Stargate Hydrogen ($57 million to develop efficient alkaline water electrolyzers for low-cost green hydrogen)

Stargate Hydrogen, an Estonian hydrogen energy startup founded in 2020, designs, manufactures, and deploys advanced alkaline water electrolyzers for green hydrogen production from renewable energy sources. Stargate Hydrogen aims to enable the decarbonization of hard-to-abate industries like steelmaking, fertilizers, and the chemical industry, where electrification alone is insufficient to reduce emissions.

Challenges: green hydrogen

Hydrogen (H₂), the most abundant element in the universe, is not just a fundamental building block of stars—it's also a vital ingredient in the synthesis of ammonia. Ammonia production is at the heart of creating a plethora of products that we rely on daily, from the fertilizers that nourish our crops to the plastics that are woven into the fabric of modern life.

Traditionally, the world has leaned heavily on steam methane reforming (SMR) to produce over 60 million tons of hydrogen annually. However, this method comes with a significant environmental cost. It's an energy-intensive process that contributes approximately 2% to the global carbon dioxide (CO₂) emissions, releasing between 5 and 9 tons of CO₂ for every ton of hydrogen it generates.

But there's a cleaner path forward: water electrolysis. This process splits water into hydrogen and oxygen using electric current and comes in various forms, including alkaline water electrolyzer (AWE), proton exchange membrane water electrolyzer (PEMWE), and solid oxide electrolysis cells (SOEC). When these electrolyzers are powered by renewable energy sources—think nuclear, solar, and wind power—the result is "green hydrogen".

Alkaline water electrolyzer

An alkaline water electrolyzer consists of two electrodes—an anode and a cathode—that are submerged in the electrolyte, which is typically potassium hydroxide (KOH). These electrodes are separated by a permeable diaphragm, which allows the passage of ions and prevents the mixing of hydrogen and oxygen.

How alkaline water electrolysis produces hydrogen
Alkaline water electrolysis produces hydrogen.

When a direct current (DC) is applied across the electrodes, water at the cathode side is reduced to hydrogen gas and hydroxide ions (OH⁻) via the half reaction:

2H₂O + 2e⁻ → H₂ + 2OH⁻

The hydroxide ions then migrate through the electrolyte to the anode side, where they are oxidized to produce oxygen gas (O₂) and water, according to the half reaction:

4OH⁻ → O₂ + 2H₂O + 4e⁻

It is desirable to operate industrial alkaline water electrolysis cells at elevated temperatures (e.g., 80 ºC) and to use concentrated alkaline solutions (e.g., 25 weight% KOH) in order to lower the required applied electric potential. However, it is challenging to develop new electrode materials that are simultaneously low-cost, result in low oxygen evolution reaction overpotentials, and are stable under elevated temperatures and concentrated alkali solutions.

Stargate Hydrogen Technology

Stargate Hydrogen has developed alkaline water electrolysis stacks based on new electrodes. Instead of precious metals like iridium and ruthenium, which are usually used in industrial alkaline water electrolysis stacks, Stargate Hydrogen’s electrodes use stable ceramic materials as catalysts for the oxygen evolution reaction. Furthermore, the electrode has a low overpotential, allowing stable electrolyzers to achieve an impressive stack-level efficiency of 80% (HHV). This makes Stargate Hydrogen one of the most efficient alkaline electrolyser stacks available.

Stargate Hydrogen electrode

Stargate Hydrogen’s innovative electrode for the oxygen evolution reaction (anode) comprises ceramic catalyst nanoparticles embedded on the surface of metallic Ni or a metallic alloy of Fe and Ni, as shown in the diagram below.

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