Scientists Boost CO₂ Conversion With a Surprisingly Simple Hack

Acid vapor prevents salt buildup in CO₂ reactors, enabling longer, more efficient operation.

A team of researchers at Rice University has found a surprisingly simple way to greatly improve the stability of electrochemical devices that convert carbon dioxide into useful fuels and chemicals: passing the CO₂ through an acid bubbler.

Their study, published in Science, tackles a major challenge in CO₂ reduction systems—salt buildup in gas flow channels. This buildup reduces efficiency and causes the systems to fail early. By using a method they call acid-humidified CO₂ the researchers extended the system’s operating life more than 50 times, achieving over 4,500 hours of stable performance in a scaled-up reactor—a major milestone for the field.

Turning CO₂ into useful products

Electrochemical CO₂ reduction, or CO₂RR, is an emerging green technology that uses electricity—preferably from renewable sources—to convert climate-warming CO₂ into valuable products such as carbon monoxide, ethylene, or alcohols. These products can then be refined into fuels or used in industrial applications, offering a way to turn a major pollutant into a useful resource.

Despite its promise, practical use of this technology has been limited by poor system stability. A common problem is the buildup of potassium bicarbonate salts in the gas flow channels. This happens when potassium ions move from the anolyte through the anion exchange membrane to the cathode reaction zone, where they 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.”

A simple acid-based solution

To address this issue, the Rice team applied a clever variation on a common technique. Rather than using water to humidify the CO₂ gas entering the reactor, they passed 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 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 contrast, systems using standard water-humidified CO₂ failed after about 80 hours because of salt buildup.

Compatible across catalysts and materials

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

They observed minimal corrosion or damage to the anion exchange membranes that are typically sensitive to chloride by keeping the acid concentrations low. The approach was also shown to be compatible with commonly used membranes and materials, reinforcing 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. With acid-humidified CO₂, however, no significant crystal accumulation was observed even after hundreds of hours, and any small deposits were eventually dissolved and carried out of 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.”

A breakthrough in durability and adoption

The work opens the door to more durable, scalable CO₂ electrolyzers, a critical need if the technology is to be deployed at industrial scales as part of carbon capture and utilization strategies. The simplicity of the approach, involving only small tweaks to existing humidification setups, means it can be adopted without significant redesigns or added 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. It’s a step toward making carbon utilization technologies more commercially viable and more sustainable.”

Reference: “Acid-humidified CO2 gas input for stable electrochemical CO2 reduction reaction” by Shaoyun Hao, Ahmad Elgazzar, Shou-Kun Zhang, Tae-Ung Wi, Feng-Yang Chen, Yuge Feng, Peng Zhu and Haotian Wang, 12 June 2025, Science.
DOI: 10.1126/science.adr3834

This work was supported by the Robert A. Welch Foundation, Rice, the National Science Foundation and the David and Lucile Packard Foundation.

Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.