PEO-b-PS Block Copolymer Templated Mesoporous Carbons: A Comparative Study of Nitrogen and Sulfur Doping in the Oxygen Reduction Reaction to Hydrogen Peroxide

Carbon materials slightly doped with heteroatoms such as nitrogen (N-RFC) or sulfur (S-RFC) are investigated as active catalysts for the electrochemical bielectronic oxygen reduction reaction (ORR) to H₂O₂. Mesoporous carbons with wide, accessible pores were prepared by pyrolysis of a resorcinol-formaldehyde resin using a PEO-b-PS block copolymer as a sacrificial templating agent and the nitrogen and sulfur doping were accomplished in a second thermal treatment employing 1,10-phenanthroline and dibenzothiophene as nitrogen and sulfur precursors, respectively. The synthetic strategy allowed to obtain carbon materials with very high surface area and mesopore volume without any further physicochemical post treatment. Voltammetric rotating ring-disk measurements in combination with potentiostatic and galvanostatic bulk electrolysis measurements in 0.5 m H₂SO₄ demonstrated a pronounced effect of heteroatom doping and mesopores volume on the catalytic activity and selectivity for H₂O₂. N-RFC electrode was employed as electrode material in a 45 h electrolysis showing a constant H₂O₂ production of 298 mmol g⁻¹ h⁻¹ (millimoles of H₂O₂ divided by mass of catalyst and electrolysis time), with a faradic efficiency (FE) up to 61 % and without any clear evidence of degradation. The undoped carbon RFC showed a lower production rate (218 mmol g⁻¹ h⁻¹) but a higher FE of 76 %, while the performances drastically dropped when S-RFC (production rate 11 mmol g⁻¹ h⁻¹ and FE=39 %) was used.