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2018/10/12 20:38:20瀏覽153|回應0|推薦0 | |
Chap. 4 electrolysis cell 當E>>E₀ at x=0, E=E₀-(RT/nF)ln(cR/cₒ)|ₓ₌₀ cR/cₒ→0 as cR<<cₒ ⸫R→O limiting current, iᴅₐ=-nFAcR*DR/XᴅR....(1), iᴅc=-nFAcₒ*Dₒ/Xᴅₒ...(2) general case: i= -nFAJ₀|ₓ₌₀=nFAJR|ₓ₌₀ Jₒ|ₓ₌₀= -Dₒ[cₒ*-cₒ(0,t)]/Xᴅₒ=-i/nFA → cₒ(0,t)=cₒ*-(i/nFA)(Xᴅₒ/Dₒ)....(3) (2)代入(3), 同理, cR(0,t)=cR*+(i/nFA)(XᴅR/DR)....(4) (1)代入(4), E=E°+(RT/nF)ln[cₒ(0,t)/cR(0,t)]....(4.16) (5), (6)代入(4.16),
(7) i.e. E½= E°+(RT/2nF)ln(DR/Dₒ)=E°-(RT/2nF)ln(Dₒ/DR) 實驗上把時間固定
applcation: ⸪t=constant, Xᴅₒ=(πDₒt)½=constant iᴅc=δₒcₒ* ….(8)→ δₒ= nFADₒ/Xᴅₒ iᴅₐ=-δRcR*....(9) O+ne⁻→R, x: mole fraction of O cₒ*=xc* and cR*=(1-x)c* (8), (9)代入(7)→ E=E½+(RT/nF)ln[(δₒxc*-i)/(i+δR(1-x)c*)] 可作i-E-x的圖, 如Fig. 4.12
⸪ Xᴅᵢ=(πDᵢt)½, and E½=E°-(RT/2nF)ln(Dₒ/DR)
constant composition, iᴅc=-nFAcₒ*Dₒ/Xᴅₒ≈kct⁻½ Xᴅₒ=(πDₒt)½
2. E=constant, Dropping mercury electrode(d.m.e.) 當V↑, Xᴅ↓ iᴅ=nFAcₒ*Dₒ/Xᴅₒ=nFAcₒ*(Dₒ/πt)½=nF4π(3ut/4πd)⅔cₒ*(7Dₒ/3πt)½=706nDₒ½cₒ*u⅔t⅙
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( 知識學習|隨堂筆記 ) |