Mesoporosity and nitrogen doping: The leading effect in oxygen reduction reaction activity and selectivity at nitrogen‐doped carbons prepared by using polyethylene oxide‐block‐polystyrene as a sacrificial template

Abstract

Four mesoporous carbons (MCs) with tunable pore size were synthesized by soft template synthesis, employing a resorcinol-formaldehyde resin as a carbon precursor and a polyethylene oxide-block-polystyrene block copolymer as a sacrificial template in which the length of the polystyrene block (165, 300, 500, and 1150 units) allowed the modulation of the surface area of MCs (567, 582, 718 and 840 m 2 g −1 , respectively). The complete set of MCs was also doped with nitrogen by ball milling in the presence of cyanamide and stabilized in a second thermal treatment at 750 • C, leading to nitrogen content of ∼2.65% in all samples. The two sets of MCs were used for evaluating both the effect of textural properties and nitrogen doping in the electrochemical reduction of oxygen in acid electrolytes. Each catalyst was characterized by means of elemental analysis and N 2 physisorption analysis, whereas the selected series of samples were also characterized by transmission electron microscopy, scanning electron microscopy, X-ray photoemission spectroscopy, inductively coupled plasma mass spectroscopy (ICP-MS), and Raman analysis. Voltammetric rotating ring-disk measurements in 0.5 M H 2 SO 4 demonstrated that the catalytic activity for the O 2 reduction scales with the surface area in the non-doped series, and also the selectivity for the two-electron process leading to H 2 O 2 increases in the samples having wider pores and higher surface area, even if the leading mechanism is the tetraelectronic process leading to H 2 O. The doping with nitrogen leads to a general increase of the catalytic activity with a shift of the O 2 peak potential to more positive values of 75-150 mV.In the doped series, nitrogen doping prevails on the textural properties for guiding the selectivity toward the two-or four-electron process, since a similar H 2 O 2 yield was observed for all N-MC samples. The possible presence of FeN x sitesThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Super Hygroscopic Non‐Stoichiometric Cerium Oxide Particles as Electrode Component for PEM Fuel Cells

“…However, the limiting current density, j d, is higher for the composite catalysts compared to plain Pt/C; especially, the Pt/C : CeO 2 1 : 1 sample exhibits the highest j d reaching a value lower than À 6 mA cm À 2 . If one considers that in the low potential region (the so-called mass diffusion region), the ORR is dominated by O 2 diffusion on the electrode surface, [46] we can assume that the oxygen storage ability of CeO 2 increases the oxygen concentration on Pt surface, improving the ORR activity. Liam et al suggested that the oxygen supplied from cerium oxide to Pt surface can contribute to the enhancement of the ORR activity of the PtÀ CeO x cathode.…”

New and Revised Aspects of the Electrochemical Synthesis of Hydrogen Peroxide: From Model Electrocatalytic Systems to Scalable Materials

“…In metal-free catalysts, the pore network is more manageable conversely to when NPs or labile sites and functional groups need to be formed or preserved. One way of controlling the porosity is to use a templating method that typically can be distinguished in hard , and soft template methods, , and several complete reviews can be found on the topic. , Others involve the use of activation methods employing thermal treatments in different feeding gases including CO 2 and H 2 O. − The role of micro and mesoporosity was also observed by Chen et al in the work we previously discussed where, in addition to the role of carbon defects, they observed that the mesoporous carbon exhibits greater activity, selectivity, and stability than the microporous one. This was also shown by Guan and co-worker who prepared carbon nanosphere with different pore channel dimensions by utilizing phenolic resin templates.…”

“…In metal-free catalysts, the pore network is more manageable conversely to when NPs or labile sites and functional groups need to be formed or preserved. One way of controlling the porosity is to use a templating method that typically can be distinguished in hard 134,135 and soft template methods, 136,137 and several complete reviews can be found on the topic. 138,139 Others involve the use of activation methods employing thermal treatments in different feeding gases including CO 2 and H 2 O.…”