The development of energy efficient photo-responsive adsorbents forcarbon dioxide capture

According to the International Energy Agency (IEA) report of 2021, 33 out of 46 gigatons of greenhouse gas emissions are CO2 emissions. In response, the 'Carbon Capture and Innovation Challenge' was launched at the United Nations' COP22, aiming for near-zero CO2 emissions from carbon-intensive industries. Further, the Net Zero by 2050 report by the IEA purports that CO2 capture from industrial processes and directly from air will play a critical role in achieving net-zero emissions. Liquid amine solutions are predominantly used for CO2 capture. However, regenerating these solutions requires energy intensive temperature and pressure alterations, which lowers the efficiency and increases the costs of CO2 capture. Recently, research efforts have been focused on the development of solid adsorbents for CO2 capture. The energy penalty for regenerating solid adsorbents is low due to their low heat capacity. Herein, research is directed towards the development of solid adsorbents that use a photo-desorption mechanism to capture CO2 with exceptionally high efficiency. These materials readily adsorb CO2 in the dark or under lowillumination conditions and photo-desorb CO2 when subjected to incident light. By using light as a "photoswitch," to desorb CO2 the need for energy-intensive pressure or temperature alterations are mitigated. In this study, density-functional theory (DFT) calculations are performed to evaluate the binding energy of CO2 on various metal surfaces in the absence and presence of light. Materials that exhibit a high binding energy in the dark and a low binding energy in the light are promising candidates to be used as photo-driven adsorbents for CO2 capture. Results show that metals can be categorized as good-performance metals (Co, Fe, V), average-performance metals (Al, Cu, Zn, Pt), and poor-performance metals (Ni). While Co, Fe, and V exhibit the largest differences between their light and dark CO2 binding energies, the results also show that CO2 dissociates when adsorbed on these surfaces. Consequently, Zn and Cu were found to be the most promising metals for the adsorption/photo-desorption phenomenon. Estimates of the regeneration energy show these materials have potential to lower the energy intensity of CO2 capture processes. Subsequent steps in this research will involve using evolutionary-based optimization techniques to identify Zn-Cu alloys that outperform their pure metal counterparts for carbon capture processes. The research presented herein paves the way for the development of a novel and energy-efficient CO2 capture process, thereby contributing to the mitigation of greenhouse gas emissions and net zero CO2 emissions.

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