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.     

PtxSn/C electrocatalysts synthesized by improved microemulsion method and their catalytic activity for ethanol oxidation

The Pt_xSn/C (x = 1, 2, 2.5, 3, 4) anodic catalysts for direct ethanol fuel cell (DEFC) have been prepared by an improved microemulsion method. Ethylene glycol is used as cosurfactant, and metal precursors are dissolved in it beforehand to prevent the hydrolysis of metal precursors. The composition, particle size and structure of these catalysts are characterized by energy dispersive X-ray spectrum (EDX), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results show that the synthesized Pt₃Sn/C catalyst has part of Pt and Sn alloying. The average diameter is about 2.9 nm, and has a narrow size distribution and a good dispersivity. The electrochemical experiments indicate that the Pt₃Sn/C catalyst prepared in the neutral microemulsion has superior catalytic activity for ethanol oxidation. The Pt_xSn/C nanoparticle formation in the improved microemulsion is also discussed.     

Anodic oxidation of ethanol on core-shell structured Ru@PtPd/C catalyst in alkaline media

The direct ethanol fuel cell has been attracting increased attention due to its safety and the wider availability of ethanol as compared with methanol. The present work investigates the anodic oxidation of ethanol on a core-shell structured Ru@PtPd/C catalyst in alkaline media. The catalyst shows high activity toward the anodic oxidation of ethanol; with 18 wt.% ruthenium as the core and 12 wt.% PtPd (Pt:Pd = 1:0.2) as the active shell, its activity in terms of PtPd loading is 1.3, 3, 1.4, and 2.0 times as high as that of PtPd/C, PtRu/C, Pd/C, and Pt/C, respectively, indicating high utilization of Pt and Pd. The ratio of forward peak current density to backward peak current density (I_f/I_b) reaches 1.5, which is 1.9 times that of PtPd/C catalyst, revealing high poisoning tolerance to the intermediates in ethanol electrooxidation. In addition, the stability of Ru@PtPd/C is higher than that of Pt/C and PtPd/C, as evidenced by chronoamperometric evaluations. The catalyst is extensively characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy. The core-shell structure of the catalyst is revealed by XRD and TEM.     

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.     

PtRu/C catalysts synthesized by a two-stage polyol reduction process for methanol oxidation reaction

Highly dispersed Ru/C catalysts are prepared using high viscosity glycerol as a reducing agent and are treated in H₂ atmosphere to ensure stability. A Pt^∧Ru/C catalyst is prepared by an ethylene glycol process based on the pre-formed Ru/C. The catalyst is tested for methanol oxidation reaction at room temperature and is compared with the activity of the as-prepared PtRu/C alloyed catalyst (prepared by co-reduction of Pt and Ru precursors) and commercial PtRu/C from E-TEK. The catalysts are extensively characterized by Transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Electrochemical measurements by cyclic voltammetry (CV) showed consistently high catalytic activities and improved CO resistance for the Pt^∧Ru/C catalyst.     

Enhancement of the electrooxidation of ethanol on Pt–Sn–P/C catalysts prepared by chemical deposition process

In this paper, five Pt₃Sn₁/C catalysts have been prepared using three different methods. It was found that phosphorus deposited on the surface of carbon with Pt and Sn when sodium hypophosphite was used as reducing agent by optimization of synthetic conditions such as pH in the synthetic solution and temperature. The deposition of phosphorus should be effective on the size reduction and markedly reduces PtSn nanoparticle size, and raise electrochemical active surface (EAS) area of catalyst and improve the catalytic performance. TEM images show PtSnP nanoparticles are highly dispersed on the carbon surface with average diameters of 2 nm. The optimum composition is Pt₃Sn₁P₂/C (note PtSn/C-3) catalyst in my work. With this composition, it shows very high activity for the electrooxidation of ethanol and exhibit enhanced performance compared with other two Pt₃Sn₁/C catalysts that prepared using ethylene glycol reduction method (note PtSn/C-EG) and borohydride reduction method (note PtSn/-B). The maximum power densities of direct ethanol fuel cell (DEFC) were 61 mW cm⁻² that is 150 and 170% higher than that of the PtSn/C-EG and PtSn/C-B catalyst.     

Catalytic activity,stability and impedance behavior of PtRu/C,PtPd/C and PtSn/C bimetallic catalysts toward methanol and formic acid oxidation

PtRu, PtPd and PtSn with weight ratios of (2:1) on carbon black (Vulcan XC-72) supported bimetallic catalysts were prepared by using microwave method via chemically reduction of H₂PtCl₆·6H₂O, RuCl₃, PdCl₂ and SnCl₂·2H₂O precursors with ethylene glycol (EG). These prepared catalysts were systematically investigated and obtained results were compared with commercial Pt black, PtRu black catalysts and with each other. The catalysts were characterized with XRD, ICP-MS, EDS and TEM. The electrocatalytic activities, stability and impedance of the catalysts were investigated in sulfuric acid/methanol and sulfuric acid/formic acid mixtures using electrochemical measurements. The results showed that PtSn/C catalyst showed comparable activity and durability with commercial Pt/C catalyst toward methanol oxidation. The synthesized PtRu/C catalyst was found to completely oxidize methanol and it showed more catalytic activity than commercial PtRu catalyst. Bimetallic PtPd/C catalyst gave better activity than both commercial Pt black and synthesized Pt/C catalyst for oxidation of formic acid. Higher electrochemical active surface areas were obtained with supported bimetallic catalysts.     

CeO2 nanoparticles improved Pt-based catalysts for direct alcohol fuel cells

We developed an ultrasonic co-deposition technique to enhance the activity of Pt/C catalyst (and Pt/CNT, PtRu/C catalysts) for direct alcohol fuel cells (DAFCs) by CeO₂ nanoparticles. The composite catalyst architecture is obtained by an ultrasonically mixing commercial Pt/C catalyst and CeO₂ nanoparticles. Both Pt and CeO₂ are dispersed uniformly in the electrodes resulting in a great deal of CeO₂–Pt–C triple junction interfaces. Unlike traditional preparation of metal oxide supported Pt catalysts, CeO₂ will not cut the connection between Pt and C in this composite catalyst structure. Electrochemical measurements confirm that CeO₂ can improve almost all Pt based catalysts (Pt/C, Pt/CNT, and PtRu/C) for almost all small molecular alcohols (methanol, ethanol, ethylene glycol, and glycerol) electro-oxidation. EIS measurement shows that reaction resistance between Pt and alcohols is decreased much by adding small CeO₂ nanoparticles. Besides, these composite catalysts have high stability. It proves CeO₂ a very promising co-catalyst of Pt based catalysts for DAFCs.     

Study of ethanol electro-oxidation in acid environment on Pt3Sn/C anode catalysts prepared by a modified polymeric precursor method under controlled synthesis conditions

A carbon-supported binary Pt₃Sn catalyst has been prepared using a modified polymeric precursor method under controlled synthesis conditions. This material was characterized using X-ray diffraction (XRD), and the results indicate that 23% (of a possible 25%) of Sn is alloyed with Pt, forming a dominant Pt₃Sn phase. Transmission electron microscopy (TEM) shows good dispersion of the electrocatalyst and small particle sizes (3.6 nm ± 1 nm). The polarization curves for a direct ethanol fuel cell using Pt₃Sn/C as the anode demonstrated improved performance compared to that of a PtSn/C E-TEK, especially in the intrinsic resistance-controlled and mass transfer regions. This behavior is probably associated with the Pt₃Sn phase. The maximum power density for the Pt₃Sn/C electrocatalyst (58 mW cm⁻²) is nearly twice that of a PtSn/C E-TEK electrocatalyst (33 mW cm⁻²). This behavior is attributed to the presence of a mixed Pt₉Sn and Pt₃Sn alloy phase in the commercial catalysts.     

Carbon supported Pt-Y electrocatalysts for the oxygen reduction reaction

Carbon supported Pt₃Y (Pt₃Y/C) and PtY (PtY/C) were investigated as oxygen reduction reaction (ORR) catalysts. After synthesis via reduction by NaBH₄, the alloy catalysts exhibited 10-20% higher mass activity (mA mg_Pt⁻¹) than comparably synthesized Pt/C catalyst. The specific activity (μA cm_Pt⁻²) was 23 and 65% higher for the Pt₃Y/C and PtY/C catalysts, respectively, compared to Pt/C. After annealing at 900 °C under a reducing atmosphere, Pt₃Y/C-900 and PtY/C-900 catalysts showed improved ORR activity; the Pt/C and Pt/C-900 (Pt/C catalyst annealed at 900 °C) catalysts exhibited specific activities of 334 and 393 μA cm_Pt⁻², respectively, while those of the Pt₃Y/C-900 and PtY/C-900 catalysts were 492 and 1050 μA cm_Pt⁻², respectively. X-ray diffraction results revealed that both the Pt₃Y/C and PtY/C catalysts have a fcc Pt structure with slight Y doping. After annealing, XRD showed that more Y was incorporated into the Pt structure in the Pt₃Y/C-900 catalyst, while the PtY/C-900 catalyst remained unchanged. Although these results suggested that the high ORR activity of the PtY/C-900 catalyst did not originate from Pt-Y alloy formation, it is clear that the Pt-Y system is a promising ORR catalyst which merits further investigation.     

High performance Pd-based catalysts for oxidation of formic acid

Two novel catalysts for anode oxidation of formic acid, Pd₂Co/C and Pd₄Co₂Ir/C, were prepared by an organic colloid method with sodium citrate as a complexing agent. These two catalysts showed better performance towards the anodic oxidation of formic acid than Pd/C catalyst and commercial Pt/C catalyst. Compared with Pd/C catalyst, potentials of the anodic peak of formic acid at the Pd₂Co/C and Pd₄Co₂Ir/C catalyst electrodes shifted towards negative value by 140 and 50 mV, respectively, meanwhile showed higher current densities. At potential of 0.05 V (vs. SCE), the current density for Pd₄Co₂Ir/C catalyst is as high as up to 13.7 mA cm⁻², which is twice of that for Pd/C catalyst, and six times of that for commercial Pt/C catalyst. The alloy catalysts were nanostructured with a diameter of ca. 3–5 nm and well dispersed on carbon according to X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. The composition of alloy catalysts was analyzed by energy dispersive X-ray analysis (EDX). Pd₄Co₂Ir/C catalyst showed the highest activity and best stability making it the best potential candidate for application in a direct formic acid fuel cell (DFAFC).     

Effect of temperature on the mechanism of ethanol oxidation on carbon supported Pt,PtRu and Pt3Sn electrocatalysts

The electrochemical oxidation of ethanol on carbon supported Pt, PtRu and Pt₃Sn catalysts was studied in acid solutions at room temperature and in direct ethanol fuel cells (DEFC) in the temperature range 70–100 °C. In all the experiments, an enhancement of the activity for the ethanol oxidation was observed on the binary catalysts. In acid solution the improvement at low current densities was higher on PtRu than on Pt₃Sn. In DEFC tests, at 70 °C the cells with PtRu and Pt₃Sn showed about the same performance, while for T > 70 °C the cells with Pt₃Sn as anode material performed better than those with PtRu as anode material. The apparent activation energy for ethanol oxidation on PtRu catalyst was lower than on Pt₃Sn, particularly at high cell potentials, i.e. at low current densities. At low temperatures and/or low current densities, the positive effect of Ru oxides on the bifunctional mechanism determined the enhancement of activity for the ethanol oxidation reaction, while at high temperatures the positive effect of Sn alloying (enlarged lattice parameter) on CH₃CH₂OH adsorption and C–C cleavage prevails.     

PAMAM-stabilized Pt-Ru nanoparticles for methanol electro-oxidation

This work utilizes poly(amidoamine) dendrimers (PAMAM) as a protective ligand in solution to produce carbon-supported, Pt-Ru bimetallic nanoparticles for use as methanol electro-oxidation catalysts. UV-vis spectra show that after initial Pt²⁺ complexation with PAMAM G4OH dendrimer in water, appropriate adjustment of solution pH permits subsequent Ru³⁺ complexation without displacing Pt²⁺, demonstrating the formation of an aqueous, bimetallic solution complex. Catalysts (nominally 20 wt% metals, confirmed by AA spectroscopy) are produced by impregnating high surface area carbon black with G4OH-(Pt²⁺)_x(Ru³⁺)_y complex solution, drying, and activation in H₂ gas at elevated temperature. XPS results show that activation in H₂ at 400 °C removes virtually all of the PAMAM and reduces all of the Pt and most of the Ru to zero valence. TEM and XRD results show that the use of G4OH in the recipe is crucial for controlling metal particle size, and that the particles are crystalline with lattice parameters indicative of bimetallic Pt-Ru alloys. XRD data also suggest that G4OH promotes greater Pt-Ru alloying when Pt:Ru = 1:1. Catalytic activity for methanol oxidation increases with Ru content and is greatest for the catalyst with 1:1 Pt:Ru ratio. Per unit mass of Pt, the methanol oxidation activity of 20 wt% G4OH-PtRu/C catalyst is about 60% greater than that of E-Tek's commercially available 20 wt% PtRu catalyst.     

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.     

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 electro-oxidation on carbon-supported Pt,PtRu and Pt3Sn catalysts: A quantitative DEMS study

The electrocatalytic activity of commercial carbon supported PtRu/Vulcan and Pt₃Sn/Vulcan bimetallic catalysts (E-TEK, Inc.) for ethanol oxidation under well defined electrolyte transport conditions and their selectivity for complete oxidation were evaluated using cyclic voltammetry combined with on-line differential electrochemistry mass spectrometry (DEMS) measurements and compared to the activity/selectivity of standard Pt/Vulcan catalysts. The main reaction products CO₂, acetaldehyde and acetic acid were determined quantitatively, by appropriate calibration procedures, current efficiencies and product yields were calculated. Addition of Ru or Sn in binary Pt catalysts lowers the onset potential for ethanol electro-oxidation and leads to a subtle increase of the total activity of the Pt₃Sn/Vulcan catalyst. It does not improve, however, the selectivity for complete oxidation to CO₂, which is about 1% for all three catalysts under present reaction conditions—incomplete ethanol oxidation to acetaldehyde and acetic acid prevails on all three catalysts. The results demonstrate that the performance of the respective catalysts is limited by their ability for C–C bond breaking rather than by their activity for the oxidation of poisoning adsorbed intermediates such as CO_ad or CH_x,ad species.     

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.     

Polyol-synthesized PtRu/C and PtRu black for direct methanol fuel cells

PtRu/C and PtRu black catalysts with nominal Pt:Ru atomic ratio of 1:1 are prepared by a modified polyol process (co-reduction of metal precursor salts) as anode catalysts for direct methanol fuel cells (DMFCs). Without the carbon support, PtRu nanoparticles tend to agglomerate, while the PtRu nanoparticles in PtRu/C have a good dispersion as shown by TEM. Both PtRu black and PtRu/C have the almost same alloy degree indicated by XRD, but PtRu supported on carbon could improve the influence of Ru on Pt toward methanol oxidization as shown by cyclic voltammetry. The microstructure of PtRu/C is further studied by high-resolution transmission electron microscopy (HRTEM), and the results indicate that the lattice constant of Pt in PtRu electrocatalyst has contracted despite a few parts of Pt not alloyed with Ru due to the lattice constant of Pt without contracting, which is further proved by the results of temperature-programmed reduction (TPR). Such parts of unalloyed Ru are further proved to have ability to reduce the methanol oxidation potential on Pt by comparing the catalytic behaviors of Pt/C and Pt + Ru/C prepared by mixing carbon with separately prepared Pt and Ru colloids. Moreover, the catalytic behaviors of PtRu black and PtRu/C are also compared with those of commercial ones.     

Ni–Pt/C as anode electrocatalyst for a direct borohydride fuel cell

In this study, a series of Ni–Pt/C and Ni/C catalysts, which were employed as anode catalysts for a direct borohydride fuel cell (DBFC), were prepared and investigated by XRD, TEM, cyclic voltammetry, chronopotentiometry and fuel cell test. The particle size of Ni₃₇–Pt₃/C (mass ratio, Ni:Pt = 37:3) catalyst was sharply reduced by the addition of ultra low amount of Pt. And the electrochemical measurements showed that the electro-catalytic activity and stability of the Ni₃₇–Pt₃/C catalysts were improved compared with Ni/C catalyst. The DBFC employing Ni₃₇–Pt₃/C catalyst on the anode (metal loading, 1 mg cm⁻²) showed a maximum power density of 221.0 mW cm⁻² at 60 °C, while under identical condition the maximum power density was 150.6 mW cm⁻² for Ni/C. Furthermore, the polarization curves and hydrogen evolution behaviors on all the catalysts were investigated on the working conditions of the DBFC.