The fridge was developed by mechanic engineering students Frederik Knop, Nicolás Ripoll, and Olivier Bernade, the last one a French exchange student.
The prototype is based on adsorption, which Wikipedia explains in the following way:
Absorptive refrigeration uses a source of heat to provide the energy needed to drive the cooling process.[...] The classic gas absorption refrigerator sends liquid ammonia into a hydrogen gas. The liquid ammonia evaporates in the presence of hydrogen gas, providing the cooling. The now-gaseous ammonia is sent into a container holding water, which absorbs the ammonia. The water-ammonia solution is then directed past a heater, which boils ammonia gas out of the water-ammonia solution. The ammonia gas is then condensed into a liquid. The liquid ammonia is then sent back through the hydrogen gas, completing the cycle.