Published in Science, the study tackles a critical challenge in CO2 reduction technology: the formation of potassium bicarbonate salts, which block gas channels, reduce efficiency, and lead to early system failure. By using what they call "acid-humidified CO2," the researchers prolonged the lifespan of a CO2 electrolyzer from under 100 hours to over 4,500 hours.
Electrochemical CO2 reduction (CO2RR) uses electricity, ideally from renewable sources, to convert CO2 into useful products such as carbon monoxide, ethylene, and alcohols. However, its practical deployment has been limited by stability issues caused by salt precipitation on the gas diffusion electrode.
"Salt precipitation blocks CO2 transport and floods the gas diffusion electrode, which leads to performance failure," said Haotian Wang, corresponding author and associate professor of chemical and biomolecular engineering at Rice.
To prevent this, the team replaced standard water-humidified CO2 with gas humidified by bubbling through a weak acid like hydrochloric, formic, or acetic acid. The acid vapor carried into the reaction chamber subtly changed the local chemical environment. Since salts formed with these acids are far more soluble than potassium bicarbonate, they dissolved instead of clogging the system.
The benefits were clear. When using a silver catalyst to generate carbon monoxide, the acid-humidified system ran continuously for more than 2,000 hours in lab-scale devices and over 4,500 hours in a scaled-up, 100-square-centimeter reactor. In contrast, standard setups failed after just 80 hours.
The method was also tested with zinc oxide, copper oxide, and bismuth oxide catalysts, proving its versatility across different CO2RR reactions. Even at scale, devices maintained high efficiency and avoided salt-related blockages over prolonged operation.
Crucially, the researchers kept acid concentrations low enough to avoid damaging sensitive components such as anion exchange membranes, which remained largely unaffected. They verified system durability using transparent reactors, observing salt formation under conventional conditions but not with acid-humidified CO2.
"Using the traditional method of water-humidified CO2 could lead to salt formation in the cathode gas flow channels," said co-first author Shaoyun Hao, postdoctoral researcher at Rice. "We hypothesized - and confirmed - that acid vapor could dissolve the salt and convert the low solubility KHCO3 into salt with higher solubility, thus shifting the solubility balance just enough to avoid clogging without affecting catalyst performance."
The approach promises more robust and commercially viable CO2 electrolysis systems, with minimal adjustments needed to existing designs. According to co-first author Ahmad Elgazzar, a Rice graduate student, "Our method addresses a long-standing obstacle with a low-cost, easily implementable solution. It's a step toward making carbon utilization technologies more commercially viable and more sustainable."
Research Report:Acid-humidified CO2 gas input for stable electrochemical CO2 reduction reaction
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