Preparation of carbon films. All electrodes were made from activated carbon (YP-50F, Kuraray, which was found to perform favorably compared to activated carbons used in the literature) and polytetrafluoroethylene (PTFE, 60% wt. dispersion in water, Aldrich) mixed in a ratio of 95:5 by weight. The PTFE serves as a binder to hold together the electrode and make it more malleable for rolling out into a film. First, activated carbon was dispersed in several mL of ethanol in an ultrasonic bath, then mixed with the PTFE dispersion on a watch-glass. The mixture was continually stirred with a spatula to ensure through mixing. As the ethanol evaporated, drying portions of the mixture were gathered into a single mass, until enough ethanol evaporated that the collected carbon and PTFE had a dough-like consistency. After kneading and adding additional ethanol as necessary to achieve the desired consistency, the carbon was transferred to a glass sheet and rolled to a uniform thickness with a steel rolling pin. The material was then transferred with a razor blade to aluminum foil, which was folded into a wallet and placed into a vacuum oven overnight at 80-100 °C to remove residual ethanol/water.