Electrocatalytic conversion of CO2 on carbon nanotube-based electrodes for producing solar fuels

• Fe, Co, Cu (mono-, bi-, and trimetallic) on CNT electrocatalysts are discussed.
• FeCu bimetallic electrocatalysts double the productivity to C1–C3 products.
• Solventless CO2 electroreduction is discussed.
• Metal inactive in a liquid electrolyte is active under solventless conditions.

The behavior of Fe, Co, Cu (mono-, bi- and trimetallic) on carbon nanotube (CNT) electrocatalysts in the solventless conversion of CO2 to C1–C3 hydrocarbons/organics (HO) has been studied as a part of the general objective of developing novel photoelectrocatalytic (PEC) solar cells to convert CO2 to solar fuels. The comparison of commercial conductive carbon black support is also analyzed, as well as the role of CNT. FeCu bimetallic electrocatalysts double the productivity to C1–C3 HO with respect to iron monometallic electrocatalysts, and the use of CNTs as conductive carbon support allows to double productivity to C1–C3 HO with respect to commercial conductive carbon black supports. The parallelism between solventless operations at atmospheric pressure and high-pressure operations in the electrocatalytic reduction of CO2 in liquid electrolyte was evidenced. The results show that Fe and other metals, which is different from Cu are inactive in forming HO during the electroreduction of CO2 at atmospheric pressure in a liquid aqueous electrolyte, are instead active and superior to copper under solventless conditions. The results indicate that the inhibition of the surface reactivity toward H2 formation rather than minimizing the energy barriers in CO2 electroreduction is the key to improve the performances and realize selective electrocatalysts.

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