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电化学·电池/腐蚀/动力学
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电化学·电池/腐蚀/动力学
12
engines
标准电极电势与电池电动势
Standard electrode potential & cell EMF
E°cell=E°阴−E°阳 · 还原电势表 · Zn|Cu=1.10V · 自发
Pick a cathode and anode from the standard reduction-potential table to get E°cell and predict spontaneity
浓差电池
Concentration cell
同电极不同浓度 · E=(0.0592/n)log([浓]/[稀])
Two identical electrodes produce an EMF purely from an ion-concentration difference — driven by the Nernst equation
氢氧燃料电池的热力学效率
H₂/O₂ fuel-cell thermodynamics
ΔG=−nFE° · H2/O2 1.23V · 效率ΔG/ΔH=83%
Electrical work and efficiency from ΔG = −nFE°, compared with a heat engine's Carnot limit
Butler–Volmer 方程(电极动力学)
Butler–Volmer equation (electrode kinetics)
j=j0[exp(αaFη/RT)−exp(−αcFη/RT)] · 阳/阴分支
Net current density vs overpotential η: the difference of anodic and cathodic branches
Tafel 分析(电极动力学)
Tafel analysis (electrode kinetics)
η=a+b·log|j| · 斜率2.303RT/αF=118mV/dec · 外推j0
Extrapolating the linear Tafel region to find j0; Tafel slope b = 2.303RT/(αF)
循环伏安法(可逆体系)
Cyclic voltammetry (reversible system)
鸭形CV · ΔEp=59/n mV · Randles-Sevcik ip∝√v
The duck-shaped CV under a triangular sweep: cathodic/anodic peaks, ΔEp = 59/n mV, ip ∝ √v
电偶腐蚀与牺牲阳极
Galvanic corrosion & sacrificial anodes
电偶序 · 活泼金属做阳极 · 牺牲阳极Zn护Fe
When two metals contact in an electrolyte: which is the anode that corrodes, which is the protected cathode
电位-pH 图(铁的 Pourbaix 图)
Pourbaix (E–pH) diagram for iron
E–pH图 · 免蚀/腐蚀/钝化区 · 水线−59mV/pH
How electrode potential E and pH decide whether iron is immune, corroding or passivated
德拜-休克尔极限定律
Debye–Hückel limiting law
log γ±=−0.509|z₊z₋|√I · 离子强度 · γ随I降
The ionic atmosphere pulls the activity coefficient γ± below 1 as ionic strength rises
电池容量与 C 倍率
Battery capacity & C-rate
续航=容量/电流 · C-rate · Wh=容量×电压 · Wh/kg
From capacity and C-rate to discharge current, runtime, energy and energy density
摩尔电导率与科尔劳施定律
Molar conductivity & Kohlrausch's law
Λm=κ/c · Kohlrausch Λm=Λ°m−K√c · 离子独立迁移
Λm = κ / c; for strong electrolytes Λm = Λ°m − K√c; Λ°m = λ°₊ + λ°₋
电化学阻抗谱(EIS)与奈奎斯特图
Electrochemical impedance spectroscopy (EIS) & Nyquist plot
EIS · Randles Rs+Rct∥Cdl · Nyquist半圆 · ω=1/RctCdl
Randles circuit Rs + (Rct ∥ Cdl): the Nyquist plot is a semicircle of diameter Rct offset by Rs