Demonstration of thermochemical oxygen pumping for atmosphere control in reduction reactions

Solar thermochemical cycles as a means to produce fuels such as hydrogen, carbon monoxide, or syngas using a metal oxide as oxygen carrier offer a promising route to the efficient conversion and storage of solar energy. Even though the theoretical potential of such cycles can be very attractive, many challenges for reaching high process efficiencies remain unsolved. One challenging aspect is the parasitic energy cost for maintaining low partial pressures of oxygen during the reduction step. As previously proposed by the authors, thermochemical oxygen pumps have the theoretical potential to maintain low partial pressures of oxygen at considerably lower energy costs than conventional mechanical pumps. The work presented here demonstrates the proof of concept of thermochemical oxygen pumping. The reduction extents of a metal oxide after temperature swing experiments are analyzed for test runs with and without thermochemical oxygen pumping, clearly showing higher reduction extents for the former cases. The effects of different operational parameters on the reduction of the metal oxide are investigated and options for reduction extent enhancement are depicted.