(381ah) Enhanced Transport Characteristics for the Electrochemically Driven Highly Selective Separation of Gases

Membrane-based gas separation represents an attractive route for the isolation of several important gases as well as an opportunity to improve the overall economic and environmental acceptability of a wide range of key industrial processes. In fact, high performance membranes offer the potential to provide game‐changing process energy advances, when sufficiently high levels of selectivity and permeability are achieved. In particular, there is a significant push to increase membrane selectivity in order to drive the process enhancement of a wide range of chemical and combustion processes as well as reduce the generation and atmospheric accumulation of greenhouse gases. The effectiveness of thin, nonporous membranes or membrane coatings has been demonstrated with processes such as facilitated transport to enhance the selectivity for a range of important target gases. However, selectivity and permeability are typically inversely related and, increasing the selectivity typically comes with a penalty of decreased permeability, as seen both for porous and nonporous membranes. Facilitated transport membranes incorporating targeted redox species have been shown to provide significant benefits in selectivity, however significant permeability penalties persist even with extremely thin, nanometer thick membrane layers.

To address these selectivity and permeability limitations, targeted biomimetic redox molecules are used to provide controlled transport of target species across the membrane, and membrane electrode assemblies (MEAs) with controlled porosity and surface chemistry are used to drive the permeability. A range of membrane chemistries and thicknesses were fabricated using highly scalable coating and processing techniques. The membranes and porous gas permeable electrode structures were integrated into MEAs. The composition and fabrication parameters were optimized to provide efficient and rapid gas adsorption and removal from the electrode structure. Electroanalytical measurements including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and linear sweep voltammetry (LSV) are used to quantify the enhancement of the membrane selectivity, kinetics, and mass transport characteristics. The electroanalytical measurements were used in the optimization of the membrane chemistry, electrode structures, and cell’s target operating conditions. The simultaneous enhancement of the gas separation selectivity and permeability has been demonstrated for the targeted separation of gases from a range of mixed gas feed compositions using low power, low voltage efficient electrochemically driven separation. Improvements in the permeability by a factor of 36 with a simultaneous improvement in the selectivity of 89 times using an electrochemical driving force for the separation of CO₂ from a range of mixed gas feed. Furthermore, we will discuss the reproducibility and durability of the electrochemical separation process.