Stable and Efficient Electron Transport Layer for CO2 Conversion

Researchers from North Carolina State University have developed a new combination of materials with both organic and inorganic properties. These materials are designed for use in devices that convert atmospheric carbon dioxide into liquid fuel. The study was published in the journal ACS Applied Energy Materials.

Fundamentally, the goal of this project was to engineer a surface that would allow us to efficiently convert atmospheric carbon dioxide into methanol, which is a liquid fuel. Our hypothesis was that a class of materials called metal cones would be a valuable tool for addressing this challenge. Our work in this paper focuses on the engineering of a metalcone thin film for this application.

Gregory Parsons, Study Corresponding Author and Celanese Acetate Professor, Chemical and Biomolecular Engineering, North Carolina State University

Inorganic materials typically have stable properties and are solid. Organic materials, in contrast, are generally more chemically reactive and can exhibit physical characteristics similar to sponges. Because metalcone thin films are both inorganic and organic, they combine the properties of both types of materials.

Parsons said, “We wanted to find a way to create a metalcone thin film that retains the inorganic properties that make it a good interface between a semiconductor material and the liquid environment surrounding it. But we also wanted the metal cone to maintain the organic properties that create efficient pathways for electrons to move.”

The problem is that metal cones face a significant obstacle for practical use in this context,. If you put metal cones in an aqueous solution, the organic properties allow the metal cones to dissolve, making them practically useless. If you anneal the metal cones at high temperatures, they become physically stable, but you lose the attractive electrochemical properties.

 Hyuenwoo Yang, Study First Author and Postdoctoral Researcher, North Carolina State University

“But now we have demonstrated an approach that improves a metalcone’s stability and electrochemical properties, making them very promising candidates for use in photoelectric chemical carbon dioxide reduction,” Yang said.

The researchers used tincone, a metal cone composed of tin oxide (SnO₂) with organic oxide components replacing oxygen atoms. In tincone, carbon chains replace oxygen atoms to bind the tin oxide molecules, unlike traditional tin oxide materials where oxygen atoms serve this role.

The team chose to experiment with annealing tincone at various lower temperatures, as annealing at high temperatures tends to remove the desired electrochemical properties.

We found that the sweet spot was a ‘mild’ annealing at 250 ℃. This made the tincone substantially more stable in an aqueous electrolyte, which is necessary for potential use in photoelectric chemical carbon dioxide reduction applications. In addition to improving its stability, the mild annealing also improved charge transport, making the electrochemical properties even more desirable for these applications.

Hyuenwoo Yang, Study First Author and Postdoctoral Researcher, North Carolina State University

Yang said, “Our next steps involve binding carbon dioxide catalysts to this mild-annealed tincone and incorporating this engineered material into an application to see how efficiently it can convert atmospheric CO₂ into methanol.”

Co-authors of the study include Christopher Oldham, Senior Project Manager at NC State; Arun Joshi Reddy, Postdoctoral Researcher at NC State; Paul Maggard, Professor of Chemistry at NC State; and Carrie Donley, Renato Sampaio, John Dickenson, Pierpaolo Vecchi, and Gerald Meyer from the University of North Carolina at Chapel Hill.

The study was partially funded by the Center for Hybrid Approaches in Solar Energy to Liquid Fuels (CHASE), an Energy Innovation Hub supported by the US Department of Energy’s Office of Science.

Journal Reference:

Yang, H., et al. (2025) Mild-Annealed Molecular Layer Deposition (MLD) Tincone Thin Film as Photoelectrochemically Stable and Efficient Electron Transport Layer for Si Photocathodes. ACS Applied Energy Materials. doi.org/10.1021/acsaem.4c02997.