Copper Hexacyanoferrate Hydrogel Electrodes for Cation Separations

Presenter: 

Kai-Jher Tan

Authors: 

Kai-Jher Tan, Johannes Elbert, Xiao Su, T. Alan Hatton

Author Affiliation: 

Department of Chemical Engineering, Massachusetts Institute of Technology, 25 Ames Street, Cambridge, MA, U.S.A. 02139

Abstract: 

Chemical purification is ubiquitous in the production of commodity chemicals, and there is a clear urgency to develop clean energy-efficient separation processes to reduce economic and environmental impacts. Electrochemical processes are an attractive platform, as they do not require solvents that change solution chemistry, as well as heat and pressure inputs. Furthermore, they can be designed to target certain chemical species, with one such candidate being the mixed-valence transition metal hexacyanoferrate (CuHCF) class of crystalline compounds. We report a new surfmer-based method to produce functionalized redox-active CuHCF composite hydrogels for electrochemically separating ions in aqueous media. The developed technique is a straightforward, inexpensive, one-pot preparation process that can consistently produce self-contained redox-active electrodes, without the need for manual filtration or grinding steps. The resulting uniform electrodes are stable in water, capable of withstanding up to ~100 separation cycles without gel leaching. Furthermore, we show that the porous hydrogels exhibit strong redox response as well as affinity for cesium cations, whose radioactive isotope, Cs137, is present in nuclear waste and is both an environmental and health concern. CuHCF nanoparticles can also be applied to remove other toxic heavy metal cations of concern with similar hydrated ionic radii. We also discuss other methods to further improve the operation of the hydrogel in an electrochemical system by using specific dual-functionalized design schemes to tune the counter electrode.