(558aa) MOF-Derived Sulfur-Nitrogen-Doped Copper Nanoparticles for the Selective Electrocatalytic Reduction of CO2 to Formate

MOF-Derived
Sulfur-Nitrogen-Doped Copper Nanoparticles for the Selective Electrocatalytic
Reduction of CO₂ to Formate

Bike Zhang, Yi He, Yao Shi

Institute
of Industrial Ecology and Environment, College of Chemical and Biological
Engineering, Zhejiang University, Hangzhou 310027, China

Abstract: Electrocatalytic reduction of CO₂ (ERC)
to valuable products using renewable sources is a promising route to mitigate the
energy and environmental crisis. Cu-based materials have been attracting
considerable interest due to their low cost and ability to form value-added
chemicals. However, pristine Cu shows impractical overpotential for ERC and
poor selectivity, owing to noticeable activity of competing hydrogen evolution
reaction (HER). To overcome these challenges, we designed a Metal-organic
frameworks (MOF)-derived sulfur and nitrogen-doped Cu (CuS_xN_x)
catalyst supported on multiwalled carbon nanotube (MWCNT),
which highly suppresses HER and is impressively proved to selectively produce
formate. Using CuS_xN_x-MWCNT as ERC
catalyst, formate is able to be produced at an overpotential as low as 270 mV
and high Faradaic efficiency of formate (71.2%) can be achieved at potential of
-0.82 V versus RHE in aqueous bicarbonate medium. The electrocatalyst is stable
for 10 h continuous electrolysis. In addition, a series of analytical
techniques are employed to investigate the correlation between ERC performance
and structure of CuS_xN_x-MWCNT. Microscopic
characterizations reveal that CuS_xN_x nanoparticles are
uniformly dispersed on the surface of MWCNT, which contributes to the low
overpotential via facilitating electron transfer process. Spectroscopic
characterizations was used to ascertain CuS_xN_x with different
content of nitrogen and sulfur. Through the analysis on the evolution of the partial
current density of the formate and hydrogen with the nitrogen/sulfur content,
we propose that nitrogen doping suppresses the HER while sulfur doping promote
formate production, which is further confirmed by DFT calculation. Based on
these results, we expect that more efficient eletrocatalyst can be designed through
facile and cost-effective synthesis process.

Key words: Copper based-catalyst; electrocatalyst
reduction; CO₂; formate

Fig.1. Faradaic efficiency (FE) over CuN_xS_0.54-MWCNT
catalyst. The data were obtained by chronoamperometry (CA) for 1 h, in 0.5 M
KHCO₃ saturated with CO₂ (pH=7.2) at room temperature.