Research & References¶

Types of Water Electrolysis for Hydrogen Production¶

Currently, there are three main types of electrolysis technologies:

Proton exchange membrane (PEM) electrolysis
- For the PEM based electrolysis cell, the water splitting is performed under acidic condition and using PEM.
- Some advantages over other conditions, such as lower gas permeability and high proton conductivity. It features high energy efficiency and fast hydrogen production rate.
- However, the requirement of acidic media limits the OER electrocatalysts to noble metal and noble metal oxide catalysts, which are the state-of-the-art OER electrocatalysts in the acidic media. This requirement leads to a high cost for the cell.
Alkaline electrolysis
- Water splitting is performed under alkaline condition.
- In comparison with cells using acidic media, water splitting in alkaline media broadens the selection of the electrocatalysts to non-noble metals or metal oxides.
- However, the activity of HER in alkaline media is usually 2–3 orders of magnitude lower than the activity of HER in acidic media.
High-temperature solid oxide water electrolysis
- The solid oxide water electrolysis requires high energy consumption because of the high temperature.

Therefore, the design of optimal electrocatalysts suitable for the different media with low-cost, high catalytic activity, and good durability for electrolytic water splitting is very challenging.

Source: Hydrogen production from water electrolysis: role of catalysts

How does a Conductivity and pH meter works?¶

pH and conductivity are key parameters to measure the acidity and the basicity of a substance while monitoring the level of nutrients, salts or impurities present.

What are pH and conductivity?¶

The potential of hydrogen or ‘pH’ is the measure of hydrogen ion (protons) concentration in a sample used to determine the acidity or alkalinity of a product. The pH scale ranges from 0-14 with 0 being acidic, 7 being neutral, and 14 being alkaline.

Electrical conductivity is the measure of the concentration of ions present within a sample. This is calculated by the ability of the substance to transmit an electrical current over a defined area. The measurement unit for electrical conductivity is called Siemens(S) (E.g. Milli Siemens per centimetre mS/cm or Micro Siemens per cm μS/cm).

Is there a relationship between pH and electrical conductivity?¶

As discussed, pH is the measurement of a specific ion (i.e. hydrogen). In contrast, electrical conductivity is a non-specific measurement of the concentration of both positively and negatively charged ions within a sample.

So to sum, the relationship between pH and conductivity is that the presence of hydrogen ions will impact the pH level of a substance, and the presence of these ions will probably influence the conductivity level. However, hydrogen ions make up only a small part of the ion concentration measured by a conductivity meter. So given this, the relevance of the relationship will depend on the presence of hydrogen in comparison with other concentrations of non pH determining ions.

How pH and conductivity meters work¶

Electrical Conductivity

Electrical conductivity is measured by conductance between two or four electrodes using amperometric or potentiometric methods. When submerged in a sample the electrodes pass a current through the sample solution. The relative concentration of ions within the solution will determine the conductivity or the resistivity of the sample. Conductivity is expressed as Siemens units.
- 2 electrode probes (Amperometric) – These work through two electrodes isolated from one another. Made from non-reactive material and constructed so both will be in contact with the sample at the same time. These two electrodes pass a current through the sample at a specific frequency and the more ions present, the higher the EC reading.
- 4 electrode probe (Potentiometric) – This has four platinum rings on the electrode body. The top and bottom rings (on the outside) apply an alternating voltage to the sample and induces a current. The centre rings (placed to the inside of the top and bottom rings) measure the potential drop in the current generated by the outside electrodes, thus giving an electrical conductivity reading. The PC8500 uses this example.
pH Meter

A pH electrode consists of a reference electrode, reference solution, reference junction and a glass bulb with a hydrated gel layer. Once the electrode is submerged in a sample this creates a current that measures the charge of the reference solution inside the bulb compared to the solution on the outside of the gel layer. The result is a pH measurement.

Temperature factor¶

One parameter which can influence your pH and conductivity meter result is temperature. If the solution is at a higher temperature the electrical resistance may drop and therefore increase the conductance. Conversely, if a solution is cooled the conductance will drop and increase the resistivity.

To ensure accuracy, pH and conductivity meters need to be properly calibrated before each use. Generally, with pH, you should use a pH buffer solution on either side of your expected results. For example, if you are expecting results of 5.3 – you can use buffer solutions. The more calibration points along the linear pH scale the more accurate you can expect your results to be.