(589f) PEM-Based Electrochemical Separation of Gases
Traditional membranes for gas separation rely on pressure (concentration or chemical potential) gradients and selective diffusion to achieve gas separation. Gases that have reversible redox reactions, e.g. H2 2H+ + 2e-, can be separated electrochemically under ambient pressure and temperature conditions in a fuel cell like device. In an electrochemical separation a gas is electrochemically converted to an ion at an electrode, transported across an ion-conductive membrane by an electric potential gradient, and electrochemically reconverted to the gas at the other electrode. The flux across the membrane is proportional to the current and controlled by the electric potential and the electrocatalytic activity of the electrodes. We have examined the transport of carbon dioxide, oxygen and hydrogen through electrochemical membranes for applications in the separation and purification of these gases. These separations could be utilized to produce relatively pure carbon dioxide streams when used in conjunction with oxy-fired power generation for eventual sequestration. Electrochemical methods in our lab have also been used to demonstrate oxygen and hydrogen transport through anionic and cationic exchange membranes, respectively and with the use of commercial and laboratory-prepared catalysts. Hydrogen transport has been shown using voltages as low as 50mV to produce current densities on the order of 20mA/cm2. Oxygen transport requires higher voltages (600mV) to produce minimal current densities of 1 mA/cm2.