A new electrochemical method turns carbon dioxide and alcohols into valuable chemicals on both sides of a single cell, using a sulfur-modified catalyst that improves efficiency and selectivity.
(Nanowerk Spotlight) Electrochemical devices that convert carbon dioxide into fuels and chemicals have made steady progress, but they still contain a built-in inefficiency. On the cathode side, carbon dioxide is reduced into products such as carbon monoxide, ethylene, or ethanol.
On the anode, however, most systems rely on the oxygen evolution reaction (OER), which splits water to form oxygen. That step requires high voltage and produces a gas with little value for chemical manufacturing. The mismatch wastes energy and limits the practicality of carbon dioxide conversion. Replacing oxygen evolution with a more productive reaction has become a central goal in electrocatalysis.
A promising alternative is the alcohol oxidation reaction (AOR). Instead of splitting water, the anode oxidizes alcohols into aldehydes or acids, compounds already valuable to industry, while consuming less energy than OER. When paired with carbon dioxide reduction at the cathode, this configuration, called paired electrocatalysis, turns both electrodes into productive sites.
The principle is straightforward, but achieving high efficiency and selectivity for both reactions in one device is difficult. Each side of the cell operates under different conditions, and few catalyst materials can manage both at once.
“We uncovered a practical approach for the simultaneous electrochemical CO2 reduction (CO2RR) and alcohol oxidation (AOR), enabling the selective valuable chemicals production,” Wee-Jun Ong, a professor in the School of Energy and Chemical Engineering at Xiamen University Malaysia, tells Nanowerk. “We paired electrochemical system performs both tasks at once, reducing carbon dioxide on the cathode while oxidizing alcohols on the anode. The result is a sharp decrease in energy consumption and a dual stream of high-value products.”
Beyond performance, the work provides direct molecular evidence of how sulfur modifies the catalyst surface to promote carbon–carbon bond formation, connecting atomic structure to measurable behavior.
At the core of the study is a hybrid catalyst composed of sulfur-modified copper bismuth oxide nanospheres supported on sheets of nitrogen-doped reduced graphene oxide (NrGO). This composite was designed to function on both electrodes while maintaining conductivity and stability.
Schematic illustration of the synthesis method for sulfur-doped CuBi₂O₄ (S-CuBi₂O₄) nanospheres supported on nitrogen-doped reduced graphene oxide (NrGO). (Image: Adapted from DOI:10.1002/anie.202513840 with permission by Wiley-VCH Verlag)
Copper-based materials are known to steer carbon dioxide reduction toward multi-carbon products, but their efficiency depends on how strongly the surface binds intermediate species. Adding sulfur alters the electronic structure of copper and bismuth atoms and creates oxygen vacancies, replacing oxygen atoms in the crystal lattice that provide reactive sites. The nitrogen-doped graphene network acts as a conductive scaffold that distributes charge evenly and prevents particle clumping during operation.
Microscopy and spectroscopy confirm that this structure behaves as intended. Transmission electron microscopy shows nanospheres about 25 nanometers wide distributed across the carbon sheets. X-ray diffraction identifies a single copper bismuth oxide phase, while surface spectroscopy reveals that sulfur increases the fraction of copper in the Cu⁺ oxidation state and raises the density of oxygen vacancies.
Both effects improve the adsorption and activation of reaction intermediates. Extended X-ray absorption spectroscopy detects copper–sulfur and copper–bismuth bonds, confirming that sulfur modifies the local environment of the active sites.
As Ong notes, “the introduction of sulfur atoms tunes the local coordination environment, leading to modulated electronic structures and enhanced charge transfer ability.”
In carbon dioxide reduction tests, the optimized material achieves more than 92 percent Faradaic efficiency for multi-carbon products at a potential of minus 1.1 volts versus the reversible hydrogen electrode.
Faradaic efficiency measures the fraction of electrical current that contributes to desired products rather than side reactions such as hydrogen formation. The catalyst sustains this performance for more than 200 hours at a current density of -50 milliamps per square centimeter, demonstrating strong durability. Electrical impedance measurements show reduced charge-transfer resistance, and capacitance data indicate a larger electrochemically active surface area.
These findings confirm that sulfur-tuning improves both charge mobility and access to reaction sites.
The graphical illustration of C2+ product formation from the electrocatalyst. (Image: Adapted from DOI:10.1002/anie.202513840 with permission by Wiley-VCH Verlag)
To understand why the catalyst behaves this way, the researchers used in situ Raman spectroscopy, which tracks molecular vibrations on the surface during operation. The spectra show signals from carbon monoxide bound to the catalyst and from a short-lived dimer formed when two carbon monoxide molecules couple.
That coupling is the first carbon–carbon bond that leads to longer-chain products. The appearance of these features shows that the sulfur-modified surface stabilizes carbon monoxide long enough for coupling to occur efficiently. Density functional theory calculations support this conclusion.
The team reports that the S-enhanced CuBi2O4 (211) surface significantly lowers the energy barrier for the formation of *CO from *COOH, as well as for the *CO dimerization process.
The energy required to convert carbon dioxide into adsorbed carbon monoxide drops from 0.97 electron volts on the unmodified surface to 0.20 on the sulfur-modified version, and the coupling step becomes easier as well. Together, the experimental and computational results explain why sulfur boosts multi-carbon selectivity.
The same material also enables alcohol oxidation in place of oxygen evolution at the anode. The researchers tested methanol, ethanol, benzyl alcohol, and furfuryl alcohol in alkaline electrolyte. Benzyl and furfuryl alcohol performed best, converting mainly to benzaldehyde and furfural, two important industrial intermediates.
The reaction proceeds with low Tafel slopes of about 37 millivolts per decade, which indicates fast kinetics, and maintains stable current for at least 12 hours. Impedance measurements show that alcohol oxidation on this surface requires less energy than oxygen evolution.
“AOR is kinetically more favorable than the sluggish OER, enabling lower cell voltage and higher energy efficiency for paired electrocatalysis,” Ong points out.
Raman analysis detects hydroxide and carbonate species forming during operation, while theoretical modeling suggests that sulfur assists the key hydrogen-removal step that produces the carbonyl group in the aldehyde products.
When both electrodes are combined, the full paired electrolyzer delivers high current density and long-term stability while producing value on both sides. The device achieves a carbon economy above 34 percent for multi-carbon products, meaning that more than one-third of the carbon entering the system ends up in useful compounds.
To test renewable integration, the team powered the cell with a commercial solar panel under simulated sunlight. Under one-sun illumination, the device operates at about 2.38 volts and maintains a current density close to 40 milliamps per square centimeter.
The solar-to-fuel efficiency reaches roughly 16 percent for carbon dioxide conversion and between 3 and 4 percent for the alcohol oxidation reactions. The system remains stable through light-dark cycling and extended continuous operation.
The importance of this study lies in how it merges two productive reactions into one coherent system. By replacing oxygen evolution with alcohol oxidation, the cell eliminates a major energy loss and generates valuable aldehydes and acids instead of oxygen gas. The sulfur-modified copper bismuth oxide catalyst supplies both electrodes, and the combined experimental and theoretical analysis clarifies how it achieves this.
Some limits remain, including the sensitivity of selectivity to sulfur content and the complexity of real electrodes, but the direction is clear. Through precise electronic tuning and balanced reaction design, the work shows how carbon dioxide conversion can evolve from an energy-intensive demonstration into a more efficient route for manufacturing essential chemicals.
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