Carbon supported Pt hollow nanospheres as anode catalysts for direct borohydride-hydrogen peroxide fuel cells

The carbon supported Pt hollow nanospheres were prepared by employing cobalt nanoparticles as sacrificial templates at room temperature in aqueous solution and used as the anode electrocatalyst for direct borohydride-hydrogen peroxide fuel cell (DBHFC). The physical and electrochemical properties of the as-prepared electrocatalysts were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry (CV), chronoamperometry (CA), chronopotentiometry (CP) and fuel cell test. The results showed that the carbon supported Pt nanospheres were coreless and composed of discrete Pt nanoparticles with the crystallite size of about 2.8 nm. Besides, it has been found that the carbon supported Pt hollow nanospheres exhibited an enhanced electrocatalytic performance for BH₄⁻ oxidation compared with the carbon supported solid Pt nanoparticles, and the DBHFC using the carbon supported Pt hollow nanospheres as electrocatalyst showed as high as 54.53 mW cm⁻² power density at a discharge current density of 44.9 mA cm⁻².     

Carbon supported PtRh catalysts for ethanol oxidation in alkaline direct ethanol fuel cell

Owing to the formation of an oxametallacyclic conformation, the C–C bond cleavage is the preferential channel for the ethanol dissociation on the Rh surface, the addition of Rh to Pt can increase the CO₂ yield during the ethanol oxidation. However, in acidic media the slow oxidation kinetics of CO_ads to CO₂ limits the overall reaction rate. In this work, we prepare carbon supported PtRh catalysts and compare their catalytic activities with that of Pt/C in alkaline media. Cyclic voltammetry tests demonstrate that the Pt₂Rh/C catalyst exhibits a higher activity for the ethanol oxidation than Pt/C does. Linear sweep voltammetry tests show that the peak current density on Pt₂Rh/C is about 2.4 times of that on Pt/C. The enhanced electro-activity can be ascribed not only to the improved C–C bond cleavage in the presence of Rh, but also to the accelerated oxidation kinetics of CO_ads to CO₂ in alkaline media.     

On alloying and low-temperature stability of thin,supported PdAg membranes

Electroless plating is the technically most facile and most frequently studied method for preparation of PdAg/ceramic composite membranes. Limited high-temperature stability of such membranes requires alloying of sequentially deposited Pd and Ag layers far below their melting points, however. Here it is demonstrated that 600–800 h are needed for forming 2–4 μm thick, homogeneous alloy layers from Pd–Ag bilayers at 823 K under atmospheric H₂ pressure. This is also the time scale on which the activation energy for H₂ permeation becomes stable so that this characteristic can be employed for non-destructive, in-process monitoring of the alloying progress. High-temperature H₂ permeation rates are shown to be less well suited for this purpose because they are not sufficiently sensitive to the homogeneity of PdAg membranes. The activation energies for the well-alloyed membranes indicate that diffusion through the bulk of the PdAg layer limits H₂ permeation through these composite membranes. It is further shown that a fully alloyed Pd₇₅Ag₂₅ membrane tolerates temperature cycling under H₂ well down to 373 K while H₂/N₂ exchanges at that temperature trigger a rapid growth of the N₂ leak rate of that membrane. The defect formation is attributed to mechanical stress caused by the substantial expansion and shrinking of the alloy lattice during hydriding and dehydriding at low temperatures.     

Anode structure with double-catalyst layers for improving the direct ethanol fuel cell performance

The conventional anode design of direct ethanol fuel cells (DEFCs) usually encounter a problem on the performance stability and ethanol mass transport, i.e., ethanol crossover. Aiming to alleviate these issues, in this study, the anode with different configurations for DEFC was designed and fabricated with different catalyst layer (CL) and microporous layer (MPL) arrangements. The four types of membrane electrode assembly (MEA) is named with MEA-1 (with pretreated carbon paper (PCP) and PtCL), MEA-2 (with PCP, MPL and PtCL), MEA-3 (with PCP, MPL, PtCL and PdCL) and MEA-4 (with PCP, MPL, PtCL, MPL and PdCL). The performance, stability and ethanol crossover of MEAs were tested and measured for continuous long-term operation for 120 h, while the morphological characterization was analyzed. Based on the results, power density for each MEA decreased with time, while ethanol crossover increased gradually. The MEA-3 with additional PdCL shows a highest performance and stability about 20 W/m², and has a lowest ethanol crossover's magnitude. The highest ethanol crossover was obtained using MEA-1 at 3.7 mg/m²·s. Higher ethanol crossover had caused low stability of DEFC performance which result higher irreversible degradation. Moreover, based on characterization, elemental mapping and EDX illustrated phenomena of membrane swelling, delamination of electrode from membrane, and CL loss after stability test for 5 days for all MEAs. The significance of anode structure design was proven in this current study. The anode design of double-layered CL has potential to use at anode structure to reduce ethanol crossover rate, thereby improving DEFC performance and stability.     

A novel direct ethanol fuel cell with high power density

A new type of direct ethanol fuel cell (DEFC) that is composed of an alkaline anode and an acid cathode separated with a charger conducting membrane is developed. Theoretically it is shown that the voltage of this novel fuel cell is 2.52 V, while, experimentally it has been demonstrated that this fuel cell can yield an open-circuit voltage (OCV) of 1.60 V and a peak power density of 240 mW cm⁻² at 60 °C, which represent the highest performance of DEFCs that has so far been reported in the open literature.     

Promising anode candidates for direct ethanol fuel cell: Carbon supported PtSn-based trimetallic catalysts prepared by Bönnemann method

To find an efficient anode catalyst for ethanol electrooxidation, several trimetallic PtSnM/C (M = Ni, Co, Rh, Pd) and their corresponding bimetallic PtX/C (X = Sn, Ni, Co, Rh, Pd) catalysts were synthesized by Bönnemann's colloidal precursor method and evaluated by comparing their electrocatalytic activity using conventional electrochemical techniques. For better understanding of the catalyst deactivation during the ethanol electrooxidation, chronoamperometric test was also combined to X-ray photoelectron spectroscopy (XPS) analysis. A significant finding is that trimetallic compositions PtSnCo/C and PtSnNi/C have enhanced activity compared to that of PtSn/C, with lower onset potential for ethanol electrooxidation and notably improved peak current densities. Thus the presence of Ni and Co heteroatom seems to promote C–C bond cleavage and facilitate the removal from the catalyst surface of adsorbed intermediates. These trends are satisfactorily confirmed by testing in a direct ethanol fuel cell (DEFC), since trimetallic PtSnNi/C and PtSnCo/C anode catalysts have significantly higher overall performance and peak power density than Pt/C, PtSn/C or other trimetallic catalyst compositions PtSnRh/C or PtSnPd/C. Furthermore, the presence of Ni or Co helps to improve the weak stability of PtSn/C by providing a stronger Pt–carbon support interaction. XPS results revealed that the surface Pt/Sn atomic ratio of PtSnNi/C catalyst only slightly decreased even after 12 h at 500 mV. On the other hand, a higher concentration of oxide species appeared on the treated PtSn/C surface as a result of a high degradation of carbon support.     

Alkali doped polybenzimidazole membrane for high performance alkaline direct ethanol fuel cell

An anion exchange membrane for alkaline direct ethanol fuel cell (ADEFC) was prepared by doping KOH in polybenzimidazole (PBI) membrane. The distributions of nitrogen, oxygen and potassium in the membrane were analyzed by means of XRD and SEM-EDX, respectively. It was found that free or combined KOH molecules may exist in the PBI matrix, which was helpful for the ionic conductivity of PBI/KOH. Ethanol permeability through this membrane was much lower than that of Nafion^®. For ADEFC based on this PBI/KOH membrane electrolyte, the power density was 3 to 6 times of the results in literatures. In addition, the micro-structure of alkali doped PBI and the interaction between KOH and PBI matrix were also speculated logically.     

Modified SPEEK membranes for direct ethanol fuel cell

Membranes with low ethanol crossover were prepared aiming their application for direct ethanol fuel cell (DEFC). They were based on (1) sulfonated poly(ether ether ketone) (SPEEK) coated with carbon molecular sieves (CMS) and (2) on SPEEK/PI homogeneous blends. The membranes were characterized concerning their water and ethanol solution uptake, water and ethanol permeability in pervaporation experiments and their performance in DEFC tests. The ethanol permeabilities for the CMS-coated (180 nm and 400 nm thick layers) SPEEK were 8.5 and 3.1 × 10⁻¹⁰ kg m s⁻¹ m⁻² and for the homogeneous SPEEK/PI blends membranes with 10, 20 and 30 wt.% of PI were 4.4, 1.0 and 0.4 × 10⁻¹⁰ kg m s⁻¹ m⁻² respectively, which is 2- to 50-fold lower than that for plain SPEEK (19 × 10⁻¹⁰ kg m s⁻¹ m⁻²). Particularly the SPEEK/PI membranes had substantially better performance than Nafion 117^® membranes in DEFC tests at 60 °C and 90 °C.     

KOH modified Nafion112 membrane for high performance alkaline direct ethanol fuel cell

A polymer electrolyte membrane for alkaline direct ethanol fuel cell (ADEFC) was prepared by dipping Nafion112 membrane into KOH solution for some time at room temperature. The obtained membrane (Nafion112/KOH) exhibited higher mechanical properties and thermal stability than Nafion112 membrane. The ionic conductivity of Nafion112/KOH in 1 M, 2 M and 6 M KOH solutions was 0.011 S/cm, 0.026 S/cm, 0.032 S/cm, respectively, depending on internal OH⁻ concentration and the volume fraction of the internal aqueous phase. Single cell performance suggested that active ADEFC with Nafion112/KOH membrane can deliver a peak power density of 58.87 mW/cm² at 90 °C, meanwhile, it can stably run for at least 12 h above 0.2 V. On the other hand, Pt-free air breathing ADEFC with Nafion112/KOH can output a peak power density of 11.5 mW/cm² at 60 °C, and the corresponding lifetime was as long as 473 h above 0.3 V.     

A study on performance stability of the passive direct borohydride fuel cell

The performance stability of the direct borohydride fuel cell (DBFC) working under passive conditions was studied in this work. The stability within hours was found to be greatly affected by mass transport properties of different cell components. It was significantly improved by modifying electrode structures, increasing hydrophobicity of the cathode and using pretreated membranes. On the other hand, the stability of the DBFC cell for more than 100 h was determined by the durabilities of these cell components. The nickel anode and silver cathode were found to degrade after prolonged operations and thus the durabilities of these non-noble metal catalysts need to be improved.     

Operational characteristics of the direct methanol fuel cell stack on fuel and energy efficiency with performance and stability

This paper is presented to investigate operational characteristics of a direct methanol fuel cell (DMFC) stack with regard to fuel and energy efficiency, including its performance and stability under various operating conditions. Fuel efficiency of the DMFC stack is strongly dependent on fuel concentration, working temperature, current density, and anode channel configuration in the bipolar plates and noticeably increases due to the reduced methanol crossover through the membrane, as the current density increases and the methanol concentration, anode channel depth, and temperature decreases. It is, however, revealed that the energy efficiency of the DMFC stack is not always improved with increased fuel efficiency, since the reduced methanol crossover does not always indicate an increase in the power of the DMFC stack. Further, a lower methanol concentration and temperature sacrifice the power and operational stability of the stack with the large difference of cell voltages, even though the stack shows more than 90% of fuel efficiency in this operating condition. The energy efficiency is therefore a more important characteristic to find optimal operating conditions in the DMFC stack than fuel efficiency based on the methanol utilization and crossover, since it considers both fuel efficiency and cell electrical power. These efforts may contribute to commercialization of the highly efficient DMFC system, through reduction of the loss of energy and fuel.     

Synthesis of PdNi catalysts for the oxidation of ethanol in alkaline direct ethanol fuel cells

Carbon-supported PdNi catalysts for the ethanol oxidation reaction in alkaline direct ethanol fuel cells are successfully synthesized by the simultaneous reduction method using NaBH₄ as reductant. X-ray diffraction characterization confirms the formation of the face-centered cubic crystalline Pd and Ni(OH)₂ on the carbon powder for the PdNi/C catalysts. Transmission electron microscopy images show that the metal particles are well-dispersed on the carbon powder, while energy-dispersive X-ray spectrometer results indicate the uniform distribution of Ni around Pd. X-ray photoelectron spectroscopy analyses reveal the chemical states of Ni, including metallic Ni, NiO, Ni(OH)₂ and NiOOH. Cyclic voltammetry and chronopotentiometry tests demonstrate that the Pd₂Ni₃/C catalyst exhibits higher activity and stability for the ethanol oxidation reaction in an alkaline medium than does the Pd/C catalyst. Fuel cell performance tests show that the application of Pd₂Ni₃/C as the anode catalyst of an alkaline direct ethanol fuel cell with an anion-exchange membrane can yield a maximum power density of 90 mW cm⁻² at 60 °C.     

Highly efficient carbon hybrid supported catalysts using nano-architecture as anode catalysts for direct methanol fuel cells

PtCo based nanoparticles in alloy structure were synthesized using the microwave-assisted reduction method. These nanoparticles were deposited on different carbon supporting materials. Here, these supporting materials such as rGO (reduced graphene oxide), rGO-VC (vulcan carbon) and AC-VC (activated carbon-vulcan carbon) were used and the methanol oxidation reaction (MOR) activity of single carbon support and hybrid carbon support material in the presence of PtCo nanoparticles were investigated at the same molar concentration. The average particle size of the PtCo nanoparticles detected in the TEM analysis was found to be 3.55 ± 0.64 nm. The MOR activity of the PtCo@rGO, PtCo@rGO-VC and PtCo@AC-VC catalysts was determined, where the anodic peak current of PtCo@AC-VC was determined as 73 mA/cm². It has been observed that PtCo nanoparticles with carbon hybrid support structures are more advantageous than single support structures due to the synergistic effect between carbon support structures and providing a larger surface area. Compared to previous studies, the MOR activity of PtCo@AC-VC is quite high. It can be stated that PtCo@AC-VC has comparable catalytic activity compared to the commercial available anode catalyst.     

Nickel/gadolinium-doped ceria anode for direct ethanol solid oxide fuel cell

This report investigates the properties of nickel/gadolinium-doped ceria (Ni/GDC) as anode material for bio-ethanol fueled SOFC. The Ni/GDC cermets with 18 and 44 wt.% Ni were prepared by a hydrothermal method. Ethanol decomposition, steam reforming, and partial oxidation of ethanol were studied using a fixed-bed reactor at 1123 K. Carbon was formed only under dry ethanol for both catalysts. The addition of water or oxygen to the feed inhibited the formation of carbon. Ni/GDC was used as the anode current collector layer and as a catalytic layer in single cells tests. No deposits of carbon were detected in single cells with Ni/GDC catalytic layer after 50 h of continuous operation under direct (dry) ethanol. This result was attributed to the catalytic properties of the Ni/GDC layer and the operation mechanism of gradual internal reforming, in which the oxidation of hydrogen provides the steam for ethanol reforming, thus avoiding carbon deposition.     

Methanol-tolerant carbon aerogel-supported Pt-Au catalysts for direct methanol fuel cell

Pt-Au nanoparticles supported on carbon aerogel, namely 2:1 has been synthesized by the microwave-assisted polyol process. The structure of Pt-Au nanoparticles is characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The electrochemical property of Pt-Au catalysts for methanol oxidation is evaluated by cyclic voltammetry (CV). The results show that Au-modified Pt catalysts exhibit a high methanol tolerance and improved electrochemical catalytic activity, suggesting that carbon aerogel supported Pt-Au catalysts are better catalysts for the electrochemical oxidation of methanol than conventional Pt catalysts.     

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.     

Effect of addition of rhenium to Pt-based anode catalysts in electro-oxidation of ethanol in direct ethanol PEM fuel cell

Breaking of C–C bond at low temperature to completely oxidize ethanol in direct ethanol fuel cell (DEFC) is the limiting factor for the development of DEFC as alternative source of power in portable electronic equipment. Binary and ternary Pt based catalysts with addition of Re, Pt–Re/C (20:20), Pt–Sn/C (20:20), Pt–Re–Sn/C (20:10:10) and Pt–Re–Sn/C (20:5:15) catalysts were prepared from their precursors by co-impregnation reduction method to study electro-oxidation of ethanol in DEFC. The electrocatalysts characterized by transmission electron microscope, scanning electron microscope, energy dispersive X-ray, and X-ray diffraction shows the formation of above mentioned bi- and tri-metallic catalyst with size ranges from 6 to 16 nm. Electrochemical analyses by cyclic voltammetry, linear sweep voltammetry and chronoamperometry show that Pt–Re–Sn/C (20:5:15) gives higher current density compared to that of Pt–Re/C (20:20) and Pt–Sn/C (20:20). The addition of Re to Pt–Sn/C is conducive to electro-oxidation of ethanol in DEFC. The power density obtained using Pt–Re–Sn/C(20% Pt, 5% Re, 15% Sn by wt) (30.5 mW/cm²) as anode catalyst in DEFC is higher than that for Pt–Re–Sn/C(20% Pt, 10% Re, 10% Sn by wt) (19.8 mW/cm²), Pt–Sn/C (20% Pt, 20% Sn by wt) (22.4 mW/cm²) and Pt–Re/C (20% Pt, 20% Re by wt) (9.8 mW/cm²) at 100 °C, 1 bar, with catalyst loading of 2 mg/cm² and 5 M ethanol as anode feed.     

Different anode catalyst for high temperature polybenzimidazole-based direct ethanol fuel cells

Five different bimetallic catalyst formulations (PtRu/C, PtSn/C, PtW/C, PtRh/C and PtOs/C) were prepared by reduction with sodium borohydride, and physico-chemically characterized by X-Ray Diffraction, Transmission Electron Microscopy, Temperature Programmed Reduction and X-Ray Photoelectron Spectroscopy. It was observed that in the case of the PtRu/C and PtRh/C a large fraction of the second metal enters the platinum lattice structure. The remaining metal, and in those catalysts in which no alloy was formed, its deposition was in a mixed metallic (Os) and/or oxide form, as TPR and XPS results displayed. Crystal sizes were in the range 3–5 nm, except for the case of the PtW/C in which there was a large agglomeration of platinum particles, as the TEM images confirmed. Electrochemical half-cell tests demonstrated the better performance of these bimetallic catalysts in terms of ethanol oxidation, with lower onset potential and larger current densities, particularly in the case of the PtOs/C, PtRu/C and PtRh/C materials, and to a lower extent in the case of the PtSn/C. Actual fuel cell tests at high temperature (150 and 200 °C) confirmed the beneficial effects of increasing the temperature in terms of cell performance, with an increase in the performance, particularly in the cases of PtOs/C and PtRu/C. Finally, the product distribution was also assessed, observing a large conversion to CO₂ by operating at high temperatures, particularly for PtRh/C at low current density, and for Pt/C at high current density (up to 35%), although acetaldehyde remained as the main oxidation product for all the catalysts.     

Methanol tolerant Pd-Based carbon supported catalysts as cathode materials for direct methanol fuel cells

Alcohol crossover and the sluggish oxygen reduction reaction (ORR) at the cathode are the main practical drawbacks of direct methanol fuel cells (DMFCs). The current work attempts to disclose and compare several strategies to study the factors affecting the performance of DMFCs. With this end in view, kinetic and mechanistic parameters of several carbon-supported palladium–based electrocatalysts towards the ORR in 0.5 M H₂SO₄ and in 0.5 M H₂SO₄ + X M CH₃OH (X = 0.5–3.0), were investigated applying rotating-ring disc electrode (RRDE) technique. Several procedures were employed and compared to scrutinize the data acquired during ORR in presence and absence of CH₃OH. Furthermore, the first derivative method as practical way to determine the methanol tolerance is reported. It was found that PdFeIr/C exhibits the highest catalytic performance for the ORR in the absence and the presence of methanol, in comparison to PdIr/C, PdFe/C and Pd/C electrocatalysts.