H2Pro ($107M to develop membrane-free water electrolyzers for producing low-cost green hydrogen)

H2Pro, an Israeli cleantech startup founded in 2019, produces green hydrogen using a membrane-free technology that reduces capital expenditure by half compared to traditional electrolyzers. The company is backed by investors such as Bill Gates’ Breakthrough Energy Ventures and ArcelorMittal. H2Pro is planning to build its first factory in Israel that should be able to produce hundreds of megawatts of capacity from 2023. The company claims that its technology will deliver green hydrogen at less than $1 per kilogram before 2030.

Challenges: hydrogen fuel

The electrolysis of water can produce green hydrogen if the electrolysis is powered by renewable energy sources such as solar and wind. Currently, alkaline electrolyzers predominate on an industrial scale.

Alkaline Electrolyzers — Alkaline Electrolyzer.

This type of electrolyzer consists of two half-cells with electrodes separated by a porous septum in the electrolyte. The oxidation and reduction of water are tightly coupled in both time and space, as they occur simultaneously at two electrodes within the same cell.

The porous septum prevents a physical separation between the produced hydrogen and oxygen. The only thing that polarizes the gasses is the current at the electrodes. Therefore, if the electrolyzer is to produce directly compressed hydrogen, it must maintain a perfect balance between the pressures of the two gasses and a perfectly constant current flow to prevent the formation of an explosive mixture.

As a result, this type of electrolyzer is typically employed to produce hydrogen at pressures not exceeding 7 bar. In addition, the power supply of this type of electrolyzers is connected to the grid and therefore cannot be coupled directly to intermittent renewable energy sources such as solar and wind. If large-scale hydrogen production by renewables-driven electrolysis is to become practical, then electrolyzers that can handle the intermittent power inputs that are characteristic of renewables must be developed.

H2Pro Technology

H2Pro employs a revolutionary approach to solve these problems. They decouple these reactions by dividing the process into two steps: first, an electrochemical step that reduces water molecules to produce hydrogen at the cathode and oxidizes the anode, followed by a spontaneous chemical (non electrochemical) step that reduces the anode back to its original state by oxidizing water to generate oxygen simply driven by hot water.

This method eliminates the most expensive and fragile component of an electrolyzer: the membrane.

This revolutionary technique is known as E-TAC (Electrochemical-Thermally Activated Chemical). E-TAC electrolyzers are suitable for high-pressure hydrogen production (greater than 100 bar), cost-effective scaling (reducing the need for compressors), and potentially direct coupling to renewable energy sources. This revolutionary process enables the production of green hydrogen while maintaining high energy efficiency (98.7% HHV) within the reactors and a system efficiency of 95%.

H2Pro electrolyzer

The E-TAC water-splitting method replaces the conventional water oxidation reaction in the anode of an alkaline electrolyzer with a two-step cycle: the anode is first charged (electrochemically) and then regenerated (chemically). In alkaline electrolyzers, the production of hydrogen at the cathode is accompanied by the production of oxygen at the anode.

In the first step of an E-TAC electrolyzer, the hydrogen evolution reaction (HER) is identical to that of an alkaline electrolyzer, except that it occurs at ambient temperature rather than elevated temperature (typically 50–80 ºC). Consequently, the same cathode materials utilized in alkaline electrolyzers can be utilized in this E-TAC water-splitting process.

However, the anode materials in an E-TAC electrolyzer must be selected and optimized with care, as the E-TAC water-splitting process at the anode is fundamentally distinct from conventional alkaline electrolysis. Under optimal operating conditions, the anodes of an E-TAC electrolyzer should inhibit oxygen evolution in the first step and increase oxygen production in the second.

There are several important selection criteria for anode materials:

Cyclability of the metal hydroxide and oxyhydroxide phases;
A redox potential greater than the reversible oxygen evolution reaction (OER) potential and less than the potential at which oxygen evolves on the anode material;
High capacity;
Rapid charging and regeneration; and
Stability in alkaline solutions.

Ni(OH)₂ / NiOOH anodes commonly used in alkaline secondary batteries meet the above criteria. Ni(OH)₂ reversibly oxidizes to NiOOH: Ni(OH)₂ + OH⁻ ↔ NiOOH + H₂O + e⁻.

Cobalt doping of Ni(OH)₂ / NiOOH anode can enhance electron and proton conductivity and expand the potential window between charging and overcharging. Therefore, Ni₁₋ₓCoₓ(OH)₂ anodes are suitable for E-TAC electrolysers, because they can be charged at a lower potential than their undoped Ni(OH)₂ counterparts, to a higher state of charge, without evolving oxygen.

Since hydrogen and oxygen are produced in separate steps, they never mix, eliminating the risk of explosive gas mixing. The separation membrane – the most expensive and fragile component of a conventional electrolyzer – is completely unnecessary.

How does the E-TAC electrolyzer work?

H2Pro E-TAC electrolyzer working process (ref. ref. WO2022029776A1).

In the electrochemical hydrogen production step, water is reduced to hydrogen at the cathode, releasing OH⁻, while of Ni₁₋ₓCoₓ(OH)₂ anode is oxidized according to the equation: 4 Ni(OH)₂ + 4 OH⁻ → 4 NiOOH + 4 H₂O + 4 e⁻. This process continues until all Ni(OH)₂ is converted to NiOOH, at which point the current in the cell drops to zero. During the hydrogen generation steps, the anode potential varied between 1.37 and 1.45 VRHE, which is significantly lower than the OER potential of Ni₁₋ₓCoₓ(OH)₂. At these potentials, there is negligible oxygen evolution.

After the generation of hydrogen, the charged anode can be removed from the electrochemical cell and heated up to 95 ºC in water. Ni(OH)₂ is regenerated by the decomposition reaction of NiOOH, and oxygen is liberated: 4 NiOOH + 2 H₂O → 4 Ni(OH)₂ + O₂. This chemical reaction is spontaneous and exothermic. In contrast, a direct electrochemical oxygen evolution process would require at least 400 mV overpotential to achieve the same current density, rendering it approximately four times less efficient.

The E-TAC process achieved a low electrical energy consumption of only 39.9 kWh per kilogram of hydrogen, whereas current electrolyzers consume up to 48 kWh per kilogram.

H2Pro Patent

WO2022029776A1 Electrochemical systems and methods of use
WO2022029777A1 Systems and methods for continuous generation of gases
WO2022064495A1 Microelectrode and method for producing same

H2Pro Technology Applications

Green hydrogen

In 2022, H2Pro announced the cornerstone ceremony for its new production facility in the Tzipporit industrial zone in Israel. This 600 MW facility, the first of its kind in Israel, will produce cost-effective systems for producing green hydrogen from water and electricity based on H2Pro’s innovative E-TAC technology.

H2Pro has also signed a strategic purchase agreement with Doral Energy to supply a total of 200 MW of H2Pro’s E-TAC electrolyzers until 2030.

Green ammonia

H2Pro has an agreement with Sumitomo Corporation to integrate H2Pro’s E-TAC electrolyzers at the hundreds of MW scale primarily for use in green ammonia projects.

H2Pro Products

By the end of 2023, H2Pro will have its first production facility. Based on H2Pro’s innovative E-TAC technology, the facility will be able to produce 600MW/year of Green Hydrogen systems.

The company believes that its technology, coupled with anticipated reductions in the cost of renewable energy, will enable $1/kg green hydrogen at scale in the second half of this decade.