Demonstration of Electrochemically-Driven CO2 Separation Using Hydroxide Exchange Membranes

Abstract

Hydroxide exchange membrane fuel cells (HEMFCs) are a potentially lower-cost hydrogen fuel cell technology; however, ambient levels of CO2 in air significantly reduce HEMFCs’ performance. In this work, we demonstrate an electrochemically-driven CO2 separator (EDCS) which can be used to remove ambient levels of CO2 from air upstream of the HEMFC stack in fuel cell vehicles, protecting it from CO2-related performance losses. The EDCS operating window was explored for current density, anode flow, and cathode flow with respect to its impact on CO2 separation performance. Additionally, gas-phase mass transport was improved by selecting flow fields and gas diffusion layers conducive to the EDCS operating regime. The use of a carbon-ionomer interlayer at the cathode was explored and improved CO2 removal performance from 77.7% to 98.2% at 20 mA cm−2. An analytical, 1-D model is used to explain the experimental observations and design improvements. A single-cell, 25 cm2 EDCS using the aforementioned improved design demonstrated greater than 98% CO2 removal at a cathode flow rate of 1300 sccm for 100 h with 2.7% hydrogen stack consumption.