One of the biggest challenges in producing fuel cells at affordable prices is to synthesize carbon materials selectively doped with graphitic nitrogen, as it is considered the most active nitrogen species for the oxygen reduction reaction (ORR). So far, all strategies focus on the use of nitrogen-containing carbon precursors, which limits the functionalization of commercially available carbon materials. Here, we present a post-functionalization method to boost the catalytic properties of carbon materials for the ORR by selectively enriching activated carbons with nitrogen graphitic species. A commercial high-surface area activated carbon was post-functionalized by a two-step procedure. First, the commercial carbon was mixed with different carbon/urea weight ratios and heated in air at 350 °C. Then, the functionalized materials were heat-treated at high temperature (from 700 to 1300 °C) to tailor the amount and distribution of the different nitrogen species in the resulting carbon structure. Nitrogen functionalization using a carbon to urea weight ratio of 1:2 and heat-treatment at 1100 °C led to highly selective doping in graphitic nitrogen species, which provided the tools to individually asses the catalytic activity of these nitrogen species. In addition, this study presents a low-cost and easily feasible synthesis route to improve the catalytic activity of carbon materials, leading to an onset potential of almost 0.9 V compared to reversible hydrogen electrode for ORR in an alkaline electrolyte. Moreover, this study provides significant evidence for the key role of graphitic nitrogen.

The French research team thanks ANR-15-IDEX-04-LUE and the TALiSMAN project (2019–000215), financed by the European Regional Development Fund (ERDF). The authors from UA thank MICINN and ERDF (project RTI2018-095291-B-I00) for financial support.

5 figures, 1 table.

Peer reviewed