Performance of supported Au–Co alloy as the anode catalyst of direct borohydride-hydrogen peroxide fuel cell

Au–Co alloys supported on Vulcan XC-72R carbon were prepared by the reverse microemulsion method and used as the anode electrocatalyst for direct borohydride-hydrogen peroxide fuel cell (DBHFC). The physical and electrochemical properties were investigated by energy dispersive X-ray (EDX), X-ray diffraction (XRD), cyclic voltammetry, chronamperometry and chronopotentiometry. The results show that supported Au–Co alloys catalysts have higher catalytic activity for the direct oxidation of BH₄⁻ than pure nanosized Au catalyst, especially the Au₄₅Co₅₅/C catalyst presents the highest catalytic activity among all as-prepared Au–Co alloys, and the DBHFC using the Au₄₅Co₅₅/C as anode electrocatalyst shows as high as 66.5 mW cm⁻² power density at a discharge current density of 85 mA cm⁻² at 25 °C.     

Carbon-supported Pd–Ir catalyst as anodic catalyst in direct formic acid fuel cell

It was reported for the first time that the electrocatalytic activity of the Carbon-supported Pd–Ir (Pd–Ir/C) catalyst with the suitable atomic ratio of Pd and Ir for the oxidation of formic acid in the direct formic acid fuel cell (DFAFC) is better than that of the Carbon-supported Pd (Pd/C) catalyst, although Ir has no electrocatalytic activity for the oxidation of formic acid. The potential of the anodic peak of formic acid at the Pd–Ir/C catalyst electrode with the atomic ratio of Pd and Ir = 5:1 is 50 mV more negative than that and the peak current density is 13% higher than that at the Pd/C catalyst electrode. This is attributed to that Ir can promote the oxidation of formic acid at Pd through the direct pathway because Ir can decrease the adsorption strength of CO on Pd. However, when the content of Ir in the Pd–Ir/C catalyst is too high the electrocatalytic activity of the Pd–Ir/C catalyst would be decreased because Ir has no electrocatalytic activity for the oxidation of formic acid.     

Ultrafine amorphous Co–W–B alloy as the anode catalyst for a direct borohydride fuel cell

The ultrafine amorphous Co–W–B alloy has been synthesized by chemical reduction and used as anode catalyst in direct borohydride fuel cell. The results show that the maximum power output of the cell is 101 mW cm⁻² at 15 °C, and the essential power density of this material can be up to 350 mW cm⁻² at 15 °C and 500 mW cm⁻² at 60 °C, respectively. The cell has also a good durability, with no attenuation observed after one week of operation.     

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.     

Effect of anode conditions on the performance of direct borohydride–hydrogen peroxide fuel cell system

Direct borohydride–hydrogen peroxide fuel cells (DBHPFCs) are attractive power sources for space applications. Although the cathode conditions are known to affect the system performance, the effect of the anode conditions is rarely investigated. Thus, in this study, a DBHPFC system was tested under various anode conditions, such as electrocatalyst, fuel concentration, and stabilizer concentration, to investigate their effects on the system performance. A virtual DBHPFC system was analyzed based on the experimental data obtained from fuel cell tests. The anode electrocatalyst had a considerable effect on the mass and electrochemical reaction rate of the fuel cell system, but had minimal effect on the decomposition reaction rate. The NaBH₄ concentration greatly influenced the mass and decomposition reaction rate of the fuel cell system; however, it had minimal impact on the electrochemical reaction rate. The NaOH concentration affected the electrochemical reaction rate, decomposition reaction rate, and mass of the fuel cell system. Therefore, the significant effects of the anode conditions on the electrochemical reaction rate, decomposition reaction rate, and mass of the fuel cell system prompt the need for their careful selection through fuel cell tests and system analysis.     

Improvement on direct ethanol fuel cell performance by using doped-Nafion 117 membranes with Pt and Pt–Ru nanoparticles

Nafion^® 117 membranes doped with Pt (4 × 10⁻⁴ mol L⁻¹ or 8 × 10⁻⁴ mol L⁻¹ H₂PtCl₆ solution), and with Pt–Ru (4 × 10⁻⁴ mol L⁻¹ H₂PtCl₆ and 2 × 10⁻⁴ mol L⁻¹ RuCl₃ solutions) nanoparticles have been synthesized using a simple and scalable absorption-reduction method. The chemical integrity of the membranes was confirmed by ¹³C and ¹⁹F solid-state NMR. The pore microstructure of the membranes was preserved after the doping process, according to SAXS measurements. The tests of the direct ethanol fuel cells (DEFC) performance at 90 °C exhibited up to 38% and 56% increase at the maximum power densities for Pt doped-Nafion^® membrane from lower and higher concentration of H₂PtCl₆ solution, respectively, compared to bare Nafion^® membranes. Additionally, a Pt–Ru doped-membrane tested at 110 °C exhibited the highest power density. Such superior performances may be attributed to a synergistic effect between the extra amount of active catalytic sites inside the pore structure for the electrochemical oxidation of ethanol, thus preventing ethanol crossover, and the excellent proton migration properties conferred by the pore microstructure of Nafion^®. These results demonstrate that the doped-Nafion^® membrane has a good capacity to improve the performance of DEFC, and provided further clarification on the synthesis process of polymer electrolyte doped-membranes in fuel cell technology.     

Performance studies of Pd–Pt and Pt–Pd–Au catalyst for electro-oxidation of glucose in direct glucose fuel cell

Platinum is employed as anode catalyst for low temperature electro-oxidation of glucose in direct glucose fuel cell (DGFC), but it suffers from poisoning by intermediate oxidation products. In the present investigation, palladium and gold precursors are added with platinum precursor to form low metal loading (∼15–20% by wt.) carbon supported catalyst by NaBH₄ reduction technique. The prepared PtPdAu/C (metal ratio 1:1:1) and PdPt/C (metal ratio 4:1) catalysts are tested in DGFC. The Physical characterization of electro-catalysts by scanning electron microscope, transmission electron microscope, energy dispersive X-ray, X-ray diffraction and thermo-gravimetric analysis confirms the formation of nano-sized metal particles on carbon substrate with two prominent homogeneous bi- or tri-metallic crystal phases for PtPdAu/C. The cyclic voltammetry studies carried out for glucose (0.05 M) oxidation in (0.5 M KOH) alkaline medium shows the metal catalysts can efficiently electro-oxidize glucose. The catalysts tested as anode in a batch type DGFC using commercial activated charcoal as cathode produced peak power density of 0.52 mW cm⁻² for both PdPt/C and PtPdAu/C in 0.3 M glucose in 1 M KOH solution.     

Endurance study of a solid polymer electrolyte direct ethanol fuel cell based on a Pt–Sn anode catalyst

The performance decay of a solid polymer electrolyte direct ethanol fuel cell (DEFC) based on a Pt₃Sn₁/C anode catalyst during an endurance test has been investigated. The effect of different cell shut-down procedures on the cycled behaviour of the DEFC has been studied. To get specific insights into the degradation mechanism, polarization and ac-impedance spectroscopy studies have been carried out. These analyses have been complemented by post-operation transmission electron microscopy and X-ray diffraction studies. The combination of these techniques has allowed to get information on recoverable and unrecoverable losses. This provides a basis for further improvement of DEFC components.     

Combinatorial investigation of Pt–Ru–Sn alloys as an anode electrocatalysts for direct alcohol fuel cells

Low-temperature direct alcohol fuel cells fed with different kinds of alcohol (methanol, ethanol and 2-propanol) have been investigated by employing ternary electrocatalysts (Pt–Ru–Sn) as anode catalysts. Combinatorial chemistry has been applied to screen the 66-PtRuSn-anode arrays at the same time to reduce cost, time, and effort when we select the optimum composition of electrocatalysts for DAFCs (Direct Alcohol Fuel Cells). PtRuSn (80:20:0) showed the lowest onset potential for methanol electro-oxidation, PtRuSn (50:0:50) for ethanol, and PtRuSn (20:70:10) for 2-propanol in CV results respectively, and single cell performance test indicated that Ru is more suitable for direct methanol fuel cell system, Sn for direct ethanol fuel cell system, and 2-propanol could be applied as fuel with low platinum composition anode electrocatalyst. The single cell performance results and electrochemical results (CV) were well matched with the combinatorial electrochemical results. As a result, we could verify the availability of combinatorial chemistry by comparing the results of each extreme electrocatalysts compositions as follows: PtRuSn (80:20:0) for methanol, PtRuSn (50:0:50) for ethanol and PtRuSn (20:70:10) for 2-propanol.     

Non-stoichiometric tungsten-carbide-oxide-supported Pt–Ru anode catalysts for PEM fuel cells – From basic electrochemistry to fuel cell performance

Durability and cost of Proton Exchange Membrane fuel cells (PEMFCs) are two major factors delaying their commercialization. Cost is associated with the price of the catalysts, while durability is associated with degradation and poisoning of the catalysts, primarily by CO. This motivated us to develop tungsten-carbide-oxide (W_xC_yO_z) as a new non-carbon based catalyst support for Pt–Ru–based anode PEMFC catalyst. The aim was to improve performance and obtain higher CO tolerance compared to commercial catalysts. The performance of obtained PtRu/W_xC_yO_z catalysts was investigated using cyclic voltammetry, linear scan voltammetry and rotating disk electrode voltammetry. Particular attention was given to the analysis of CO poisoning, to better understand how W_xC_yO_z species can contribute to the CO tolerance of PtRu/W_xC_yO_z. Improved oxidation of CO_ads at low potentials (E < 0.5 V vs. RHE) was ascribed to OH provided by the oxide phase at the interfacial region between the support and the PtRu particles. On the other hand, at high potentials (E > 0.5 V vs. RHE) CO removal proceeds dominantly via OH provided from the oxidized metal sites. The obtained catalyst with the best performance (30% PtRu/W_xC_yO_z) was tested as an anode catalyst in PEM fuel cell. When using synthetic reformate as a fuel in PEMFC, there is a significant power drop of 35.3 % for the commercial 30% PtRu/C catalyst, while for the PtRu/W_xC_yO_z anode catalyst this drop is around 16 %.     

Pd decorated Co–Ni nanowires as a highly efficient catalyst for direct ethanol fuel cells

The storage and conversion of energy necessitates the use of appropriate electrochemical systems and chemical reaction catalysts. This work presents newly developed catalysts for electrooxidation of ethanol in an alkaline medium. Nanocatalysts composed of Co–Ni nanowires (Co–Ni NWs) decorated with Pd nanoparticles (Pd NPs) were made at varying metal ratios and their chemical composition and structure was investigated in detail. The synthesis involved a wet chemical reduction assisted by a magnetic field, which led to the generation of NWs, followed by the deposition of spherical Pd NPs on their surface. The best catalytic activity was obtained for the catalyst made of Co₃–Ni₇ decorated with Pd NPs, which exhibited EOR of 8003 mA/mg_Pd for only 0.86 wt% of Pd loading. The results can be explained by the synergistic effect between the morphology of the bimetallic support and the favorable interaction of oxophilic Co, Ni with catalytic Pd.     

Nanostructured Pt–Fe/C cathode catalysts for direct methanol fuel cell: The effect of catalyst composition

A series of carbon supported Pt–Fe bimetallic nanocatalysts (Pt–Fe/C) with varying Pt:Fe ratio were prepared by a modified ethylene glycol (EG) method, and then heat-treated under H₂–Ar (10 vol%-H₂) atmosphere at 900 °C. The Pt–Fe/C catalysts were characterized by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), energy dispersive analysis by X-rays (EDX) and induced coupled plasma-atomic emission spectroscopy (ICP-AES). XRD analysis shows that Pt–Fe/C catalysts have small crystalline particles and form better Pt–Fe alloy structure with Fe amount increasing. TEM images evidence that small Pt–Fe nanoparticles homogeneously deposited on carbon support and addition of Fe can effectively prevent Pt particles agglomeration. EDX and ICP-AES show that Fe precursor cannot be fully reduced and deposited on carbon support through the adopted EG reduction approach. The electrochemical surface area of Pt–Fe/C catalyst obtained through hydrogen desorption areas in the CV curve increases with Fe atomic percentage increasing from 0 to ca. 50%, and then decreases with more Fe in the Pt–Fe/C catalyst. RDE tests show that the Pt–Fe/C with a Pt:Fe ratio of 1.2:1 and an optimized lattice parameter of around 3.894 Å has the highest mass activity and specific activity to oxygen reduction reaction (ORR). As cathode catalyst, this Pt–Fe/C (Pt:Fe ratio of 1.2:1) exhibits higher direct methanol fuel cell performance at 90 °C than Pt/C and other Pt–Fe/C catalysts, this could be attributed to its smaller particle size and better Pt–Fe alloy structure.     

Ru@Pt core–shell nanoparticles for methanol fuel cell catalyst: Control and effects of shell composition

The present work presents a method to encapsulate pre-synthesised Ru nanoparticles (NPs) by Pt using a polyol method without capping agents at various pH values (6, 7, 8 and 10). The structural and surface properties of the catalysts were characterised using X-ray diffraction, transmission electron microscopy, CO stripping, and energy-dispersive X-ray spectroscopy. The studies suggest that the pH during encapsulation of Ru by Pt plays an important role in controlling of shell composition. A core–shell catalyst with an alloy shell was obtained at a pH of 6, whereas a monometallic Pt shell was obtained at a pH of 10. The core–shell catalysts gave higher steady-state current for methanol oxidation: 10-fold higher for alloy shells and 5-fold higher for Pt-enriched shells compared to the pure Pt catalyst. It is suggested that the highest catalytic enhancement of the core–shell catalysts is obtained through the bi-functional character that dominates the alloy shells rather than the ligand-effect-promoted Pt-enriched shells.     

Electrocatalysts supported on multiwalled carbon nanotubes for direct borohydride–hydrogen peroxide fuel cell

Electrocatalysts of Rh, Ru, Pt, Au, Ag, Pd, Ni, and Cu supported on multiwalled carbon nanotubes for direct borohydride–hydrogen peroxide fuel cells are investigated. Metal/γ-Al₂O₃ catalysts for NaBH₄ and H₂O₂ decomposition tests are manufactured and their catalytic activities upon decomposition are compared. Also, the effects of XC-72 and multiwalled carbon nanotube (MWCNT) carbon supports on fuel cell performance are determined. The performance of the catalyst with MWCNTs is better than that of the catalyst with XC-72 owing to a large amount of reduced Pd and the good electrical conductivity of MWCNTs. Finally, the effect of electrodes with various catalysts on fuel cell performance is investigated. Based on test results, Pd (anode) and Au (cathode) are selected as catalysts for the electrodes. When Pd and Au are used together for electrodes, the maximum power density obtained is 170.9 mW/cm² (25 °C).     

Enhanced performance of direct peroxide–peroxide fuel cells by employing three-dimensional Ni and Co@TiC nanoarrays anodes

Thorn-like Ni@TiC NAs and flake-like Co@TiC NAs electrodes without any conductive agent and binder are simply fabricated by the potentiostatic electrodeposition of Ni and Co catalysts on the TiC nanowire arrays (NAs). The electrocatalytic activity of H₂O₂ oxidation on the Ni@TiC NAs electrodes is better than that on the Co@TiC NAs electrodes. The Ni@TiC NAs electrodes demonstrate a rough surface and have many nano-needles on the rod edges, which assures the high utilized efficiency of Ni catalysts. These particular three-dimensional structures may be very suitable for H₂O₂ electrooxidation. The anodic current of Ni@TiC NAs anode reaches 0.32 A cm^?2 at 0.3 V in 1.0 M H₂O₂ + 4 M KOH solution. The DPFCs employing Ni@TiC NAs anodes display the peak power density of 30.2 mW cm^?2 and open circuit voltage of 0.90 V at 85.1 mA cm^?2 with desirable cell stability at 10 mL min^?1 flow rate and 20 °C, which is much higher than those previously reported.     

Electrodeposition of Pt–Ru and Pt–Ru–Ni nanoclusters on multi-walled carbon nanotubes for direct methanol fuel cell

A full-electrochemical method is developed to deposit three dimension structure (3D) flowerlike platinum-ruthenium (PtRu) and platinum-ruthenium-nickel (PtRuNi) alloy nanoparticle clusters on multi-walled carbon nanotubes (MWCNTs) through a three-step process. The structure and elemental composition of the PtRu/MWCNTs and PtRuNi/MWCNTs catalysts are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray polycrystalline diffraction (XRD), IRIS advantage inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The presence of Pt(0), Ru(0), Ni(0), Ni(OH)₂, NiOOH, RuO₂ and NiO is deduced from XPS data. Electrocatalytic properties of the resulting PtRu/MWCNTs and PtRuNi/MWCNTs nanocomposites for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) are investigated. Compared with the Pt/MWCNTs, PtNi/MWCNTs and PtRu/MWCNTs electrodes, an enhanced electrocatalytic activity and an appreciably improved resistance to CO poisoning are observed for the PtRuNi/MWCNTs electrode, which are attributed to the synergetic effect of bifunctional catalysis, three dimension structure, and oxygen functional groups which generated after electrochemical activation treatment on MWCNTs surface. The effect of electrodeposition conditions for the metal complexes on the composition and performance of the alloy nanoparticle clusters is also investigated. The optimized ratios for PtRu and PtRuNi alloy nanoparticle clusters are 8:2 and 8:1:1, respectively, in this experiment condition. The PtRuNi catalyst thus prepared exhibits excellent performance in the direct methanol fuel cells (DMFCs). The enhanced activity of the catalyst is surely throwing some light on the research and development of effective DMFCs catalysts.     

Effect of carbon substrate materials as a Pt–Ru catalyst support on the performance of direct methanol fuel cells

The support effect of carbon nanotubes (CNTs) for direct methanol fuel cell (DMFC) was studied using CNTs with and without defect preparation, carbon black, and fishbone-type CNTs. The Pt–Ru/defect-free CNTs afforded the highest catalytic activity of methanol oxidation reaction (MOR) in rotating disk electrode experiments and the highest performance as the anode catalysts in DMFC single cell tests with the one-half platinum loading compared to Pt–Ru/VulcanXC-72R. CO stripping voltammograms with Pt–Ru/defect-free CNTs also revealed the lowest CO oxidation potential among other Pt–Ru catalysts using different carbon support. It is thus considered that the carbon substrates significantly affect the CO oxidation activity of anode electrocatalysts in DMFC. This is ascribed to the geometrical effect that the flat interface between CNTs and metal catalysts has a unique feature, at which the electron transfer occurs, and this interface would modify the catalytic properties of Pt–Ru particles.     

Co2+-P(W3O10)43− modified activated carbon as an efficient anode catalyst for direct glucose alkaline fuel cell

Highly efficient and economical electrocatalysts is crucial to the large-scale application of direct glucose alkaline fuel cells (DGAFC). Here, we present a DGAFC with excellent performance by using a Lewis-acidic POM (Co²⁺-P(W₃O₁₀)₄^3?) modified activated carbon (AC) as anode catalyst. Three kinds of Lewis-acidic cations (Ni²⁺, Co²⁺, Fe³⁺) were introduced into polyoxometalates (POMs) and the obtained Lewis-acidic POMs were immobilized on AC anode via a simple doping and rolling method. Our results demonstrated that the catalytic activities of POMs for glucose oxidation can be remarkably improved by the introduction of Lewis acidity. The maximum power density of the DGAFC reached 35.78 W m^?2 at ambient temperature, which is almost 1.64 times higher than the bare AC control (21.88 W m^?2), considerably outperforming the performance of previously published low-temperature DGAFCs. The catalytic enhancement by the Lewis-acidic POMs is speculatively attributed to the synergic effect between two redox couples (Co²⁺/Co³⁺ and [(PW)₁₂]_Re/[(PW)₁₂]_Ox) on glucose oxidation. Our study will help develop cost-effective, high-performance and environmentally benign catalyst for glucose oxidation and electricity generation.     

Binary Pt–Pd and ternary Pt–Pd–Ru nanoelectrocatalysts for direct methanol fuel cells

Nano-sized binary and ternary alloys are synthesized by polyol process on Vulcan XC72-R support. Nanostructured binary Pt–Pd/C catalysts are prepared either by co-deposition or by depositing on each other. Ternary Pt–Pd–Ru/C catalysts are prepared by co-deposition. The structural characteristics of the nanocatalysts are examined by TEM and XRD. Their electrocatalytic activity toward methanol oxidation and CO stripping curves were measured by electrochemical measurements and compared with that of commercial Pt/C catalyst. The results show that the binary nanocatalyst prepared by depositing the Pt precursor colloids on Pd-Vulcan XC-72R are more active toward methanol oxidation than that of the co-deposited binary alloy nanocatalyst. The co-deposited ternary Pt–Pd–Ru/C nanocatalyst based membrane electrodes assembly shows higher power density compared to the binary nanocatalysts as well as commercial Pt/C catalyst in direct methanol fuel cell. Significantly higher catalytic activity of the nanocatalysts toward methanol oxidation compared to that of the commercial Pt/C is believed to be due to lower level of catalyst poisoning.