The concept

Electrolysis and hydrogen production

The project NEXTAEC addresses a key technology in the green transition, electrolysis. Electrolysis is the dominating technology for conversion of electrical energy to chemical energy, i.e., fuels. In a future carbon neutral (or low emission) energy system based on renewable energy sources, a major part of the energy will be harvested from wind and sunshine and will be electrical. The intermittent nature of these sources calls for energy storage, and chemical storage is the only realistic form at this scale. Moreover, some sectors, in particular parts of the transport sector, cannot be powered electrically and need fuel. 

In the electrolysis process, water (H₂O) is converted to hydrogen (H₂) and oxygen (O₂) by means of electrical energy. Hydrogen is a fuel and contains a major part of the original electrical energy as chemical energy. It can be stored or converted to other fuels, like hydrocarbons and alcohols.

Different types of electrolyzers

There are three main types of electrolyzers (the device behind the process) each with its advantages and drawbacks, the alkaline electrolyzer (AEC), the PEM electrolyzer (PEMEC) and the solid oxide electrolyzer (SOEC). The AEC is the original state of art. It has been around for a century; it is robust and made from inexpensive materials, but it is bulky and needs much space. The PEMEC is much more compact and elegant with much higher production rates, but it suffers from high cost due to expensive materials including the scarce noble metal iridium. The SOEC is promising with the highest conversion efficiency of the three due to a very high working temperature, but large-scale devices are still under development. There will be a tremendous need for affordable electrolyzers at the multi-GW scale in the coming years. The EU Hydrogen Strategy of 2020 foresees 6 GW of hydrogen by electrolysis by 2024 increasing to 40 GW in 2030, just in the EU. BloombergNEF mentions 1.9 TW or electrolysis worldwide already in 2030 in their Green Scenario. Such numbers cannot be met by PEMEC because of the dependency of scarce elements, and it is questionable whether SOEC can be ready at scale for this first wave. 

This has led to a renewed interest in the alkaline system that does not rely on strategic elements, and it is tempting to imagine that the AEC can be developed further to match the performance of the PEMEC without the use of expensive or scarce materials. A steady development has taken place over recent years, but the real game-changer would be to introduce a thin ion conducting membrane as separator and porous three-dimensional electrodes (both like the ones used in the PEMEC). This is what NEXAEC is about. 

The project idea

The project is formulated around a thin so-called ion-solvating membrane to separate the electrodes at which the electrochemical processes take place. This will lead to a lower internal resistance and allow for larger production rates. The concept of the ion-solvating membrane is different from the common approach of an ion-exchange membrane, like in the PEMEC. The big challenge for both concepts is stability in the alkaline environment. 

The parallel development of electrodes is aiming at optimized three-dimensional structures which utilize the space available better and like the membrane contribute to higher production rates. Different advanced techniques are applied to manufacture these electrodes and to apply an active catalyst surface for the electrochemical reactions.

The objective of the project was to develop stable and highly conductive membranes as well as stable and highly active electrodes for the electrolyzer. These components were to be scaled up and assembled in electrolyzer cells and tested in a full-size commercial electrolyzer stack (an assembly of many cells) with performance comparable to the PEMEC, but without the use of noble or strategic materials.

References

Previous demonstration: Ion-solvating membranes as a new approach towards high rate alkaline electrolyzers

Review: Electrode Separators for the Next-Generation Alkaline Water Electrolyzers

Review: Separators and Membranes for Advances Alkaline Water Electrolysis