Effects of nitrogen and oxygen on electrochemical reduction of CO2 in nitrogen-doped carbon black

Using carbon black and formamide as raw materials, a N-doped carbon black electrocatalyst (NC) with good performance was prepared by a simple method for the electrochemical CO2 reduction reaction (ECRR). At −0.86 V vs. RHE, the prepared NC800 catalyst achieves 97.8% of CO selectivity and 9.1 mA cm−2 of CO partial current density, which is higher than most carbon-based electrocatalysts reported so far. In order to better explore the role of nitrogen and oxygen functional groups in carbon-based materials, the nitrogen and oxygen contents in the NC800 catalyst were changed by nitric acid oxidation and thermal desorption. The results show that nitrogen content can effectively improve the CO selectivity of nitrogen-doped carbon materials, but excessive oxygen content inhibits the ECRR activity. It was found for the first time that the ratio of N/(N + O) in carbon catalysts was positively correlated with CO Faraday efficiency and its partial current density, indicating that carbon materials with high nitrogen doping amount and low oxygen content would benefit the ECRR performance, which was also supported by density functional theory calculation. These new understandings provide new insights into the preparation of highly efficient carbon-based catalysts for ECRR.