Schematic diagram of Mn SAC preparation and mechanism of electrochemical CO2 reduction.

Electrochemical CO₂ reduction reaction (CO₂RR) is a promising approach to convert CO₂ into useful chemicals.

A research team led by Prof. ZHANG Suojiang from the Institute of Process Engineering (IPE) of the Chinese Academy of Sciences prepared a manganese (Mn) single-atom catalyst (SAC) with Mn-N₃ site supported by graphitic C₃N₄, which exhibited efficient performance of CO₂ electroreduction.

It is a great challenge to obtain high Faradaic efficiency (FE) and high current density simultaneously by cheap catalysts for CO₂RR.

The prepared catalyst exhibited a maximum CO FE of 98.8% with 14.0 mA cm^-2 CO current density (j_CO) at overpotential of 0.44 V in KHCO₃ electrolyte, outperforming all reported Mn SACs.

Moreover, a higher j_CO value of 29.7 mA cm^-2 was obtained at overpotential of 0.62 V, when ionic liquid was used as electrolyte.

X-ray absorption spectroscopy and high-angle annular dark-field scanning transmission electron microscopy confirmed atomically dispersed Mn in the catalyst, and the best-fitting analysis indicated that the isolated Mn atom was three-fold coordinated by N atoms.

"In situ X-ray absorption spectra and density functional theory calculations demonstrated that the remarkable performance of the catalyst was attributed to the Mn-N₃ site, which facilitated the formation of the key intermediate COOH* through a lowered free energy barrier," said Prof. ZHANG Suojiang.

This work shows that the CO₂RR activity of Mn-based catalysts can be enhanced through changing coordinated environment.

"It provides an important scientific basis and feasibility for low cost and high efficient electrochemical CO₂ reduction to useful chemicals," said Prof. ZHANG Xiangping, a co-corresponding author of the paper.