Magnesiothermic synthesis of sulfur-doped graphene as an efficient metal-free electrocatalyst for oxygen reduction

Abstract

Efficient metal-free electrocatalysts for oxygen reduction reaction (ORR) are highly expected in future low-cost energy systems. We have successfully prepared crumpled, sheet-like, sulfur-doped graphene by magnesiothermic reduction of easily available, low-cost, nontoxic CO2 (in the form of Na2CO3) and Na2SO4 as the carbon and sulfur sources, respectively. At high temperature, Mg can reduce not only carbon in the oxidation state of +4 in CO32− to form graphene, but also sulfur in SO42− from its highest (+6) to lowest valence which was hybridized into the carbon sp2 framework. Various characterization results show that sulfur-doped graphene with only few layers has an appropriate sulfur content, hierarchically robust porous structure, large surface area/pore volume, and highly graphitized textures. The S-doped graphene samples exhibit not only a high activity for ORR with a four-electron pathway, but also superior durability and tolerance to MeOH crossover to 40% Pt/C. This is mainly ascribed to the combination of sulfur-related active sites and hierarchical porous textures, facilitating fast diffusion of oxygen molecules and electrolyte to catalytic sites and release of products from the sites.

Sulfur-doped carbon spheres as efficient metal-free electrocatalysts for oxygen reduction reaction

“…The diffusion limiting current density of S-C-2 (-5.06 mAcm À2 ) reaches that of Pt/C (-5.87 mAcm À2 ) though the half-wave potential of the former is 101 mV lower than that of the latter. Note that the ORR activity of S-doped carbon spheres in this work is comparable to that of S-doped graphene (onset potential negatively shifted by 120 mV related to that of commercial Pt/C) prepared by magnesiothermic reduction of CO 2 and Na 2 SO 4 [39] and that of sulfur-doped ordered mesoporous carbon (onset potential is about 100 mV lower than that of commercial Pt/C) prepared by SBA-15 [40]. To verify the ORR catalytic pathways of the catalysts, the formation of peroxide species (HO 2 À ) as well as the corresponding transferred electron number (n) during the ORR process were monitored with RRDE measurements as shown in Fig.…”

N-doped crumpled graphene: bottom-up synthesis and its superior oxygen reduction performance

“…2b reproduces the linear scanning voltammetry (LSV) curve for the CrG-900, showing a highly comparable onset and even better half-wave potential to those of the Pt/C electrode, but left big gap of limiting current density being much less than that of 20 wt.% Pt/C. The CrG-900 exhibited advanced onset and half-wave potentials than that of the previously reported CrG which made by the conventional top-down methods (Table S1) [51][52][53][54][55]. Fig.…”

One‐step Preparation of Carbon‐based Solid Acid Catalyst from Water Hyacinth Leaves for Esterification of Oleic Acid and Dehydration of Xylose

“…Furthermore, S 2p spectra (Figure B) suggest that the surface sulfur atoms in samples prepared at 180–200 °C are predominantly in oxidized forms, as indicated by the peaks in region B . On the contrary, region C belonging to the C‐S‐C structure, or thiol (‐SH) groups, becomes the main contributor to the S 2p peak at higher (220–240 °C) HTC temperatures. This indicates that the acidity of WH‐PTSA‐220 is likely due to several factors: a large number of acid sites, the presence of oxy‐acid groups (e.g.…”