Thiourea sole doping reagent approach for controllable N, S co-doping of pre-synthesized large-sized carbon nanospheres as electrocatalyst for oxygen reduction reaction

The co-doping of heteroatoms into the pre-synthesized graphitic carbons normally requires the use of different doping reagents as heteroatom sources, leading to difficulties in controlling the contents of doped heteroatoms and their chemical bonding forms with graphitic structures. Graphitic carbon-based electrocatalysts with a relatively large size, rich microporous structure and high surface area could possess better structural stability and enhanced conductivity than those of small-sized carbon nanostructures (e.g., nanodots). This study reported the use of a sole reagent (thiourea) as heteroatoms doping source to achieve controllable N, S co-doping of the pre-synthesized graphitic microporous carbon nanospheres (∼100 nm in diameter) via a facial thermolysis process to produce high performance oxygen reduction reaction electrocatalysts. Results showed that the contents of the doped N, S and their chemical bonds with graphitic carbon structures could be simply controlled by controlling the thermolysis temperatures. With the experimental conditions investigated, the best performed electrocatalyst was obtained from 1100 °C doping process that possessed the most suitable N, S doping contents with 100% of doped N being in electrocatalytically active pyridinic-N and graphitic-N forms. The approach reported in this work could be useful for controllable heteroatoms co-doping of other types of new generation graphitic carbon materials.