Saltwater electrolysis flow regulation for green hydrogen production

The electrolysis water purity problem  

In totality, only some 3% of all water on the Earth is freshwater. The remaining 97% is made up of brackish water and saltwater that contain elevated levels of dissolved salts and minerals.  

Traditional hydrogen producing PEM electrolysis systems depend on a supply of deionized freshwater to operate at highest efficiency. In fact, at a certain concentration of salt and above, most traditional electrolysis systems will not operate at all.  

University of Adelaide’s saltwater green hydrogen electrolysis system  

Researchers led by the University of Adelaide School Of Chemical Engineering have successfully developed a green hydrogen electrolysis system that directly uses saltwater at nearly 100% efficiency. In their process, the system is able to directly use seawater without any preliminary steps such as deionization, desalinization, and alkali addition with a similar performance to traditional metal-based pure water electrolyzers. However, at this early stage of early development, the saltwater electrolyzer is affected by current attenuation from corrosion of its catalysts by chlorine species as well as precipitate formation which limits the longevity of the system.    

The University of Adelaide’s electrolysis system is configured of a two-electrode cell which uses carbon fibre papers loaded with Cr2O3–CoOx nanorods as the anode and cathode. The carbon fibre substrate is protected with gold before the growth of the Cr2O3–CoOx nanorods in order to avoid contact of the carbon fibre with the electrolyte as well as to prevent electrochemical oxidation.  

Just as in a typical PEM electrolysis system for green hydrogen production, the anode and cathode split the water into hydrogen and oxygen and are able to be powered by a renewable energy source such as solar or wind energy.  

Flow regulation for saltwater green hydrogen electrolysis  

In the University of Adelaide’s research experiment setup, liquid mass flow controllers automate the flow of seawater into and out of the system at a rate of 60 ml/min combined with a peristaltic pump. At the same time, hydrogen and oxygen gases produced at the cathode and anode chamber are collected through a gas–liquid separation tank while also having their outflows recorded and totalized by a gas flow meter.  

Liquid flow control  

In order to optimize the operating conditions for this electrolysis system with high validity of test results, Alicat’s liquid mass flow controllers offer impressive control stability, high accuracy, and precision of the seawater liquid flow, ensuring that there is a constant rate of water coming into and out of the electrolysis system.  

For this specific use, Alicat’s CODA KC-Series provides a great solution. Alicat’s CODA KC-Series customization can include a pump attachment and high accuracy flow control for low flow electrolysis, down to a full-scale of just 40 g/h. 

CODA KC-Series features and specs: 

  • 40 g/h full scale to 100 kg/h full scale with a turndown of 2% – 100% of full scale 
  • NIST-traceable accuracy up to ±0.2% of reading or ±0.05% of full scale, whichever is greater 
  • Repeatability ± ±0.05% of reading or ±0.025% of full scale, whichever is greater 

Gas metering 

As mentioned previously, gas flow meters are used in this system to record the outflow of oxygen and hydrogen, ensuring that researchers know exactly how much hydrogen is produced as well as the efficiency of the system.  

For this purpose, either Alicat’s M-Series or CODA K-Series are excellent to use due to wide measurement range, extensive communication options, and totalizing and batching features. As a result, high quality, accurate gas flow data can be seamlessly sent to a PLC or computer for continuous data collection and automation.  

M-Series features and specs: 

  • 0.5 SCCM full scale to 5,000 SLPM full scale with a measurement range of 0.01% – 100% of full scale  
  • Repeatability up to 0.1% of reading and 0.02% of full scale 

CODA K-Series features and specs: 

  • 40 g/h full scale to 100 kg/h full scale with a measurement range of 0.2% –100% of full scale 
  • NIST-traceable gas accuracy up to ±0.5% of reading or ±0.05% of full scale, whichever is greater 
  • Repeatability ± ±0.05% of reading or ±0.025% of full scale, whichever is greater 

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