Mechanistic Insight into Formate Production via CO2 Reduction in C–C Coupled Carbon Nanotube Molecular Junctions

Electronic band structure modification of carbon nanotubes (CNTs) through Suzuki coupling has been predicted recently. Here, scanning tunneling microscopy/spectroscopy studies of a molecular junction developed through C-C coupled CNTs are conducted to probe the local density of states variation along the junction, and the distorted band structure of CNT at the junction is unraveled, in agreement with the predictions. The band structure modification aided by charge transfer, among CNTs and C6H4 in the junction, helps to achieve a more efficient *COOH adsorption in coupled CNTs (CCNTs) than in pristine CNTs, proven via density functional theory-based calculations. This indicates the possibilities of CCNT-based electrochemical CO2 reduction. Formate production at low potential (-0.9 V vs reversible hydrogen electrode) in neutral pH (6.8) is demonstrated with CCNT, while no formic acid production is observed in uncoupled CNTs. This study opens a fundamental insight into novel catalysts based on carbon materials "beyond doping" toward CO2 reduction via band engineering.