:0.333 mol L--11 ss--11 ;; formation C:0.333 mol Lformation C:0.333 mol L--11 ss--11 ; D:0.666 mol L; D:0.666 mol L--11 ss--11 ;; rate of reaction 0.333 mol Lrate of reaction 0.333 mol L--11 ss--11 1 1 1 [ ] 1 [ ] [ ] 1 [ ] 3 2 [ ]: 1.0 i i dcd d A d B d C d D dt v dt dt dt dt dt d Bin case mol L s dt ξ − − −= = − = = = = 33 E 25.14(b)E 25.14(b) zz A + 2B A + 2B →→ C + D, C + D, k k = 0.21 L mol= 0.21 L mol--1 1 ss--11, , nn=2=2 ccA,0 A,0 = 0.025mol/L, = 0.025mol/L, ccB,0 B,0 = 0.150mol/L= 0.150mol/L zz The problem implies The problem implies r = kcr = kcAAccBB ,0 ,0 ,0 ,0 0 0 ,0 ,0 2 2 : ( )( 2 ) : ( )( 2 ) A B A B x t A B A B C D c x c x x x dxrate law k c x c x dt dxintegration kdt c x c x + → + − − = − − =− −∫ ∫ 44 E 25.14(b)E 25.14(b) ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 3 1 1 1 1 1 2 ( )( 2 ) 2 2 ( 2 ) /1 ln 2 ( ) / ( ) 10 , 6.488 10 ( ) 10min, 0.02500 A B B A A B B B B A A A C C c x c x c c c x c x c x c kt c c c x c a If t s x c mol L b If t x c mol L − − − ⎛ ⎞= −⎜ ⎟⎜ ⎟− − − − −⎝ ⎠ −∴ =− − = = = × = = = Q 55 Atkins P 25.2Atkins P 25.2 3 3 2 3 3 2 1 (CH ) CBr(A)+H O(B) (CH ) COH(C)+HBr(D) dynamic reasearch: / / 10 0 10.39 3.15 8.96 6.20 7.76 10.0 6.39 18.3 3.53 30.8 2.07 Act h mol L− − → (CH3)3CBr decomposition y = 0.007380 x2 - 0.502544 x + 10.488557 R2 = 0.997766 0 2 4 6 8 10 12 0 10 20 30 t/h cA /(1 0- 2 m ol /L ) t1/2 t’1/2 66 P 25.2P 25.2 zz In plot, In plot, tt1/21/2≈≈tt’’1/21/2, this is the feature of , this is the feature of nn=1=1 zz Plot lnPlot lnccAA with with t t shows linear expression identify 1shows linear expression identify 1stst order reaction and order reaction and kk=0.0542 h=0.0542 h--11 (CH3)3CBr decomposition (n=1) k=0.0542 h-1 y = -0.0542x + 2.3563 R2 = 0.9922 0 0.5 1 1.5 2 2.5 0 10 20 30 40 t/h ln (c A/ (1 0- 2 mo l/ L) ) 2 77 P 25.2P 25.2 ,0 ,0 2 3 ln ( 43.8 ) exp( ) 10.39 10 / exp( 0.0542 / 43.8 ) 9.674 10 / A A A A c kt c c t h c kt mol L h h mol L − − = − ∴ = = − = × × − × = × Q 天津大学天津大学: 11: 11--2424 totaltotalPH total HPPHtotal pppppppp ppp pppppppppp ppt pt 3 4 3 7)]( 3 4[-- )( 3 4 4 3 4 6 4 1- 4 6 4 1 - 0 0 0 6H P (g)PH4 0000 0 00 0 0 243 3 243 −=−== −=∴ +=++=++= = = +→ Q 天津大学天津大学: 11: 11--2424 1 1 toaccordingconstant a be tocalculated is min0276.0 47.1 33.13ln 80 1 47.122.22 3 433.13 3 7 min80 min0275.0 43.4 33.13ln 40 1 43.400.20 3 433.13 3 7 min40 33.13 0 ln1 lnln 1noder reaction if : )1( 1 1 1 1 0 0 11 0 3 3 3 3 =∴ = == =×−×== == =×−×== == ==− = − − n nk k kPapt k kPapt kPapt p p t ktkpp Amethod PH PH PH PH Q 天津大学天津大学: 11: 11--2424 1 3/2 3/2 min40 0 0 min0275.0 40 099.13ln 1 1nreaction of feature just the is this (40min),constant a be tocalculated is )( 3 1 47.122.22 3 433.13 3 7 min80 )( 3 1 43.400.20 3 433.13 3 7 min40 33.13 0 : )1( 33 33 3 − = = === =∴ = ==×−×== ==×−×== === t k n t pkPapt pkPapt kPappt Bmethod tPHPH tPHPH PH Q 1111 天津大学天津大学: 11: 11--2525 1212 AtkinsAtkins’’ P898 P898 -- P 25.32P 25.32 12.29 12.39 12.59 12.85 13.02 13.11 15.08 15.12 lnk 5.1282 5.0000 4.8544 4.6948 4.5872 4.4843 3.3898 3.3898 1000/(T/K) 0.2170.2410.2950.3790.4520.4943.553.70k/(106 L/mol s) 195200206213218223295295T/K CH4+OH→P CH4+OH→P y = -1.6752x + 20.747 R2 = 0.9956 12.00 12.50 13.00 13.50 14.00 14.50 15.00 15.50 3.000 3.500 4.000 4.500 5.000 5.500 1/T ln (k /1 e6 L/ m ol /s) 1.40E+04Ea/(J/mol)= 1.02E+09A/(L mol-1 s-1)= 3 1313 Overpotential (Overpotential (超电势超电势)) zz EEir, anodicir, anodic > > EEr,anodicr,anodic ;; EEir, cathodicir, cathodic < < EEr,cathodicr,cathodic ηη j EE- E+ Electrolytic cell Anode: η = Eir - Er Cathode: η = Εr − Εir 1414 reactions on the electrodereactions on the electrode Cell discharge/discharge -E e H+/H2 0.0V O2/H2O Cl2/Cl- Zn2+/Zn -0.7628V 1.229V 1.360V Cu2+/Cu 0.521V ~~ Anode -E e H+/H2 O2/H2O Cl2/Cl- Zn2+/Zn Cu2+/Cu ~~ Cathode 原电池 阳极(负极): Zn →Zn2+ +2e (氧化反应) 阴极(正极): Cu2+ + 2e → Cu 或 Cl2 + 2e → 2Cl- 电解池 阴极: Zn2+ +2e→Zn 阳极: 2Cl-→ Cl2+ 2e 1515 补充补充 zz 为更有效地将两种离子分开为更有效地将两种离子分开, , 两种金属的析两种金属的析 出电势至少应该相差出电势至少应该相差 0.2 V.0.2 V. zz 形成合金形成合金: : 两种金属的析出电势相等两种金属的析出电势相等.. ηη j EE- E+ Electrolytic cell 1616 Exchange current, Exchange current, ii00 0ln | | lna a Fi i RT α η= + 0ln | | lnc c Fi i RT β η= + ln iTafel expression : a b j j A η = + = Anode: Cathode: α+β = 1 金属腐蚀金属腐蚀 zz化学腐蚀化学腐蚀 zz电化学腐蚀电化学腐蚀 --其它介质其它介质: : 潮湿空气、其他潮湿气体、水或潮湿空气、其他潮湿气体、水或 电解质溶液电解质溶液 --有电流产生有电流产生((微电池微电池)) 15.5 Electrochemical corrosion15.5 Electrochemical corrosion 1818 ) 337.0( 617.0 4402.0 , 10)( 2 62 VEVEVE CuCu Fe +=−=⎯⎯⎯⎯ →⎯−= +−+ = θαθ VEVE H 413.0 0.0 710 −=⎯⎯⎯ →⎯= −+ =αθ FeFe CuCu HH22OO 2 2 2 1 / 2 2 1ln 2O O O H RTE E F a a θ + = − AnodeAnode:: Fe Fe →→ FeFe2+2+ +2e+2e-- CathodeCathode:: 2H2H++ + 2e+ 2e-- →→ HH22 HH22 evolutionevolution ½½ OO22 + 2H+ 2H++ + 2e+ 2e--→→2H2H22OO OO22 absorptionabsorption Mechanism of corrosion:Mechanism of corrosion: VEVE 816.0 229.1 =→+=θ kPapO 212 ≈ 4 1919 HH22OO FeFeFe above water exposed in higher Fe above water exposed in higher OO22 and acts as cathode (higher and acts as cathode (higher EE) ) while Fe in water became anode while Fe in water became anode (lower (lower EE).). EE--: Fe : Fe →→ FeFe2+2+ +2e+2e-- EE++::½½ OO22 + 2H+ 2H++ + 2e+ 2e--→→2H2H22OO Concentration cell:Concentration cell: 4402.0 VE −=θ VE 229.1+=θ 2020 The rate law of corrosionThe rate law of corrosion zz If two electrolytic reactions happened on an If two electrolytic reactions happened on an electrode, the apparent potential was electrode, the apparent potential was different from potentials of each reaction.different from potentials of each reaction. zz For simplifying the case, the For simplifying the case, the i~Ei~E relations are considering relations are considering as Tafel expressionsas Tafel expressions zz For two reactions on a For two reactions on a materialmaterial 2H2H++ + 2e H+ 2e H22 M MM Mnn++ + + nnee H 2 →2 H + +2 e 2H ++ 2e→ H 2 M→ M n+ + ne M n++ ne→ M Ee,c Ee,a Emix E lni H 2 →2 H + +2 e 2H ++ 2e→ H 2 M→ M n+ + ne M n++ ne→ M Ee,c Ee,a Emix E lni 2121 The mixture potential (1)The mixture potential (1) , , 0e c e aIf E E - >> : ( ) + 2 0 , 1H e H 2 expc c e c dominate RTi i E E nFβ + → ⎛ ⎞= −⎜ ⎟⎝ ⎠ ( ) n+ 0 , M M e expa a e a n dominate RTi i E E nFα → + ⎛ ⎞= − − −⎜ ⎟⎝ ⎠ HnMnHM n 22 ++ ++ Combining reaction at electrode 2222 The mixture potential (2)The mixture potential (2) ( ) ( ) 0 mi , 0 , exp and exp x c mix e c mix a mix e a RTI i E E nF RTI i E E nF β α ⎛ ⎞= −⎜ ⎟⎝ ⎠ ⎛ ⎞= − −⎜ ⎟⎝ ⎠ Q H 2 →2 H + +2 e 2H ++ 2e→ H 2 M→ M n+ + ne M n++ ne→ M Ee,c Ee,a Emix E lni H 2 →2 H + +2 e 2H ++ 2e→ H 2 M→ M n+ + ne M n++ ne→ M Ee,c Ee,a Emix E lni ( ) ( ) mi mi exp exp c mix x a mix x i RT E E I nF i RT E E I nF β β ⎛ ⎞∴ = −⎜ ⎟⎝ ⎠ − ⎛ ⎞= − −⎜ ⎟⎝ ⎠ : , 0mix maiI corrosion current I > 2323 The mixture potential (3)The mixture potential (3) zz If bias act on electrode:If bias act on electrode: ( ) ( ) ( ) ( ) 0 0 , ,exp exp exp exp exp exp A K c e c a e a mix mix mix mix I i i RT RTi E E i E E nF nF RT RTI E E E E nF nF RT RTI E E nF nF β α β α β α = − ⎛ ⎞ ⎛ ⎞= − − − −⎜ ⎟ ⎜ ⎟⎝ ⎠⎝ ⎠ ⎡ ⎤⎛ ⎞ ⎛ ⎞− − − −⎢ ⎥⎜ ⎟ ⎜ ⎟⎝ ⎠⎝ ⎠⎣ ⎦ ⎡ ⎤⎛ ⎞ ⎛ ⎞∆ − − ∆⎢ ⎥⎜ ⎟ ⎜ ⎟⎝ ⎠⎝ ⎠⎣ ⎦ = = HnMnHM n 22 ++ ++ A K 2424 Factors about corrosionFactors about corrosion zz Properties of the Properties of the materials: slopes on materials: slopes on polarizationpolarization zz EE(eq.) of the primary (eq.) of the primary cellcell zz Surface charactersSurface characters zz Composition of Composition of solutionsolution H 2 →2 H + +2 e 2H ++ 2e→ H 2 M→ M n+ + ne M n++ ne→ M Ee,c Ee,a Emix E lni H 2 →2 H + +2 e 2H ++ 2e→ H 2 M→ M n+ + ne M n++ ne→ M Ee,c Ee,a Emix E lni 5 2525 Corrosion measurementCorrosion measurement Icorr 2626 Corrosion protectionCorrosion protection z Anticorrosion materials stainless steels,… z Coating protection (覆盖保护层覆盖保护层) 1)非金属涂层: 油漆、瓷、玻璃、高分子材料等;(使金 属与腐蚀介质隔开) 2)金属保护层 电镀法 阳极保护层:如 Zn / Fe(白铁皮) 阴极保护层:如 Sn / Fe(马口铁) 2727 Electrolytic protection - Sacrificial anode (Sacrificial anode (牺牲阳极保护法牺牲阳极保护法)) zz 将电势较负的金属和被保护的金属连接在一起构将电势较负的金属和被保护的金属连接在一起构 成原电池,其作为阳极而溶解,被保护的金属作成原电池,其作为阳极而溶解,被保护的金属作 为阴极可以避免被腐蚀。为阴极可以避免被腐蚀。 zz 例如例如,海上航行的船舶在船底四周镶嵌锌块。,海上航行的船舶在船底四周镶嵌锌块。 牺牲阳极 受保护阴极 VE VE FeFe ZnZn 4402.0 7628.0 , , 2 2 −= −= + + θ θ 2828 Electrolytic protection - Cathode protection zz 接外电源的负极上,正极接到废铁作阳接外电源的负极上,正极接到废铁作阳 极,使它受腐蚀(人为的牺牲阳极)极,使它受腐蚀(人为的牺牲阳极)—— 外外 加电压下的加电压下的阴极保护阴极保护。。 zz 例如:石油输油管道的防腐:例如:石油输油管道的防腐: 每隔一段 路,需有一 个阴极保护 装置。 2929 Corrosion inhibitor (Corrosion inhibitor (加缓蚀剂)) z无机盐、有机缓蚀剂等。 z其作用是增大极化、减慢电极过程速度或 覆盖电极表面而使金属防腐。 阴极缓蚀剂吸附 在阴极表面(附 近),增大阴极 极化,使腐蚀电 流 Icorr 下降。 如图: 3030 „ 阳极:Fe + H2SO4 „„ 阴极:甘汞参比电极阴极:甘汞参比电极 (理想的非极化电极,(理想的非极化电极, ϕϕ阴阴 不变)不变) „ 逐渐增加外加电压,即增加阳极电势(因为 ϕ阴 不变),观察其腐蚀电流的变化。 Passivating treatment (电化学钝化) 6 3131 由图可知,只要维持 金属 Fe 的电位 ϕ 在 C ∼ D 之间,金属就 处于稳定的钝化状 态—电化学钝化。 即可通过控制电位, 达到金属的电化学钝 化。 3232 15.6 Chemical cells as energy supplier15.6 Chemical cells as energy supplier zz New chemical batteriesNew chemical batteries zz High power/massHigh power/mass zz High quantity of energyHigh quantity of energy zz Small sizeSmall size zz SecuritySecurity zz Free of pollutionFree of pollution zz Primary batteriesPrimary batteries--chemical batteries chemical batteries zz Secondary batteriesSecondary batteries--chargeable batterieschargeable batteries 3333 LeadLead--acid batteriesacid batteries zz Pb|HPb|H22SOSO44|PbO|PbO22 PbOPbO2 2 + + PbPb + 2H+ 2H22SOSO4 4 2PbSO2PbSO4 4 + 2H+ 2H22OOcharge discharge 最大优点是价廉;但其重量大,保养要求高,易损坏 3434 NickelNickel--hydrogen batterieshydrogen batteries((MHMH--Ni) Ni) zz HH22(M)(M)││ KOH KOH ││NiOOHNiOOH zz Cell reactionsCell reactions:: ( ( -- ) 1/2H) 1/2H22 + OH+ OH-- →→ HH22O + eO + e (+) NiOOH + H(+) NiOOH + H22O + eO + e →→ Ni(OH)Ni(OH)22 + OH+ OH-- 1/2H1/2H22 + NiOOH+ NiOOH →→ Ni(OH)Ni(OH)22 特点:不产生 Cd污染,为 “绿色电池”; 3535 Lithium battery (1)Lithium battery (1) 20世纪60年代开始研制锂电池 1990年日本Sony公司率先研制成功锂离子电池 zz Li(C) Li(C) ││LiLi--ion solutionion solution││ embed Liembed Li ((--) Li ) Li →→LiLi++ + e+ e-- (+) Li(+) Li++ + e+ e--→→LiLi zz Cathode materialsCathode materials:: zz LiMOLiMO22::LiCoOLiCoO22, , LiVOLiVO22 , LiNiO, LiNiO22,, LiMnOLiMnO22 zz LiMLiM22OO44: LiCo: LiCo22OO44,, LiVLiV22OO44, LiMn, LiMn22OO44 工作电压: 3.6 V 左右,约为 Cd-Ni、MH-Ni 电池的 3 倍 (用于手机、笔记本电脑等)。 3636 zz Anode materials of Lithium battery :Anode materials of Lithium battery : 碳 材 料 石墨 天然或人工石墨 石墨化碳 碳纤维 介稳相球状碳 非石墨 软碳(焦炭) 硬碳 Polyacene线性石墨混合物 掺杂型碳 金属氧化物:SnO、WO2、MoO2、TiO2、 VO2、LixFe2O3、Li4Ti5O12等 7 3737 Properties of some chargeable batteriesProperties of some chargeable batteries 10无>1000300120~1403.6 Li离 子 20无>500240~30060~801.2NiMH 25有400~500150501.2NiCd 3无400~600--2.0铅酸 自放 电率 (%/月) 记忆 效应 循环 次数 体积比 能量 (Wh/1) 重量比 能量 (Wh/kg) 工作 电压 (V) 电池 类型 3838 Hydrogen energyHydrogen energy zz An energy system using hydrogen as energy carrierAn energy system using hydrogen as energy carrier 3939 Fuel cellFuel cell zz 对于原电池而言,电池所放出的能量取决 于电池中储存的化学物质量,对于可充电 电池而言,则可以通过外部电源进行充电 ,使电池工作时发生的化学反应逆向进行 ,得到新的活性化学物质,电池可重新工 作。因此实际上普通电池只是一个有限的 电能输出和储存装置。而燃料电池则不同 ,参与反应的化学物质如氢和氧,分别由 燃料电池外部的单独储存系统提供,因而 只要能保证氢氧反应物的供给,燃料电池 就可以连续不断地产生电能,从这个意义 上说,燃料电池是一个氢氧发电装置。 4040 Fuel cellFuel cell zz Working principlesWorking principles kJ/mol -237.19298K)( kJ/mol -285.85K)298( O(l)HO 2 1H 0 222 =∆ =∆ →+ m m G H kJ/mol -698.56298K)( kJ/mol -719.23298K)( O(l)HCOO 2 3OH(l)CH 2223 =∆ =∆ +→+ m m G H Hydrogen fuel cell Methanol fuel cell 4141 效率 z热机的理论效率 ~60% 实际效率 20% ~30% z燃料电池的理论效率 >80% 实际效率 >60% 4242 AtkinsAtkins 29.24 A single cell of a 29.24 A single cell of a hydrogen/oxygen fuel cell. hydrogen/oxygen fuel cell. In practice, a stack of manyIn practice, a stack of many cells is used.cells is used. 8 4343 Hydrogen fuel cellHydrogen fuel cell 4444 Reactions in Fuel CellReactions in Fuel Cell Anode: H2 + M →MH2 MH2 + M → 2MH MH + H2O →M + H3O+ + e- MH, MH2: the molecules of hydrogen oxygen adsorbed on surface of catalyst Cathode:M + O2 + 2 H+ + e-→MH2O2 MH2O2 + 2 H+ + e-→M + 2 H2O M + O2→ 2 MO 2 MO + 2 H+ + e-→ 2 MOH 2 MOH + 2 H+ + e-→ 2 MO + 2 H2O Or 4545 Zero Emission VehiclesZero Emission Vehicles 4646 Hydrogen supply and storageHydrogen supply and storage 4747 燃料电池分类 按电解质划分,燃料电池大致上可分为五 类: z碱性燃料电池(AFC); z磷酸型燃料电池(PAFC); z固体氧化物燃料电池(SOFC); z熔融碳酸盐燃料电池(MCFC); z质子交换膜燃料电池(PEMFC)。 4848 9 4949 目前世界上主要燃料电池特性目前世界上主要燃料电池特性 军用潜艇 移动电源 电动汽车 洁净电站 卫星飞船 洁净电站洁净电站洁净电站航天飞机应用方向 1000007000130001500010000寿命/hr <5s>10min>10min几分钟几分钟启动时间 340-300015-2030-40120-18035-105比功率/W.kg-1 <1001000600200100工作温度/℃ 无弱强强强腐蚀性 质子膜YSZ(s)K3/Li2CO3H3PO4KOH电解质 Pt/CSr/LaMnO3Li/NiOPt/CPt/Ag阴极 Pt/CNi/ZrO2Ni/AlPt/CPt/Ni阳极 PEMFCSOFCMCFCPAFCAFC电池类型 5050 Hydrogen storage by organicsHydrogen storage by organics 5151 Reversible hydrogen storage and Reversible hydrogen storage and releasing by organicsreleasing by organics CC66HH66+H+H22OO CC66HH1212+3/2O+3/2O22电解电解 PtPt--SnSn CC66HH66+3H+3H22 膜膜 分分 离离 3H3H22 部分部分HH22燃烧供热燃烧供热 5252 Hybrid process: hydrogen Hybrid process: hydrogen evolution and storageevolution and storage 6 6 6 6 2 2 2 2 6 6 2 6 6 2 2 2 2 2 2 2 2 2 2 4 4 2 2 2 n n Cathodic reaction C H nH ne C H H e H Anodic reaction H O H O e Total reaction in cell nElectricityC H nH O C H O ElectricityH O H O + + + + + + + → + → → + + + ⎯⎯⎯⎯⎯⎯→ + ⎯⎯⎯⎯⎯⎯→ + : : : 5353 Hydrogen release: breaking equilibriumHydrogen release: breaking equilibrium zz CC66HH1212→→CC66HH66+3H+3H22 500 520 540 560 580 600 620 640 0.0 0.2 0.4 0.6 0.8 1.0 0.1 MPa 0.2 MPa 0.3 MPa 平 衡 转 化 率 温度 (K) 500 520 540 560 580 600 620 640 0.0 0.2 0.4 0.6 0.8 1.0 0.1 MPa 0.2 MPa 0.3 MPa 温度(K) 500 520 540 560 580 600 620 640 0.0 0.2 0.4 0.6 0.8 1.0 0.1 MPa 0.2 MPa 0.3 MPa 平 衡 转 化 率 温度 (K) 500 520 540 560 580 600 620 640 0.0 0.2 0.4 0.6 0.8 1.0 0.1 MPa 0.2 MPa 0.3 MPa 温度(K) C at al yt ic d eh yd ro ge na tio n CC66HH1212 CC66HH1212 3H3H22 5454 PhotoPhoto--induced electrolytic cellinduced electrolytic cell zz The features of semiconductorThe features of semiconductor zzConductanceConductance::101044 <<κκ<<101066 S mS m--11 zzThe forbidden gaps of semiconductors, The forbidden gaps of semiconductors, metals and nonconductorsmetals and nonconductors zzMetals, graphite: Metals, graphite: EEgg≈≈ 0 0 zzNonconductors: Nonconductors: EEgg>>4 eV4 eV zzSemiconductors: Semiconductors: EEgg =1 =1 ~~ 3 eV3 eV (本节以下内容仅供一般了解) 10 5555 Semiconductor/electrolyte interfaceSemiconductor/electrolyte interface zz Equilibrium state: (Equilibrium state: (EEFF, the energy of , the energy of Fermi level)Fermi level) zz假设半导体与含有一对假设半导体与含有一对Redox(ARedox(A2+2+/A/A++)) 的电解质溶液接触的电解质溶液接触 zz接触前:接触前: zzEE’’FF((半导体)>半导体)>EEFF((溶液)溶液) zz接触时:接触时: zz ee++由半导体流向溶液由半导体流向溶液 AA2+2+ + e+ e--→→ AA++ zz达平衡时达平衡时 zzEE’’FF((半导体)半导体)= = EEFF ((溶液溶液)) 导带导带 价带价带 EE’’FF EEFF NN--半导体半导体 溶液溶液 EEgg 5656 The effect of photoThe effect of photo--electricityelectricity zz 光照半导体光照半导体,,若若 hhνν>>EEgg ,,则价带则价带 中的部分电子可被激发到导带中的部分电子可被激发到导带, , 产生电子产生电子--空穴对空穴对————光生载流光生载流 子:子:A + A + hv hv →→ AA+ + + e+ e-- zz 在半导体内在半导体内,,光生载流子的寿命光生载流子的寿命 很短,很快会被复合掉。很短,很快会被复合掉。 zz 若存在强电场的空间电荷区若存在强电场的空间电荷区, , 则则 可实现光生载流子的分离可实现光生载流子的分离 zz 例如例如::对对NN型半导体型半导体,,在空间电荷在空间电荷 区电场的作用下区电场的作用下, , 空穴流向电极空穴流向电极 表面表面,,而电子流向半导体内部而电子流向半导体内部 NN--半导体半导体 溶液溶液 导带导带 价带价带 EE’’FF EEFF EEgg CBCB VBVB EE’’FF EEFF EEgg 空间电荷区空间电荷区 hvhv 光照前光照前 光照时光照时 ee-- AA++ 5757 电场方向电场方向 + - 半导体半导体 溶液溶液 zz 空间电荷区增加了光生载流子后空间电荷区增加了光生载流子后,,φφ, E, EF ,F ,,V,VBB 均会发生变化均会发生变化 5858 PhotoPhoto--electrical chemical cellselectrical chemical cells ①① Renewable photoRenewable photo--electric cellselectric cells NN--GaAs(1GaAs(1--x) Px) Pxx││NaOH,NaNaOH,Na22SS││PtPt R n-type semiconductor S-/S2- M et al electrolyte M et al 5959 zz Under irradiation:Under irradiation: zz Anode:Anode: zz少数载流子少数载流子minority minority carriercarriers(s(空穴空穴) flow ) flow into surfaceinto surface zz SS22--→→SS-- + e+ e-- zz Cathode:Cathode: zz多数载流子多数载流子majority majority carriercarriers(s(电子电子) pass ) pass through circle into through circle into cathodecathode zz SS-- + e+ e--→→ SS22-- zz No net changes in No net changes in solutionsolution Load SS--/S/S22-- II hvhv 6060 PhotoPhoto--induced electrolysisinduced electrolysis zz Anode: 2HAnode: 2H22O O →→ 4H4H++ + O+ O22 + 4e+ 4e-- zz Cathode: 4HCathode: 4H++ + 4e+ 4e--→→ 2H2H22 zz Whole reaction: 2HWhole reaction: 2H22O O →→ 2H2H22 +O+O22 Φ0(H+/H2) Φ0(H2O/O2) + -- -- hv 11 6161 Homework Homework zz Atkins Page 1044Atkins Page 1044--10451045 zz E29.8(b) cathode reaction E29.8(b) cathode reaction zz E29.9(b)E29.9(b) zz E29.13(b): assuming E29.13(b): assuming aa(H(H++)=1)=1
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