Thermochemical solar-driven reduction of CO2 into separate streams of CO and O2 via an isothermal oxygen-conducting ceria membrane reactor

Abstract

• Demonstration of single-step CO 2 thermolysis in a novel solar-driven membrane reactor. • In-situ separation of CO and O 2 via lattice oxygen transfer through ceria dense membrane. • Continuous and isothermal operation of the MIEC tubular membrane reactor at 1450–1550 °C. • Increasing the temperature, CO 2 concentration or flow rate enhanced CO and O 2 production rates. • The fuel production rate was up to 4.26 μmol/cm 2 /min at 1550 °C under pure CO 2 feeding. CO 2 single-step thermolysis was achieved using oxygen permeable MIEC (mixed ionic-electronic conducting) membranes made of ceria for separate production of CO on the feed side and O 2 on the sweep side. The CO 2 -dissociation reaction was driven by concentrated solar energy as a renewable thermal energy source and by applying a chemical potential gradient between both membrane sides. A continuous oxygen transfer across the membrane was achieved thanks to a flow of inert gas on the permeate side. This created the required oxygen partial pressure gradient and favored oxygen permeation via oxygen ion diffusion through the ceria membrane thickness. A novel solar chemical reactor integrating the reactive ceria membrane was designed and tested under real concentrated solar radiation, with operating temperatures up to 1550 °C. The reactive part of the tubular redox membrane was located inside a well-insulated cavity receiver for homogeneous heating, which was fed with a carrier argon flow on the sweep side to facilitate the transport and removal of the permeated oxygen. The dynamic response of the solar fuel production upon changing the operating conditions (temperature, CO 2 mole fraction, and feed gas flow rate) in the membrane reactor was investigated by quantifying the evolved gas production rates. Continuous CO 2 dissociation was achieved on the feed side inside the tubular membrane with in-situ spatial separation of O 2 and CO streams across the membrane. Reliable solar membrane reactor operation under real concentrated sunlight was successfully demonstrated for the first time, with stable and unprecedented CO production rates up to 0.071 μmol/cm 2 /s at 1550 °C and CO/O 2 ratio of 2.