What are the technical challenges of seawater hydrogen production?
Water is an abundant natural resource, covering approximately 71% of the earth’s surface. Among them, seawater accounts for 96.5% of the total water on the earth. Unlike freshwater, its composition is very complex, involving 92 kinds of chemical substances and elements.
A large number of impurities such as ions, microorganisms and particles contained in seawater will cause problems such as side reaction competition, catalyst deactivation, and diaphragm blockage when producing hydrogen. For this reason, two different technical routes, direct seawater hydrogen production and seawater indirect hydrogen production, have been formed using seawater as a raw material for hydrogen production.
• The route of direct hydrogen production from seawater is mainly produced by electrolysis of water or photolysis of water;
• Indirect seawater hydrogen production is to desalinate seawater first to form high-purity fresh water and then produce hydrogen, that is, the combination of seawater desalination technology and electrolysis, photolysis, pyrolysis and other hydrolysis hydrogen production technologies.
Research on seawater electrolysis has progressed significantly over the past few decades, with more than 700 papers published, more than 340 patents, and millions of dollars in research funding.
Water Electrolysis Technology Two electrolysis technologies that exist commercially are alkaline electrolysis and proton exchange membrane (PEM) systems. Alkaline electrolysis is a well-established commercial technology, but these electrolyzers were almost completely retired in the 1970s when natural gas and SMR were used for hydrogen production.
Alkaline electrolyzers feature the avoidance of precious catalysts and lower capital costs. The high efficiency (~55-70% LHV), low current density (<0.45 A/cm²) and low operating pressure (<30 bar) of alkaline electrolysis systems have side effects on the system and hydrogen production costs.
Furthermore, the dynamic operation of alkaline electrolyzers (frequent startups and changing power input) can negatively impact efficiency and gas purity.
PEM electrolysis was pioneered by Grubb in the early 1950s and developed by General Electric in the 1960s to overcome the shortcomings of alkaline electrolysis. The PEM system uses pure water as the electrolyte, avoiding the recovery and circulation of the necessary corrosive potassium hydroxide electrolyte in the alkaline electrolyte.
To date, due to the compact design of the PEM system, high system efficiency, fast response, dynamic operation, low temperature and the ability to generate ultrapure hydrogen at high pressure, PEM has seen a significant reduction in the cost of electrolyzer stacks over the past few years, and is expected to reach 2030 will become the leading technology for sustainable hydrogen production.
Seawater electrolysis can produce both chlorine by chlorine oxidation and oxygen by water oxidation. Although chlorine is a valuable chemical, the growing hydrogen market will produce volumes that far exceed the global demand for Cl₂. Therefore, research on anode catalysts for selective oxygen evolution is a major challenge at present.
In addition, carbonate and borate ions are present in seawater, but their average concentrations are too low to sustain high current densities. Furthermore, since seawater is essentially a non-buffered electrolyte, during electrolysis it can cause pH changes near the electrode surface (up to 5-9 pH units), leading to salt precipitation, catalyst and electrode degradation of other ions, bacteria , microorganisms, and the possibility of small particles, which limit the long-term stability of catalysts and membranes.
Therefore, most reports use seawater with additives such as borate buffers or KOH, on the premise of reaching industrial-grade current densities.
Despite significant resources and efforts invested in the technology of direct seawater electrolysis, direct seawater separation technology is still in its infancy and is far from commercialization.
Article source: Energy Planet
Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.
