Electrochemical carbon capture processes for mitigation of CO2 emissions

This review discusses the emerging science and research progress underlying electrochemical processes for carbon capture for mitigation of CO2 emissions, and assesses their current maturity and trajectory.

Current Understanding of Nonaqueous Electrolytes for Calcium-Based Batteries

Calcium metal batteries are receiving growing research attention due to significant breakthroughs in recent years that have indicated reversible Ca plating/stripping with attractive Coulombic efficiencies (90-95%), once thought to be out of reach. While the Ca anode is often described as being surface film-controlled, the ability to access reversible Ca electrochemistry is highly electrolyte-dependent in general, which affects both interfacial chemistry on plated Ca along with more fundamental Ca2+/Ca redox properties. This mini-review describes recent progress towards a reversible Ca anode from the point of view of the most successful electrolyte chemistries identified to date. This includes, centrally, what is currently known about the Ca2+ solvation environment in these systems. Experimental (physico-chemical and spectroscopy) and computational results are summarized for the two major solvent classes - carbonates and ethers - that have yielded promising results so far. Current knowledge gaps and opportunities to improve fundamental understanding of Ca2+/Ca redox are also identified.

Governing Role of Solvent on Discharge Activity in Lithium-CO2 Batteries

Non-aqueous Li-CO₂ batteries reported in  literature have almost exclusively relied upon glyme-based electrolytes, leading to a hypothesis that they are uniquely active for CO₂ discharge. Here, we study the effect of electrolyte composition on CO₂ activity to examine whether this is the case. The results indicate that TEGDME-based electrolytes containing moderate concentrations of Li⁺ salts (roughly within the range of 0.7-2 M examined herein) are most conducive to CO₂ activation, especially compared to dimethyl sulfoxide and propylene carbonate-based electrolytes. Through electrochemical, spectroscopic, and computational methods, we determine that glymes have lower desolvation energies for Li⁺  compared to other solvent candidates, whereas high salt concentrations increase the local density of Li⁺ surrounding CO₂ and reduction intermediates. These attributes collectively increase the availability of Li⁺, crossing a threshold necessary to support CO₂  activation. Discharge voltage and reaction rates are also sensitive to the alkali cation identity, further invoking its key role in enabling or suppressing reactivity.