📚 Electrode Potentials | 电极电势
Electrode potentials lie at the heart of electrochemistry, linking redox reactions to measurable voltages. They allow chemists to predict whether a reaction will proceed spontaneously, to design batteries and to understand corrosion. In this article, we explore standard electrode potentials (E°), the hydrogen reference, the electrochemical series and the Nernst equation, building a solid foundation for Cambridge A-Level Chemistry.
电极电势是电化学的核心，它将氧化还原反应与可测量的电压联系起来。借助电极电势，化学家可以预言一个反应是否能自发进行、设计电池以及理解腐蚀现象。本文将探讨标准电极电势(E°)、氢参比电极、电化学序列和能斯特方程，为剑桥A-Level化学建立扎实的基础。
1. What are Electrode Potentials? | 什么是电极电势？
When a metal strip is dipped into a solution of its own ions, a potential difference builds up between the metal and the solution. This voltage, called the electrode potential, arises from the tendency of the metal to lose electrons (oxidation) or of the ions to gain electrons (reduction). The measured value depends on the nature of the metal, the ion concentration and the temperature.
当一根金属条浸入其自身离子的溶液中时，金属与溶液之间会建立起电势差。这一电压称为电极电势，它源自金属失去电子（氧化）或离子得到电子（还原）的趋势。测量值取决于金属的种类、离子浓度和温度。
A lone electrode potential cannot be measured in isolation; it must be coupled with a second electrode to form a complete cell. By convention, we always compare it to a reference – the standard hydrogen electrode – and record the voltage under agreed standard conditions.
单独一个电极的电势无法孤立测量，必须与第二个电极组成完整电池。按照惯例，我们总是将它与一个参比电极——标准氢电极——进行比较，并在约定的标准条件下记录电压。
2. Half-Cells and Redox Couples | 半电池与氧化还原对
Every electrode potential measurement involves two half-cells. A half-cell contains a reduced form and an oxidized form of the same element, called a redox couple, such as Zn²⁺/Zn or Cu²⁺/Cu. The half-cell where reduction occurs is the cathode (+), and the half-cell where oxidation occurs is the anode (−).
每个电极电势的测量都涉及两个半电池。一个半电池中含有同一元素的还原态和氧化态，称为氧化还原对，例如 Zn²⁺/Zn 或 Cu²⁺/Cu。发生还原的半电池是正极（阴极），发生氧化的半电池是负极（阳极）。
The two half-cells are connected by a salt bridge – often a strip of filter paper soaked in KNO₃ – which allows ions to migrate and complete the circuit without letting the solutions mix.
两个半电池通过盐桥（通常是一条浸有 KNO₃ 的滤纸条）相连，盐桥允许离子迁移以完成回路，同时防止两种溶液混合。
3. Standard Conditions for Measurement | 测量的标准条件
To ensure reproducibility, standard electrode potentials are measured under exact conditions: 298 K (25 °C), all ion concentrations at 1.00 mol dm⁻³ and any gases at 100 kPa pressure. If a solution contains multiple ions, all must be at 1.00 mol dm⁻³. These conditions are essential because potential varies with concentration and temperature.
为保证可重复性，标准电极电势在精确的条件下测量：温度 298 K (25 °C)，所有离子浓度为 1.00 mol dm⁻³，任何气体压力为 100 kPa。如果溶液含有多种离子，所有离子的浓度都必须为 1.00 mol dm⁻³。这些条件至关重要，因为电势会随浓度和温度改变。
4. The Standard Hydrogen Electrode (SHE) | 标准氢电极 (SHE)
The primary reference is the standard hydrogen electrode, whose potential is defined as exactly 0.00 V. It consists of a platinum electrode coated with finely divided platinum (platinum black) immersed in 1.00 mol dm⁻³ H⁺(aq), with hydrogen gas bubbled through at 100 kPa. The half-cell is represented as:
最根本的参比电极是标准氢电极，其电势被定义为 0.00 V。它由一块镀有铂黑的铂电极浸入 1.00 mol dm⁻³ H⁺(aq) 溶液中组成，同时向溶液中通入 100 kPa 的氢气。该半电池可表示为：
Pt(s) | H₂(g) | H⁺(aq)
The equilibrium is 2H⁺(aq) + 2e⁻ ⇌ H₂(g). The platinum black provides a large surface area for adsorption of hydrogen, ensuring a fast, reversible reaction.
其平衡为 2H⁺(aq) + 2e⁻ ⇌ H₂(g)。铂黑提供了大的比表面积用于吸附氢气，确保了快速、可逆的反应。
5. Measuring Standard Electrode Potentials (E°) | 测量标准电极电势 (E°)
To determine the standard electrode potential of a half-cell (e.g. Zn²⁺/Zn), it is connected to the SHE via a high-resistance voltmeter. The cell diagram would be:
要测定某个半电池（如 Zn²⁺/Zn）的标准电极电势，需将其通过高电阻电压表与 SHE 相连。电池图示为：
Zn(s) | Zn²⁺(aq, 1 mol dm⁻³) || H⁺(aq, 1 mol dm⁻³) | H₂(g, 100 kPa) | Pt(s)
If electrons flow from the zinc electrode to the hydrogen electrode, the voltmeter reads a negative value, by convention. The E° for Zn²⁺/Zn is recorded as −0.76 V, meaning zinc has a greater tendency to release electrons than hydrogen.
如果电子从锌电极流向氢电极，电压表读数按惯例为负值。Zn²⁺/Zn 的 E° 记为 −0.76 V，这意味着锌比氢更容易释放电子。
If a half-cell has a positive E° (e.g. Cu²⁺/Cu = +0.34 V), the ion gains electrons more readily than H⁺, and reduction is favoured.
若某半电池的 E° 为正值（如 Cu²⁺/Cu = +0.34 V），则该离子比 H⁺ 更容易获得电子，还原更占优势。
6. The Electrochemical Series | 电化学序列
Arranging redox couples in order of their standard electrode potentials gives the electrochemical series, a powerful tool for predicting reactivity. The more negative the E°, the stronger the reducing agent (the reduced form is easily oxidized). The more positive the E°, the stronger the oxidizing agent (the oxidized form is easily reduced).
将氧化还原对按标准电极电势排序，就得到了电化学序列，它是预测反应性的有力工具。E° 越负，还原剂的还原能力越强（其还原态容易被氧化）；E° 越正，氧化剂的氧化能力越强（其氧化态容易被还原）。
Key entries include:
| Redox couple | E° / V |
|---|---|
| Li⁺/Li | −3.04 |
| Zn²⁺/Zn | −0.76 |
| Fe²⁺/Fe | −0.44 |
| 2H⁺/H₂ | 0.00 |
| Cu²⁺/Cu | +0.34 |
| Fe³⁺/Fe²⁺ | +0.77 |
| MnO₄⁻ / Mn²⁺ | +1.51 |
| F₂/F⁻ | +2.87 |
Any metal higher in the series will displace a metal lower down from its salt solution.
在序列中位置更靠上的金属，能将位于其下方的金属从其盐溶液中置换出来。
7. Calculating Cell EMF | 计算电池电动势
The electromotive force (EMF) of a cell is the potential difference between the two half-cells when no current is flowing. It is calculated as:
电池的电动势（EMF）是在没有电流流动时两个半电池之间的电势差，可由下式计算：
E°(cell) = E°(cathode) − E°(anode)
Or equivalently, E°(cell) = E°(right-hand electrode) − E°(left-hand electrode) in the conventional cell diagram. For a zinc–copper cell, E°(cell) = +0.34 V − (−0.76 V) = +1.10 V. The positive sign indicates the reaction is thermodynamically feasible.
或者等价地，在常规电池图示中，E°(cell) = E°(右侧电极) − E°(左侧电极)。对于锌–铜电池，E°(cell) = +0.34 V − (−0.76 V) = +1.10 V。正值表明该反应在热力学上是可行的。
Always write the cell diagram with the half-cell of higher reduction potential on the right; this yields a positive EMF for a spontaneous reaction.
务必将还原电势更高的半电池写在右侧，这样自发的反应就会得到正的电动势。
8. Using E° to Predict Reaction Feasibility | 使用 E° 预测反应可行性
Feasibility is linked to the Gibbs free energy change: ΔG° = −nFE°(cell). A positive E°(cell) gives a negative ΔG°, meaning the forward reaction is spontaneous under standard conditions. However, E° values only tell us about thermodynamics, not about the rate – a reaction may be feasible but impossibly slow.
可行性与吉布斯自由能变有关：ΔG° = −nFE°(cell)。正的 E°(cell) 得到负的 ΔG°，表明在标准条件下正反应自发。但是，E° 数值只反映热力学，不反映速率——一个反应可能可行但极其缓慢。
When predicting, compare the oxidizing agent in one couple with the reducing agent in the other. If the couple with more positive E° is reduced while the more negative one is oxidized, the overall reaction will have a positive E°(cell).
预测时，比较某一氧化还原对中的氧化剂与另一对中的还原剂。若 E° 较正的被还原，E° 较负的被氧化，则总反应的 E°(cell) 为正。
9. The Nernst Equation: Effect of Concentration | 能斯特方程：浓度的影响
When concentrations are not standard, the electrode potential changes according to the Nernst equation. For a half-reaction aOxidized + ne⁻ ⇌ bReduced, at 298 K:
当浓度非标准时，电极电势根据能斯特方程变化。对于半反应 a氧化态 + ne⁻ ⇌ b还原态，在 298 K 时：
E = E° − (0.0592 / n) × log₁₀([Reduced]ᵇ / [Oxidized]ᵃ)
The equation shows that increasing the concentration of the oxidized form makes E more positive, while increasing the reduced form makes E more negative. This explains why cells run down: as reactants are consumed, E(cell) drops towards zero.
该方程表明，增加氧化态浓度使 E 更正，增加还原态浓度则使 E 更负。这就解释了为何电池会耗尽：随着反应物被消耗，电池电动势 E(cell) 逐渐降至零。
10. Concentration Cells | 浓差电池
A concentration cell consists of two identical half-cells differing only in ion concentration. The electrode in the more dilute solution tends to release ions, making it more negative. The cell EMF is generated purely by the concentration gradient and can be predicted by the Nernst equation.
浓差电池由两个相同但离子浓度不同的半电池构成。处在较稀溶液中的电极倾向于释放离子，因而电势更负。电池的电动势完全由浓度梯度产生，并可通过能斯特方程预测。
For example, a cell with Cu²⁺(0.1 mol dm⁻³) and Cu²⁺(1.0 mol dm⁻³) will produce a small voltage until the concentrations equalise. Such cells illustrate the direct link between chemical potential and electrical potential.
例如，一个含有 0.1 mol dm⁻³ Cu²⁺ 和 1.0 mol dm⁻³ Cu²⁺ 的电池会产生一个小电压，直到浓度相等。这种电池展现了化学势与电势之间的直接联系。
11. Electrochemical Cells in Practice: Batteries | 实际电化学电池：电池
Practical cells are designed to be compact, safe and long-lasting. Three common types are: primary cells (non-rechargeable, e.g. zinc–manganese dioxide alkaline cells), secondary cells (rechargeable, e.g. lithium-ion and lead–acid batteries) and fuel cells (continuous supply of reactants, e.g. hydrogen–oxygen fuel cell).
实用电池被设计得紧凑、安全且持久。三种常见类型是：一次电池（不可充电，如锌–二氧化锰碱性电池）、二次电池（可充电，如锂离子电池和铅酸蓄电池）以及燃料电池（连续供给反应物，如氢–氧燃料电池）。
In a hydrogen fuel cell, the electrode reactions are:
Anode: H₂(g) + 2OH⁻(aq) → 2H₂O(l) + 2e⁻
Cathode: O₂(g) + 2H₂O(l) + 4e⁻ → 4OH⁻(aq)
The overall cell reaction is 2H₂ + O₂ → 2H₂O, with a theoretical E° of +1.23 V. Fuel cells offer high efficiency and water as the only product, making them attractive for green energy.
总反应为 2H₂ + O₂ → 2H₂O，理论标准电动势为 +1.23 V。燃料电池效率高，唯一产物是水，使其在绿色能源领域极具吸引力。
12. Corrosion and its Prevention | 腐蚀与防护
Corrosion, especially rusting of iron, is an electrochemical process. On the surface of iron, tiny cells form where some areas act as anodes (Fe → Fe²⁺ + 2e⁻) and others as cathodes (O₂ + 2H₂O + 4e⁻ → 4OH⁻). These combine to give hydrated iron(III) oxide, rust.
腐蚀，尤其是铁的生锈，是一个电化学过程。在铁的表面会形成微小的原电池，某些区域作阳极（Fe → Fe²⁺ + 2e⁻），另一些区域作阴极（O₂ + 2H₂O + 4e⁻ → 4OH⁻），最终生成水合氧化铁，即铁锈。
Protection strategies exploit electrode potentials. Sacrificial protection uses a more reactive metal (e.g. zinc on galvanised steel) that corrodes preferentially. Cathodic protection connects the metal to a more negative electrode, forcing it to be the cathode. Coatings and alloying (e.g. stainless steel) also reduce corrosion.
防护策略利用了电极电势。牺牲阳极保护法使用更活泼的金属（如镀锌钢上的锌）优先腐蚀。阴极保护法将金属连接到更负的电极上，迫使被保护金属成为阴极。覆盖层与合金化（如不锈钢）也能降低腐蚀。
Published by TutorHao | Chemistry Revision Series | aleveler.com
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