We will pursue reactive capture of CO2 to CO: i.e. the integrated capture of CO2 (using carbonate in our studies) combined with its electrochemical release-and-upgrade to CO, a fuel precursor. Direct air capture uses alkali hydroxide solution to form alkali carbonate, and this requires additional energy-intensive steps to dry and calcine the carbonate salt to generate a pure gas-phase CO2 stream. A pure stream of CO2 is typically achieved by thermally cycling at 900 °C. The subsequent valorization of the gas-phase CO2 to CO introduces further energy losses and system complications. This approach based on inputting CO2 in the gas phase for ensuing electrolysis suffers from a CO2 utilization limit since CO2 gas is lost to carbonate formation in local alkaline conditions, and carbonate crosses over to the anodic side during electrolysis. The carbonate formation mandates energy-consuming regeneration of carbonate to CO2. The crossover mandates separation of CO2 on the anodic side from O2. Furthermore, the downstream is diluted by unreacted CO2 which requiring additional energy cost for the product separation. To provide syngas, hydrogen is fed at $1/kg~$12/kg depending on the technology used in its generation. Here we instead use direct electrolysis: in a single step, we take CO2 from capture (carbonate) solution, and generate an upgraded chemical feedstock: syngas. Carbonate is used as the carbon supply. It reacts at the cathodic surface, converting into carbon monoxide, with the remaining current going to hydrogen evolution from water. The products at downstream are pure syngas: only when CO2 is converted to CO does it evolve into the gas phase; the unreacted CO2 remains captured. The lean carbonate (hydroxide) solution we return to the direct air capture (contacting) unit. In this way, the technology avoids the energy-intensive/carbon-positive steps associated with concentrating CO2 and regenerating lost CO2. In this project we will elaborate the science of, and demonstrate experimentally, the electrosynthesis of syngas directly from carbonate direct air capture (DAC) liquid. We will report initial scaling of the system, demonstrating a pilot providing a tunable syngas ratio across the range 1:1 to 7:1 at current densities exceeding 300 mA/m2, and also incorporating initial reliability studies (100 hours operando) and scale to 15 cm2 electrolysis reactors.
|Effective start/end date||8/1/22 → 7/31/24|
- Office of Naval Research (N00014-22-1-2690)
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