(186e) Vapor-Fed Membrane Electrode Assemblies for Electrochemical Oxidation
Electrochemical partial oxidation of chemical feeds, such as hydrocarbons, can be a low energy intense option for directly producing high-valued alcohols and carbon-free hydrogen. However, for economic feasibility, one needs to operate efficiently and at high current densities (greater than 100 mA/cm2). One architecture that provides these attributes is the membrane-electrode assembly (MEA), which has been optimized for performance in fuel cells. A similar architecture is used in electrolyzers although with liquid feeds, which is not tenable for hydrocarbon partial oxidation due to the inherently low solubility of hydrocarbons. In this talk, we will explore a vapor-fed MEA for partial oxidation, with an initial focus on water oxidation to understand the mass-transport and hydration concerns with vapor feeds. Experiments demonstrate a water-vapor fed electrolyzer performance of over 100 mA/cm2 current density at less than 1.7 V cell potential, and at different temperature and humidity feeds. To probe the limitations of the electrolyzer further, a model was used to identify the overpotentials, local water activity, water content values, and temperature within the cell at various conditions. The major limitations within the water-vapor fed electrolyzer are caused by a decreased water content within the membrane phase, indicated by increased ohmic and mass-transport losses seen in the applied-voltage breakdown. Using our model, we show how mass transport limitations can be alleviated by considering the role of water as both a reactant and a hydrating agent through swapping the carrier gas, testing a thinner membrane, and reducing the relative humidity of the feed streams. In addition, we will also discuss the operation of the MEA with different hydrocarbons, specifically methane and propane, and different electrocatalysts.