However, a disadvantage of a thin film Ag/AgCl is a short lifetime due to the small amount of Ag/AgCl. Furthermore, their potential is very sensitive to the testing solution due to the lack of a filling solution. Therefore, their application as reference electrodes is limited.

Ag/AgCl electrode is mercury-free. Chloride ions can contaminate your system as small leakage of inner electrolyte through the frit enables electric contact of Ag/AgCl reference electrode with test solution. Calomel electrode contains mercury.

The reference electrode provides a constant potential regardless of the composition of the solution it is placed in. The voltage difference between the reference and measuring electrodes is a function of the pH value of a solution.

The exact standard potential given by an IUPACreview paper is +0.22249 V, with a standard deviation of 0.13 mV at 25 °C. The potential is, however, very sensitive to traces of bromide ions which make it more negative.

在腐蚀研究中，标准甘汞电极（SCE）通常比Ag/AgCl电极更常用的原因如下：

1. **电解液兼容性**

甘汞电极（Hg/Hg₂Cl₂/KCl）的内置溶液为饱和KCl，其Cl⁻浓度高且稳定，与许多腐蚀体系（尤其是酸性或中性环境）兼容。而Ag/AgCl电极的电位对Cl⁻浓度敏感，若腐蚀体系中Cl⁻浓度波动或存在其他干扰物质（如硫化物），可能导致电位漂移或电极污染。

2. **温度稳定性**

甘汞电极的电位在常温下更稳定，而Ag/AgCl电极在高温（>80°C）时可能因Cl⁻溶解度变化导致电位偏移。腐蚀研究常涉及温度变化，SCE在此场景下表现更可靠。

3. **长期稳定性与重现性**

甘汞电极的制备工艺成熟，其电极反应可逆性高，电位重现性好，适合需要长期监测的腐蚀实验。Ag/AgCl电极（尤其是粉压型）可能需要较长时间达到稳定状态，且电极表面可能因氧化或污染导致电位漂移。

4. **历史使用习惯与标准化**

腐蚀领域长期使用SCE作为参比电极，相关文献和标准（如ASTM G215）多基于SCE的数据，便于结果对比。Ag/AgCl电极更多用于中性或生物电化学体系。

**例外情况**：

若腐蚀体系为中性或碱性环境，或需避免汞污染（如环保要求），Ag/AgCl电极可能是更优选择。此外，在含有机电解液或非水体系中，Ag/AgCl电极的适应性更好。

For me, calomels generally got used in corrosion studies because corrosion labs had them. Silver/silver chlorides are much more common. The ref is actually a silver/silver chloride / chloride solution electrode. The number you get depends on the concentration of the chlorides in the solution. Normally they're packaged in a solution containing a fixed amount of chloride eg 0.5M potassium chloride. It doesn't have to be 0.5M, but if you're looking at absolute values then you do have to report the concentration. The silver chloride also degrades if exposed to light, so most of them come in opaque tubes that stops this, although some lab commercial ones i bought came in a clear tube, which wasn't helpful. The potential can be affected by the presence of bromide ions in solution, but not by much. Not had problems with short lifetime mentioned above, and we use them in bridges where i've got 20 + years out of them. Mots standards say the life is governed by the mass of silver, but am yet to be convinced how silver is consumed in a reversible reaction in a readily polarisable electrode. Basically use what you have, and state that's what you've used. For cathodic protection of steel in concrete the default in the BS EN ISO is silver/silver chloride 0.5M. If you're working on pipelines the most common is a copper / saturated copper sulfate because they're easy to strip down and clean up if you're in the middle of nowhere surveying a long pipe.

Some people shy away from the calomel electrode because it contains mercury. In terms of usability, you can use either. You just need to know the type of electrode (what kind of potassium chloride solution is inside, saturated, 3M, or whatever).