📚 Cells and Batteries | 原电池与化学电池
An electrochemical cell converts chemical energy into electrical energy through spontaneous redox reactions. These cells are fundamental to batteries, which store and deliver power for countless applications, from portable electronics to electric vehicles. This article explores the principles of galvanic cells, standard electrode potentials, the Nernst equation, and the design of primary, secondary, and fuel cells, all key topics in Cambridge A-Level Chemistry.
电化学电池通过自发的氧化还原反应将化学能转化为电能。这些电池是化学电源的基础，为数不清的应用储存并输出能量——从便携电子产品到电动汽车。本文探讨原电池原理、标准电极电势、能斯特方程，以及一次电池、二次电池和燃料电池的设计，这些都是剑桥 A-Level 化学的核心主题。
1. Electrochemical Cells and Redox Reactions | 电化学电池与氧化还原反应
An electrochemical cell consists of two half-cells connected by a salt bridge and an external wire. In one half-cell, oxidation takes place at the anode, releasing electrons; in the other, reduction occurs at the cathode, consuming electrons. The overall cell reaction is a redox process, with electrons flowing from the anode to the cathode through the external circuit, generating an electric current.
电化学电池由两个半电池通过盐桥和外部导线连接而成。在一个半电池中，阳极发生氧化反应释放电子；在另一个半电池中，阴极发生还原反应消耗电子。整个电池反应是一个氧化还原过程，电子通过外电路从阳极流向阴极，产生电流。
The driving force for electron flow arises from the difference in the tendencies of the two half-cells to undergo reduction. A species with a higher reduction potential will draw electrons from a species with a lower reduction potential, creating a potential difference. This voltage, measured in volts, is the cell electromotive force (EMF).
电子流动的驱动力来自两个半电池发生还原倾向的差异。具有较高还原电位的物种会从具有较低还原电位的物种那里夺取电子，从而产生电势差。这个以伏特为单位的电压就是电池的电动势（EMF）。
2. Half-Cells and Electrode Potentials | 半电池与电极电势
A half-cell consists of an electrode dipping into an electrolyte containing ions of the same element in two oxidation states. For example, a zinc half-cell contains a zinc metal electrode immersed in a solution of Zn²⁺ ions. At the electrode surface, a dynamic equilibrium is established: Zn(s) ⇌ Zn²⁺(aq) + 2e⁻. The position of this equilibrium determines the electrode potential of that half-cell.
半电池由浸在含有同一元素两种氧化态的离子溶液中的电极构成。例如，锌半电池包含一片金属锌电极，浸入 Zn²⁺ 离子溶液中。在电极表面建立起动态平衡：Zn(s) ⇌ Zn²⁺(aq) + 2e⁻。这个平衡的位置决定了该半电池的电极电势。
The electrode potential cannot be measured in isolation; it must be compared to a reference electrode. The potential of a half-cell reflects the tendency of the ions to be reduced and is therefore a reduction potential. More positive values indicate a greater tendency to gain electrons and undergo reduction.
电极电势不能孤立测量；必须与一个参比电极进行比较。半电池的电势反映了离子被还原的倾向，因此是一个还原电势。数值越正，表示获得电子发生还原的倾向越大。
3. The Standard Hydrogen Electrode | 标准氢电极
The standard hydrogen electrode (SHE) is the universal reference for measuring electrode potentials. It consists of a platinum electrode coated with finely divided platinum black, immersed in a solution of 1 mol dm⁻³ H⁺ ions, with hydrogen gas bubbled through at 1 atm pressure and 298 K. The half-reaction is: 2H⁺(aq) + 2e⁻ ⇌ H₂(g).
标准氢电极（SHE）是测量电极电势的通用参考。它由一个涂有铂黑的铂电极构成，浸入 1 mol dm⁻³ H⁺ 离子溶液中，并在 298 K 和 1 atm 压力下通入氢气。半电池反应为：2H⁺(aq) + 2e⁻ ⇌ H₂(g)。
By convention, the standard electrode potential of the SHE is defined as exactly 0.00 V at all temperatures. To measure the standard electrode potential of another half-cell, it is connected to the SHE under standard conditions. The EMF of the resulting cell is the standard electrode potential of that half-cell, assigned with a sign according to whether reduction or oxidation occurs relative to hydrogen.
按照惯例，标准氢电极的标准电极电势在所有温度下被定义为零整 0.00 V。要测量另一个半电池的标准电极电势，需在标准条件下将其与 SHE 连接。所得电池的电动势即为该半电池的标准电极电势，并根据相对于氢是发生还原还是氧化来赋予正负号。
4. Standard Conditions and Conventions | 标准条件与惯例
Standard electrode potentials (E°) are measured under strictly defined conditions: all ion concentrations at 1 mol dm⁻³, any gases at 1 atm (101 kPa) pressure, and a temperature of 298 K. If the half-reaction involves solids or liquids, they must be present in their standard states. These conditions ensure reproducibility and allow fair comparison of different half-cells.
标准电极电势（E°）是在严格定义的条件下测量的：所有离子浓度为 1 mol dm⁻³，任何气体压强为 1 atm（101 kPa），温度为 298 K。如果半反应涉及固体或液体，必须以其标准状态存在。这些条件保证了结果的再现性，并允许不同半电池之间的公平比较。
The cell notation follows the convention: anode | anodic solution || cathodic solution | duction potentials are used for both electrodes. A positive cell EMF indicates a spontaneous reaction.
电池符号遵循惯例：阳极 | 阳极溶液 || 阴极溶液 | 阴极。双竖线代表盐桥。全电池的电动势计算为 E°(cell) = E°(阴极) − E°(阳极)，这里两个电极均使用还原电势。正的电池电动势表示反应是自发的。
5. The Electrochemical Series | 电化学序
rong reducing agents, readily losing electrons. Species at the bottom (most positive E°) are strong oxidising agents, readily gaining electrons. For example, Li⁺/Li has E° = −3.04 V, making lithium a powerful reductant; F₂/F⁻ has E° = +2.87 V, making fluorine a powerful oxidant.
电化学序按照标准电极电势递增的顺序排列半电池。系列顶部（最负的 E°）的物质是强还原剂，容易失去电子。底部（最正的 E°）的物质是强氧化剂，容易得到电子。例如，Li⁺/Li 的 E° = −3.04 V，使锂成为强还原剂；F₂/F⁻ 的 E° = +2.87 V，使氟成为强氧化剂。
76 V) can reduce copper(II) ions (E° = +0.34 V), a reaction exploited in the Daniell cell: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s).
电化学序中的任何一种物质都可以氧化位于其上方（更负）的物质，并还原位于其下方（更正）的物质。因此，锌（E° = −0.76 V）可以还原铜（II）离子（E° = +0.34 V），这一反应用于丹尼尔电池：Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)。
6. Calculating Cell EMF | 计算电池电动势
-hand electrode) − E°(left-hand electrode) as written in cell notation, the EMF is always positive for a spontaneous reaction. For the Daniell cell: E°(cell) = +0.34 − (−0.76) = +1.10 V. This voltage represents the maximum work the cell can perform per unit charge transferred.
原电池的电动势是两个半电池标准还原电势的差值。使用公式 E°(cell) = E°(右侧电极) − E°(左侧电极)（如电池符号所示），自发性反应的电动势总是正值。对于丹尼尔电池：E°(cell) = +0.34 − (−0.76) = +1.10 V。这个电压代表了电池每转移单位电荷所能做的最大功。
When conditions deviate from standard, the cell potential changes. The relationship between concentration and cell EMF is described by the Nernst equation, allowing calculation of actual potential under non-standard conditions. Measuring cell EMF with a high-resistance voltmeter ensures negligible current flows, so the measured voltage approximates the thermodynamic EMF.
当条件偏离标准时，电池电势会发生变化。浓度与电池电动势之间的关系由能斯特方程描述，从而可以计算非标准条件下的实际电势。用高阻抗电压表测量电池电动势可确保几乎没有电流流过，因此测得的电压接近热力学电动势。
7. The Nernst Equation | 能斯特方程
For a general half-reaction aA + ne⁻ ⇌ log Q, where n is the number of electrons transferred in the balanced equation. This shows that a cell's voltage decreases as reactants are consumed and products accumulate.
对于一般半反应 aA + ne⁻ ⇌ bB，298 K 时的能斯特方程为：E = E° − (0.059/n) log Q，其中 Q 是反应商 [B]ᵇ / [A]ᵃ。对于全电池，E(cell) = E°(cell) − (0.059/n) log Q，n 是配平方程式中转移的电子数。这表明，随着反应物消耗和生成物积累，电池电压会降低。
When Q = K (equilibrium constant), E(cell) = 0; the battery is 'flat' action, converting products back to reactants. This principle underpins secondary battery operation.
当 Q = K（平衡常数）时，E(cell) = 0；电池就“没电”了。能斯特方程解释了可充电电池能够充电的原因：施加一个大于电池电动势的外部电压可使反应逆转，将生成物转化回反应物。这一原理是二次电池工作的基础。
8. Primary Batteries | 一次电池
kaline manganese battery: anode: Zn(s) + 2OH⁻(aq) → ZnO(s) + H₂O(l) + 2e⁻; cathode: 2MnO₂(s) + H₂O(l) + 2e⁻ → Mn₂O₃(s) + 2OH⁻(aq). These batteries deliver about 1.5 V and are used in torches and remote controls.
一次电池设计为一次性使用，且无法充电，因为电池反应不易可逆。常见的例子是碱性锰电池：阳极：Zn(s) + 2OH⁻(aq) → ZnO(s) + H₂O(l) + 2e⁻；阴极：2MnO₂(s) + H₂O(l) + 2e⁻ → Mn₂O₃(s) + 2OH⁻(aq)。这种电池提供约 1.5 V 电压，用于手电筒和遥控器。
Lithium primary cells offer higher energy density (voltage about 3 V) and long shelf life. They use lithium metal as the anode and a variety of cathodes, such as manganese dioxide or carbon monofluride. These are ideal for medical devices and memory backup systems where reliability and longevity are essential.
锂一次电池具有更高的能量密度（电压约 3 V）和长储存寿命。它们使用金属锂作为阳极，以及多种阴极材料，如二氧化锰或一氟化碳。这类电池非常适合于医疗设备和存储器备用电源等要求可靠性和长寿命的应用。
9. Secondary Batteries | 二次电池
ad anode, a lead dioxide cathode, and sulfuric acid electrolyte. Discharge: Pb(s) + PbO₂(s) + 2H₂SO₄(aq) → 2PbSO₄(s) + 2H₂O(l), E° ≈ 2 V per cell. Charging reverses this reaction.
二次电池，即可充电电池，依赖可逆的氧化还原反应。用于汽车发动机的铅酸电池由铅阳极、二氧化铅阴极和硫酸电解液组成。放电反应：Pb(s) + PbO₂(s) + 2H₂SO₄(aq) → 2PbSO₄(s) + 2H₂O(l)，每格电池 E° ≈ 2 V。充电时该反应逆向进行。
Lithium-ion batteries dominate portable electronics and electric vehicles. During discharge, lithium ions move from the graphite anode to the metal oxide cathode (e.g., LiCoO₂), while electrons flow through the external circuit. The cell voltage is typically 3.6–3.7 V. Their high energy density and light weight make them superior to many older technologies.
锂离子电池在便携电子设备和电动汽车中占主导地位。放电时，锂离子从石墨阳极移动到金属氧化物阴极（如 LiCoO₂），同时电子通过外电路流动。电池电压通常在 3.6–3.7 V 之间。其高能量密度和轻重量使它优于许多旧技术。
| Type | Anode / Cathode | Voltage | Uses |
| Lead-acid | Pb / PbO₂ | ~2 V | Car batteries |
| Lithium-ion | Graphite/LiCoO₂ | 3.6–3.7 V | Phones, EVs |
| Nickel-metal hydride | MH / NiO(OH) | 1.2 V | Hybrid vehicles |
Table: Common secondary battery types
表格：常见二次电池类型
10. Fuel Cells | 燃料电池
Fuel cells convert chemical energy directly into electrical energy by reacting a fuel (often hydrogen) with an oxidant (often oxygen) without combustion. They offer high efficiency and produce only water as the by-product in hydrogen-oxygen systems. Unlike conventional batteries, fuel cells require a continuous supply of reactants and do not run down or require recharging.
燃料电池通过使燃料（通常是氢气）与氧化剂（通常是氧气）发生无燃烧反应，直接将化学能转化为电能。它们效率高，且在氢氧系统中仅产生水作为副产物。与传统电池不同，燃料电池需要持续供应反应物，不会耗尽也无需充电。
ction is: 2H₂(g) + O₂(g) → 2H₂O(l). The electrode reactions differ depending on the electrolyte, but the principle remains the same: hydrogen is oxidised at the anode and oxygen is reduced at the cathode, generating a current.
A-Level 主要学习两类燃料电池：酸性氢氧燃料电池和碱性氢氧燃料电池。两者的总反应均为：2H₂(g) + O₂(g) → 2H₂O(l)。根据电解质不同，电极反应有所不同，但原理相同：氢在阳极被氧化，氧在阴极被还原，从而产生电流。
11. Hydrogen-Oxygen Fuel Cell Reactions | 氢氧燃料电池反应
g) + 4H⁺ + 4e⁻ → 2H₂O(l). Protons migrate through the electrolyte, and electrons flow externally. The standard cell EMF is about 1.23 V.
在酸性电解质中（如磷酸 H₃PO₄ 或质子交换膜），半反应为：阳极：H₂(g) → 2H⁺ + 2e⁻；阴极：O₂(g) + 4H⁺ + 4e⁻ → 2H₂O(l)。质子穿过电解质迁移，电子在外部电路中流动。标准电池电动势约为 1.23 V。
⁻(aq). Hydroxide ions are consumed at the anode and generated at the cathode. Alkaline cells can use non-precious metal catalysts, reducing cost, but suffer from carbonation if exposed to CO₂.
在碱性电解质中（如 KOH 水溶液），半反应为：阳极：H₂(g) + 2OH⁻(aq) → 2H₂O(l) + 2e⁻；阴极：O₂(g) + 2H₂O(l) + 4e⁻ → 4OH⁻(aq)。氢氧根离子在阳极消耗，在阴极生成。碱性电池可使用非贵金属催化剂，降低成本，但如果暴露于 CO₂ 会因碳酸化而受损。
12. Comparison of Battery Technologies | 电池技术比较
When evaluating battery types, key factors include energy density (W h kg⁻¹), power density, cycle life, cost, safety, and environmental impact. Primary batteries score high on shelf life and convenience but low on economy. Secondary batteries offer repeated use but have limited cycle life. Fuel cells promise high efficiency and zero emissions but require hydrogen infrastructure and precious metal catalysts.
在评价电池类型时，关键因素包括能量密度（W h kg⁻¹）、功率密度、循环寿命、成本、安全性和环境影响。一次电池在储存寿命和便利性上得分高，但经济性差。二次电池可反复使用但循环寿命有限。燃料电池前景高效、零排放，但需要氢基础设施和贵金属催化剂。
Lithium-ion technology currently leads in portable electronics and electric vehicles due to its excellent energy-to-weight ratio and acceptable cycle life. However, issues such as thermal runaway, resource scarcity of lithium and cobalt, and end-of-life disposal remain challenges. Research into solid-state batteries and sodium-ion alternatives aims to overcome these limitations.
锂离子技术目前在便携电子设备和电动汽车领域处于领先地位，因其出色的能量重量比和可接受的循环寿命。然而，热失控、锂和钴资源稀缺以及报废处理等问题仍然是挑战。固态电池和钠离子替代品的研究旨在克服这些限制。
In summary, understanding the electrochemistry of cells and batteries allows chemists to design new power sources that are more efficient, durable, and sustainable. From basic zinc-copper cells to advanced lithium-polymer systems and hydrogen fuel cells, the principles of electrode potentials and thermodynamics remain the guiding framework.
总之，理解电池和化学电源的电化学原理使化学家能够设计出更高效、更耐用、更可持续的新型电源。从基本的锌铜电池到先进的锂聚合物系统和氢燃料电池，电极电势和热力学原理始终是指南框架。
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