Reference Electrodes

Reference Electrodes for Electrochemistry

Introduction

A reference electrode is a half-cell with a well-defined, stable potential that does not change with current. It anchors the potential scale in three-electrode experiments so that working-electrode kinetics, thermodynamics, and mechanisms can be measured accurately and compared across labs and time. Common options include Ag/AgCl in KCl (aqueous), saturated calomel (SCE), mercury/mercuric oxide (Hg/HgO) for alkaline media, mercury/mercurous sulphate (Hg/Hg₂SO₄) for acidic media, and reversible hydrogen electrodes (RHE) for pH-dependent systems. Typical 25 °C potentials vs NHE: Ag/AgCl (sat. KCl) ≈ +0.197 V; SCE ≈ +0.241 V; Hg/HgO (1 M KOH) ≈ +0.098 V; Hg/Hg₂SO₄ (sat. K₂SO₄) ≈ +0.615 V; RHE shifts by ~59 mV per pH unit.

Key Features & Specifications

• Stable, well-characterised potentials with low drift in intended media (aqueous/alkaline/acidic/non-aqueous).
  Junction options: single liquid junction for routine work; double-junction/salt-bridge designs to minimise chloride or silver contamination into sensitive electrolytes.
• Non-aqueous Ag/Ag+ designs accept organic solvents (e.g., acetonitrile) with supporting salt (e.g., TBAP/TBAPF6); keep the same solvent/salt as the test electrolyte to reduce junction errors.
• Practical potentials (25 °C vs NHE): Ag/AgCl (sat. KCl) ~+0.197 V; SCE ~+0.241 V; Hg/HgO (1 M KOH) ~+0.098 V; Hg/Hg₂SO₄ (sat. K₂SO₄) ~+0.615 V; RHE = 0 V at pH 0, shifts by 59 mV/pH.
  
  

Applications

• Batteries and alkaline fuel cells (Hg/HgO in KOH).
• Acidic corrosion and electrocatalysis studies (Hg/Hg₂SO₄).
• General aqueous electrochemistry and corrosion (Ag/AgCl, SCE).
• Organic electrosynthesis and redox in non-aqueous solvents (Ag/Ag+).
• pH-dependent mechanistic studies and fuel-cell R&D (RHE).
  
  

Material Options

• Ag/AgCl (KCl): Widely used, mercury-free, robust; select KCl concentration for the desired potential.
• SCE: Classic, stable aqueous reference; mercury-based; often replaced by Ag/AgCl for safety.
• Hg/HgO (1 M KOH): Ideal for alkaline systems; E° ≈ +0.098 V vs NHE.
• Hg/Hg₂SO₄ (sat. K₂SO₄): Preferred in acidic media where chloride contamination must be avoided.
• RHE: True hydrogen equilibrium; potential shifts ~59 mV per pH at 25 °C; excellent for pH-dependent studies.
• Non-aqueous Ag/Ag+: Silver/silver-ion in matching solvent/supporting electrolyte to minimise junction potentials.
  
  

Why Buy from ScienceGears

• Application-driven guidance (choose the right reference for your electrolyte and technique).
• Local AU/NZ support and fast supply.
• Option sets for double-junction bridges and compatible holders/frits.
• Integration advice for potentiostats, cells, and Luggin capillaries.

FAQs

1. How do I choose between Ag/AgCl and SCE?
Both are stable in aqueous media; Ag/AgCl is mercury-free and commonly preferred. SCE offers excellent stability but contains mercury. Match the KCl concentration and temperature to the quoted potential.

2. When is a double-junction (double salt bridge) helpful?
Use it to isolate KCl or Ag+ from sensitive samples (e.g., chloride-free systems); the outer bridge can be filled with a more compatible salt such as KNO3.

3. Which reference is best for alkaline electrolytes?
A: Hg/HgO (typically in 1 M KOH; E° ≈ +0.098 V vs NHE at 25 °C).

4. What should I use in a strong acid when avoiding chloride?
A: Hg/Hg₂SO₄ in saturated K₂SO₄ is a common choice (≈ +0.615 V vs NHE at 25 °C).

5. How does RHE differ from SHE/NHE?
A: RHE tracks pH (~59 mV per pH at 25 °C), making it ideal when you need a pH-independent kinetic reference.

Final Call-to-Action
Do you need help selecting the right reference electrode? Please feel free to contact ScienceGears for expert guidance and a fast quote.