Electrochemical medium temperature CO2 reduction to fuels

The focus will be on developing selective catalysts and functionalizing an existing solid electrolyte as well as performing a techno-economic evaluation with comparison to high temperature CO₂-electrolysis. The proposed project will combine the cross-disciplinary competences of DTU, Danish Power Sources (DPS) and Elplatek with the following measurable objectives:

• Develop a catalyst with more than 30 % selectivity towards either methanol, ethanol or

DME at a current density of minimum 50 mA/cm² and a maximum cell voltage of 2V.

• Develop the processing of the solid CsH₂PO₄ electrolyte to include a thickness below 200 μm. • Demonstrate scalability of components (electrode and electrolyte) at a 280 cm² functional size.

• Document product uniformity by testing 3 sets (each 7cm²) of a 280 cm² component set.

• Show stable operation (7cm²) for 500 h’s at more than 25 % selectivity towards either methanol, ethanol or DME at 50 mA/cm² and 2V.

• Provide a techno-economic evaluation and comparison to high temperature CO₂-electrolysis.

The thickness of the electrolyte components is a proposed compromise between minimizing resistive losses and ability to maintain gas separation and avoid point-contact (short circuit) between electrodes in compression. For reference, MCFC operate with electrolytes of 250-500 μm, and initial work on 1 mm CsH₂PO₄ electrolytes indicate that 200 μm is favorable and possible to handle.

At this point optimum cell geometry and dimensions are unknown. Reference is taken to technologies like MCFC, as well as flow batteries and PEM type systems where a complex balance between e.g. heat, current distribution, gas access and fuel utilization is balanced against scaled cost of manufacture of components. These balances cannot be made anywhere near reliably prior to knowing the achievable electrochemical performance. Hence at this point the objective is to show producibility of realistic component sizes and characterize these to demonstrate uniformity, in order to provide a stack/system manufacturer with basis for evaluation.

High cathode selectivity along with high current density will favor cost. However, most electrochemical P2X production of higher value chemicals than H₂ in aqueous environment fail to perform well on both parameters at the same time. The set target of 30% selectivity at 50 mA/cm² and 2V is proposed as very ambitious compared to the latter, but not unrealistic based on the already demonstrated 5% in a non-optimized lab cell.