📚 2 Electrochemical cells | 电化学电池
Electrochemical cells are devices that interconvert chemical energy and electrical energy. They form the basis of batteries, electrolysis industries, and sensors. In this revision guide, we explore the principles, types, calculations, and real-world applications of electrochemical cells for IB and Cambridge chemistry courses.
电化学电池是实现化学能与电能相互转化的装置，是电池、电解工业和传感器的基础。在本复习指南中，我们将为IB与剑桥化学课程探讨电化学电池的原理、类型、计算和实际应用。
1. What Are Electrochemical Cells? | 什么是电化学电池？
An electrochemical cell consists of two electrodes (electronic conductors) immersed in an electrolyte (an ion‑conducting medium). The cell can either convert the energy released by a spontaneous redox reaction into electricity (galvanic or voltaic cell) or use an external electrical supply to drive a non‑spontaneous reaction (electrolytic cell). Regardless of the mode, oxidation always takes place at the anode and reduction always takes place at the cathode.
电化学电池由两个电极（电子导体）浸入电解质（离子导体）中构成。电池既可以把自发氧化还原反应释放的能量转变为电能（原电池或伏打电池），也可以利用外部电源驱动非自发反应（电解池）。无论哪一种工作模式，氧化总是发生在阳极，还原总是发生在阴极。
2. Galvanic (Voltaic) Cells | 原电池（伏打电池）
In a galvanic cell, a spontaneous redox reaction generates an electric current. The two half‑reactions occur in separate half‑cells connected by a salt bridge and an external wire. Electrons flow through the external circuit from the anode (where oxidation occurs) to the cathode (where reduction occurs). A classic example is the Daniell cell: Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s).
在原电池中，自发的氧化还原反应产生电流。两个半反应发生在由盐桥和外部导线连接的两个半电池中。电子通过外电路从阳极（氧化处）流向阴极（还原处）。一个经典的例子是丹尼尔电池：Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s)。
The salt bridge completes the circuit by allowing ions to migrate between the half‑cells, maintaining electrical neutrality. Without it, charge build‑up would halt the reaction almost immediately. A strip of filter paper soaked in a saturated KNO₃ or KCl solution is often used.
盐桥允许离子在半电池间迁移以维持电中性，从而构成完整回路。没有盐桥，电荷积聚会使反应几乎立刻停止。通常使用浸透饱和 KNO₃ 或 KCl 溶液的滤纸条。
3. Electrolytic Cells | 电解池
An electrolytic cell uses an external power source to force a non‑spontaneous redox reaction to take place. Here the anode is connected to the positive terminal of the supply and attracts anions; the cathode is connected to the negative terminal and attracts cations. Energy is stored as chemical potential energy in the products.
电解池利用外部电源迫使非自发的氧化还原反应发生。此时阳极与电源正极相连，吸引阴离子；阴极与电源负极相连，吸引阳离子。能量以化学势能的形式储存在产物中。
ing of metals, and the extraction of aluminium from bauxite. The products can be predicted using standard electrode potentials and the reactivity series.
常见应用包括熔融盐的电解（例如 2NaCl(l) → 2Na(l) + Cl₂(g)）、金属电镀以及从铝土矿中提炼铝。产物可借助标准电极电势和活动性顺序进行预测。
4. Standard Electrode Potentials | 标准电极电势
The standard electrode potential, E°, measures the tendency of a half‑cell to be reduced relative to the standard hydrogen electrode under standard conditions: 298 K, 1 mol dm⁻³ for all aqueous ions, 100 kPa for gases, and any solid or liquid in its standard state. The more positive the E° value, the greater the driving force for reduction.
标准电极电势 E° 表示在标准条件下（298 K、所有水合离子浓度 1 mol dm⁻³、气体压强 100 kPa、任何固态或液态处于其标准状态）半电池相对于标准氢电极的还原趋势。E° 值越正，还原倾向越大。
e, Zn²⁺(aq) + 2e⁻ → Zn(s) has E° = −0.76 V, while Cu²⁺(aq) + 2e⁻ → Cu(s) has E° = +0.34 V.
标准电极电势以还原电势形式列出。例如 Zn²⁺(aq) + 2e⁻ → Zn(s) 的 E° = −0.76 V，而 Cu²⁺(aq) + 2e⁻ → Cu(s) 的 E° = +0.34 V。
5. The Standard Hydrogen Electrode (SHE) | 标准氢电极
nely divided platinum (to catalyse the equilibrium) immersed in 1 mol dm⁻³ H⁺(aq), with hydrogen gas bubbled through at 100 kPa. The half‑reacted is 2H⁺(aq) + 2e⁻ → H₂(g).
标准氢电极（SHE）是通用的参比电极，其电势人为规定为 0.00 V。它由表面镀有铂黑的铂电极浸泡在 1 mol dm⁻³ H⁺(aq) 中，并在 100 kPa 下通入氢气构成。半反应为 2H⁺(aq) + 2e⁻ → H₂(g)。
By connecting any other half‑cell to the SHE and measuring the cell potential, we obtain the standard electrode potential of that half‑cell. The sign convention is consistent: E° is negative if the half‑cell tends to oxidise H₂, and positive if it tends to reduce H⁺.
将任一其他半电池与 SHE 连接并测定电池电动势，即可得到该半电池的标准电极电势。符号规则为：若该半电池倾向于氧化 H₂，则 E° 为负；若倾向于还原 H⁺，则 E° 为正。
6. Calculating Cell Potential (EMF) | 计算电池电动势
The standard cell potential (E°cell) is obtained from the standard electrode potentials of the two half‑cells using:
标准电池电动势（E°cell）通过两个半电池的标准电极电势按以下公式求得：
E°cell = E°(cathode) − E°(anode)
Alternatively, E°cell = E°(right half‑cell) − E°(left half‑ n is spontaneous as written. For the Daniell cell: E°cell = +0.34 V − (−0.76 V) = +1.10 V.
或者 E°cell = E°(右半电池) − E°(左半电池)。如果 E°cell 为正，表示该反应方向是自发的。以丹尼尔电池为例：E°cell = +0.34 V − (−0.76 V) = +1.10 V。
A table of some common standard reduction potentials is shown below:
下表列出了一些常见标准还原电势：
| Half-reaction (reduction) | E° / V |
|---|---|
| F₂(g) + 2e⁻ → 2F⁻(aq) | +2.87 |
| O₂(g) + 4H⁺(aq) + 4e⁻ → 2H₂O(l) | +1.23 |
| Cu²⁺(aq) + 2e⁻ → Cu(s) | +0.34 |
| 2H⁺(aq) + 2e⁻ → H₂(g) | 0.00 |
| Fe²⁺(aq) + 2e⁻ → Fe(s) | −0.44 |
| Zn²⁺(aq) + 2e⁻ → Zn(s) | −0.76 |
| Li⁺(aq) + e⁻ → Li(s) | −3.04 |
7. Cell Notation | 电池符号记法
Electrochemical cells are represented by a shorthand notation that summarises the construction. The anode (oxidation) half‑cell is written on the left, and the cathode (reduction) half‑cell on the right. A single vertical line | indicates a phase boundary, and a double vertical line || denotes the salt bridge.
电化学电池可用简写符号表示其构造。阳极（氧化）半电池写在左侧，阴极（还原）半电池写在右侧。单竖线 | 表示相界面，双竖线 || 表示盐桥。
For example, the Daniell cell is written as:
例如，丹尼尔电池记为：
Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s)
If a half‑cell lacks a solid metal, an inert platinum electrode is included. The hydrogen half‑cell is: Pt(s) | H₂(g) | H⁺(aq). The phase of each species is indicated.
如果半电池缺少固态金属，需加入惰性铂电极。氢半电池记为：Pt(s) | H₂(g) | H⁺(aq)。每种物质的相态都得到标示。
8. Spontaneity and Gibbs Free Energy | 自发性与吉布斯自由能
The electrical work done by a cell under reversible conditions is related to the change in Gibbs free energy:
在可逆条件下电池所做的电功与吉布斯自由能变化相关：
ΔG° = −n F E°cell
× 10⁴ C mol⁻¹). A positive E°cell gives a negative ΔG°, indicating a spontaneous reaction.
其中 n 是每摩尔反应转移的电子的物质的量，F 是法拉第常数（96 485 C mol⁻¹，常取近似值 9.65 × 10⁴ C mol⁻¹）。正的 E°cell 对应负的 ΔG°，表明反应自发。
be used to calculate equilibrium constants: ΔG° = −R T ln K, so ln K = n F E°cell / (R T).
该公式直接将热力学与电化学联系起来。也可用于计算
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