Hydrogen Generation by different Electrolysis Technologies: Status and Future Development

Hydrogen generation by electrolysis is expected to play an important role as a crosslinking technology between power generation on one hand and transport and industry on the other hand. When produced by water electrolysis from renewable energies - such as solar or wind - hydrogen can directly replace fossil fuels in transport and industry, thereby helping in the integration of renewable energies in other energy sectors. The relevant technologies are either the mature alkaline water electrolysis (AEL), the newer proton exchange membrane (PEMEL) water electrolysis, or the less-mature high-temperature solid oxide electrolysis (SOEL). The AEL has the benefit of using inexpensive materials and a superb durability record, whereas the PEMEL can excel with small footprint, high current densities and simplified system design. SOEL has the potential of highest electrical efficiencies when high-temperature heat is available but still requires scale-up efforts for reaching MW power levels. \n \n\tThe electrolysis research activities at DLR date back to the late 80s of the last century when the first technical “power-to-gas” projects was demonstrated in Saudi Arabia with the name of HySolar. This was the beginning of the electrochemical research activities which later-on focused on fuel cell development. With the increasing share of renewables in the German electricity sector, the need for hydrogen energy as a sector coupling technology became evident restarting the activities at DLR which presently have the following priority areas: \n \n•\tPolymer electrolyte membrane electrolysis \n•\tHigh temperature co-electrolysis of steam and CO2 \n•\tAlkaline membrane electrolysis \n \n\tSome examples from this research will be presented. In PEMEL gas diffusion layers (GDL), such as felts, foams, meshes and sintered plates, are key stack components, but these are either inefficient or expensive. Therefore a new type of GDL produced via vacuum plasma spraying (VPS) is presented, which offers a large potential for cost reduction. With this technology, it is possible to introduce a gradient in the pore-size distribution along the thickness of the GDL by varying the plasma parameters and titanium powder particle sizes. The results presented herein demonstrate a promising solution to reduce the cost of one of the most expensive components of the stack.3 \n \n\tFor SOEL degradation effect for co-electrolysis of steam and CO2 will be shown and the possible mitigation strategies discussed. Furthermore, the successful integration of solar heat into a solid oxide electrolyzer will be presented. The experimental setup of the prototype system consisting of a solar simulator, a solar steam generator, a steam accumulator and a solid oxide electrolyzer as well as first results with regard to solar steam generation and electrochemical performance of the electrolyzer are shown.4 \n \n\tLastly, the recent progress in achieving similar performance levels of Alkaline membrane electrolysis (AEMEL) compared to PEMEL will be discussed. \n \nThe three electrolysis technologies are expected to find applications due to highly diversified applications and markets. All three technologies have a significant potential for further technology development and cost reduction.