Developing improved methods for CO2 capture and concentration (CCC) is essential to mitigating the impact of our current emissions and can lead to net carbon negative technologies.
Electrochemical carbon capture and concentration (eCCC) offers a promising alternative to thermochemical processes as it circumvents the limitations of temperature-driven capture and release. This review will discuss a wide range of eCCC approaches, starting with the first examples reported in the 1960s and 1970s, then transitioning into more recent approaches and future outlooks. For each approach, the achievements in the field, current challenges, and opportunities for improvement will be described. This review is a comprehensive survey of the eCCC field and evaluates the chemical, theoretical, and electrochemical engineering aspects of different methods to aid in the development of modern economical eCCC technologies that can be utilized in largescale carbon capture and sequestration (CCS) processes. CONTENTS 5.4.
Current state-of-the-art thermal technologies for CO 2 capture and concentration (CCC) from industrial emissions and air are energetically inefficient. In contrast, electrochemical CCC (eCCC) using redox carriers can theoretically approach 100% efficiency. However, there are currently few oxygen-stable redox carriers suitable for eCCC. Quinone derivatives have previously been studied as redox carriers as they have no affinity for CO 2 in the fully oxidized state and an enhanced affinity for CO 2 in their reduced states. Unfortunately, the quinones used in prior studies displayed an unfavorable tradeoff between their second reduction potential (E 1/2 ) and CO 2 binding constant (K COd 2 ). As a result, reduced quinones that exhibit a sufficient K COd 2 for flue gas or atmospheric CO 2 capture have E 1/2 values negative of the O 2 /O 2 •− reduction potential. To improve our understanding of the structural and electronic relationships that correlate K COd 2 and E 1/2 , we report the largest set of quinones that have been experimentally evaluated for their K COd 2 and E 1/2 properties. The trends in the E 1/2 and K COd 2 properties were further investigated through extensive quantum chemical calculations to inform experimental carrier design. Notably, we identified structural handles to manipulate E 1/2 and K COd 2 properties of quinones; however, the altered steric and electronic effects did not disrupt their linear dependence.
Electrochemical carbon capture and concentration (eCCC) offers a promising alternative to thermochemical processes as it circumvents the limitations of temperature-driven capture and release. This review will begin by discussing the history of eCCC, describing early work in the field and the motivation for pursuing such a process. We will then transition towards discussing more recent approaches, with a heavier emphasis on methods that employ redox mediators to facilitate CO2 capture and release. These methods rely more on optimization through chemical design and include pH-mediated systems, electrochemically-mediated amine regeneration, and direct capture with redox-active molecules. For each approach, we provide a general overview of the system, discuss redox mediator chemistries that have been studied in literature, and highlight requirements for future generations of redox mediators. We also describe previous demonstrations of each method and current cell/system designs that have been used at the lab-scale. To conclude, we summarize achievements in the field, current challenges, and opportunities for improving these technologies. Overall, this review is a comprehensive survey of the eCCC field and evaluates the chemical, theoretical, and electrochemical engineering aspects of this approach. We hope this work can be used to assist the community in the development of modern economical eCCC technologies that can be utilized in large-scale CCS processes.
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