On the viability of chitosan-derived mesoporous carbons as supports for PtCu electrocatalysts in PEMFC

Chitosan is an abundant and non-toxic natural polysaccharide rich in nitrogen, which is used here to obtain N-doped mesoporous carbons (NMCs) as supports for Pt-saving PtCu alloy elecrocatalysts, which can be of interest for low-temperature fuels cells. NMCs with different textural properties were synthesized from cheap silica templates. They presented relative dominance of disordered graphitic lattice and comparable amounts of pyrrolic and pyridinic N, with different specific BET surface areas (715-1040 m2 g−1) and mesopore (1.2-2.4 cm3 g−1) and micropore volumes (0.1-0.6 cm3 g−1). PtCu nanoparticles were deposited by Cu electroless deposition and further galvanic exchange with Pt, with overall Pt loadings about 20 wt.%. Pt-rich PtCu alloy crystallites with contracted Pt fcc lattices and sizes of 3.1-4.7 nm were formed. The synthesized PtCu/NMCs catalysts presented better specific current densities for the oxygen reduction and better CO tolerance and specific current densities for the methanol oxidation reaction than those of commercial Pt/C and PtCu/CMK-3. The PtCu/NMC prepared with the H2SO4-activated NMC was the most active catalyst. The different textural properties of the carbonaceous materials appeared to determine the surface structure of the PtCu nanoparticles

Synthesis and characterization of materials for PEM-FC, based on Pt alloyed nanoparticles supported on next generation mesoporous carbon.

Proton Exchange Membrane (PEM) Fuel Cells are a promising technology for the clean energy production, especially in the automotive field. Actually, the main commercial catalysts employed in this system are based on Pt Nanoparticles supported on high surface area Carbon. The main issues associated to PEM Fuel Cells deal with the sluggish kinetic of oxygen reduction (ORR) at Platinum based electrode, with the low stability of both the carbon support and the metal phase, that tend respectively to oxidize and dissolve or diffuse and with the high cost due to rare and expensive Pt. In fact, nowadays high costs and low durability are the two factors that make PEM fuel cells still not competitive with internal combustion engine. For these reasons, research now focuses on obtaining more stable material with higher performances toward ORR. Two strategies are possible to improve catalyst for oxygen reduction. The first one deals with the enhancing of Pt activity modifying its electronic properties by alloying Pt with other transition metal (ligand effect) or by reducing the Pt-Pt distance (geometric effect). In both cases a Pt d-band shift occurs, which is responsible for the modification of adsorption and desorption energies of all species involved in ORR and has as a direct consequence a modulation in the electrochemical activity. The second strategy deals with the utilization of supports more stable respect to corrosion, like graphene, carbon nanotubes or mesoporous carbons. Furthermore, doping of carbon support with heteroatoms like N or S, can help to stabilize the metal nanoparticles. In fact, doping creates homogeneous and narrow dispersion of small metallic nanoparticles, strongly bound to the surface of carbon support and with a higher resistance to agglomeration. Furthermore, doping has as well an influence on the electronic structure of the Pt catalyst, resulting in a modulation of its electrochemical activity. Doping is not beneficial only in noble-metal catalyst but may also modify properties of the carbon support in which heteroatoms are present. Wettability, electrical conductivity and electrochemical activity are generally boosted when heteroatoms are inserted in carbonaceous substrates such as carbon blacks (CBs). The topics of this PhD thesis are Platinum NPs on doped carbon and Platinum-Yttrium alloy NPs on carbon. The goal consists in the understanding how the different synthesis parameters can influence the Pt-Y alloy formation and can modify the NPs growing. An increment of interact means increasing the electrochemical performance vs. the Oxygen Reduction Reaction (ORR). The Platinum deposition investigation is conducted via solid state reduction of several Platinum and Yttrium salts, in order to find the best conditions which, allow to have a good Pt NPs distribution over all surface of the carbon support. The synthetized PtxY@C catalysts are characterized by TEM, SEM, ICP, XRD, XPS and TGA techniques. Cyclic Voltammetry in steady conditions and with Rotating Disk Electrode are employed for the determination of electrochemical surface area (ECSA) and catalytic activity toward ORR, respectively, and compared to a commercial Pt/C catalyst. The catalytic activity of pure platinum can be increase by interaction with heteroatoms which permits to modify the absorption energy of oxygen and increase the Oxygen Reduction Reaction rate. The typical heteroatoms which interact very strongly with the platinum are sulphur and nitrogen. Platinum on nitrogen doped carbon was synthetized via solid state synthesis using particular platinum complex which contain nitrogen ligand. The goal consists in the synthesis of catalysts with a nitrogen surface distribution very close to the platinum NPs for increasing the Pt-N interaction and so for increasing the electrochemical performance. The metal-support interactions (MSI) between sulphur doped carbon and Pt nanoparticles (NPs) were investigated, for understanding how sulphur functional groups can improve the electrocatalytic activity of Pt NPs towards the oxygen reduction reaction (ORR). Sulphur doped carbons were synthetized by hard template method, tailoring the density of sulphur functional groups, and Pt NPs were deposited by thermal reduction of Pt(acac)2. The metal-support interaction was evaluated and proved by X ray photoelectron spectroscopy and X ray diffraction, the analysis revealed a strong electronic interaction between Pt and S proportional to the density of sulphur group. The combination between the micro-strain and the electronic effects resulted in a high catalytic activity of Pt NPs vs. ORR, showing a correlation of the electrochemical activity with the sulphur content in the carbon support. Sulphur affords a clear metal support interaction between Pt NPs and the doped carbon support; the NPs dimension and distribution are influence by heteroatom concentration in the support but especially by the morphology (in terms of surface area, pore dimension and pose distribution) of the carbon matrix. The surface area of sulphur doped carbon was modify by steam treatment. The carbon matrixes were completely physic-chemical characterized with TEM, Raman BET, AE. The platinum NPs were deposited by high temperature solid state synthesis with Pt(acac)2 using a temperature of 300 °C for 3 h and 8% H2. XPS, XRD and N2 Adsorption/Desorption analysis show a double correlation between the electrochemical activity and the sulphur concentration and the carbon morphology

Synthesis and characterization of materials for PEM-FC, based on Pt alloyed nanoparticles supported on next generation mesoporous carbon.

Proton Exchange Membrane (PEM) Fuel Cells are a promising technology for the clean energy production, especially in the automotive field. Actually, the main commercial catalysts employed in this system are based on Pt Nanoparticles supported on high surface area Carbon. The main issues associated to PEM Fuel Cells deal with the sluggish kinetic of oxygen reduction (ORR) at Platinum based electrode, with the low stability of both the carbon support and the metal phase, that tend respectively to oxidize and dissolve or diffuse and with the high cost due to rare and expensive Pt. In fact, nowadays high costs and low durability are the two factors that make PEM fuel cells still not competitive with internal combustion engine. For these reasons, research now focuses on obtaining more stable material with higher performances toward ORR. Two strategies are possible to improve catalyst for oxygen reduction. The first one deals with the enhancing of Pt activity modifying its electronic properties by alloying Pt with other transition metal (ligand effect) or by reducing the Pt-Pt distance (geometric effect). In both cases a Pt d-band shift occurs, which is responsible for the modification of adsorption and desorption energies of all species involved in ORR and has as a direct consequence a modulation in the electrochemical activity. The second strategy deals with the utilization of supports more stable respect to corrosion, like graphene, carbon nanotubes or mesoporous carbons. Furthermore, doping of carbon support with heteroatoms like N or S, can help to stabilize the metal nanoparticles. In fact, doping creates homogeneous and narrow dispersion of small metallic nanoparticles, strongly bound to the surface of carbon support and with a higher resistance to agglomeration. Furthermore, doping has as well an influence on the electronic structure of the Pt catalyst, resulting in a modulation of its electrochemical activity. Doping is not beneficial only in noble-metal catalyst but may also modify properties of the carbon support in which heteroatoms are present. Wettability, electrical conductivity and electrochemical activity are generally boosted when heteroatoms are inserted in carbonaceous substrates such as carbon blacks (CBs). The topics of this PhD thesis are Platinum NPs on doped carbon and Platinum-Yttrium alloy NPs on carbon. The goal consists in the understanding how the different synthesis parameters can influence the Pt-Y alloy formation and can modify the NPs growing. An increment of interact means increasing the electrochemical performance vs. the Oxygen Reduction Reaction (ORR). The Platinum deposition investigation is conducted via solid state reduction of several Platinum and Yttrium salts, in order to find the best conditions which, allow to have a good Pt NPs distribution over all surface of the carbon support. The synthetized PtxY@C catalysts are characterized by TEM, SEM, ICP, XRD, XPS and TGA techniques. Cyclic Voltammetry in steady conditions and with Rotating Disk Electrode are employed for the determination of electrochemical surface area (ECSA) and catalytic activity toward ORR, respectively, and compared to a commercial Pt/C catalyst. The catalytic activity of pure platinum can be increase by interaction with heteroatoms which permits to modify the absorption energy of oxygen and increase the Oxygen Reduction Reaction rate. The typical heteroatoms which interact very strongly with the platinum are sulphur and nitrogen. Platinum on nitrogen doped carbon was synthetized via solid state synthesis using particular platinum complex which contain nitrogen ligand. The goal consists in the synthesis of catalysts with a nitrogen surface distribution very close to the platinum NPs for increasing the Pt-N interaction and so for increasing the electrochemical performance. The metal-support interactions (MSI) between sulphur doped carbon and Pt nanoparticles (NPs) were investigated, for understanding how sulphur functional groups can improve the electrocatalytic activity of Pt NPs towards the oxygen reduction reaction (ORR). Sulphur doped carbons were synthetized by hard template method, tailoring the density of sulphur functional groups, and Pt NPs were deposited by thermal reduction of Pt(acac)2. The metal-support interaction was evaluated and proved by X ray photoelectron spectroscopy and X ray diffraction, the analysis revealed a strong electronic interaction between Pt and S proportional to the density of sulphur group. The combination between the micro-strain and the electronic effects resulted in a high catalytic activity of Pt NPs vs. ORR, showing a correlation of the electrochemical activity with the sulphur content in the carbon support. Sulphur affords a clear metal support interaction between Pt NPs and the doped carbon support; the NPs dimension and distribution are influence by heteroatom concentration in the support but especially by the morphology (in terms of surface area, pore dimension and pose distribution) of the carbon matrix. The surface area of sulphur doped carbon was modify by steam treatment. The carbon matrixes were completely physic-chemical characterized with TEM, Raman BET, AE. The platinum NPs were deposited by high temperature solid state synthesis with Pt(acac)2 using a temperature of 300 °C for 3 h and 8% H2. XPS, XRD and N2 Adsorption/Desorption analysis show a double correlation between the electrochemical activity and the sulphur concentration and the carbon morphology

Physico-Chemical, Electrochemical and Structural Insights Into Poly(3,4-ethylenedioxythiophene) Grafted from Molecularly Engineered Multi-Walled Carbon Nanotube Surfaces

Composites of multi-walled carbon nanotubes (MWCNTs) and poly(3,4-ethylenedioxythiophene) (PEDOT) are attracting the attention of material scientists since more than a decade as potential next-generation optoelectronic materials for their peculiar features, arising from the combination of the intrinsic electrical, thermal and morphological properties of the two components. They are indeed a promising platform for the development of low-cost, portable and environmentally friendly electronic devices such as supercapacitors, sensors and actuators. Here a novel synthetic strategy for their preparation is envisaged, exploiting the possibility to covalently functionalize the external surface of MWCNTs with tailored molecular units, starting from which the growth of the conjugated polymer can be induced oxidatively. The approach demonstrates its value in being able to effectively promote the formation of PEDOT chains in direct contact with the surface of MWCNTs, differently from what results when the monomer is polymerized in the presence of the pristine carbon nanomaterial. In addition, significant differences are found in the physico-chemical properties and electrochemical behavior when MWCNT-PEDOT covalent composites are studied in comparison to a non-covalent analogue, here illustrated in detail. These evidences constitute a starting point for the future development of novel more finely tuned functional materials based on MWCNT-PEDOT composites, featuring the required optoelectronic properties to precisely target the desired application

Mesoporous Carbon Modified with Different Density of Thiophenic-Like Functional Groups and Their Effect on Platinum Nanoparticles Activity for Oxygen Reduction

Metal-support interaction between sulfur-doped carbon support (SMC) and Pt NPs was investigated, aiming at verifying how sulfur functional groups can improve the electrocatalytic performance of Pt NPs towards oxygen reduction (ORR). SMC were synthetized, tailoring the density of sulfur functional groups, while Pt NPs were deposited by thermal reduction of Pt(acac)2. The extent of the metal support interaction was proved by XPS analysis which revealed a strong electronic interaction, proportional to the density of sulfur defects, whereas XRD spectra evidenced a 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 E1/2 or 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. RHE, was determined

PEO-b-PS Block Copolymer Templated Mesoporous Carbons: A Comparative Study of Nitrogen and Sulfur Doping in the Oxygen Reduction Reaction to Hydrogen Peroxide

Carbon materials slightly doped with heteroatoms such as nitrogen (N-RFC) or sulfur (S-RFC) are investigated as active catalysts for the electrochemical bioelectronic oxygen reduction reaction (ORR) to H 2 O 2 . 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 physico-chemical post treatment. Voltammetric rotating ring-disk measurements in combination with potentiostatic and galvanostatic bulk electrolysis measurements in 0.5 M H 2 SO 4 demonstrated a pronounced effect of heteroatom doping and mesopores volume on the catalytic activity and selectivity for H 2 O 2 . N-RFC electrode was employed as electrode material in a 45 h electrolysis showing a constant H 2 O 2 production of 298 mmol\ua0g -1 \ua0h -1 (millimoles of H 2 O 2 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 mM\ua0g -1 \ua0h -1 ) but a higher FE of 76 %, while the performances drastically dropped when S-RFC (production rate 11 mmol\ua0g -1 \ua0h -1 and FE = 39 %) was used

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 pre- cursor and a polyethylene oxide-block-polystyrene block copolymer as a sacrifi- cial template in which the length ofthe polystyrene block (165, 300, 500, and 1150 units) allowed the modulation of the surface area of MCs (567, 582, 718 and 840 m2 g−1, respectively). The complete set of MCs was also doped with nitrogen by ball milling in the presence ofcyanamide and stabilized in a second thermal treat- ment 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 nitro- gen doping in the electrochemical reduction of oxygen in acid electrolytes. Each catalyst was characterized by means of elemental analysis and N2 physisorption analysis, whereas the selected series ofsamples were also characterized by trans- mission electron microscopy, scanning electron microscopy, X-ray photoemis- sion spectroscopy, inductively coupled plasma mass spectroscopy (ICP-MS), and Raman analysis. Voltammetric rotating ring-disk measurements in 0.5 MH2SO4 demonstrated that the catalytic activity for the O2 reduction scales with the sur- face area in the non-doped series, and also the selectivity for the two-electron process leading to H2O2 increases in the samples having wider pores and higher surface area, even if the leading mechanism is the tetraelectronic process lead- ing to H2O. The doping with nitrogen leads to a general increase of the catalytic activity with a shift ofthe O2 peak potential tomore positive values of75–150mV. In the doped series, nitrogen doping prevails on the textural properties for guid- ing the selectivity toward the two- or four-electron process, since a similar H2O2 yield was observed for all N-MC samples. The possible presence of FeNx site

Density Functional Theory (DFT) and Experimental Evidences of Metal\u2013Support Interaction in Platinum Nanoparticles Supported on Nitrogen- and Sulfur-Doped Mesoporous Carbons: Synthesis, Activity, and Stability

In this paper, we report a comprehensive investigation of Pt nanoparticles (NPs) deposition on nitrogenand sulfur-doped or codoped mesoporous carbons (N-MC, SMC, 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 N2/H2 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 H2SO4 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 H2SO4: the influence of the doped support on the durability of the catalyst under harsh operational conditions has been highlighted

Mesoporous Carbon with Different Density of Thiophenic‐Like Functional Groups and Their Effect on Oxygen Reduction

Metal-support interaction between sulfur-doped carbon support (SMC) and Pt NPs was investigated, aiming at verifying how sulfur functional groups can improve the electrocatalytic performance of Pt NPs towards oxygen reduction (ORR). SMC were synthetized, tailoring the density of sulfur functional groups, while Pt NPs were deposited by thermal reduction of Pt(acac)2. The extent of the metal support interaction was proved by XPS analysis which revealed a strong electronic interaction, proportional to the density of sulfur defects, whereas XRD spectra evidenced a 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 E1/2 or 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. RHE, was determined