Green Hydrogen production Technologies and Components

The electrolyzers are key component for green hydrogen production along with other balance of plant systems / support systems. The electrolyzer is composed of the stack (where the actual splitting of water into hydrogen and oxygen occurs) and the balance of plant which comprises power supply, water supply and purification, compression, possibly hydrogen buffers and hydrogen processing.

All of these components are important for the cost, since they have similar cost shares. The largest potential for near term cost reduction is in this balance of plant, while R&D is required to reduce electrolyzer stack cost and increase its performance, life cycle and reliability.

The flexibility of alkaline and PEM stacks is enough to follow fluctuations in renewable energy source i.e. wind and solar. There is no single electrolyzer technology which performs better across all attributes. The future technology mix will depend on innovation and competition among key technologies and manufacturers, leading to technological improvements and a better fit for different technologies and system designs in each specific application.

In general, one attribute improvement in the performance of the electrolyzer stack usually parallels with compromised performance in other attribute (i.e. efficiency, cost, lifetime, mechanical strength & manufacturing). This leads to reach for best optimized solution which can be handled through innovation in materials and production. This may lead to a various specific system designs tailored to different applications in the future.

The potential breakthroughs in technology development can lead to speed up the cost reductions of electrolyzer stack wherein the balance of plant attribute can be addressed through economies of scale, standardization of design and supply chains, and lessons learned during the operations.

Electrolyzer Construction

The water electrolyzers are devices used to split water molecules into hydrogen and oxygen by passage of an electrical current. For understanding, the setup can be divided in below stages.

  • The cell is the core of the electrolyzer and it is where the electrochemical process takes place. It is composed of the two electrodes – Anode and Cathode, immersed in a liquid electrolyte or adjacent to a solid electrolyte membrane, two porous transport layers to facilitate the transport of reactants and removal of products and the bipolar plates which provide mechanical support and distribute the flow.
  • At higher level, the stack is formed with multiple cells in series. The stack includes multiple cells connected in series, spacers (insulating material between two opposite electrodes), seals, frames for mechanical support and end plates to avoid leaks and collect fluids.
  • At next level i.e. system level / balance of plant level, other support and auxiliary systems / equipments are coming in picture along with stack. These systems include equipment for cooling, processing the hydrogen to achieve purity and compressing H2, converting the electricity input from AC to DC i.e. transformer / rectifier etc, treating the water supply for deionization and oxygen output.

Cell level (Image source: IRENA)

Stack level (Image source: IRENA)

System level (Image source: IRENA)

System Level

The purified water / DM water is fed into the system using circulating pumps. The water and electrolyte come in direct contact the electrodes by flowing through the bipolar plates and through the porous transport layers. At the electrode, the water is split into oxygen and hydrogen, with H+ and OH- ions crossing though a liquid or solid membrane electrolyte. The membrane or diaphragm between both electrodes is also responsible for keeping the hydrogen and oxygen separated and avoiding their mixture. This general principle has remained the same for centuries, and the technology has evolved since 1850.

There are different OEMs which manufacture AEW electrolyzer based on current density and pressure it handles.

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