Supported PtRu on mesoporous carbons for direct methanol fuel cells

We prepared and characterized several cryogel mesoporous carbons of different pore size distribution and report the catalytic activity of PtRu supported on mesoporous carbons of pore size >15 nm in passive and in active direct methanol fuel cells (DMFCs). At room temperature (RT), the specific maximum power of the passive DMFCs with mesoporous carbon/PtRu systems as anode was in the range 3–5 W g⁻¹. Passive DMFC assembly and RT tests limit the performance of the electrocatalytic systems and the anodes were thus tested in active DMFCs at 30, 60 and 80 °C. Their responses were also compared to those of commercial Vulcan carbon/PtRu. At 80 °C, the specific maximum power of the active DMFC with C656/PtRu was 37 W g⁻¹ and the required amount of Pt per kW estimated at 0.4 V cell voltage was 31 g kW⁻¹, a value less than half that of Vulcan carbon/PtRu.     

Novel synthesis of PtRu/multi-walled carbon nanotube catalyst via a microwave-assisted imidazolium ionic liquid method for methanol oxidation

A facile and fast microwave-assisted ionic liquid method has been developed to prepare PtRu nanoparticles onto multi-walled carbon nanotubes (MWCNTs). This novel method has some advantages, such as the high electrocatalytic activity of the catalysts for the methanol oxidation, simple preparation procedures, and recycle of the ionic liquids. Transmission electron micrograph shows that PtRu nanoparticles with diameter of 2-5 nm are uniformly deposited along the length of the MWCNTs (PtRu/MWCNTs). The structure and nature of the resulting PtRu/MWCNT catalysts are also characterized by X-ray diffraction. Electrochemical measurements show that the electrocatalytic oxidation of methanol shows very high catalytic efficiency compared with commercial E-TEK Pt/C (20 wt%Pt) catalysts, which is crucial for anode electrocatalysis in direct methanol fuel cells.     

Promotion of the electrocatalytic activity of a bimetallic platinum-ruthenium catalyst by repetitive redox treatments for direct methanol fuel cell

Pt-Ru/C catalyst (12 wt%) was prepared by the incipient wetness impregnation method followed by a redox heat-treatment. Transmission electron microscopy (TEM) results revealed uniformly distributed metallic crystallites of Pt-Ru alloy nanoparticles (d_PtRu = 2.1 ± 1.0 nm). The effect of redox treatments of the impregnated catalysts on methanol oxidation reaction (MOR) was examined by cyclic voltammetry (CV). The MOR activity of the PtRu/C was significantly improved after each oxidation step of the redox treatment cycles. The enhanced catalytic activity was found to be quite stable in chronoamperometry (CA) measurements. CV, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) results strongly suggested that the improved catalytic activity was due to the formation of a stable c-RuO_x (x = 2-3) domain during the oxidation treatments. A bifunctional based mechanism was proposed for the MOR on the oxidized PtRu/C catalysts. Formation of Ru-OH species on the surface of c-RuO_x domains was suggested as stale sites for the oxidation of carbon monoxide adsorbed on the Pt catalytic sites.     

Sol-gel based silica electrodes for inorganic membrane direct methanol fuel cells

Inorganic glass electrodes are of interest for use with inorganic proton exchange membranes for direct methanol fuel cells. Platinum-ruthenium glass electrodes (PtRu/C-SiO₂) have been prepared by incorporating the PtRu/C nanoparticles into a silica-based matrix. The SiO₂ matrix was synthesized through the sol-gel reaction of 3-(trihydroxysilyl)-1-propanesulfonic acid (3TPS) and 3-glycidoxypropyltrimethoxysilane (GPTMS). The distribution of the PtRu/C particles can be controlled by changing the properties of the gel matrix. The effect of gelation time, mole fraction of reactants within the sol, curing temperature, and glass ionomer content were investigated. The adhesion of the catalyst layer on the membrane, catalytic activity for methanol oxidation, and inhibition of methanol permeation through the membrane have been characterized and optimized. The electroless deposition of PtRu onto the PtRu/C nanoparticles was performed to increase the sheet conductivity of the electrode. It was found that the electrolessly deposited metal improved the catalytic activity for methanol oxidation and decreased the methanol cross-over. The methanol fuel cell performance using the inorganic membrane electrode assembly was 236 μA cm⁻² at 0.4 V and was stable for more than 10 days.     

Enhanced electrocatalytic activity of platinum supported on nitrogen modified ordered mesoporous carbon

Nitrogen-modified ordered mesoporous carbon is synthesized via the 900 °C carbonization of polyaniline-coated mesoporous carbon. The electronic states of nitrogen atoms are investigated by XPS technique. Pyridinic nitrogen and quaternary nitrogen generate disorders and curvatures on the surface of graphitic carbon layers with nitrogen atoms replacing carbon atoms at the edges and the interior of carbon stacking, and thus offering beneficial anchoring sites for PtCl₆²⁻ ions. Pyridinic nitrogen and pyrrolic nitrogen offer p electrons to the sp² hybridized graphitic carbon layers, decreasing the inner electrical resistance of the catalytic carbon layer, enhancing the rate of proton diffusion, and transporting more free electrons to oxidative platinum. Due to the advantageous modification of the electronic structure of carbon atoms, platinum nanoparticles with a narrow size distribution are homogenously dispersed onto the surface of nitrogen-modified ordered mesoporous carbon, as evidenced by TEM images. Electrochemical tests show that the samples loaded platinum calcined at the 900 °C exhibit the optimum loading performance among as-made catalysts and a gradually decreased decay in electro-catalytic activity with time, with the current density stabilized at 3.64 mA cm⁻², which is far higher than that of mesoporous carbon (0.15 mA cm⁻²).     

Novel hollow PtRu nanospheres supported on multi-walled carbon nanotube for methanol electrooxidation

A multi-walled carbon nanotube supported hollow PtRu nanosphere electrocatalysts was prepared at room temperature in a homogeneous solution employing cobalt metal nanoparticles as sacrificial templates. Transmission electron micrograph (TEM) measurements showed that carbon nanotube supported PtRu nanospheres were coreless and composed of discrete PtRu nanoparticles with the crystallite size of about 2.1 nm. X-ray diffraction (XRD) results showed that the hollow PtRu nanospheres had a face-centered cubic structure. Electrochemical measurements demonstrated that the carbon nanotube supported hollow PtRu nanosphere electrocatalysts exhibited enhanced electrocatalytic performance for methanol oxidation compared with carbon nanotube supported solid PtRu nanoparticles and commercial E-TEK PtRu/C (20 wt%) catalysts, which is crucial for anode electrocatalysis in direct methanol fuel cells (DMFCs).     

Synthesis and electrocatalysis of 1-aminopyrene-functionalized carbon nanofiber-supported platinum-ruthenium nanoparticles

Platinum-ruthenium/carbon composite nanofibers were prepared by depositing PtRu nanoparticles directly onto electrospun carbon nanofibers using a polyol processing technique. The morphology and size of PtRu nanoparticles were controlled by 1-aminopyrene functionalization. The noncovalent functionalization of carbon nanofibers by 1-aminopyrene is simple and can be carried out at ambient temperature without damaging the integrity and electronic structure of carbon nanofibers. The resulting PtRu/carbon composite nanofibers were characterized by cyclic voltammogram in 0.5 M H₂SO₄ and 0.125 M CH₃OH + 0.2 M H₂SO₄ solutions, respectively. The PtRu/carbon composite nanofibers with 1-aminopyrene functionalization have smaller nanoparticles and a more uniform distribution, compared with those pretreated with conventional acids. Moreover, PtRu/1-aminopyrene functionalized carbon nanofibers have high active surface area and improved performance towards the electrocatalytic oxidation of methanol.     

Noncovalently functionalized graphitic mesoporous carbon as a stable support of Pt nanoparticles for oxygen reduction

We report a durable electrocatalyst support, highly graphitized mesoporous carbon (GMPC), for oxygen reduction in polymer electrolyte membrane (PEM) fuel cells. GMPC is prepared through graphitizing the self-assembled soft-template mesoporous carbon (MPC) under high temperature. Heat-treatment at 2800 °C greatly improves the degree of graphitization while most of the mesoporous structures and the specific surface area of MPC are retained. GMPC is then noncovalently functionalized with poly(diallyldimethylammonium chloride) (PDDA) and loaded with Pt nanoparticles by reducing Pt precursor (H₂PtCl₆) in ethylene glycol. Pt nanoparticles of ∼3.0 nm in diameter are uniformly dispersed on GMPC. Compared to Pt supported on Vulcan XC-72 carbon black (Pt/XC-72), Pt/GMPC exhibits a higher mass activity towards oxygen reduction reaction (ORR) and the mass activity retention (in percentage) is improved by a factor of ∼2 after 44 h accelerated degradation test under the potential step (1.4-0.85 V) electrochemical stressing condition which focuses on support corrosion. The enhanced activity and durability of Pt/GMPC are attributed to the graphitic structure of GMPC which is more resistant to corrosion. These findings demonstrate that GMPC is a promising oxygen reduction electrocatalyst support for PEM fuel cells. The approach reported in this work provides a facile, eco-friendly promising strategy for synthesizing stable metal nanoparticles on hydrophobic support materials.     

Studies of electrochemical performance of carbon supported Pt-Cu nanoparticles as anode catalysts for direct borohydride-hydrogen peroxide fuel cell

Carbon supported Pt-Cu bimetallic nanoparticles are prepared by a modified NaBH₄ reduction method in aqueous solution and used as the anode electrocatalyst of direct borohydride-hydrogen peroxide fuel cell (DBHFC). The physical and electrochemical properties of the as-prepared electrocatalysts are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry (CV), chronoamperometry (CA), chronopotentiometry (CP) and fuel cell test. The results show that the carbon supported Pt-Cu bimetallic catalysts have much higher catalytic activity for the direct oxidation of BH₄⁻ than the carbon supported pure nanosized Pt catalyst, especially the Pt₅₀Cu₅₀/C catalyst presents the highest catalytic activity among all as-prepared catalysts, and the DBHFC using Pt₅₀Cu₅₀/C as anode electrocatalyst and Pt/C as cathode electrocatalyst shows as high as 71.6 mW cm⁻² power density at a discharge current density of 54.7 mA cm⁻² at 25 °C.     

Investigation of grain boundary formation in PtRu/C catalyst obtained in a polyol process with post-treatment

The grain boundary formation in PtRu/C catalyst obtained in a polyol process with post-treatment was investigated by scanning transmission electron microscopy, transmission electron microscopy (TEM) and High resolution TEM. The crystalline structure and surface composition of the PtRu/C catalysts were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The electrochemical activities were evaluated by CO stripping voltammetry and linear sweep voltammetry measurements in combination with in situ IR reflection-absorption spectroscopy. As-prepared isolated spherical nanoparticles on the carbon support started to interconnect after washing procedure, and the interconnection between the particles was greatly promoted by reduction post-treatment at 80 °C; grain boundary formation occurred in the interconnected particles with increasing reduction temperature to 200 °C, and the particles reconstructed severely with further increasing reduction temperature to 400 °C. The defects at the grain boundary served as active sites for methanol electro-oxidation by weakening CO_ads adsorption on Pt sites and facilitating OH_ads formation, and the PtRu/C catalyst treated in 5% H₂/Ar at 200 °C for 10 h had the greatest catalytic activity for methanol electro-oxidation among the PtRu/C catalysts treated under various atmospheres and temperatures.     

Platinum/tin oxide/carbon cathode catalyst for high temperature PEM fuel cell

The performance of high temperature polymer electrolyte fuel cell (HT-PEMFC) using platinum supported over tin oxide and Vulcan carbon (Pt/SnOx/C) as cathode catalyst was evaluated at 160-200 °C and compared with Pt/C. This paper reports first time the Pt/SnOx/C preparation, fuel cell performance, and durability test up to 200 h. Pt/SnOx/C of varying SnO compositions were characterized using XRD, SEM, TEM, EDX and EIS. The face-centered cubic structure of nanosized Pt becomes evident from XRD data. TEM and EDX measurements established that the average size of the Pt nanoparticles were ∼6 nm. Low ionic resistances were derived from EIS, which ranged from 0.5 to 5 Ω-cm² for cathode and 0.05 to 0.1 Ω-cm² for phosphoric acid, doped PBI membrane. The addition of the SnOx to Pt/C significantly promoted the catalytic activity for the oxygen reduction reaction (ORR). The 7 wt.% SnO in Pt/SnO₂/C catalyst showed the highest electro-oxidation activity for ORR. High temperature PEMFC measurements performed at 180 °C under dry gases (H₂ and O₂) showed 0.58 V at a current density of 200 mA cm⁻², while only 0.40 V was obtained in the case of Pt/C catalyst. When the catalyst contained higher concentrations of tin oxide, the performance decreased as a result of mass transport limitations within the electrode. Durability tests showed that Pt/SnOx/C catalysts prepared in this work were stable under fuel cell working conditions, during 200 h at 180 °C demonstrate as potential cathode catalyst for HT-PEMFCs.     

Pt and PtRu nanoparticles deposited on single-wall carbon nanotubes for methanol electro-oxidation

Platinum (Pt) and platinum–ruthenium (PtRu) nanoparticles supported on Vulcan XC-72 carbon and single-wall carbon nanotubes (SWCNT) are prepared by a microwave-assisted polyol process. The catalysts are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The PtRu nanoparticles, which are uniformly dispersed on carbon, have diameters of 2–6 nm. All the PtRu/C catalysts display the characteristic diffraction peaks of a face centred cubic Pt structure, excepting that the 2θ values are shifted to slightly higher values. The results from XPS analysis reveal that the catalysts contain mostly Pt(0) and Ru(0), with traces of Pt(II), Pt(IV) and Ru(IV). The electrooxidation of methanol is studied by cyclic voltammetry, linear sweep voltammetry, and chronoamperometry. Both PtRu/C catalysts have high and more durable electrocatalytic activities for methanol oxidation than a comparative Pt/C catalyst. Preliminary data from a single direct methanol fuel cell using the SWCNT supported PtRu alloy as the anode catalyst delivers high power density.     

A novel binary Pt3Tex/C nanocatalyst for ethanol electro-oxidation

The Pt₃Te_x/C nanocatalyst was prepared and its catalytic performance for ethanol oxidation was investigated for the first time. The Pt₃Te/C nanoparticles were characterized by an X-ray diffractometer (XRD), transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy equipped with TEM (TEM-EDX). The Pt₃Te/C catalyst has a typical fcc structure of platinum alloys with the presence of Te. Its particle size is about 2.8 nm. Among the synthesized catalysts with different atomic ratios, the Pt₃Te/C catalyst has the highest anodic peak current density. The cyclic voltammograms (CV) show that the anodic peak current density for the Pt₃Te/C, commercial PtRu/C and Pt/C catalysts reaches 1002, 832 and 533 A g⁻¹, respectively. On the current–time curve, the anodic current on the Pt₃Te/C catalyst was higher than those for the catalysts reported. So, these findings show that the Pt₃Te/C catalyst has uniform nanoparticles and the best activity among the synthesized catalysts, and it is better than commercial PtRu/C and Pt/C catalysts for ethanol oxidation at room temperature.     

Improvement of methanol electro-oxidation activity of PtRu/C and PtNiCr/C catalysts by anodic treatment

The effect of an anodic treatment on the methanol oxidation activity of PtRu/C (50:50 at.%) and PtNiCr/C (Pt:Ni:Cr = 28:36:36 at.%) catalysts was investigated for various potential limits of 0.9, 1.1, 1.3 and 1.4 V (vs. reference hydrogen electrode, RHE). NaBH₄ reduced catalysts were further reduced at 900 °C for 5 min in an argon balanced hydrogen flow stream. Improved alloying was obtained by the hydrogen reduction procedure as confirmed by X-ray diffraction results. In the PtRu/C catalyst, a decrease of irreversible Ru (hydrous) oxide formation was observed when the anodic treatment was performed at 1.1 V (vs. RHE) or higher potentials. In chronoamperometry testing performed for 60 min at 0.6 V (vs. RHE), the highest activity of the PtRu/C catalyst was observed when anodic treatment was performed at 1.3 V (vs. RHE). The current density increased from 1.71 to 4.06 A g_cat.⁻¹ after the anodic treatment. In the PtNiCr/C catalyst, dissolution of Ni and Cr was observed when potentials ≥1.3 V (vs. RHE) were applied during the anodic treatment. In MOR activity tests, the current density of the PtNiCr/C catalyst dramatically increased by more than 13.5 times (from 0.182 to 2.47 A g_cat.⁻¹) when an anodic treatment was performed at 1.4 V. On an A g_{noble metal}⁻¹ basis, the current density of PtNiCr-1.4V is slightly higher than the best anodically treated PtRu-1.3V catalyst, suggesting the PtNiCr catalyst is a promising candidate to replace the PtRu catalysts.     

Online analysis of carbon dioxide from a direct ethanol fuel cell

Carbon dioxide yields from a direct ethanol fuel cell have been monitored by using a commercial infrared CO₂ monitor. The time dependence is reported as a function of temperature, current density, and anode catalyst (Pt vs. PtRu). Yields increased strongly with temperature, with a Faradaic yield of 76% being obtained at 100 °C with a Pt black anode. PtRu gave lower yields than Pt by a factor of ca. 3 at 80 and 100 °C, but higher yields than Pt at ambient temperature. The superior ability of PtRu to strip adsorbed CO is important at low temperatures, but not a key factor at 100 °C.     

Ethanol oxidation on PtRuMo/C catalysts: In situ FTIR spectroscopy and DEMS studies

The electrooxidation of ethanol on carbon supported PtRuMo nanoparticles of different Mo compositions has been studied in the temperature range of 30–70 °C. Current–time curves have shown an increase of the current density with the Mo introduction during the ethanol oxidation at 0.5 V in a whole temperature range. The incorporation of different amount of MoO_x (∼Mo⁵⁺) like species over PtRu systems produces ternary catalyst with similar structural characteristics as particle size or crystal phases, but the catalytic behavior depended on both the surface amount of Mo and on the applied potential. In situ spectroelectrochemical studies have been used to identity adsorbed reaction intermediates and products (in situ Fourier transform infrared spectroscopy, FTIR) and volatile reaction products (differential electrochemical mass spectrometry, DEMS). For all catalysts, incomplete ethanol oxidation to C2 products (acetaldehyde and acetic acid) prevails under the conditions selected in this study. The higher CO tolerance of PtRuMo/C catalysts at very low potentials (<0.3 V) results to minimum or no CO poisoning of the Pt and Ru surfaces, in contrast to the PtRu/C catalyst, which are rapidly blocked by CO. Therefore, catalyst with higher amount of Mo allows a fast “replenishment” of the active sites leading to the formation of acetaldehyde and, especially, acetic acid at potentials above 0.3 V.     

High performance direct ethanol fuel cell with double-layered anode catalyst layer

Double-layered anode catalyst layers with two reverse configurations, which consist of 45 wt.% Pt₃Sn/C and PtRu black catalyst layers, were fabricated to improve the performance of a direct ethanol fuel cell (DEFC). The in-house 45 wt.% Pt₃Sn/C catalyst was characterized by XRD and TEM. The cross-sectional double-layered anode catalyst layer was observed by SEM. In DEFC performance test and anode linear sweep voltammetry measurement, the anode with double-layered catalyst layer exhibited better catalytic activity for ethanol electro-oxidation than those with single-layered 45 wt.% Pt₃Sn/C and PtRu black catalyst layers. In terms of anode product distribution, the DEFC with double-layered anode catalyst layer showed a higher yield of acetic acid than that with single-layered PtRu black catalyst layer and a higher yield of CO₂ than that with single-layered 45 wt.% Pt₃Sn/C catalyst layer, respectively. These results suggest that the double-layered anode catalyst layer possessed the advantages of both Pt₃Sn/C and PtRu black catalysts for ethanol electro-oxidation, and thus showed a higher ethanol electro-oxidation efficiency and DEFC performance in the practical polarization potential region.     

Activity of dealloyed PtCo3 and PtCu3 nanoparticle electrocatalyst for oxygen reduction reaction in polymer electrolyte membrane fuel cell

We report a comparative study of the alloy formation and electrochemical activity of dealloyed PtCo₃ and PtCu₃ nanoparticle electrocatalysts for the oxygen reduction reaction (ORR). For the Pt-Co system the maximum annealing temperatures were 650 °C, 800 °C and 900 °C for 7 h to drive the Pt-Co alloy formation and the particle growth. EDS and XRD were employed for the characterization of catalyst powders. The RDE and RRDE experiments were conducted in 0.1 M HClO₄ at room temperature.We demonstrate that the mass and surface area specific ORR activities of Pt-Co and Pt-Cu alloys after voltammetric activation exhibit a considerable improvement compared to those of pure Pt/C. The dealloyed PtCo₃ (800 °C/7 h) electrocatalyst performs 3 times higher in terms of Pt-based mass activity and 4-5 times higher in terms of ECSA-based specific activity than a 28.2 wt.% Pt/C. Dealloyed Pt-Co catalysts (800 °C/7 h) show the most favorable balance between mass and specific ORR activity with a particle size of 2.2 ± 0.1 nm. We hypothesize that geometric strain effects of the dealloyed Pt-Co nanoparticles, similar to those found in dealloyed PtCu₃ nanoparticles, are responsible for the improvement in ORR activity [1].     

Oxygen-reduction activity of silk-derived carbons

Carbonized silk fibroin (CS), which is free of metallic elements, showed high catalytic activity for oxygen-reduction reaction (ORR). The catalytic activity of CS for ORR was greatly enhanced by steam activation forming silk-derived activated carbon (CS-AC). The surface morphology, surface area, pore structure and remaining nitrogen species of the CSs were compared with those of the CS-ACs. The open-circuit potential and the power density of a polymer electrolyte fuel cell using a CS900-AC, which was heat-treated at 900 °C prior to the steam activation, and a platinum/C (C: carbon black) anode under pure oxygen and hydrogen gases, respectively, both at 0.2 MPa, were 0.92 V and 142 mW cm⁻² at 80 °C. The ORR on the activated carbon, CS900-AC, proceeded with a 3.5-electron reaction at 0.6 V (vs. RHE); however, this was improved to a 3.9-electron reaction with the addition of zirconium oxide at 20 wt% to CS900-AC.     

Nanocomposite Ni/ZrO2: Highly active and stable catalyst for H2 production via cyclic stepwise methane reforming reactions

This work investigates the catalytic performance of nanocomposite Ni/ZrO₂-AN catalyst consisting of comparably sized Ni (10–15 nm) and ZrO₂ (15–25 nm) particles for hydrogen production from the cyclic stepwise methane reforming reaction with either steam (H₂O) or CO₂ at 500–650 °C, in comparison with a conventional Ni/ZrO₂-CP catalyst featuring Ni particles supported by large and widely sized ZrO₂ particles (20–400 nm). Though both catalysts exhibited similar activity and stability during the reactions at 500 and 550 °C, they showed remarkably different catalytic stabilities at higher temperatures. The Ni/ZrO₂-CP catalyst featured a significant deactivation even during the methane decomposition step in the first cycle of the reactions at ≥600 °C, but the Ni/ZrO₂-AN catalyst showed a very stable activity during at least 17 consecutive cycles in the cyclic reaction with steam. Changes in the catalyst beds at varying stages of the reactions were characterized with TEM, XRD and TPO–DTG and were correlated with the amount and nature of the carbon deposits. The Ni particles in Ni/ZrO₂-AN became stabilized at the sizes of around 20 nm but those in Ni/ZrO₂-CP kept on growing in the methane decomposition steps of the cyclic reaction. The small and narrowly sized Ni particles in the nanocomposite Ni/ZrO₂-AN catalyst led to a selective formation of filamentous carbons whereas the larger Ni particles in the Ni/ZrO₂-CP catalyst a preferred formation of graphitic encapsulating carbons. The filamentous carbons were favorably volatilized in the steam treatment step but the CO₂ treatment selectively volatilized the encapsulating carbons. These results identify that the nature but not the amount of carbon deposits is the key to the stability of Ni/ZrO₂ catalyst and that the nanocomposite Ni/ZrO₂-AN would be a promising catalyst for hydrogen production via cyclic stepwise methane reforming reactions.