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Enhancing Carbon Dioxide Reduction

The results are an important step forward towards the use of 2D electrocatalysts in CO2 reduction applications

by Kanazawa University
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Researchers at Kanazawa University report in ACS Nano how ultrathin layers of tin disulfide can be used to accelerate the chemical reduction of carbon dioxide—a finding that is highly relevant for our quest towards a carbon-neutral society.

Recycling carbon dioxide (CO2) released by industrial processes is a must in humanity’s urgent quest for a sustainable, carbon-neutral society. For this purpose, electrocatalysts that can efficiently convert CO2 into other, less impactful chemical products are widely researched today. A category of materials known as two-dimensional (2D) metal dichalcogenides are candidate electrocatalysts for CO2 conversion, but these materials also typically facilitate competing reactions, which compromises their efficiency. Yasufumi Takahashi from Nano Life Science Institute (WPI-NanoLSI), Kanazawa University and colleagues have now identified a 2D metal dichalcogenide that can efficiently reduce CO2 to formic acid, a compound that not only occurs naturally but also is an intermediate product in chemical synthesis.

Takahashi and colleagues compared the catalytic performance of 2D sheets of disulfide (MoS2) and tin disulfide (SnS2). Both are 2D metal dichalcogenides, with the latter of particular interest because pure tin is a known catalyst for the production of formic acid. Electrochemical tests of these compounds revealed that with MoS2, instead of CO2 conversion, hydrogen evolution reaction (HER) was promoted. HER refers to a reaction yielding hydrogen, which can be useful when the production of hydrogen gas fuel is intended, but in the context of CO2 reduction it is an unwanted competing process. SnS2, on the other hand, showed good CO2 reduction activity and suppressed HER. The researchers also carried out electrochemical measurements for bulk SnS2 powder, which was found to have less catalytic CO2 reduction activity.

To understand where the catalytically active sites are in SnS2, and why the 2D material performs better than the bulk compound, the scientists applied a method called scanning electrochemical cell microscopy (SECCM). SECCM is used as a nanopipette to form the meniscus shape nanoscale electrochemical cell for the surface reactivity sensing probe on the sample. The measurements revealed that the whole surface of the SnS2 sheet is catalytically active, not only “terrace” or “edge” features in the structure. This also explains why 2D SnS2 has enhanced activity compared to bulk SnS2.

Calculations provided further insights into the chemical reactions at play. Specifically, the formation of formic acid was confirmed as an energetically favorable reaction pathway for when using 2D SnS2 as catalyst.

The results of Takahashi and colleagues signify an important step forward towards the use of 2D electrocatalysts in electrochemical CO2 reduction applications. Quoting the scientists: “These findings will provide a better understanding and design strategies for metal dichalcogenide-based 2D electrocatalysis for electrochemical CO2 reduction to produce hydrocarbons, alcohols, fatty acids, and olefins without by-products.”

- This press release was provided by Kanazawa University