Hydrogen-fuelled internal combustion engines (ICEs) are quite similar to traditional diesel internal combustion engine generators, except that they run on hydrogen, which can be a clean and carbon-free fuel. Unlike hydrogen fuel cell generators, hydrogen internal combustion engine generators are not completely emission-free. They can still emit a small amount of CO2 (from air and oil) and NOx at point of use, so they may not be suitable for locations where gas exhaust can be a concern.
Generally speaking, the initial capital cost of using an internal combustion engine generator will be lower than that of a fuel cell generator, but the long-term operating cost may be higher, due to the difference in efficiency between the two technologies. In a typical use case, fuel cells will convert hydrogen into useable electricity more efficiently than a hydrogen-powered ICE.