The storage of electrical energy is of utmost importance in the context of the energy transition, since the German ‘Renewable Energy Act’ means that the increased production of renewable and inherently discontinuous energy sources endangers the technical and economic stability of the electricity distribution grid. Certainly, a number of distinct storage techniques will have to be combined for storing and releasing various amounts of energy on various time scales. However, all storage technologies must meet some common requirements: high energy efficiency, low costs, and resource conservation. In addition to mechanical (compressed air, water columns) and thermal storage solutions, electrochemical systems (batteries, electrolysis / fuel cells) are an indispensable pillar of such storage solutions. The combination of water (H2O) electrolysis for the production of hydrogen (H2) and oxygen (O2) with fuel cells for releasing the energy contained in the fuel H2 features a particular economic appeal associated with the fact that hydrogen gas not only acts as an energy source but also serves as a raw material of the chemical industry. This dual function gives it a unique added value.
The electrolysis of water is industrially operated mainly in two types of cells. In the alkaline electrolyte, relatively inexpensive electrode materials can be used and high current levels can be achieved, but typically at high voltages, which means low energy efficiency and is thus unfavorable for energy storage. On the other hand, if the electrolysis is carried out in acidic conditions (PEM electrolysis), low overvoltages become possible, but with the use of the noble metals platinum and iridium as catalysts. The significant amounts needed of those rare elements is problematic in terms of both costs and raw materials availability.
Cost reduction in the production of PEM electrolysis cells is a goal pursued throughout Germany by several companies with a variety of approaches, but always via the incremental improvement of cost and performance parameters through a fine-tuning of the parameters available in conventional planar stack systems. Although the tubular geometry has been investigated in the field of electrochemical energy conversion, it has not been exploited to enable new production techniques. Against this background, Tubulyze intends to offer significant and rapid cost savings through the use of completely new manufacturing techniques in the field of electrolysis technology.
The groundbreaking novelty explored in the project "Tubulyze", funded by the German Ministry of Education and Research, is the tubular design of the water electrolysis cell, which will enable the partners in the consortium of exploiting innovative production processes:
- Shaping an electrode framework by additive manufacturing ("3D printing");
- Coating with electrocatalyst by atomic layer deposition (ALD);
- Direct extrusion of the ion exchange membrane onto the inner electrode.
The first innovation will allow consortium members to quickly and directly test different electrode geometries with optimized surface and flow behavior, with direct feedback from theoretical modeling. The second will allow the noble metal catalyst loading to be systematically and precisely minimized to the optimum. The third is meant to simplify the production process significantly.