Sulfur-Doped Graphene via Thermal Exfoliation of Graphite Oxide in H₂S, SO₂, or CS₂ Gas

Abstract

Doping of graphene with heteroatoms is an effective way to tailor its properties. Here we describe a simple and scalable method of doping graphene lattice with sulfur atoms during the thermal exfoliation process of graphite oxides. The graphite oxides were first prepared by Staudenmaier, Hofmann, and Hummers methods followed by treatments in hydrogen sulfide, sulfur dioxide, or carbon disulfide. The doped materials were characterized by scanning electron microscopy, high-resolution X-ray photoelectron spectroscopy, combustible elemental analysis, and Raman spectroscopy. The ζ-potential and conductivity of sulfur-doped graphenes were also investigated in this paper. It was found that the level of doping is more dramatically influenced by the type of graphite oxide used rather than the type of sulfur-containing gas used during exfoliation. Resulting sulfur-doped graphenes act as metal-free electrocatalysts for an oxygen reduction reaction.

S- and N-Doped Graphene Nanomaterials for the Oxygen Reduction Reaction

“…On the other hand, all the other carbon-based materials develop the typical Raman spectra for heteroatom-doped rGO as a result of carbon hybridization by heteroatom-C bond formation and/or for some structural disorder (impurities, edges, finite size effects, etc.) that breaks the translational symmetry [18,19]. In agreement with the literature, Figure 3 indicates an increment of the disorder degree when N and S elements were used as doping agents [2,[10][11][12].…”

“…In this regard, the slow kinetics of the ORR on carbon-based catalysts in acidic media, which strongly increases at higher pH values, is remarkable [8,19,24,25]. Figure 5 and the top panel of Figure 6 demonstrate that the catalytic activity of graphitic-based catalysts toward the ORR rises in alkaline media (curves for graphite (GC) are included for comparison).…”

“…All the described morphological and chemical changes induced by heteroatoms in the graphenic structure modify relevant physicochemical properties with profound impacts on the ORR, such as by affecting the electrical conductivity (higher in basal planes than in edge planes), electron transfer (higher in edge planes than in basal planes), different adsorption and bond cleavage of O 2 (tuned by N insertion into the graphene network), diverse electronic density of states near the Fermi level (tuned by S insertion into the graphene network) and the overall catalytic performance (activity and stability) of graphene-based materials during the ORR [2,5,8,[10][11][12]19,20,23]. …”

Recent Advances in Heteroatom-Doped Graphene Materials as Efficient Electrocatalysts towards the Oxygen Reduction Reaction

“…Pumera"s group synthesized a series of sulfur-doped graphene via thermal exfoliation of graphite oxide in H 2 S, SO 2 , or CS 2 gas as shown in Figure 7. 42 The shift of the reduction potential by 40 mV from undoped graphene to S-doped graphene shows that S-doped graphene provides an electrocatalytic surface of ORR. More recently, we also fabricated sulfur-doped graphene by a one-step magnesiothermic reduction strategy to transform greenhouse gas CO 2 (in the form of Na 2 CO 3 ) in the presence of small amount of Na 2 SO 4 as an inorganic S source to form S-doped graphene, as shown in Figure 8.…”

Exploring the stability and electronic structure of beryllium and sulphur co-doped graphene: a first principles study

“…Similarly, OA, OA1, OB1 and OC have lower FE than S-doped graphene. Meanwhile, past reports 62,63 showed S-doped graphene has been successfully synthesised. Therefore we could generalise that it would be easier to synthesise Be-S co-doped graphene with these conformations than to synthesise S-doped graphene.…”