Carbon dioxide, CO₂, has been in the spotlight in the last decades due to its high concentration in the Earth's atmosphere. Many industries such as fossil fuels combustion companies are in the public eye, but humanity is still dependable of them and for that reason a solution needs to be found to reduce their emissions.

Electrochemical reduction of carbon dioxide (CO₂ER) can combine the processes of capturing CO₂ while also converting it into a value-added product like ethylene (C₂H₄), a commonly used petrochemical building block. Commercialization of this technology has been hindered by challenges in energy efficiency, electrode stability, and introducing gas feedstocks to a liquid phase reaction.

In this study, an integrated device was developed and applied to a 3-electrode conventional cell, wherein a porous metal organic framework (MOF) serves as CO₂ concentrator and subsequently a Cu-based nanostructured catalyst which electrochemically converts CO₂ into valuable C₂⁺ based products. The MOF and Cu catalyst, which were sprayed into a carbon fibre (CF) sheet that acts as a platform to conduct the current, facilitates the CO₂ capture and the electrochemical reduction reaction of CO₂, respectively, from wet stream.

The capture material is a porous MOF, called CALF20, which is used to capture CO₂ from industrial combustion flue gases in a cement-making company Svante (Vancouver), capturing 1t-CO₂/day. CALF20 has shown a high capacity and selectivity towards CO₂ gas adsorption with the presence of other gases (figure 1a) even at ambient temperature and under humid conditions; being the first MOF to be scaled up (made in ton quantities) and used in the field. The significant capacity of CALF20 can be represented by its 528 m²/g Langmuir surface area. It is a promising material with a cost-effective and easy synthesis that acts as CO₂-concentrator.

CO₂ERR experiments were performed on CuO on one side of the carbon fibres (CF-CuO) and CALF20 on the other side (CALF20-CF-CuO), separately.

The optimization of the CuO layer side was performed based on the highest current density passing through the sheet when applying 3.5 V and 3 M KOH electrolytes to the cell. CALF20 layer was optimized based on the permeability test achieving a selectivity of 1.68 Barrer towards passing CO₂ over N₂, this was also confirmed with the gas sorption isotherms (figure 1a); and with a 250 nm copper layer on the other side.

At low CO₂ partial pressure stream, the presence of CALF20 improved Faradaic Efficiency of ethylene production (FE_C2H4) and reduced the H₂ evolution reaction (HER). The main challenge relied on the competitive adsorption of the products at MOF separation sites. However, adsorption isotherm data showed higher uptake capacity for CO₂ in comparison with C₂H₄ and CH₄ (figure 1a).

The increase of relative humidity (RH) resulted in increasing HER due to the competitivity of H₂O with CO₂ molecules on CuO active sites surface. Many MOF structures get saturated with H₂O even at low RH. However, CALF20 simulations showed that adsorption kinetics are unaffected by water even at 40% RH which illustrates the exceptional nature of this material. This can explain the increase of FE_C2H4 at 10%, and 30% relative humidity. This degree of water resistance in the CO₂ adsorption of CALF20 has currently not been noticed in other MOF.

Different loading amounts of CuO on the CF sheets showed the highest current density at 250‑280 mA/cm². This complexity of high current density CO₂ electrolysis is particularly important for CO₂ reduction on copper electrodes due to the sensitivity of the KOH concentration and current density on H₂, CO, and C₂⁺ products formation.

The CF sheets showed stable FE for C₂H₄, CH₄, CO, and H₂ production as shown in Figure 1b. And, as it has been discussed before, the addition of CALF20 to the catalyst layer enhanced C₂H₄ production and reduced HER leading to a very selective catalyst for CO₂ reduction.

In conclusion, the beforementioned device uses carbon fibre sheets as a platform to conduct current and support an integrated CO₂ capture and electrochemical reduction reaction. It uses a MOF-based membrane as a GDL that acts to concentrate and permeate only CO₂ through one side, while the other side of the fibre is coated with CuO particles to catalyse the mentioned reaction into valuable C₂⁺ based products.

This technology could revolutionize CO₂ conversion and management through being highly efficient, environmentally sustainable, and cost-effective. Once the CO₂ conversion to ethylene with minimal electrical power is optimized, we can access unused CO₂ feedstocks anywhere and convert it into valuable petrochemical fuels.