(535f) CO2–CO Energy Conversion Cycle Enabled By a CO2-Selective Membrane

This presentation describes a method of CO₂ utilization for the production of CO and electricity via a fuel cell system that is enabled by a CO₂-selective membrane. We have synthesized highly CO₂-selective facilitated transport membranes, showing an extraordinarily high CO₂/CO selectivity of >1200 at 100–120°C (see the left figure below). The CO₂-selective membranes comprised polyvinylamine as the fixed-site carrier and the salt of potassium 2-aminoisobutyrate (AIBA-K) or 2-(1-piperazinyl)ethylamine 2-aminoisobutyrate (AIBA-PZEA) as the mobile carrier to facilitate the CO₂ transport.

One approach to utilize CO₂ for electricity production is a CO₂–CO energy conversion cycle as shown in the right figure below. CO₂ enters the cathode side of the first solid oxide fuel cell (SOFC) where it is partially reduced to CO while using H₂ as the fuel to the anode side of this fuel cell. The CO₂ and CO mixture is fed to the membrane, which separates it into a CO₂-rich permeate and a CO-rich retentate. The enriched CO₂ is recycled back to the H₂–CO₂ SOFC. The CO-rich retentate, for electricity generation, enters the anode side of the second SOFC, where air is used as the oxidant and the anode exhaust is also recycled to the first SOFC. Preliminary techno-economic analysis indicates that the developed facilitated transport membrane can render a retentate of >80% CO with a <1% CO loss. Owing to the high CO content, the CO–air fuel cell can produce a power density of ca. 350 mW/cm², which is 75% higher than the scenario where the CO₂ is not removed by the membrane. Experimentally, we have also demonstrated that the H₂–CO₂ SOFC can provide a power density of 0.11–0.37 mW/cm² at partial CO₂ conversion. Overall, the electricity generation can be achieved with zero carbon emission.