Graphdiyne enables Cu nanoparticles for highly selective electroreduction of CO2 to formate

Undoped Cu nanoparticles (NPs) generally show poor selectivity and activity for electroreduction of CO2 to formate due to hard desorption of HCOO* intermediate on Cu site. Here we report a Cu/pyrenyl-graphdiyne (Pyr-GDY) composite catalyst, in which Cu2O and CuO NPs were in-situ formed and embedded in the matrix of a two-dimensional (2D) Pyr-GDY, during the synthesis of 2D Pyr-GDY using monolayer graphene covered Cu foil as a template, and copper acetate as a coupling catalyst. Cu2O and CuO NPs in Cu/Pyr-GDY can be electrochemically reduced to cubic metallic CuNPs to get Cu/Pyr-GDY-R electrocatalyst, with the average size of metallic Cu NPs being 42 nm. The Cu/Pyr-GDY-R on Cu foil can be directly used as a highly efficient electrocatalyst for CO2-to-formate conversion in a CO2-saturated 0.1 M KHCO3 electrolyte, with a formate Faradaic efficiency (FEformate) as high as 95% (at -1.2 V vs reversible hydrogen electrode), far superior to that of Pyr-GDY-free Cu NPs (with a FEformate of only 29%). The key reaction intermediate of HCOO* during CO2-to-formate conversion was identified by in situ Raman spectroscopy. The results of density functional theory calculations revealed that the Pyr-GDY support can decrease the reaction free energy for the adsorption of HCOO* on Cu site, due to the electron transfer from metallic Cu NPs to conjugated diacetylene groups in 2D Pyr-GDY support, which leads to the high selectivity for formate over hydrogen production.

Automated summary

The study presents a novel Cu/pyrenyl-graphdiyne composite catalyst for efficient conversion of CO2 to formate in electroreduction, exhibiting excellent selectivity and activity achieved through the combined use of metallic Cu nanoparticles and 2D Pyr-GDY support.