Hystar, a Norway cleantech startup founded in 2020, develops PEM electrolyzers for large-scale green hydrogen production. The company’s PEM electrolyzer uses a thin proton exchange membrane below 30 microns and consumes humidified air and liquid water to produce hydrogen. This design results in 20% less energy consumption and a low-cost green hydrogen.
Challenges: hydrogen fuel
Electrolysis of water (H₂O) can produce hydrogen gas (H₂) using an electrolyzer, such as proton exchange membrane (PEM) electrolyzer. The PEM is preferably made of perfluorosulfonic acid (PSFA) polymers, such as Nafion® or Aquvion®. The diagram below schematically depicts the structure and operation of a conventional PEM electrolyzer.
During operation, H₂O must be supplied continuously to the anode, where H₂O is oxidized to oxygen gas (O₂), protons (H⁺), and electrons (e⁻). An electric field across the PEM causes protons to migrate from the anode to the cathode. At the cathode, protons combine with electrons transferred through an external circuit to produce H₂. Produced H₂ and O₂ can diffuse through the membrane due to their partial pressure gradient across the membrane. A negligible amount of H₂ in O₂ in the anode can form explosive gas mixtures. In this regard, conventional PEM electrolyzers use PEM that is thicker than over 125 microns (μm) to effectively reduce H₂ and O₂ diffusion through the membrane.
However, this thick PEM limits the rate of gas generation, which is governed by Faraday's law. An increase in the current passing through the electrolyzer increases the gas production and H₂O consumption proportionally. However, the use of such a thick membrane results in a significant ohmic resistance and, consequently, a decrease in the electrolyzer’s efficiency, particularly at current densities above 1 A cm⁻².
Currently, water electrolyzers are operated with a stack efficiency around 65-70% (higher heating value HHV), resulting in a power demand of about 55 kWh per kilogram of H₂. About 50 kWh are consumed by the electrolysis process, while the remaining 5 kWh are utilized by circulation and feed water pump, heat exchanger, ion exchanger, gas/water separators, valves and sensors, etc.
Therefore, an increase in the efficiency of the electrolyzer stack will rescue both the total amount of primary electrical energy consumption and the total cost of H₂.
Hystar Technology
Hystar has developed more efficient PEM electrolyzers simply by reducing the thickness of PEM to below 35 microns (μm) and supplying humidified air to the anode and H₂O to the cathode. The use of a thin PEM reduces the ohmic resistance of the electrolysis cell, thereby decreasing the energy consumption of the process by 15-20%. Supplying humidified air to the anode and H₂O to the cathode eliminates the risk of explosive gas mixtures and improves the stability of the electrolyzer.
Hystar electrolyzer
The diagram below schematically depicts the structure and operation of Hystar’s PEM electrolyzer.