new findings

Rice research team's study keeps CO2-to-fuel devices running 50 times longer

Ahmad Elgazzar, Haotian Wang and Shaoyun Hao were members of a Rice University team that recently published findings on how acid bubbling can improve CO2 reduction systems. Photo courtesy Rice.

In a new study published in the journal Science, a team of Rice University researchers shared findings on how acid bubbles can improve the stability of electrochemical devices that convert carbon dioxide into useful fuels and chemicals.

The team led by Rice associate professor Hoatian Wang addressed an issue in the performance and stability of CO2 reduction systems. The gas flow channels in the systems often clog due to salt buildup, reducing efficiency and causing the devices to fail prematurely after about 80 hours of operation.

“Salt precipitation blocks CO2 transport and floods the gas diffusion electrode, which leads to performance failure,” Wang said in a news release. “This typically happens within a few hundred hours, which is far from commercial viability.”

By using an acid-humidified CO2 technique, the team was able to extend the operational life of a CO2 reduction system more than 50-fold, demonstrating more than 4,500 hours of stable operation in a scaled-up reactor.

The Rice team made a simple swap with a significant impact. Instead of using water to humidify the CO2 gas input into the reactor, the team bubbled the gas through an acid solution such as hydrochloric, formic or acetic acid. This process made more soluble salt formations that did not crystallize or block the channels.

The process has major implications for an emerging green technology known as electrochemical CO2 reduction, or CO2RR, that transforms climate-warming CO2 into products like carbon monoxide, ethylene, or alcohols. The products can be further refined into fuels or feedstocks.

“Using the traditional method of water-humidified CO2 could lead to salt formation in the cathode gas flow channels,” Shaoyun Hao, postdoctoral research associate in chemical and biomolecular engineering at Rice and co-first author, explained in the news release. “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 Rice team believes the work can lead to more scalable CO2 electrolyzers, which is vital if the technology is to be deployed at industrial scales as part of carbon capture and utilization strategies. Since the approach itself is relatively simple, it could lead to a more cost-effective and efficient solution. It also worked well with multiple catalyst types, including zinc oxide, copper oxide and bismuth oxide, which are allo used to target different CO2RR products.

“Our method addresses a long-standing obstacle with a low-cost, easily implementable solution,” Ahmad Elgazzar, co-first author and graduate student in chemical and biomolecular engineering at Rice, added in the release. “It’s a step toward making carbon utilization technologies more commercially viable and more sustainable.”

A team led by Wang and in collaboration with researchers from the University of Houston also shared findings on salt precipitation buildup and CO2RR in a recent edition of the journal Nature Energy. Read more here.

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A View From HETI

A team led by M.A.S.R. Saadi and Muhammad Maksud Rahman has developed a biomaterial that they hope could be used for the “next disposable water bottle." Photo courtesy Rice University.

Collaborators from two Houston universities are leading the way in engineering a biomaterial into a scalable, multifunctional material that could potentially replace plastic.

The research was led by Muhammad Maksud Rahman, an assistant professor of mechanical and aerospace engineering at the University of Houston and an adjunct assistant professor of materials science and nanoengineering at Rice University. The team shared its findings in a study in the journal Nature Communications earlier this month. M.A.S.R. Saadi, a doctoral student in material science and nanoengineering at Rice, served as the first author.

The study introduced a biosynthesis technique that aligns bacterial cellulose fibers in real-time, which resulted in robust biopolymer sheets with “exceptional mechanical properties,” according to the researchers.

Biomaterials typically have weaker mechanical properties than their synthetic counterparts. However, the team was able to develop sheets of material with similar strengths to some metals and glasses. And still, the material was foldable and fully biodegradable.

To achieve this, the team developed a rotational bioreactor and utilized fluid motion to guide the bacteria fibers into a consistent alignment, rather than allowing them to align randomly, as they would in nature.

The process also allowed the team to easily integrate nanoscale additives—like graphene, carbon nanotubes and boron nitride—making the sheets stronger and improving the thermal properties.

“This dynamic biosynthesis approach enables the creation of stronger materials with greater functionality,” Saadi said in a release. “The method allows for the easy integration of various nanoscale additives directly into the bacterial cellulose, making it possible to customize material properties for specific applications.”

Ultimately, the scientists at UH and Rice hope this discovery could be used for the “next disposable water bottle,” which would be made by biodegradable biopolymers in bacterial cellulose, an abundant resource on Earth.

Additionally, the team sees applications for the materials in the packaging, breathable textiles, electronics, food and energy sectors.

“We envision these strong, multifunctional and eco-friendly bacterial cellulose sheets becoming ubiquitous, replacing plastics in various industries and helping mitigate environmental damage,” Rahman said the release.

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