Enhanced ORR activity of S- and N-modified non-noble metal-doped carbons with bamboo-like C nanotubes grafted onto their surface

Discovering low-cost and earth-abundant electrocatalysts for oxygen reduction reaction (ORR) is essential for advanced energy conversion technologies. A large set of carbon-based ORR electrocatalysts was prepared by a two-step pyrolysis at 600 ◦C and then at 900 ◦C. Gelling sugar, guanidine acetate and cysteine were used as carbon, nitrogen and sulphur sources, respectively; iron and copper salts were utilised to produce non-noble metal-doped carbons. Silica was used as templating agent. The produced materials were thoroughly characterized by means of BET, XPS, XRPD and micro-Raman spectroscopy to investigate their physicochemical properties, and by means of RDE and RRDE methods to study their electrocatalytical properties towards ORR. They consist in sulphur- and/or nitrogen-modified carbons, some of which iron- and/or copper-doped. The massive carbonaceous structure bears bamboo-like C nanotubes onto the surface of iron-containing electrocatalysts. The best ORR electrocatalytic performance pertains to S- and N-modified carbons bearing nanotubes, which points to the occurrence of synergistic effects between heteroatoms and active sites associated to the presence of nanotubes.