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

Abstract

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.

Highly Graphitized Fe-N-C Electrocatalysts Prepared from Chitosan Hydrogel Frameworks

“…To obtain a good dispersion, the ink was sonicated both in a bath and probe sonicator. The loading was chosen to be 0.6 mg cm −2 as used in previous works [19,40].…”

“…Furthermore, the presence of different heteroatom functional groups embedded on a 3D hierarchical porous structure and the graphitization degree can induce higher catalytic performance and stability, respectively [34]. To control textural and porous structure of MCs, the use of inorganic templates (hard template approach) [10,[35][36][37][38][39], or self-assembled nanostructure of organic molecules (soft template approach) [40,41] can be exploited. In the latter method, the chemical interactions between the template and the carbon precursor determine the success of the templating.…”

Highly Graphitized Fe-N-C Electrocatalysts Prepared from Chitosan Hydrogel Frameworks

“…To obtain a good dispersion the ink was sonicated both in a bath and probe sonicator. The loading was chosen to be 0.6 mg cm -2 as used in previous works [20,42].…”

“…Furthermore, the presence of different heteroatom functional groups embedded on a 3D hierarchical porous structure and the graphitization degree can induce higher catalytic performance and stability, respectively [36]. To control textural and porous structure of MCs, the use of inorganic templates (hard template approach) [10,[37][38][39][40][41], or self-assembled nanostructure of organic molecules (soft template approach) [42,43] can be exploited. In the latter method, the chemical interactions between the template and the carbon precursor rule the success of the templating.…”

Oxygen Reduction Reaction at Single‐Site Catalysts: A Combined Electrochemical Scanning Tunnelling Microscopy and DFT Investigation on Iron Octaethylporphyrin Chloride on HOPG**

“…Understanding which of the two mechanisms predominates would allow to design more performing catalysts avoiding the formation of H 2 O 2 , which is harmful for a Nafion‐based membrane in a low temperature fuel cell. Conversely, the ability to selectively drive the ORR reaction to H 2 O 2 opens new perspectives in the production of hydrogen peroxide market, which is extensively used as a bleaching agent in the paper and pulp industry [9–11] …”