Supercritical Solutions, a UK cleantech company founded in 2020, develops a membrane-less alkaline water electrolyzer that uses supercritical alkaline electrolyte at high temperature and pressure to produce pre-pressurized hydrogen. This technology significantly reduces the overall cost and complexity of hydrogen production, making it more accessible for various industrial applications.
Challenges: hydrogen fuel
Green hydrogen (H₂) is a crucial element of the future net-zero world. Using electricity from renewable sources, such as nuclear, solar, and wind, to split water produces green hydrogen. Green hydrogen can decarbonize hard-to-abate industries, such as steel manufacture, long-distance transportation, shipping, and aviation. Seasonally, it can also store renewable electricity and serve as a chemical feedstock.
There are several ways to use electricity to turn water into hydrogen right now. These include alkaline electrolyzers, proton exchange membrane (PEM) electrolyzers, anion-exchange membrane (AEM) electrolyzers, and solid oxide electrolysis cells.
When it comes to commercial water electrolysis technology in the megawatt range, alkaline electrolyzers are the most common type. An alkaline water electrolyzer consists of two electrodes—an anode and a cathode—that are submerged in an electrolyte. The electrolyte is typically a potassium hydroxide (KOH) or sodium hydroxide (NaOH) solution. The electrodes are separated by a thick, porous permeable diaphragm.
The alkaline electrolyzer can use cheap parts, like steel bipolar plates, inexpensive diaphragm separators, and non-precious catalysts for hydrogen and oxygen evolution reactions.
Alkaline electrolyzers typically operate at temperatures between 70-100 ºC. The operating pressure is usually less than 40 bar. The produced hydrogen needs to be compressed for storage and transport. The operating temperature and pressure is mainly limited by the structural stability of the diaphragm.
Supercritical Solutions Technology
Supercritical Solutions has developed a membrane-less alkaline water electrolyzer. Such an electrolyzer uses a supercritical alkaline aqueous electrolyte at high temperature and pressure (220 − 270 bar and 374 − 400 ºC) to produce pre-pressurized hydrogen. Supercritical Solutions technology eliminates the need for expensive membranes, materials, and external gas pressurization, allowing for the direct use or storage of hydrogen outputs without further intermediate steps.
Supercritical Solutions electrolyzer
The diagram below illustrates the structure of Supercritical Solutions membrane-less electrolyzer.
The electrolyzer consists of three annular chambers: an outer annular chamber, an intermediate annular chamber, and a core inner chamber. The outer and intermediate chambers have a larger annular porous wall, while the intermediate and core inner chambers have a smaller annular porous wall.
Electrodes coat the surfaces of porous walls. The bigger porous wall’s outer surface coats a cathode, while the smaller porous wall’s inner surface coats an anode. Platinum makes up the cathode, while nickel makes up the anode.
The porous walls have inclined channels. The inclined channels have the following advantages:
- They promote the fluid reaction products generated at the respective electrodes, which flow upward along the channels into the respective reaction chambers.
- They prevent a reverse flow of such fluid reaction products downward through the channels against buoyancy forces.
How Supercritical Solutions produces hydrogen
During operation, the supercritical electrolyte continuously feeds into the intermediate inlet chamber. This chamber has no outlet port. Therefore, the supercritical electrolyte fluid is driven through the inclined channels of porous walls, enters the outer and inner chambers, and exits through their outlet ports.
When a direct current (DC) is applied across the electrodes, water at the cathode is reduced to hydrogen gas and hydroxide ions (OH⁻) via the half reaction:
2H₂O + 2e⁻ → H₂ + 2OH⁻
The hydroxide ions at the anode side are oxidized to produce oxygen gas (O₂) and water, according to the half reaction:
4OH⁻ → O₂ + 2H₂O + 4e⁻
The porous walls stop the flow of the reaction products backwards, which separates the reaction products made at each electrode without using an ion exchange membrane. As the porous walls are sufficiently porous to allow fluid flow through them, they inherently also permit ion exchange in either direction.
Advantages of supercritical electrolyte
The supercritical electrolyte has two distinctive advantages over a subcritical electrolyte:
- The supercritical electrolyte has a higher conductivity at elevated temperatures and pressures. This reduces ohmic losses and increases the electrolyzer’s efficiency. For example, the conductivity of a 0.5 M NaOH solution at 225 bar and 375 ºC is approximately 150 − 200 mS cm⁻¹, whereas at 1 bar and 25 ºC, the conductivity is around 100 mS cm⁻¹.
- Supercritical fluids are completely miscible with each other. Reaction products remain completely miscible with the electrolyte fluid when they maintain their supercritical state instead of becoming gaseous during generation. As a result, reaction product bubbles do not accumulate on the electrode surfaces. Otherwise, such accumulations inhibit the reaction by preventing local interaction between the electrolyte and the electrode.
Supercritical Solutions Patent
- WO2022195110A3 An electrolyser
Supercritical Solutions Technology Applications
- WhiskHy: decarbonized drams with hydrogen
This case study focuses on enabling Scotch Whisky distilleries to produce and store hydrogen on-site, significantly reducing their reliance on non-renewable fuels. The project aims to revive traditional practices of direct firing in whisky production, which were largely replaced by indirect steam heating due to modernization and safety regulations. By using zero-emission hydrogen for direct firing, the project seeks to bring back the unique character and flavor to the whisky that comes from direct flame application, while also minimizing CO₂ emissions.
- GreeNH₃: green ammonia as a hydrogen transport Vector
GreeNH₃ explores the potential of ammonia as a promising solution for transporting hydrogen over long distances. The case study highlights the historical context of ammonia synthesis through water electrolysis powered by renewable energy sources, such as hydropower, before the dominance of natural gas due to its low cost. Supercritical Solutions aims to leverage its technology to enable the resurgence of green water electrolysis plants for ammonia synthesis, offering a sustainable alternative with no emissions. This approach addresses the significant carbon footprint associated with traditional ammonia production from natural gas.
- Zero Mining: sustainable natural resources
The Zero Mining case study investigates how Supercritical’s high-pressure electrolyzer can contribute to the mining sector’s journey towards net zero emissions. By meeting the demand for 350 bar of hydrogen, the technology could reduce compression energy by tenfold compared to traditional methods. This application demonstrates the potential of green hydrogen in making the energy-intensive and carbon-intensive process of mining more sustainable.
Supercritical Solutions Products
Supercritical Solutions focuses on the development of innovative electrolyzer technology for the generation of green hydrogen. Their products and technology are designed to address the challenges of traditional hydrogen production methods by offering solutions that are more efficient, cost-effective, and environmentally friendly.
Supercritical Solutions Funding
Supercritical Solutions raised $3.6 million in a seed funding round on 19 Jan 2022.
Supercritical Solutions Investor
Supercritical Solutions is funded by Jericho Energy Ventures.
Supercritical Solutions Founder
Matt Bird, Mike Russ, Luke Tan, and Gaël Gobaille-Shaw are Co-Founder.
Supercritical Solutions CEO
Matt Bird is CEO.