Sulfur-Doped Fe–N–C Nanomaterials as Catalysts for the Oxygen Reduction Reaction in Acidic Medium

Abstract

Iron atoms coordinated with nitrogen (FeN x ) sites in Fe–N–C catalysts are widely accepted as the main active sites for the oxygen reduction reaction (ORR). Introducing sulfur (S)-functionalities in the carbon to tailor FeN x active centers can further promote their ORR performance in acidic media. Here, we report an approach to synthesize the FeN4 active sites supported on N/S-codoped graphitic carbon (FeN4/NSC) by the in situ addition of thiourea molecules into Fe-doped zeolitic imidazole framework (ZIF-8) precursors and subsequent pyrolysis. The thiourea molecules positively provoke changes in the catalyst structure, including S-doping into the graphitic carbon, improved density of FeN4 active sites, and an increase in the Brunauer–Emmett–Teller surface area (up to 760 m2 g–1). FeN4/NSC exhibits an enhanced ORR activity with a higher half-wave potential of 0.83 V (vs reversible hydrogen electrode (RHE)) compared to that of pristine FeN4/NC (0.80 V), in addition to superior durability with a small activity decay that occurs after 40 000 cycles. The improved catalytic performance is mainly due to the high site density of FeN4 sites and electron-withdrawing S-doping.

Synthesis of N/Fe/S-Codoped Cathode Catalysts on Gasification Residue Carbon for Zinc–Air Batteries

“…Fe and S have large atomic radii and relative atomic masses. Doping them into the RC can cause collapse and defects in its carbon skeleton structure, resulting in an increase in the SSA . The adsorption isotherm of CKN 6 Fe is a typical type I isotherm, indicating that its pores are mainly microporous, and the presence of H4-type hysteresis loops indicates the existence of a mixed micromesoporous structure and some narrow cleavage pores in its pores.…”

Remote p–d orbital hybridization via first/second-layer coordination of Fe single atoms with heteroatoms for enhanced electrochemical CO2-to-CO reduction

“…2a), corresponding to the C-SO x -C species, and 2p 1/2 and 2p 3/2 of C-S-C (N) species, respectively. [42][43][44][45][46][47] In the C 1s XPS spectra, the peaks observed at 284.7 eV, 285.7 eV, and 287.5 eV belonged to C-C/C]C, C-N/(C-S), and C]N structures, respectively (Fig. S7 †).…”

M−N−C Materials for Electrochemical Reduction Reactions: Recent Strategies for Improving Electrocatalytic Activity and Stability

“…In this context, it has been demonstrated that FeÀ NÀ C catalysts having pyridinic FeÀ N 4 present better selectivity for four-electron ORR in acidic medium compared to the FeÀ NÀ C catalyst coordinated with pyrrolic-N. [45] Another recent strategy that permitted the enhancement of stability and ORR electrocatalytic performance is the introduction of dopants, such as sulphur. [36,46] In this regard, a stepwise synthesis strategy (Figure 7b) has enabled to obtain FeÀ NÀ C materials featuring sulphur doping of a rich carbon mesoporous structure, obtained by pyrolysis at temperatures in the range of 600-900 °C (Figure 7c-d). The catalyst pyrolyzed at 800 °C delivered a remarkable activity and impressive stability for the ORR compared to that of the Pt/C catalyst in acidic media.…”