In this paper, we report a comprehensive investigation of Pt nanoparticles (NPs) deposition on nitrogenand sulfur-doped or codoped mesoporous carbons (N-MC, S-MC, and N,S-MC) to develop active and durable oxygen reduction catalysts for fuel cells. N-MC, S-MC, and N,S-MC were prepared by employing mesoporous silica as hard template and suitable organic precursors. Pt NPs were deposited by solidstate reduction of platinum acetylacetonate under N 2 /H 2 flow on the three different supports. Pt NPs resulted to be welldispersed over the doped MC supports with size distributions (from 1.8 nm to 3.5 nm) that are dependent on the type of doping heteroatom (N, S, or N and S). The influence of nitrogen and/or sulfur incorporated into the carbon matrix on the nucleation and growth of Pt NPs was also rationalized based on density functional theory (DFT) simulations. They highlighted that both nitrogen and sulfur increase the interactions between Pt and carbon support, but the interaction decreases as the nitrogen and sulfur functional groups become closer. The effect of sulfur content on the size and activity of Pt NPs was also evaluated. Electrochemical measurements in 0.5 M H 2 SO 4 electrolyte allowed us to investigate the behavior of Pt NPs and to assess the relationship with electrochemical activity and stability. The Pt/S-MC showed mass activity and specific activity comparable with the state-of-the-art commercial standard Pt/C Tanaka (Pt 46% on Vulcan XC72), and the highest catalytic activity, with respect to Pt/N-MC and Pt/N,S-MC, was associated with a stronger interaction between Pt NPs and a thiophenic-like group, as proven by DFT calculations and X-ray photoelectron spectroscopy (XPS) analysis. Pt/S-MC was incorporated in a membrane electrode assembly and tested as cathode material in a PEM fuel cell, while accelerated degradation tests up to 10 000 voltammetric cycles were carried out in 0.5 M H 2 SO 4 : the influence of the doped support on the durability of the catalyst under harsh operational conditions has been highlighted.

In this paper, we report the synthesis and characterization of nanoparticles of a PtxY alloy supported on a commercial mesoporous carbon with high mass and specific activity.

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The metal–support interactions between sulfur‐doped carbon supports (SMCs) and Pt nanoparticles (NPs) were investigated, aiming at verifying how sulfur functional groups can improve the electrocatalytic performance of Pt NPs towards the oxygen reduction reaction (ORR). SMCs were synthetized, tailoring the density of sulfur functional groups, and Pt NPs were deposited by thermal reduction of Pt(acac)2. The extent of the metal–support interaction was proved by X‐ray photoelectron spectroscopy (XPS) analysis, which revealed a strong electronic interaction, proportional to the density of sulfur defects, whereas XRD spectra provided evidence of higher strain in Pt NPs loaded on SMC. DFT simulations confirmed that the metal–support interaction was strongest in the presence of a high density of sulfur defects. The combination of microstrain and electronic effects resulted in a high catalytic activity of supported Pt NPs towards ORR, with linear correlations of the half‐wave potential E1/2 or the kinetic current jk with the sulfur content in the support. Furthermore, a mass activity value (550 A g−1) well above the United States Department of Energy target of 440 A g−1 at 0.9 V (vs. reversible hydrogen electrode, RHE), was determined.

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Nitrogen doping has been always regarded as one of the major factors responsible for the increased catalytic activity of Fe–N–C catalysts in the oxygen reduction reaction, and recently, sulfur has emerged as a co-doping element capable of increasing the catalytic activity even more because of electronic effects, which modify the d-band center of the Fe–N–C catalysts or because of its capability to increase the Fe–N x site density (SD). Herein, we investigate in detail the effect of sulfur doping of carbon support on the Fe–N x site formation and on the textural properties (micro- and mesopore surface area and volume) in the resulting Fe–N–C catalysts. The Fe–N–C catalysts were prepared from mesoporous carbon with tunable sulfur doping (0–16 wt %), which was achieved by the modulation of the relative amount of sucrose/dibenzothiophene precursors. The carbon with the highest sulfur content was also activated through steam treatment at 800 °C for different durations, which allowed us to modulate the carbon pore volume and surface area (1296–1726 m 2 g –1 ). The resulting catalysts were tested in O 2 -saturated 0.5 M H 2 SO 4 electrolyte, and the site density (SD) was determined using the NO-stripping technique. Here, we demonstrate that sulfur doping has a porogenic effect increasing the microporosity of the carbon support, and it also facilitates the nitrogen fixation on the carbon support as well as the formation of Fe–N x sites. It was found that the Fe–N–C catalytic activity [ E 1/2 ranges between 0.609 and 0.731 V vs reversible hydrogen electrode (RHE)] does not directly depend on sulfur content, but rather on the microporous surface and therefore any electronic effect appears not to be determinant as confirmed by X-ray photoemission spectroscopy (XPS). The graph reporting Fe–N x SD versus sulfur content assumes a volcano-like shape, where the maximum value is obtained for a sulfur/iron ratio close to 18, i.e., a too high or too low sulfur doping has a detrimental effect on Fe–N x formation. However, it was highlighted that the increase of Fe–N x SD is a necessary but not sufficient condition for increasing the catalytic activity of the material, unless the textural properties are also optimized, i.e., there must be an optimized hierarchical porosity that facilitates the mass transport to the active sites.

PtxY nanoparticles were synthesized by laser ablation in ethanol and proved to efficiently catalyze the oxygen reduction reaction in acid electrolyte.

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.