Electrochemical Conversion of Carbon Dioxide to Useful Products

Utilization of captured CO₂ provides an advantageous alternative especially in locations where CO₂ sequestration in geologic media is not feasible. Making high value chemical products from CO₂, although not sufficient to convert a significant portion of the GHG emissions, provides an opportunity of extensive production of green chemicals when combined with renewable sources to feed the energy requirements. At DNV, we are developing the technology to economically convert CO₂ to formate salts/ formic acid using an electrochemical process. Tin is the preferred electrocatalyst due to high selectivity of CO₂ reduction to formate ion and high overpotential for cathodic hydrogen evolution. Gaseous CO₂ is continuously purged into the catholyte (2M KCl) through a porous tin electrode on which it is cathodically reduced. This cathode chamber is separated from the anodic chamber using a selective ion exchange membrane for allowing positive ion transport but not allowing the product (formate) ions to get oxidized on the anode. Oxygen evolution reaction occurs on a mixed metal oxide anode in either acidic or alkaline anolyte solutions to complete the electrochemical reaction. Electrode development in terms of high surface area of catalyst to match existing commercial electrochemical processes and reduce capital costs related to reactors will be presented. A process was developed to electroplate tin on high surface area carbon fiber substrate. Electroplating solution and substrate properties were evaluated for achieving maximum current densities at optimal product selectivity. Another focus area is understanding and optimizing the process chemistry. Selection of anolyte and catholytes, along with the applied potential regime, affects product selectivity, electrode degradation, expenditure due to chemicals consumption and the ability to reach high enough product concentrations before feasibly employing separation processes. In this presentation, a technical and economic analysis of the aforementioned factors affecting the commercial feasibility will be presented and evaluated as a guide for performance criteria of the proposed technology.