Use of the Hydrogen Electrodes HydroFlex and Mini-HydroFlex
Electrolytes and Solutions
You can use these hydrogen electrodes in the following solutions, for example:
- diluted and concentrated sodium hydroxide/potassium hydroxide solution
- hydrochloric acid
- salt solutions (e.g. sodium chloride, potassium chloride, potassium sulfate)
- sulfuric acid (< 50 %)
- phosphoric acid up to 85 %
- concentrated hydrofluoric acid
- hypochlorous acid
- perchloric acid
- carbonic acid
- formic acid
- acetic acid
- lactic acid
- citric acid
- nitric acid up to max. 2 mol/L
HydroFlex as RHE (Reversible Hydrogen Electrode – Indicator Electrode)
The use of the hydrogen electrode HydroFlex as a RHE is certainly the most common application in everyday laboratory work.
Simply place the HydroFlex in your measurement solution.
The benefits are quite obvious. They do not require an electrolyte bridge, have no diffusion potentials and are not subject to contamination by ions flowing out of your reference system.
Since HydroFlex is maintenance-free apart from changing the hydrogen source every 6 months, it is very useful for continuous measurements.
HydroFlex as NHE (Normal Hydrogen Electrode)
When you use the hydrogen electrode HydroFlex in 1 mol/L hydrochloric acid at ambient pressure, you have a normal hydrogen electrode (NHE).
The potential deviations of a normal hydrogen electrode from a standard hydrogen electrode (SHE) are small, while the experimental effort is limited.
HydroFlex as SHE (Standard Hydrogen Electrode)
The standard hydrogen electrode is the most important reference electrode of all, since its potential is defined as the zero point of the electrochemical series:
“For solutions in protic solutions, the universal reference electrode for which, under standard conditions, the standard electrode potential H+/H2 is zero at all temperatures.”
(IUPAC Compendium of Chemical Terminology, Goldbook, Version 2.3.3., 24.03.2014).
Standard hydrogen electrode:
“The standard hydrogen electrode consists of a platinum electrode in contact with a solution of H+ at unit activity and saturated with H2 gas with a fugacity referred to the standard pressure p∅ of 105 Pa.”
(Quantities, units and symbols in physical chemistry, IUPAC Green Book, 3rd edn, 2nd printing, IUPAC & RSC Publishing, Cambridge, 2008).
Since 1982, the IUPAC has specified a standard pressure of 1.000 bar (100 kPa).
However, in the years before 1982, the standard pressure was set at 1.01325 bar (101.325 kPa = 1 atm).
For this reason, the value 1.01325 bar is often found in credentials and is still the preferred standard in electrochemistry.
To use the hydrogen electrode HydroFlex as a SHE, the hydrogen electrode has to be placed in an electrolyte with a hydrogen ion activity of 1 mol/l. At 25°C, for example, 1.18 molar hydrochloric acid has a hydrogen ion activity of 1 mol/l.
The temperature has to be 298.15 K und the pressure has to be 1013 hPa (standard conditions).
Since adjusting pressure and temperature is particularly difficult, this application plays a minor role.
Would you like to learn more about our hydrogen reference electrodes HydroFlex and Mini-HydroFlex?
Hydrogen Reference Electrode HydroFlex
The platinum-hydrogen reference electrode is the first choice to measure potentials conforming to standards. Here you will find some general information about it.
Mini Hydrogen Reference Electrode Mini-HydroFlex
We have further developed and reduced the size of our hydrogen electrode HydroFlex for use in confined spaces. Here you will find some general information about our Mini-HydroFlex.
Checking the Functionality of the HydroFlex and Mini-HydroFlex
Ideally, you should check the hydrogen electrode against a so-called master electrode, e.g. a calomel electrode, before your actual measurements. Here you will find more information about checking your HydroFlex or Mini-HydroFlex.
Pourbaix Diagram - helpful tools in electrochemistry
The potential of the RHE itself changes with the pH of the electrolyte by 59 mV/pH @25°C. This means that for any pH-dependent system changing its potential by 59 mV/pH, you will measure a stable pH-independent potential. The so-called Pourbaix diagram gives an overview of the pH dependence of potentials.
Are you convinced to purchase one of our reference electrodes?
Hydrogen Reference Electrode HydroFlex Starterkit
Ideal starter kit for anyone who has not yet worked with the HydroFlex reference electrode.
Hydrogen Reference Electrode HydroFlex
Our Standard Hydrogen Reference Electrode HydroFlex can be used in almost any electrolyte. It is ideal for corrosion measurements. Long-term measurements of up to 6 months are also possible without user intervention.
Mini Hydrogen Reference Electrode Mini-HydroFlex
Gaskatel has further developed and reduced the size of the hydrogen reference electrode for use in confined spaces. The structure and functionality correspond to the hydrogen electrode HydroFlex – just smaller. Ideal for use in FlexCell and ElyFlow.