At the heart of most Power-to-X (PtX) concepts is the utilization of renewable electricity to produce hydrogen through the electrolysis of water. This hydrogen can be used directly as a final energy carrier or it can be converted into, for example, methane, synthesis gas, liquid fuels, electricity, or chemicals. Technical demonstration and systems integration are of major importance for integrating PtX into energy systems. As of June 2020, a total of 220 PtX research and demonstration projects in Europe have either been realized, completed, or are currently being planned. The central aim of this review is to identify and assess relevant projects in terms of their year of commissioning, location, electricity and carbon dioxide sources, applied technologies for electrolysis, capacity, type of hydrogen post-processing, and the targeted field of application. The latter aspect has changed over the years. At first, the targeted field of application was fuel production, for example for hydrogen buses, combined heat and power generation, and subsequent injection into the natural gas grid. Today, alongside fuel production, industrial applications are also important. Synthetic gaseous fuels are the focus of fuel production, while liquid fuel production is severely under-represented. Solid oxide electrolyzer cells (SOECs) represent a very small proportion of projects compared to polymer electrolyte membranes (PEMs) and alkaline electrolyzers. This is also reflected by the difference in installed capacities. While alkaline electrolyzers are installed with capacities between 50 and 5000 kW (2019/20) and PEM electrolyzers between 100 and 6000 kW, SOECs have a capacity of 150 kW. France and Germany are undertaking the biggest efforts to develop PtX technologies compared to other European countries. On the whole, however, activities have progressed at a considerably faster rate than had been predicted just a couple of years ago.

Industrial hydrogen production via alkaline water electrolysis (AEL) is a mature hydrogen production method. One argument in favor of AEL when supplied with renewable energy is its environmental superiority against conventional fossil-based hydrogen production. However, today electricity from the national grid is widely utilized for industrial applications of AEL. Also, the ban on asbestos membranes led to a change in performance patterns, making a detailed assessment necessary. This study presents a comparative Life Cycle Assessment (LCA) using the GaBi software (version 6.115, thinkstep, Leinfelden-Echterdingen, Germany), revealing inventory data and environmental impacts for industrial hydrogen production by latest AELs (6 MW, Zirfon membranes) in three different countries (Austria, Germany and Spain) with corresponding grid mixes. The results confirm the dependence of most environmental effects from the operation phase and specifically the site-dependent electricity mix. Construction of system components and the replacement of cell stacks make a minor contribution. At present, considering the three countries, AEL can be operated in the most environmentally friendly fashion in Austria. Concerning the construction of AEL plants the materials nickel and polytetrafluoroethylene in particular, used for cell manufacturing, revealed significant contributions to the environmental burden.