Hydrolite, an Israeli cleantech startup founded in 2016, specializes in electrolyzer and fuel cell technology. They offer low-cost green hydrogen generation and power delivery solutions to accelerate the green energy revolution. The company’s unique AEM (Alkaline Exchange Membrane) technology enables high-efficiency power-to-hydrogen and hydrogen-to-power devices.
Challenges: hydrogen fuel
Hydrogen (H₂) is an energy carrier that can be used to store and deliver energy. It can be produced through the electrolysis of water.
Alkaline electrolyzers are a mature technology for producing hydrogen on an industrial scale. In a liquid alkane electrolyte, cathode and anode are separated by an insulating porous separator. The separator separates the hydrogen and oxygen produced from the cathode and anode, respectively. Due to the permeability of the separator, the pressure of both gasses should be equalized to avoid the formation of explosive mixture gas. Hydrogen cannot be directly electrochemically pressurized to a high pressure. Typically, an additional mechanical compressor is required to compress hydrogen, increasing capital expenditures. In addition, alkaline electrolyzers are not suitable for reversible fuel cells.
Proton exchange membrane (PEM) electrolyzers use a gas-impermeable polymer membrane. They can be made to operate reversibly to function as fuel cells. The PEM electrolyzer can directly produce electrochemically compressed gas and can operate with pressure differences exceeding 100 bar. However, it operates at hydrogen pressures up to 30 bar because the membrane is permeable to hydrogen. Hydrogen will cross through the PEM and mix with oxygen if the hydrogen pressure is increased, which raises safety concerns. In addition, PEM electrolyzers use very expensive corrosion-resistant materials, which impedes its widespread commercial adoption.
Anion exchange membrane (AEM) electrolyzers use significantly cheaper materials than PEM electrolyzers to produce electrochemically pressurized hydrogen over 200 bar. High storage pressure reduces mass and volume and increases storage efficiency. AEM electrolyzers can function as reversible fuel cells. However, AEM electrolyzers and fuel cells have the challenge of the degradation of ionomers and the AEM. Specifically, the high voltage oxygen electrode accelerates the degradation of ionomers. Highly active oxygen- and hydrogen-oxygen-containing intermediate species, such as free radical species, can attack and degrade polymeric hydrocarbon AEMs adjacent to the oxygen electrode.
Hydrolite has developed advanced anion exchange membranes (AEM) for electrolyzers, fuel cells, reversible fuel cells, and ammonia fuel cells. The Hydrolyte’s AEM comprises thick polymer layers and thin porous composite ionomer/nanoparticles layers. The thick polymer layers serve as the main gas separator,while the thin composite layers protect polymer layers from degradation by electrode catalysts.
Hydrolite AEM electorlyzer or fuel cell
The diagram below depicts the structure of Hydrolite’s electrochemical cell (electrolyzer or fuel cell) based on its innovative AEM separator.
The electrochemical cell comprises the following main components:
- Hydrogen and oxygen electrode end plate
The hydrogen or oxygen end plates include inlet and outlet ports for hydrogen or oxygen as well as a tab for current collection. It also has flow patterns to direct the flow of gasses and reactants in electrodes. It is made of stainless steel or nickel alloy for conducting electricity and transferring compressive forces.
- Gas diffusion layers
Gas diffusion layers (GDLs) ensure a uniform distribution of reactive gasses on the surface of the electrodes and the transport of electrons to or from the external electrical circuit. Gas diffusion layers can be selected from carbon paper, non-woven carbon felt, woven carbon cloth and the like, nickel, titanium or stainless steel meshes, felts, foams, sintered microspheres, or other porous and electrically conductive substrates. Gas diffusion layers can be attached to a microporous layer made from sintered carbon and polytetrafluoroethylene (PTFE) or from various porous metallic conductive layers.
- Hydrogen-side catalyst layer
Hydrogen-side catalyst layer should be stable over the entire voltage range of electrode operation, e.g., from below about −0.2 V in electrolyzer mode to over +0.4 V in fuel cell mode. Its thickness ranges between 2 and 20 μm. The hydrogen-side catalyst layer comprises ionomer with embedded hydrogen oxidizing or hydrogen evolving (generating) catalyst nanoparticles, such as Pt, Ir, Pd, Ru, Ni, Co, and Fe, that are supported on carbon substrates. The hydrogen-side catalyst layer contains up to 40 wt% ionomer.
- Oxygen-side catalyst layer
The oxygen-side catalyst layer comprises metal oxide or metal hydroxide that is stable over the full voltage range of electrode operation, e.g., from below about 0.6 V in fuel cell mode to about 2.0 V in electrolyzer mode. Its thickness ranges between 10 and 30 μm. The oxygen-side catalyst layer comprises ionomer with embedded oxygen reducing and/or oxygen evolving (generating) catalyst nanoparticles, such as Ag, Ag alloyed with Pt, Pd, Cu, Zr, Ni, Fe, Mn, Co, Pt, Ir, or Ru blended with metal oxides, such as cerium oxide and zirconium oxide, and/or metal hydroxide.
- AEM separator
The diagram below depicts the structure of a typical AEM separator of Hydrolite.
The separator comprises two thick polymer layers and three thinner porous ionomer/nanoparticle composite layers. As the thick polymer layers serve as the main gas barrier, the protective layers and the intermediate layer can be very thin and porous. The intermediate layer with surface-charged particles enhances the mechanical strength and stability while maintaining the ionic conductivity of the AEM separator.
The protective layers can also mechanically reinforce the AEM separator. Importantly, the protective layers and electrode layers form respective interfaces to protect the edges of thick polymer layers from dehydration by exposure to dry gasses and catalytically active materials. Due to the tendency of the electrode layers to remove water and dehydrate adjacent polymer membranes, resulting in reduced ionic conductivity, such protection is beneficial.
The polymer matrix is a polymer ionomer with ionic groups that are neutralized by mobile counterions. It conducts anions such as OH⁻ and Cl⁻. The ionomer materials can be selected from polymers or copolymers of (vinylbenzyl)trimethylammonium chloride, copolymers of diallyldimethylammonium chloride (DADMAC), styrene-based polymers, quaternized poly(vinylalcohol) (QPVA), bi-phenyl or tri-phenyl backboned polymers. The anion conducting ionomer can be crosslinked using crosslinking agent, such as divinylbenzne, N,N,N′,N′-tetramethyl-1,6-hexanediamine (TMHDA), 1,4-diazabicyclo[2.2.2]octane (DABCO), glyoxal, and glutaraldehyde.
Nanoparticles can be surface-charged and ion-conducting in hydrated media by means of excess surface charge. Nanoparticles can be selected from bentonite, montmorillonite, laponite, smectite, halloysite, hydrotalcite, zirconium oxide, titanium oxide, reduced or partially reduced graphene oxide, boron nitride, functionalized polyethylene, polytetrafluoroethylene, polyethylene tetrafluoroethylene, or other polymer nanoparticles. Nanoparticles do not react with the ionomers. Chemically inactive nanoparticles reinforce the ionomer matrix and increase its mechanical strength. 1 to 10 wt% of chemically inactive nanoparticles are present in layers with low solid content, 20 to 50 wt% in layers with medium solid content, and 50 to 90 wt% in layers with high solid content.
The diagram below shows the working mechanism of the Hydrolite’s AEM electrolyzer.
The oxygen electrode is supplied with KOH electrolyte solution. The electrolyte hydrates the AEM membrane and oxygen-side catalyst layer on the gas diffusion layer. At the oxygen electrode, when an external electrical potential is applied across the electrodes, hydroxide ions (OH⁻) are oxidized to oxygen and water. Water molecules diffuse across the AEM membrane and are reduced to hydrogen gas and hydroxide ions at the hydrogen electrode, where hydroxide ions then transport across the AEM membrane towards the oxygen side electrode.
The diagram below shows the working mechanism of the Hydrolite’s AEM fuel cell.
The oxygen electrode is supplied with KOH electrolyte solution and oxygen gas. The hydrogen electrode is supplied with hydrogen gas. At the oxygen electrode, oxygen and water react to generate hydroxide ions, which diffuse across the AEM membrane to the hydrogen electrode. At the hydrogen electrode, hydrogen gas reacts with hydroxide ions to form water. Electrons that are released from the reactions circulate through an external load.
Hydrolite reversible fuel cell
Reversible fuel cells are a unique technology that combines both energy storage and fuel cell technologies. Typically, reversible fuel cells use hydrogen as the fuel. They can produce hydrogen fuel by electrolyzing water. The produced hydrogen can be stored in large gas cylinders for less than $20/kW-hr, significantly less than the cost of batteries. Through an electrochemical process, reversible fuel cells are able to convert the chemical energy stored in hydrogen into electrical energy. They offer high energy conversion efficiency, long-term reliability, and the ability to store energy, making them a promising technology for transportation and grid energy storage applications. As more and more renewable energy sources are added to the grid, reversible fuel cells will be a promising technology for transportation and grid energy storage applications.
The figure below depicts the system of Hydrolite’s AEM reversible fuel cell.
The AEM reversible fuel cell system comprises the following units:
- AEM reversible fuel cell
The AEM reversible fuel cell comprises a stack of electrochemical cells as described above. The reversible fuel cell alternates between fuel cell mode and electrolyzer mode.
- Oxidant unit
When operating in fuel cell mode, the oxidant unit supplies oxygen to the reversible fuel cell, and when operating in electrolyzer mode, it receives oxygen from the reversible fuel cell. The oxidant unit comprises an oxygen tank for storing oxygen and a compressor for compressing oxygen from AEM reversible fuel cell into the oxygen tank. Supplying pure oxygen to the oxygen electrode during power generation in fuel cell mode can increase the system efficiency and reduce complexity.
- Hydrogen unit
When operating in fuel cell mode, the hydrogen unit supplies hydrogen to the reversible fuel cell, and when operating in electrolyzer mode, it receives hydrogen from the reversible fuel cell. The hydrogen unit comprises a hydrogen tank for storing hydrogen and a compressor for compressing hydrogen from the reversible fuel cell into the hydrogen tank. In electrolyzer mode, the generated hydrogen can be electrochemically compressed within the AEM reversible fuel cell.
- Water unit
The water unit supplies the oxygen electrode of the reversible fuel cell with water or dilutes electrolyte in a closed circuit and in conjunction with the supply of oxygen to the reversible fuel cell. The circulated water or alkaline water serves as the water supply for hydrogen generation in the electrolyzer mode. Water produced by the consumption of hydrogen during power generation in fuel cell mode is separated and returned to the water circulation circuit to replenish any water consumed during the hydrogen generation in the electrolyzer mode.
Water unit comprises a radiator, a liquid/gas separation module, and a water pump. The radiator dissipates heat and condenses water from the reversible fuel cell in fuel cell mode. The liquid/gas separation module separates oxygen from the fluids received from the reversible fuel cell. The water pump pumps water to the reversible fuel cell. Dilute alkaline electrolyte (less than 3 M) or deionized water is circulated to control the operation temperature.
- Gas/liquid separation
Gas/liquid separation separates oxygen from the output flow of the oxygen electrode of the reversible fuel cell operating in electrolyzer mode and delivers the oxygen gas to the compressor and then to the oxygen tank. The separated water or dilute electrolyte may be stored in a liquid/gas separation tank for circulating in the water unit.
- Power connection unit (not shown)
When operating in fuel cell mode, the power connection unit receives power from the reversible fuel cell, and when operating in an electrolyzer mode, it supplies power to the reversible fuel cell. Power input receives power from various sources, such as an electric grid, renewable energy resources (solar panels or wind turbines), or batteries, based on their respective time-dependent cost and availability. The reversible fuel cell can generate power and be used as either a backup electrical power generation system or a portable power generation system.
- Controllers (not shown)
Controllers comprise processors coupled to respective memory and interfaces to the units of reversible fuel cell, such as power connection unit, oxidant unit, water unit, and hydrogen unit.
Hydrolite ammonia fuel cell
An ammonia (NH₃) fuel cell is a type of fuel cell that uses ammonia as the fuel source instead of hydrogen. The operation of an ammonia fuel cell is similar to that of a hydrogen fuel cell. Ammonia has a significantly higher volumetric energy density than compressed hydrogen because it can be liquefied at room temperature under a pressure of 7 bar, whereas hydrogen can only be liquefied cryogenically and is typically compressed to at least 200 bar to achieve the desired energy density.
Ammonia-based fuels have been restricted to a class of fuel cells that can successfully oxidize ammonia, largely through the use of high cell temperatures to improve the performance of the ammonia oxidation reaction (AOR) catalysis. Examples for fuel cells operated at elevated temperatures are Solid Oxide Fuel Cell (SOFC). Due to their operation under high temperature (typically above 600 ºC), these fuel cells can easily handle ammonia as a fuel. However, ammonia SOFC is unsuitable for applications requiring rapid start-up and shut-down, such as when the fuel cell is the primary energy conversion device in automotive applications.
Ammonia is a potentially suitable fuel in AEM fuel cells because the metal hydroxide electrolyte (such as KOH electrolyte) provides a strongly alkaline aqueous environment that improves the kinetics of the ammonia oxidation reaction (AOR). Furthermore, the AFC can operate at relatively high temperatures up to near the boiling point of the electrolyte.
The diagram below shows the system of Hydrolite’s ammonia AEM fuel cell.
The ammonia AEM fuel cell comprises the following components:
- AEM fuel cell
The ammonia AEM fuel cell has a similar structure to the hydrogen AEM fuel cell described previously. The ammonia AEM fuel cell comprises a solid electrolyte membrane free of aqueous electrolyte, an anode inlet for receiving ammonia source, and a cathode inlet for receiving oxygen containing gas. The ammonia AEM fuel cell operates at temperatures above 95 ºC.
- Ammonia source
The ammonia source is in fluid connection with the anode. The ammonia source may be ammonia gas or an ammonia aqueous solution. When ammonia is supplied in a gas phase, the ammonia source is coupled with a humidifier to add moisture to the ammonia. When the ammonia is provided as an ammonia aqueous solution, the ammonia concentration can be 16 M.
- Oxygen containing gas source
The oxygen containing gas source is in fluid connection with the cathode. Oxygen containing gas source provides pure oxygen, air, or nitrogen/oxygen mixture to the cathode. The pressure of the oxygen containing gas near the cathode is maintained above the equilibrium vapor pressure of water at the operating temperature.
Using cooling water pipes, heat is extracted from the ammonia AEM fuel cell so that the temperature can be kept above 80 ºC.
During operation, ammonia is oxidized in the anode to nitrogen gas and water, while oxygen is reduced in the cathode to hydroxide ions. The complete ammonia oxidation reaction (AOR) to nitrogen gas and water is more difficult than the oxidation reaction of hydrogen, requiring the breaking of N—H bonds as well as the formation of N—N bonds to form N2 and the release of three electrons per ammonia molecule, according to the reaction:
2NH₃ + 6OH⁻ → N₂ + 6H₂O + 6e⁻
This reduction reaction is enabled by a suitable cathodic process in the cathode where oxygen is reduced with water consumption to generate hydroxide ions (OH⁻) according to reaction:
O₂ + 2H₂O + 4e⁻ → 4OH⁻
The overall oxidation-reduction reaction is according to the reaction:
4NH₃ + 3O₂ → 2N₂ + 6H₂O
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Hydrolite Technology Applications
Fuel cell systems
Hydrolite aims to develop low-cost, mass-produced alkaline membrane fuel cell systems that can meet automotive standards. The company’s technology has the potential to generate an electric vehicle power source satisfying key demands such as a range of over 500 km per refuel, fast refueling, and low cost.
Electrolyzers and Fuel Cells for Hydrogen Economy
Hydrolite’s technology generates hydrogen to store available power and utilize hydrogen to generate power when needed. These devices can be deployed in numerous areas where energy demand and supply are mismatched, greatly amplifying the benefits of existing non-fuel-based storage systems.
Hydrolite Electrolyzer Hydrogen Generator, eHG, is a low-cost, high-simplicity electronic hydrogen generator. Input only water and renewable power for certified Green Hydrogen and generate hydrogen fuel for the Hydrolite Full Cell System–FCS, or for any other hydrogen applications.
The technical info of the Generation 1 Hydrolite Electrolyzer Hydrogen Generator – eHG:
- Nominal system size (Power Output): 10-50kW
- Peak efficiency: 42-45 kWh/kg H2
- Output hydrogen purity: 99.999%
- Water purity: Conductivity
Hydrolite Fuel cell system–FCS provides reliable, flexible, emissions-free power. Well suited to UPS / Backup, Critical power applications, Off-Grid / Edge-of-grid sites, etc.
The technical info of Generation 1 Hydrolite FCS:
- System size (Power Output): 5-10 kW
- Minimum Run-time at full power: 10 h
- Run-time at nominal power: over 20 h
- Run-time with a partner battery: 24-100 h
- Size with fuel cylinders: 75 x 250 x 200 cm
- FCS unit size: 75 x 140 x 200 cm
Hydrolite has received Grant funding from the Ministry of Energy, European Commission, Israel-USA Binational Industrial Research and Development, and The University of Delaware.
Ervin Tal-Gutelmacher is Founder.
Ervin Tal-Gutelmacher is CEO.