Chitosan/SIFSIX-3-Cu Cryogels on Printed Laser-Induced Graphene for CO2 Electric Swing Capture

Abstract

To achieve global net zero greenhouse gas emissions, carbon dioxide (CO2) removal technologies (CDR) must be deployed at gigatonne scale by the end of the decade. Direct air capture (DAC) is one category of CDR technology which shows promise due to its more straightforward measurability and verifiability. Low temperature, solid sorbent-based DAC systems in particular offer a lower energy demand and when paired with renewable electrical systems, avoid the use of fossil fuels and the generation of additional CO2 emissions in the process. Several sorbents have been investigated for electric swing adsorption (ESA) DAC, where heat generated using the Joule heating principle is used for the desorption of CO2 from the sorbent. Most of the sorbents are carbonaceous due to their semi-conductive nature which allows for electrical current travel. However, these sorbents suffer from reduced capacity at low CO2 partial pressures, making them less suitable for DAC.

As an alternative, we explore an indirect ESA process using laser-induced graphene (LIG) which acts as a flexible heater layer. For the adsorbent layer, chitosan (CS) cryogel with in situ synthesized SIFSIX-3-Cu metal organic framework (MOF) is fabricated for its high capacity, appreciable CO2 selectivity, and sustainability. The pure MOF powder reached its maximum adsorption capacity of approximately 2.5 mmol g⁻¹ within just five minutes, demonstrating its exceptionally fast adsorption kinetics. In contrast, the pure chitosan (CS) cryogel required more than 30 minutes to reach the same capacity. The CS/MOF hybrid cryogel exhibited intermediate kinetics, achieving a maximum adsorption capacity of 2.92 mmol g⁻¹. It was shown that the adsorbents could be regenerated in temperature range of 70-80°C, had low N2 uptake, and 88% of the CS/MOF cryogel capacity was maintained after 4 cycles. Patterned LIG grids were subsequently fabricated and could raise the temperature of the CS/MOF cryogel adsorbent via Joule heating to the target regeneration temperature in 66 s with only 15 V. The LIG grid could also consistently generate the desired temperature range over 4 cycles. Lastly, the chitosan cryogel was fabricated directly on a LIG grid without compromising its heating capability. This successfully demonstrates how an environmentally conscious and efficient ESA system can be engineered by combining LIG optimized for heating and eco-friendly adsorbents with high CO2 capacity.