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7Applications of Solid Electrolyte

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					7.Applications of Solid Electrolyte
 Compared with liquid electrolytes, solid electrolytes is used much more widely owing to their high choice permeability and high strength as they can be made into a certain shape. Compared with liquid electrolytes, solid electrolytes has certain shape and strength, Its conduction ion is quite unitary, so it has a more widespread application.  Chemical power sources:e.g. high energy density battery, micro-power battery and so on.  Chemical sensors: Oxygen sensor, gas sensors, Oxygen probe for steel liquid, and so on.  Electrochemical units: Integral component, Micro-coulometer, timing components, memory components.  Electrochemistry catalysis : Carbon oxygen compound hydrogenation.  Separation and depuration :depuration of Natrium, separation of oxygen and so on.  Physical chemistry thermodynamics and dynamics research.  Gives off heat the luminous element. When solid electrolyte works, it generally must be constructed the electrochemistry installment. The most basic form is the battery or the electrolytic cell. (-) cathode | solid electrolyte | anode(+)



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7.1 ZrO2-based solid electrolytes oxygen sensors
 When the partial pressure of oxygen of the two side of ZrO2 solid electrolyte is different: PⅠO2 ZrO2(Y2O3) PⅡO2 PO2Ⅱ>PO2Ⅰ

(-) 

(+)

There is a reversible reaction describe as the following equation:
½ O2 + 2e = O2k=[O2-]/(n2PO21/2) n2=k’[O2-] PO2-1/2 High PO2: ½ O2 (PO2Ⅱ) + 2e = O2(正极,阴极) Low PO2 : O2- - 2e = ½ O2 (PO2Ⅰ) (负极,阳极) Total reaction: ½ O2 (PO2Ⅱ) = ½ O2 (PO2Ⅰ)
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7.1 ZrO2-based solid electrolytes oxygen sensors
 The free energy change of the chemical reaction is given by:
 G  G   RT ln PO 2  G   RT ln PO 2   RT ln
 

PO 2 PO 2




while  

 G   nEF

so

E 

 G nF



RT nF

ln

PO 2 PO 2




Principle: the PO2Ⅱ is invariable,we can figure out the value of PO2Ⅰ by measure the values of E and T. Here, the system provides the PO2Ⅱ is called the reference electrode.

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7.2 reference electrode
 The reference electrode will provide a invariable partial pressure of oxygen at a certain temperature.  We can choose the following systems as reference electrolyte: (1)Air(PO2=0.21 atm). Or other systems with a invariable partial pressure of oxygen, such as CO/CO2 mixture. (2)metal/metal-oxide mixture, M/MOx: like, Ni/NiO, Cr/Cr2O3, Cu/Cu2O, Mo/MoO2 When the system achieve its equilibrium at a certain temperature, the decomposition pressure of the oxides is the very partial pressure of oxygen.  For example: Ni (s) + 1/2O2 = NiO (s) according to the phase rule:f=C-P+2 since, C=2 and P=3,So f=1 There is only one degree of freedom. So, when the temperature is given, the pressure is invariable.

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7.3 Oxygen Sensor
 Oxygen content has been determined by the solid-electrolyte method in molten copper, copper alloys, tin, tin alloys, lead, silver, lead-silver alloys, and sodium. Only calcia-stabilized zirconia tubes have been employed in all these instances. CaO was the most common dopant, the concentration of which ranged from 3-4 wt% to 7.5 wt%. Reasons for using lower CaO content were to improve thermal shock resistance as well as to increase the resistance with a view to cut down the short-circuiting effect due to electronic conduction. Yttria-doped thoria in conjunction with yttriastabilized zirconia was also used to minimize the latter effect. Some investigators have also employed MgO-stabilized zirconia for measurement in molten copper and copper alloys. The major advantages in the use of tubes are their commercial availability and separation of the two electrode compartments. However, extra care is required to protect the tubes from cracking due to thermal shocks.
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7.3 Oxygen Sensor
 It is worthwhile to note that the oxygen probe cannot be employed in conjunction with reactive metals such as Al, Mg, etc. because the dissolved oxygen content in these cases is negligible. Also these metals may attack the solid electrolyte. Barring these reactive metals, other common metals can be divided into two categories-metals melting below 1200℃ (Cu, Pb, Sn, Ag, etc.) and metallic materials melting above 1200℃, such as iron and steel. Assuming that equilibrium prevails amongst dissolved oxygen and other solutes, it is possible to determine the concentration of other solutes from oxygen probe data.

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7.4 Oxygen probe for steel liquid
 2[O] + 4e- = 2O24/3Cr + 2O2- =2/3 Cr2O3 + 4eTotal reaction: 4/3Cr +2[O] =2/3Cr2O3
 G   4 EF   G   RT ln a [ O ] 
2

2 3

 G Cr 2 O 3  2  G [ O ]  RT ln a [ O ]
0 0 2

 G   nEF
E  RT 4F
0

ln a [ O ] 
2

1 2 4F 3

 G Cr 2 O 3 
0

1 4F

 2  G[O ]
0

 G [ O ]   56000  1 . 38 T
 G Cr 2 O 3   180360  40 . 90 T
0

So:

lg a [ O ] 

 (13580  10 . 08 E ) T

 4 . 62
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7.4 Oxygen probe for steel liquid
 Mo|[O]Fe|ZrO2(MgO)|Mo, MoO2|Mo MoO2 + 4e-=2O2-+Mo(s) 2O2- =2[O] +4eTotal reaction:MoO2=2[O]+Mo(s)

 G   G  RT ln a [ O ]
0 2

 4 EF   G [ O ] / O 2   G Mo / MoO 2  RT ln a [ O ]
0 0 2

 G Mo / MoO 2   126700  34 . 18 T
0

 G O 2 / 2 [ O ]   56000  1 . 38 T
0

lg a [ O ] 

 ( 7725  10 . 08 E ) T

 3 . 885

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7.4 Oxygen probe for steel liquid
 At high temperature and very low partial pressure of oxygen, there exits a reaction described as following: OO=1/2O2+VO∙∙ + 2e The temperature of the molten steel is quite high, 1600 ℃, and the partial pressure of oxygen is very low.  For example: Assume that O2=[O], and [O]=20 ppm. since then PO2=5.83×10-13 atm=5.8×10-8 Pa 1   1933年,C.Wagner E   t d 4F 
 O2  O2

i

O2

由  O 2   O 2  RT ln PO 2
0

可知:

E 

RT F

ln

PO 2




1/ 4

 Pe

1/ 4

PO 2  Pe

1/ 4

1/ 4

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7.4 Oxygen probe for steel liquid


the Oxygen pressure with electronic characters,


t e  t O 2  0 .5

 For ionic conductivity:

 i  nF [V O ]u i  constant

 While electrical conductivity :
 e [ e ] Fu e  Fu e KPO
1 / 4
2



 i  c onstant

 So

e i
 e  K ' PO
1 / 4
2

Pe is oxygen pressure with electronic characters.
Pe
PO 2
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7.4 Oxygen probe for steel liquid
 Under the special molten steel condition, the choice of contact conductor is also very important .It should meet
   Good electronic condutor Hith melting point, high chemical stability (not react with molten steel) Take account of the potential compensation when using different leads.



为了保证电池的可逆性,要求电池工作时,通过的电流是无限小的。这不仅可以避 免电池发生极化,也可保证尽可能少的热电转化。以往,电动势测定要用对消法, 从图可以看出:


I 

E R0  Ri

I E

A V B R0

要使I小,必须(R0+Ri)大 增大Ri是不可取的,因为我们测得的 信号值实际为AB间的电位差,V=R0I

Ri

V E



R0 R0  Ri

只有当R0>>Ri,才会有V≈E,而Ri总是存在的,所以 只能尽可能加大R0
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7.5 NASICON sensor
 NASICON/SO2 sensor
 NASICON片状样品(Φ10x2mm)和片状的氧化钇稳定的氧化锆在1250℃ 烧结结合在一起。在氧化锆表面涂多孔的铂电极(氯铂酸800℃热分解); 在NASICON表面用机械挤压方法固定一层Na2SO4辅助电极(将Na2SO4粉 末与金粉按1:2混匀压片,在1073K烧结10小时制成)。铂丝作为电极引 线。 Na2SO4辅助电极  传感器示意图: NASICON固体电解质
ZrO2(Y2O3)固体电解质 多孔铂电极



将传感器置于石英管中,石英管中放入V2O5或涂铂的陶瓷环作催化剂;石英 管放置在550-750℃的铁铬铝丝炉中。含有二氧化硫的待测气体经过催化剂作 用,其中的二氧化硫气体与氧气反应,生成三氧化硫气体。经过传感器,测量 传感器产生的电动势,可计算出待测气体中的三氧化硫含量。
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7.5 NASICON sensor
 The battery composed by the sensor is : Pt |SOx,O2 |Na2SO4‖NASICON | YSZ‖SOx,O2| Pt Anode Reaction Na2SO4=2Na++SO3+1/2O2+2e Cathodic Reaction 1/2O2+2e’=O2Interface Reaction 2Na++O2-=Na2O (NASICON) Total Response Na2SO4=Na2O (NASICON)+SO3 气相中的氧在氧化锆表面取得电子成为氧离子,进入氧化锆;辅助电极中的Na2SO4被分解,生 成钠离子,进入NASICON;在NASICON中钠离子与从氧化锆过来的氧离子结合成Na2O。 从总反应式可看出,参加反应的活性物质是三氧化硫,而不是二氧化硫。
E  G 2F
0

 



2 . 303 RT log a Na 2 O 2F



RT ln( PSO 3 ) 2F



总反应的Gibbs标准自由能 G0,电池的电动势E 其中F是Farady常数、T是测量时的绝对温度、R为气体常数;aNa2O表示NASICON中Na2O的活度。 根据文献报道,NASICON中Na2O的活度可表示为:
log a Na 2 O   12050 T  2 . 15

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7.5 NASICON sensor
 CO2传感器
 采用热浸镀的方法,在氧化锆基片上形成一层NASICON薄膜(将抛光的氧化 锆片埋在NASICON粉末中,经1150-1230℃热处理,使氧化锆表面形成厚 度为15μm的NASICON薄膜)。将其中一面的薄膜全部磨掉、抛光;在样片 两面涂多孔透气铂电极;在有NASICON薄膜的一面再涂上一层Na2CO3厚膜, 加上铂丝引线,制成二氧化碳传感器。 示意图
Na2CO3厚膜 NASICON薄膜 ZrO2基片 透气铂电极



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7.5 NASICON sensor
 传感器组成的电池表示成: CO2,O2,Pt |Na2CO3||NASICON |YSZ||Pt,O2,CO2 阳极: Na2CO3 = Na+ + 1/2O2 + CO2 + 2e 阴极: 1/2O2 +2e = O2界面反应: 2Na+ + O2- =Na2O(NASICON) 在阳离子导体一边,辅助电极Na2CO3分解出钠离子,进入NASICON;氧化 锆一边,气相中氧原子得电子成氧离子进入氧化锆;在氧化锆和NASICON 的界面上,钠离子和氧离子结合成氧化钠。  电池的总反应: Na2CO3 = Na2O + CO2  电池电动势E与气相中二氧化碳分压PCO2的关系为:

E 

G 2F

o



RT 2F

ln( a Na 2 O PCO 2 )
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7.6 Simple Introduction to Fuel Cell
• Fuel cells are electrochemical devices that convert the chemical energy of a reaction directly into electrical energy. • Fuel cells are an important technology for a potentially wide variety of applications including micropower, auxiliary power, transportation power, stationary power for building and other distributed generation applications, and central power.

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Summary of Major Differences of the Fuel Cell Types
PEFC (Polymer Electrolyte Fuel Cell) Electrolyte Ion Exchange Membranes Operating Temperature Charge Carrier External Reformer for CH4 Prime Cell Components Catalyst Product Water Management Product Heat Management 80°C H+ Yes Carbon-based Platinum Evaporative Process Gas+Independe nt Cooling Medium AFC (Alkaline Fuel Cell) PAFC (Phosphoric Aid Fuel Cell) MCFC (Molten Carbonate Fuel Cell) Immobilized Liquid Molten Carbonate 650 °C CO3= No Stainless-based Nickel ITSOFC (Intermediate Temperature Solid Oxide Fuel Cell) Ceramic TSOFC (Tubular Solid Oxide Fuel Cell)

Mobilized or Immobilized Potassium Hydroxide 65°C - 220°C OHYes Carbon-based Platinum Evaporative Process Gas+Electrolyte Calculation

Immobilized Liquid Phosphoric Acid 205°C OHYes Graphite-based Platinum Evaporative Process Gas+Independe nt Cooling Medium

Ceramic

600-800°C O= No Ceramic Perovskites

800-1000°C O= No Ceramic Perovskites

Gaseous Product
Internal Reforming+Proc ess Gas

Gaseous Product
Internal Reforming+Proc ess Gas

Gaseous Product
Internal Reforming+ Process Gas

17

Cathode: Carbon with fine particles of Platinum dispersed on its particle surface Anode: Carbon with fine particles of Platinum dispersed on its particle surface Electrolyte: Proton-exchange membrane (fluorinated sulfonic acid polymer)

Anode:

2H2

4 H+ + 4e2H2O
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Cathode: O2 + 4e- + 4H+

7.6 SOFC Working Mechanism

• Cathode: La0.8Sr0.2MnO3 • Anode: Ni+8 mol%Y2O3 stabilized ZrO2 (Cermet) • Electrolyte: 8 mol%Y2O3 stabilized ZrO2
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20

7.6 SOFC Working Mechanism
 The ideal performance of a fuel cell depends on the electrochemical reactions that occur with different fuels and oxygen as summarized in Table 2-1. Lowtemperature fuel cells (PEFC, AFC, and PAFC) require noble metal electrocatalysts to achieve practical reaction rates at the anode and cathode, and H2 is the only acceptable fuel. With high-temperature fuel cells (MCFC, ITSOFC, and SOFC), the requirements for catalysis are relaxed, and the number of potential fuels expands.

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7.6 SOFC Working Mechanism

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7.6 SOFC Working Mechanism

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7.6 SOFC Working Mechanism
 Figure 2-1 shows the relation of E���� to cell temperature. Because the figure shows the potential of higher temperature cells, the ideal potential corresponds to a reaction where the water products in a gaseous state. Hence, E is less than 1.229 at standard conditions when considering gaseous water product.

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7.7 Structure of oxygen probe for steel liquid
• Under low oxygen condition
([O]<0.01%) we use Cr, Cr2O3 as reference electrode • Under high oxygen condition([O]>0.01%) we use Mo, MoO2 as reference electrode

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谢谢各位!

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