Researchers at Rice University have announced a surprisingly straightforward technique that significantly enhances the stability of electrochemical devices designed to convert carbon dioxide into valuable fuels and chemicals. The method involves passing the CO₂ through an acid bubbler.

The findings, published in Science, address a major challenge in CO₂ reduction systems: salt buildup that obstructs gas flow, diminishes efficiency, and leads to premature device failure. The team’s approach, termed acid-humidified CO₂, extended the operational lifespan of a CO₂ reduction system by over 50 times, achieving more than 4,500 hours of stable operation in a scaled-up reactor-a significant advancement in the field.

Electrochemical CO₂ reduction (CO₂RR) is an innovative green technology that uses electricity, ideally from renewable sources, to transform CO₂ into valuable products like carbon monoxide, ethylene, or alcohols. These products can be further processed into fuels or used in industrial applications, potentially converting a major pollutant into a valuable resource.

However, the practical application of CO₂RR has been limited by poor system stability. A recurring problem is the accumulation of potassium bicarbonate salts in the gas flow channels. This occurs when potassium ions migrate from the anolyte across the anion exchange membrane to the cathode reaction zone and combine with CO₂ under high pH conditions.

“Salt precipitation blocks CO₂ transport and floods the gas diffusion electrode,which leads to performance failure,” said Haotian Wang ,the corresponding author of the study and associate professor of chemical and biomolecular engineering,materials science and nanoengineering and chemistry at Rice.”This typically happens within a few hundred hours,which is far from commercial viability.”

To overcome this issue, the rice team introduced a modification to a standard procedure. Instead of using water to humidify the CO₂ gas entering the reactor, they bubbled the gas through an acid solution, such as hydrochloric, formic, or acetic acid.

The acid vapor is carried into the cathode reaction chamber in small amounts, enough to modify the local chemistry. As the salts formed with these acids are much more soluble than potassium bicarbonate, they do not crystallize and block the channels.

“Salt precipitation blocks CO₂ transport and floods the gas diffusion electrode, which leads to performance failure.”

The results were significant. In tests using a silver catalyst-a common benchmark for converting CO₂ 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 comparison, systems using standard water-humidified CO₂ failed after approximately 80 hours due to salt buildup.

The acid-humidified method was effective across multiple catalyst types, including zinc oxide, copper oxide, and bismuth oxide, which are used to target different CO₂RR products.The researchers also showed that the method could be scaled without compromising performance,with large-scale devices maintaining energy efficiency and preventing salt blockage over extended periods.

Minimal corrosion or damage to the anion exchange membranes, which are typically sensitive to chloride, was observed by maintaining low acid concentrations. the approach was also compatible with commonly used membranes and materials, enhancing its potential for integration into existing systems.

To observe salt formation in real-time, the team used custom-built reactors with transparent flow plates. Under conventional water humidification, salt crystals began forming within 48 hours. However, with acid-humidified CO₂, no significant crystal accumulation was observed even after hundreds of hours, and any small deposits were eventually dissolved and removed from the system.

“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 research associate in chemical and biomolecular engineering 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.”

This research paves the way for more durable and scalable CO₂ electrolyzers, which are essential for deploying the technology at industrial scales as part of carbon capture and utilization strategies. The simplicity of the approach, involving only minor adjustments to existing humidification setups, means it can be adopted without major redesigns or increased costs.

“This is a major finding for CO₂ electrolysis,” said Ahmad Elgazzar, co-first author and graduate student in chemical and biomolecular engineering at Rice. “Our method addresses a long-standing obstacle with a low-cost, easily implementable solution. Its a step toward making carbon utilization technologies more commercially viable and more sustainable.”