Project News

Progress on the anion exchange membrane

Hydrolite has continuously improved its anion exchange membrane, reaching several important milestones. Ethanol crossover has been reduced by an order of magnitude, from 12 mA/cm2 to 0.3 mA/cm2 (70 °C, 0.5 M in 1 M OH) as shown in Figure 1.

As ethanol is one of the desired products from the CO2 electrolysis, it is crucial to prevent from crossing over the membrane.

Figure 1: Ethanol crossover versus temperature for older generation (left) and newer generation (right) membranes produced at Hydrolite.

Using a setup specially developed at DTU, CO2 crossover could be measured for various membranes. It is now understood that CO2 crossover increases significantly with increasing current, meaning the CO2 is mainly driven by ionic current crossing the membrane from the cathode to the anode. It was shown the Hydrolite membrane displays lower crossover of CO2 than a commercially available membrane as showed in Figure 2.

It is important to mention that those improvements were achieved without compromising the hydroxide conductivity of the membrane (> 150  mS/cm at 60 C, in-plane, 100 %RH). One remaining challenge is reaching the mechanical tensile strength target of 20 MPa at 60 °C. Recent developments have shown an improvement of the tensile strength of Hydrolite membranes from 4 to 17 MPa, hence approaching the target. We are confident that this milestone will be reached soon.

On the fabrication side, Hydrolite delivered to its partners about 10 m2 of large size membrane for the CO2 electrolyser prototype. Significant efforts are being invested to further scale up the membrane fabrication for the supply of 100 m2 of high quality membranes for the demonstrator stack in early 2025.

Figure 2: Hydrolite membrane (bottom) showing improved CO2 barrier as compared to commercial membrane (top)

Project News

Exploring the Impact of Membrane Characteristics on CO2 Electrolysis Performance

A Deep Dive into Energy Conversion and Storage

Energy conversion and storage are pivotal to a sustainable society that harnesses renewable energy sources such as solar and wind power. At the Department of Energy Conversion and Storage, Technical University of Denmark (DTU), we are at the forefront of developing electrolysis, fuel cells, batteries, thermal energy storage, and other power-to-X technologies. Our group’s primary focus is on low-temperature electrochemical systems, including polymer electrolyte fuel cells, alkaline electrolysers, flow batteries, and carbon capture and CO2 reduction. Our research encompasses the development and characterization of functional materials and components, as well as single cells, stacks, and systems.

The Role of Anion-Exchange Membranes in CO2 Reduction

Anion-exchange membranes (AEMs) are the heart of CO2 reduction reaction (CO2RR) electrolysers, serving as charge carrier conductors and electrode separators. Their performance and durability significantly impact cell performance. As part of the ECO2Fuel project, DTU is investigating various electrolyte materials provided by our ECO2Fuel partner, Hydrolite. The investigation focuses on evaluating their mechanical stability, ion conductivity, and gas crossover, particularly CO2, by diffusion and migration. The lab setups for these evaluations are briefly described below.

Evaluating Mechanical Stability

The AEMs’ satisfactory mechanical properties are crucial for handling membrane electrode assembly (MEA) and ensuring cell durability. Therefore, we conducted mechanical stability tests to examine the membranes’ stress-strain.

The setup for the tensile strength measurements was modified (Instron 3344) to include an additional chamber constructed around the membrane sample, equipped with heating elements for temperature control and an inlet and outlet for humidified air to achieve varying atmospheric humidity levels. A humidity sensor was installed next to the membrane sample to monitor temperature and humidity during tensile strength measurements.

Exploring the Impact of Membrane Characteristics on CO2 Electrolysis Performance
Figure: Shows the photograph of instrument and mechanical properties of Hydrolite membrane, Source: DTU

Assessing Ion Conductivity

The ion conductivity of the membrane, especially under ambient conditions, is a key factor influencing an electrochemical cell’s performance. We measured the anion (OH-, HCO3-, CO3-2) conductivities of the membranes using a four-probe electrochemical alternating current impedance spectroscopy method with a Scribner B-112 over a frequency range of 100 mHz to 1 MHz. A rectangular membrane was sandwiched between platinum electrodes, and conductivity was measured from 20 °C to 80 °C at 30-minute intervals under hydrous conditions.

Exploring the Impact of Membrane Characteristics on CO2 Electrolysis Performance
DTU’s In-plane conductivity measurement setup, Source: DTU

Understanding Gas Crossover

The CO2 electrolysis process faces a significant challenge related to the carbonation of the electrolyte, a consequence of performing CO2RR in alkaline conditions to suppress the H2 evolution reaction. The parasitic reactions of CO2 with the alkaline electrolytes result in bicarbonate precipitation and flooding in gas diffusion electrodes, CO2 crossover to the anode, low carbon utilization efficiencies, and additional costs for CO2 and electrolyte recycling. These issues seriously hinder the scale-up and commercialization of CO2 electrolysers.

To address these challenges, as part of the ECO2Fuel project, DTU aims to investigate the carbon crossover mechanisms and factors influencing CO2 crossover in electrolysers in terms of the concentration of the electrolytes (anolyte and/or catholyte), the CO2 supply rate, and cell configuration.

Device Setup and Crossover Measurement

The DTU’s test rig for CO2 crossover flow cell and the hardware for providing the gas mixture and analysing the exhaust are shown in Figure 1. The outlet gas composition on the anode side was controlled by mass flow controllers (MFCs).

The total CO2 gas flow rate was measured using a CO2 sensor. Prior to membrane electrode assembly (MEA), membranes were washed with deionized water to remove excess electrolyte. Membrane and gas diffusion electrode (GDEs) were pressed into a cell with gaskets and graphite flow fields. The cell was connected to a modified alkaline electrolyser stand with temperature and pressure control. MFCs were used to supply humidified N2 and CO2 on the cathode side and argon (Ar) on the anode side. A potentiostat was used to apply current and take impedance measurements for determining the cell resistance. Outlet gases on both sides were analysed for CO2 concentration using a CO2 sensor. The sensors were calibrated to ranges of 0-1000 and 0-10000 ppm of CO2.

Exploring the Impact of Membrane Characteristics on CO2 Electrolysis Performance
Figure 1: Shows the pictures of DTU’s test rig for CO2 crossover measurement, Source: DTU
Project News

How We Guarantee Durable And Efficient CO2 Electrolysis At Scale – The Role Of The Membrane

Headquartered in Caesarea, Israel, HYDROLITE is one of the industrial partners directly involved in the ECO2Fuel project. As the global demand for hydrogen solutions starts to grow exponentially – in recognition of the critical role of hydrogen as a carbon-free fuel in a zero-carbon economy – HYDROLITE’s superior Anion exchange membrane (AEM) technology offers a compelling solution that combines the cost advantages of liquid Alkaline Fuel Cells and Electrolyzers, with the high performance of solid-state Proton Exchange Membrane devices.

Over the past decade HYDROLITE has developed extensive, proprietary AEM materials technology, pilot-scale production, and device operation capabilities, and holds an extensive IP portfolio of 70 patent cases with more in the pipeline.

In the ECO2Fuel project, Hydrolite contributes to the following areas:

  • Investigating membrane and ionomer requirements in a CO2 Electrolyzer environment
  • Providing optimized membranes and ionomers to fit requirements
  • Scaling up membrane production and size

The membrane is at the heart of electrolyser. Bearing multiple roles for the reliable and durable operation of the device, the membrane must excel in the following:

  • High ionic conductivity
  • Gas tight to H2, O2, CO2 and other gaseous products (crossover)
  • Mechanical properties
  • Low swelling
  • Chemical stability under harsh conditions (temperature, pH, oxidation)
Principle of operation of an AEM Water Electrolyzer; Source: Hydrolite

As compared to H2 Electrolyzer, the CO2 Electrolyzer developed in the ECO2Fuel project poses new challenges due to the harsher conditions, in particular the need for the membrane to sustain the presence of carbonates (showing lower conductivity than hydroxide anions) as well as hydrocarbons and alcohols, some of which are often used to dissolve the membrane during production.

Roll of AEM made at Hydrolite
Roll of AEM made at Hydrolite; Source: Hydrolite

Hydrolite uses various strategies to handle those difficulties, such as using materials with known tolerance to alcohols and hydrocarbons as well as, crosslinking to reduce swelling and avoid slow dissolution. This in turn causes challenges in terms of adaptation of the fabrication process and scaleup. Hydrolite successfully implemented manufacturing process to produce membranes of large size showing high barrier properties without compromising on ion conductivity and chemical stability. This was achieved by fine tuning the molecular structure, amount of cationic groups, crosslinking degree and addition of non-conducting polymers to obtain all the desired characteristics. Hydrolite provides ECO2Fuel with ionomers and membranes tailored for the target application.

Chemical stability of Hydrolite membrane in 1 M KOH at 80 °C. Source: Hydrolite.
Chemical stability of Hydrolite membrane in 1 M KOH at 80 °C. Source: Hydrolite.

Using only hydrocarbon-based ionomers and membranes, Hydrolite avoids the use of environmentally dangerous perfluorinated polymers as used in other electrolyzers, in line with long term objectives of ECO2Fuel for a sustainable future.

Looking toward the future, Hydrolite plans to further develop and establish the manufacturing process and facilities to supply membranes in large scales and footprints, exhibiting satisfactory uniformity and mechanical robustness with high ionic conductivity.

Project News

Handling the challenges of advanced CO2 electrolysis: Ion conduction, alcohol exclusion and salt exclusion

The membrane is at the heart of any electrochemical membrane reactor, with the general tasks of separating the anode and cathode electrodes and chambers from each other while allowing ion conduction to complete the electrochemical circuit.

However, for the ECO2Fuel technology, the membrane must fulfil three additional tasks to allow the efficient conversion of CO2 into green fuels and valuable chemicals:

High ion conduction

The conductivity of ions through the membrane dictates the ohmic resistance and therefore the energy efficiency of the ECO2Fuel technology. High ion conduction means low ohmic resistance, leading to better energy efficiency.

Alcohol exclusion

The ECO2Fuel technology produces among other carbonaceous chemicals also alcohols by combining CO2, water and electrons from renewable sources. However, ion-conducting membranes normally swell in contact with alcohols, allowing them to cross from the cathode to the anode chamber.

Alcohols that cross the membrane to the anode chamber will face the anode electrode, where they will be oxidised back to CO, reducing the efficiency of the technology. Therefore, membranes in the ECO2Fuel technology need to possess ultra-low alcohol crossover.

Salt exclusion

Finally, the ECO2Fuel process relies on a supporting alkaline electrolyte (salt) to maintain optimum conditions for the electrochemical reactions.

This electrolyte is introduced on the anode electrode, whereas the CO2-to-fuel conversion occurs in the cathode. Only the membrane prevents access of salt to the fuel output line, the third critical function of the ECO2Fuel membrane.

Achieving these three tasks together, Ion conduction, alcohol and salt exclusion, is especially challenging.

In ECO2Fuel, Hydrolite directs the membrane development work package and will develop membranes with unique separation properties, allowing high performance and robustness for the ECO2Fuel technology.

To implement molecular-scale and solution-phase sieving effects tailored to the specific species that need to be excluded to achieve the selective passage of the various reactants and products to where they are needed, Hydrolite is taking advantage of their advanced fabrication techniques.

Our academic partners in the consortium – CNR (Italy), DTU (Denmark), DLR (Germany) and UPV (Spain) provide critical feedback in the form of characterization and evaluation of these speciality components.

Hydrolite also works closely with industry partners including Electrolyzer Stack designer Vito (Belgium) to refine specifications – assuring that required separation and sealing quality are achieved, and Membrane-Electrode Assembly developer De Nora (Italy) to help achieve optimal integration between membranes and electrodes, and thus maximizing the overall performance of the Electrolyzer device.

CNR – Consiglio Nazionale delle Ricerche

DTU – Danmarks Tekniske Universitet

DLR – Deutsches Zentrum für Luft- und Raumfahrt

UPV – Universitat Politècnica de València

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