Fischer-Tropsch Products from Co-Electrolysis of H₂O and CO₂ with Iron-Based Catalysts Using a Solid Phosphate Electrolyzer at 240 °C and 28 Bar

The present report demonstrates a one-step co-electrolysis of water and carbon dioxide in the vapor phase catalyzed by iron-based compounds to form C1 to C5 hydrocarbons. The medium-temperature electrolyzer works at 240 °C and 28 bar overpressure; the solid electrolyte consists of CsH₂PO₄ with polyvinyl butyral (PVB) as binder. The cathode is a porous platinum electrode followed by a layer of iron/Fischer-Tropsch catalysts sandwiched between Fe foams. The anode consists of tantalum coated steel felt covered by RuO₂. Both electrodes are in contact with the electrolyte. Current densities of up to 200 mA cm⁻² with a voltage of up to 2.2 volts were applied. The product selectivity and Faradaic efficiencies, together with the detailed analysis of the structure of the catalyst before and after use, show thermal Fischer-Tropsch catalysis parallel to electrolysis. Initially formed CO, in conjunction with high amounts of electrochemically produced hydrogen, reacts to form the hydrocarbons. The mechanistic conclusions are in agreement with the catalytic properties of metallic iron, iron carbide and iron oxide nanoparticles identified in the spent catalysts.