Rice University researchers improve CO2 to fuel and chemical conversion with acid bubbler

In Texas, team of researchers at Rice University has discovered a surprisingly simple method for vastly improving the stability of electrochemical devices that convert carbon dioxide into useful fuels and chemicals, and it involves nothing more than sending the CO 2 through an acid bubbler.

Their study, published in Science, addresses a major bottleneck in the performance and stability of CO 2 reduction systems: the buildup of salt that clogs gas flow channels, reduces efficiency and causes the devices to fail prematurely. Using a technique they call acid-humidified CO2, the researchers extended the operational life of a CO 2 reduction system more than 50-fold, demonstrating more than 4,500 hours of stable operation in a scaled-up reactor — a milestone for the field.

Electrochemical CO 2 reduction, or CO2RR, is an emerging green technology that uses electricity, ideally from renewable sources, to transform climate-warming CO 2 into valuable products like carbon monoxide, ethylene or alcohols. These products can be further refined into fuels or used in industrial processes, potentially turning a major pollutant into a feedstock.

However, practical implementation has been hindered by poor system stability. One persistent issue is the accumulation of potassium bicarbonate salts in the gas flow channels, which occurs when potassium ions migrate from the anolyte across the anion exchange membrane to the cathode reaction zone and combine with CO 2 under high pH conditions.

To combat this, the Rice team tried an elegant twist on a standard procedure. Instead of using water to humidify the CO 2 gas input into the reactor, they bubbled the gas through an acid solution such as hydrochloric, formic or acetic acid.

The vapor from the acid is carried into the cathode reaction chamber in trace amounts, just enough to alter the local chemistry. Because the salts formed with these acids are much more soluble than potassium bicarbonate, they don’t crystallize and block the channels.

The effect was dramatic. In tests using a silver catalyst — a common benchmark for converting CO 2 to carbon monoxide — the system operated stably for over 2,000 hours in a lab-scale device and more than 4,500 hours in a 100-square-centimeter, scaled-up electrolyzer. In contrast, systems using standard water-humidified CO 2 failed after about 80 hours because of salt buildup.