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
pp
t
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