This type of vessels is operated by a hydrogen fuel cell. Due to limited power output, this technology is likely to be used preferably for small and medium vessels, as currently proved by the on-going demonstrations.
Different fuel-cell types exist, and their names reflect the materials used in the electrolyte membrane.
DNV GL evaluated 7 fuel-cell technologies and concluded that the following are the most promising for maritime applications (source: www.dnvgl.com/maritime/publications/alternative-fuel-assessment-download.html ).
According to the study from DNV-GL, Proton exchange membrane (PEM) fuel cell is considered a mature technology. Its operating temperature is 50-100 degrees Celsius and has a typical efficiency of is 50-60% and a moderate lifetime. It has medium sensitivity to impurity, thus requiring hydrogen as a fuel, and a low cost (compared to other fuel cell technologies for maritime applications).
Manufacturing compact fuel cells with high power densities is quite challenging. Thus, this technology is likely to be used preferably for small and medium vessels.