Translatable reporting of energy demand and rates in electrochemical carbon capture

Abstract

Electrochemical carbon capture has recently emerged as a viable alternative to temperature-swing carbon capture due to its comparatively low energy demands. However, as a new research area, the experimental and measurement practices have not been standardized, making it difficult to make comparisons among studies. Guided by questions of relationships, we critically review the energy and rate evaluation metrics in the electrochemical carbon capture literature to develop a set of guidelines to make new studies more meaningful and useful for future technology transfer efforts. We demonstrate the need both for more transparent reporting due to the ways that experimental choices such as feed and outlet gas compositions influence these metrics and for careful consideration of how experimental details translate to practical applications at scale. This work is centered on capture from stationary energy generators but briefly mentions special considerations when applying the technology to direct air capture.

Keywords: Applied sciences; Electrochemistry; Engineering.

Graphical abstract

Figure 1

Electrochemical ${\text{CO}}_2$ capture process and relevant variables (A) Example schematic diagram of an electrochemical carbon capture plant with key bench-scale experiment design decisions (green boxes) and their direct impacts noted. (B) One example of the processes taking place in the absorber, anode chamber, stripper, and cathode chamber. For a complete description of possible mechanisms, see.^,,,

Figure 2

Minimum energy demand depends on ${\text{CO}}_2$ partial pressures Minimum work of separation as a function of the ${\text{CO}}_2$ capture efficiency and product gas purity calculated assuming a 15v% ${\text{CO}}_2$ feed gas.

Figure 3

${\text{CO}}_2$ dilution in the desorber affects absorption rate Predicted mean absorber ${\text{CO}}_2$ flux (left, black circles) and solution pH entering the absorber (right, orange triangles) as the outlet ${\text{CO}}_2$ partial pressure changes (50 mM quinone, p$K$_a = 6.01 and 7.75, 0.15 atm ${\text{CO}}_2$ feed gas). Calculated using the electrochemical pH-swing model developed for. Points are a subset of the data for visualization only. Dilution effect is the proportional change in flux relative to a 1 atm ${\text{CO}}_2$ product.