A shorted membrane electrochemical cell powered by hydrogen to remove CO2 from the air feed of hydroxide exchange membrane fuel cells

February 15, 2022

A hydrogen economy has long been promoted as a ground-breaking aspect of a low-carbon future. However, there is little consensus on what this future entails, with The alkaline environment of hydroxide exchange membrane fuel cells (HEMFCs) potentially allows use of cost-effective catalysts and bipolar plates in devices. However, HEMFC performance is adversely affected by CO2 present in the ambient air feed. Here, we demonstrate an electrochemically driven CO2 separator (EDCS) to remove CO2 from the air feed using a shorted membrane that conducts both anions and electrons. This EDCS is powered by hydrogen like a fuel cell but needs no electrical wires, bipolar plates or current collectors, and thus can be modularized like a typical separation membrane. We show that a 25 cm2 shorted membrane EDCS can achieve >99% CO2 removal from 2,000 standard cubic centimetres per minute (sccm) of air for 450 hours and operate effectively under load-following dynamic conditions. A spiral-wound EDCS module can remove >98% CO2 from 10,000 sccm of air. Our technoeconomic analysis indicates a compact and efficient module at >99% CO2 removal costs US$112 for an 80 kWnet HEMFC stack.

As an alternative to proton exchange membrane fuel cells (PEMFCs), hydroxide exchange membrane fuel cells (HEMFCs) hold promises to reach the system cost target of US$30 per kW (ref. 1). The HEMFC’s less corrosive, alkaline environment offers stack cost advantages including cheaper catalysts, bipolar plates and membranes. The past few years have witnessed the rapid progress in HEMFC development, including the demonstration of alkaline-stable membranes, inexpensive cathode catalysts and high-performance single cells of increasing durability. However, one major remaining barrier is the deleterious effect of atmospheric CO2, which readily reacts with hydroxide anions at the HEMFC cathode forming carbonates, and thereby brings about a substantial loss in cell performance due to reduction of pH at the anode where carbonates accumulate and, to a lesser degree, the reduced ionic conductivity of the polymer electrolyte.