An Approach to Electrochemically-Mediated Air Separation Using Co Salen Complexes

Biomass gasification for fuel production is a lower-carbon alternative as compared to the use of fossil resources. In biomass gasification, organic material is converted to gases including hydrogen, carbon monoxide, and carbon dioxide. This process has lower net carbon emissions than combusting fossil fuels because the plants used for fuel uptake carbon dioxide while they are growing. However, biomass gasification faces several technical challenges to widespread implementation, including the need for a pure oxygen stream for optimal gasification. 1 Cryogenic distillation is a common method of producing pure oxygen from air at a higher efficiency than other technologies, but its energy requirements are significant and it is most efficient at very large production volumes. 2 As a result, there is motivation for an energy-efficient method of producing oxygen in systems better suited for lower production volumes. In this presentation, we describe an electro-swing approach for oxygen sorption based on Co(II)-salen complexes. Their known affinity towards oxygen, which reduces upon oxidation to the respective Co(III) adduct, allows selective binding of oxygen from air and potential release into a pure oxygen stream. There has previously been limited investigation into electrochemically-triggered release of oxygen through the application of a positive potential. 3 We first characterize several Co(salen) complexes and associated electrolyte solutions via cyclic voltammetry and chronoamperometry. We then investigate the conditions required to trigger release of oxygen from the oxidized complex. Finally, we demonstrate use of Co(salen) complexes in a 2-stage electrochemical cell, in which oxygen binding and release occur at the electrodes where oxidation and reduction of the Co(salen) complex take place. Overall, this work provides a proof-of-concept for a new oxygen separation strategy that can be further assessed and optimized in the future. Acknowledgements: This research was funded by the U.S. Department of Energy’s Office of Fossil Energy under award number FE0032348. References: National Energy Technology Laboratory. (n.d.). 3.2 Biomass. Gasifipedia. https://netl.doe.gov/research/coal/energy-systems/gasification/gasifipedia/biomass Q. Xiong, P. Luo and B. Hua, "Energy consumption analysis of air separation process for oxy-fuel combustion system," Adv. Mater. Res., vol. 1033–1034, p. 146, 2014. Cameron, James H., and Steven C. Turner. "Electrochemically controlled dissociation of dioxygen from a µ-peroxo cobalt (III) dimer." Journal of the Chemical Society, Dalton Transactions 23 (1992): 3285-3289.