Over the years, the sustained increase in anthropogenic activities has accelerated the need for decarbonization strategies to mitigate or reverse a looming climate breakdown, leading to the adoption of the Paris Climate Agreement (PRA) in 2015 with the goal to limit the increase in the global average temperature to 2 °C above pre-industrial levels in this century [1]. Direct air capture (DAC) of carbon dioxide is one of the strategies available for achieving negative carbon emissions when coupled with renewable energy and carbon storage [2-3]. Unlike point source carbon capture from fossil fuel power generation plants, oil refineries, cement and steel manufacturers, where CO₂ concentrations range from 5-30%, the low concentration in air, 0.04%, complicates capture, leading to the exploration of solvents and sorbents with strong CO₂ binding capacities for capture followed by energy-intensive regeneration using temperature, moisture, and pressure swing [4-5]. Instead of a purely physicochemical process, an electrochemically mediated process offers the benefit of potentially low energy consumption combined with room-temperature operation, flexible operational control by simply regulating the electric field, simplified water management, reduced number of unit operations, the potential for carbon utilization, and easy integration with renewable energy sources for an electrified carbon economy.

UK CAER developed a coupled electrochemical regenerator and absorber DAC process leveraging electrochemically induced pH swings for carbon-up concentration and release at the anode and hydroxide-based facile carbon capture solvent regeneration at the cathode to facilitate carbon capture from air in the absorber. Hydrogen is co-generated at the cathode, affording process flexibility from its sale, energy storage coupled with grid management capability, and/or anode depolarization to reduce operational voltage by > 1V. A major focus of this work is to facilitate capture with electrochemically generated hydroxide and promote CO₂ liberation from CO₃^2- and/or HCO₃^- -containing solvent and investigate the impact of regenerator and absorber operating parameters such as the loading factor, charging current, volumetric flow rates, depolarization and solvent concentration on process performance. Experimental results will be discussed.

References:

1. https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement.
2. Socolow, Robert, Michael Desmond, Roger Aines, Jason Blackstock, Olav Bolland, Tina Kaarsberg, Nathan Lewis et al. Direct air capture of CO₂ with chemicals: a technology assessment for the APS Panel on Public Affairs. American Physical Society, 2011.
3. National Academies of Sciences, Engineering, and Medicine. "Negative emissions technologies and reliable sequestration: a research agenda." Negative emissions technologies and reliable sequestration: a research agenda. (2018).
4. https://netl.doe.gov/coal/carbon-capture/post-combustion.
5. https://climate.nasa.gov/news/2915/the-atmosphere-getting-a-handle-on-carbon-dioxide/.