Sulfur-doped carbons prepared from eutectic mixtures containing hydroxymethylthiophene as metal-free oxygen reduction catalysts

Abstract

A template-free approach based on the use of eutectic mixtures composed of 2-hydroxymethylthiophene and furfuryl alcohol has been designed for the preparation of hierarchical sulfur-doped carbons (SPCs) in monolithic form. The temperature used for carbonization, for example, 600, 800, or 900 °C, determined most of the physicochemical properties of the resulting SPCs. Thus, the surface area increased from below 400 to up 775 m(2) g(-1) , along with the carbonization temperature, whereas the sulfur content decreased from approximately 15 to 5 wt %. The oxygen reduction reaction performance in samples carbonized at 900 °C was good, with the four-electron-transfer reaction prevailing over the two-electron-transfer one. Interestingly, the methanol tolerance and stability of these SPCs were also remarkable, with less than 5% current decrease immediately after methanol addition, whereas, in terms of stability, the current decrease was below 8 % after 20000 s. This performance was in the range of that found not only for other SPCs, but also for many nitrogen-doped and even some dual-doped (S and N) ones.

Keywords: carbon; fuel cells; heterogeneous catalysis; oxygen reduction reaction; sulfur.