Improved performance using tungsten carbide/carbon nanofiber based anode catalysts for alkaline direct ethanol fuel cells

Tungsten carbides (WC) nanoparticles on platelet type-carbon nanofibers (p-CNFs) catalysts have been synthesized for alkaline direct ethanol fuel cells (ADEFC). Physical properties of WC/CNFs samples with various WC contents are analyzed by transmission electron microscope (TEM), thermal gravimetric analysis (TGA) and nitrogen isotherm (BET). The WC/CNFs catalysts showed an improved kinetics for the ethanol oxidation than p-CNFs did. It indicates that the significant increase in the catalytic activity for ethanol oxidation on WC/CNFs than p-CNFs did due to the synergistic structural effect between WC nanoparticles and the p-CNFs supports. WC/CNFs also showed good performances in ADEFC single cells. The maximum current density of P4W3 and P4W4 was 9.0 and 4.4 mA cm⁻², respectively. These catalysts can be used as the ethanol oxidation in direct ethanol fuel cells in alkaline media.     

Enhanced efficiency of organic photovoltaic cells using solution-processed metal oxide as an anode buffer layer

We report performance improvement of organic (P3HT:PCBM) photovoltaic cell by introducing a solution-based WO_x anode buffer layer, between the PH500 conducting polymer and the active layer. By introducing a solution-based WO_x on PH500, the cell efficiency increases by 13% compared to that of the organic photovoltaic cell with only PH500. The organic cell exhibits J_SC of 12.31 mA/cm², V_OC of 0.61 V, FF of 58.22%, and the power conversion efficiency of 4.35%. The improved cell performance is due to effective hole collection injected from electron donors (P3HT) in P3HT:PCBM active layer by forming WO_x nanoparticle on the conducting anode.     

High-performance anode for solid acid fuel cells prepared by mixing carbon substances with anode catalysts

Optimization of Pt-based electrode structure is a key to enhance power generation performance of fuel cells and to reduce the Pt loading. This paper presents a new methodology for anode fabrication for solid acid fuel cells (SAFCs) operating at ca. 200 °C. Our membrane electrode assembly for SAFCs consisted of a CsH₂PO₄/SiP₂O₇ composite electrolyte and Pt-based electrodes. To obtain the anode, a commercial Pt/C catalyst and carbon substance, such as carbon black and carbon nanofiber, were mixed. The composite anode with Pt loading = 0.5 mg cm⁻² demonstrated superior current-voltage characteristics to a benchmark Pt/C anode with Pt loading = 1 mg cm⁻². We consider that the mixing of Pt/C catalyst and carbon substrate facilitated H₂ mass transfer and increased the number of active sites.     

A novel proton exchange membrane fuel cell anode for enhancing CO tolerance

A novel proton exchange membrane fuel cell (PEMFC) anode which can facilitate the CO oxidation by air bleeding and reduce the direct combustion of hydrogen with oxygen within the electrode is described. This novel anode consists of placing Pt or Au particles in the diffusion layer which is called Pt- or Au-refined diffusion layer. Thus, the chemical oxidation of CO occurs at Pt or Au particles before it reaches the electrochemical catalyst layer when trace amount of oxygen is injected into the anode. All membrane electrode assemblies (MEAs) composed of Pt- or Au-refined diffusion layer do perform better than the traditionary MEA when 100 ppm CO/H₂ and 2% air are fed and have the performance as excellent as the traditionary MEA with neat hydrogen. Furthermore, CO tolerance of the MEAs composed of Au-refined diffusion layer was also assessed without oxygen injection. When 100 ppm CO/H₂ is fed, MEAs composed of Au-refined diffusion layer have the slightly better performance than traditionary MEA do because Au particles in the diffusion layer have activity in the water gas shift (WGS) reaction at low temperature.     

Carbon nanotube/polyaniline composite as anode material for microbial fuel cells

A carbon nanotube (CNT)/polyaniline (PANI) composite is evaluated as an anode material for high-power microbial fuel cells (MFCs). Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) are employed to characterize the chemical composition and morphology of plain PANI and the CNT/PANI composite. The electrocatalytic behaviour of the composite anode is investigated by means of electrochemical impedance spectroscopy (EIS) and discharge experiments. The current generation profile and constant current discharge curves of anodes made from plain PANI, 1 wt.% and 20 wt.% CNT in CNT–PANI composites reveal that the performance of the composite anodes is superior. The 20 wt.% CNT composite anode has the highest electrochemical activity and its maximum power density is 42 mW m⁻² with Escherichia coli as the microbial catalyst. In comparison with the reported performance of different anodes used in E. coli-based MFCs, the CNT/PANI composite anode is excellent and is promising for MFC applications.     

Two-layer anode electrode with non-noble catalysts as CO tolerant structure for PEM fuel cell

Many studies on platinum-based dual-metal or multi-metal alloys catalysts are underway to strengthen the resistance of the anode catalyst layer against hydrogen fuel contamination, especially carbon monoxide. The change in the structure of the catalyst layer can also be a new and effective way to remove Carbon Monoxide. In the few multi-layer electrode structure reported cases, ruthenium metal is used in the outer layer, for sieving the Carbon Monoxide molecules before reaching to the Pt/C catalyst in the inner layer. In this study, we make two-layer catalyst anode electrode with SnO₂/C and Sn₂₀.Co₈₀/C in outer layer and commercial Pt/C in inner layer. The performance of these electrodes for Carbon Monoxide electro-oxidation evaluate by cyclic voltammetry and the results compare with the activity of an electrode with commercial platinum catalyst only. Our two-layer electrodes have the same efficiency as commercial platinum electrodes and even more for pure hydrogen oxidation and much better activity for pure Carbon Monoxide electro-oxidation at low potentials, in half-cell media. These electrodes have better stability for Carbon Monoxide oxidation after 100 cycles along with Carbon Monoxide gas bubbling and electrode with bi-metal catalyst in outer layer has almost no loss in performance.     

Investigation of tungsten carbide supported Pd or Pt as anode catalysts for PEM fuel cells

In this contribution, we present results of electrochemical characterization of prepared tungsten carbide supported palladium and platinum and Vulcan XC-72 supported palladium. These catalysts were employed as anode catalysts in PEMFC and results are compared to commercial platinum catalyst. Platinum seems to be irreplaceable as a proton exchange membrane fuel cell (PEMFC) catalyst for both the anode and the cathode, yet the high price and limited natural resources are holding back the commercialization of the PEMFCs. Tungsten carbide is recognized as promising catalyst support having the best conductivity among interstitial carbides. Higher natural resources and significantly lower price make palladium good candidate for replacement of the platinum catalyst. The presented results show that all prepared catalysts are very active for the hydrogen oxidation reaction. Linear sweep voltammetry curves of Pd/C and Pd/WC show existence of peaks at 0.07 V vs. RHE, which is assigned to absorbed hydrogen. H₂|Pd/WC|Nafion117|Pt/C|O₂ fuel cell has almost the same efficiency and similar power output as commercial platinum catalyst.     

Particle size dependence of CO tolerance of anode PtRu catalysts for polymer electrolyte fuel cells

An anode catalyst for a polymer electrolyte fuel cell must be CO-tolerant, that is, it must have the function of hydrogen oxidation in the presence of CO, because hydrogen fuel gas generated by the steam reforming process of natural gas contains a small amount of CO. In the present study, PtRu/C catalysts were prepared with control of the degree of Pt-Ru alloying and the size of PtRu particles. This control has become possible by a new method of heat treatment at the final step in the preparation of catalysts. The CO tolerances of PtRu/C catalysts with the same degree of Pt-Ru alloying and with different average sizes of PtRu particles were thus compared. Polarization curves were obtained with pure H₂ and CO/H₂ (CO concentrations of 500-2040 ppm). It was found that the CO tolerance of highly dispersed PtRu/C (high dispersion (HD)) with small PtRu particles was much higher than that of poorly dispersed PtRu/C (low dispersion (LD)) with large metal particles. The CO tolerance of PtRu/C (HD) was higher than that of any commercial PtRu/C. The high CO tolerance of PtRu/C (HD) is thought to be due to efficient concerted functions of Pt, Ru, and their alloy.     

Platinum-antimony doped tin oxide nanoparticles supported on carbon black as anode catalysts for direct methanol fuel cells

Antimony doped tin oxide supported on carbon black (ATO/C) has been synthesized using an in situ co-precipitation method, and platinum-ATO/C nanoparticles have been prepared using a consecutive polyol process to enhance the catalyst activity for the methanol oxidation reaction. The Pt-ATO/C electrocatalyst is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microcopy (SEM), energy dispersive X-ray spectroscopy (EDS) and cyclic voltammetry. The Pt-ATO/C catalyst exhibits a relatively high activity for the methanol oxidation reaction compared to Pt-SnO₂/C or commercial Pt/C catalyst. This activity can be attributed to the high electrical conductivities of the Sb-doped SnO₂, which induces the electronic effects with Pt catalysts. Pt-ATO/C is a promising methanol oxidation catalyst with high activity for the reaction in direct methanol fuel cells.     

Investigation of the anode reactions in solid oxide electrolyte based carbon fuel cells

The anode reactions of solid oxide electrolyte based carbon fuel cells (SO-CFCs) are explored by comparing the electrochemical behaviors of SO-CFCs under varying anode carrier gas flow rates (FAr) and at different contact modes. The electrochemical performance of four raw carbon fuels, including a graphitic carbon (GC), two coals (lignite CF and anthracite YQ) and an activated carbon (AC), and their chars is tested to investigate the influence of carbon fuel properties on the cell performance. The results show that CO electro-oxidation and C-CO₂ gasification were main anode reactions. The direct carbon electro-oxidation is insignificant under high F_Ar. Polarization performance of the chars under high F_Ar was similar with that of 5–10% CO. It is also concluded that the cell performance is greatly dependent on the carbon fuel gasification reactivity with CO₂. Thermal pretreated AC displays the best durability performance for its stable and moderate CO₂ gasification rate. Additionally, the coal ash does not affect the cell performance significantly.     

Ultrahigh figure-of-merit for hydrogen generation from sodium borohydride using ternary metal catalysts

We report further increase in the figure-of-merit (FOM) for hydrogen generation from NaBH₄ than reported in an earlier paper [1], where a sub-nanometer layer of metal catalysts are deposited on carbon nanotube paper (CNT paper) that has been functionalized with polymer-derived silicon carbonitride (SiCN) ceramic film. Ternary, Ru-Pd-Pt, instead of the binary Pd-Pt catalyst used earlier, together with a thinner CNT paper is shown to increase the figure-of-merit by up to a factor of six, putting is above any other known catalyst for hydrogen generation from NaBH₄. The catalysts are prepared by first impregnating the functionalized CNT-paper with solutions of the metal salts, followed by reduction in a sodium borohydride solution. The reaction mechanism and the catalyst efficiency are described in terms of an electric charge transfer, whereby the negative charge on the BH₄⁻ ion is exchanged with hydrogen via the electronically conducting SiCN/CNT substrate [1].     

Ultra-thin metal layer passivation of the transparent conductive anode in organic solar cells

Efficiency of organic solar cells shows a strong improvement when the transparent conductive anode (indium tin oxide—ITO, aluminium-doped zinc oxide—AZO, fluorine-doped tin oxide—FTO), is covered with an ultra-thin metallic film. It is shown that the best results are achieved with a gold film (0.5 nm). The efficiency of the solar cells using AZO or FTO is improved up to one order of magnitude, while in the case of ITO it is at least 50%. It is shown that if the matching between the work function of the anode and the highest occupied molecular orbital (HOMO) of the organic electron donor is the most important factor limiting the hole transfer efficiency, others factors such as transparent conductive oxide (TCO) surface roughness and adhesion of the organic layer are also key factors.     

Impact of anode catalyst loadings and carbon supports to CO contamination in PEM fuel cells

Hydrogen fuel quality is important for the successful commercialization of PEM (proton exchange membrane) fuel cell vehicles (FCVs) because impurities can adversely affect the normal operation of FCVs both immediately and during their lifetime operation. Among the impurities specified in H₂ quality standards, CO (carbon monoxide) is known to have one of the greatest impacts on fuel cells because of the immediate decrease in performance at low concentrations. CO impurity levels of only 0.2 ppm, as specified in the H₂ quality standards, were found in H₂ refueling stations with adverse impacts to PEM fuel cell operation. In this study CO impurity testing was conducted on single cells based on an extensive design of experiments (DOE) that was performed using several MEAs with two levels of anode platinum loading (0.05 mg_Pt/cm² and 0.1 mg_Pt/cm²) and two different materials for platinum carbon support (Highly Graphitized Carbon and High Surface Area Carbon). Contamination testing for each MEA design configuration was performed at four different CO impurity levels (0.1 ppm, 0.2 ppm, 0.3 ppm, and 0.4 ppm) and three current densities (0.1 A/cm², 1.0 A/cm², and 1.7 A/cm²) at each impurity level. The results indicate that the most significant factor to improve MEA tolerance to CO contamination was the choice of carbon support. The use of high surface area carbon had an even greater impact than the use of higher Pt loading, which suggests paths toward addressing CO contamination that avoid higher catalyst cost.     

Enhanced performance of microbial fuel cells by electrospinning carbon nanofibers hybrid carbon nanotubes composite anode

A novel carboxylated multiwalled carbon nanotubes/carbon nanofibers (CNTs/CNFs) composite electrode was fabricated by electrospinning. Heat pressing process was applied to improve the interconnection of fiber aggregates, mechanical stability and reduce the contact resistance. Optimal dose of carbon nanotubes was selected to fabricate the anode in microbial fuel cells after comparing with plain electrospinning CNFs anode and commercial carbon felt (CF) anode. As a result, the optimal anode delivered a maximum power density of 362 ± 20 mW m⁻², which is 110%, 122% higher than that of carbon nanofibers and carbon felt anodes. Cyclic voltammograms, Tafel and electrochemical impedance spectroscopy tests also verified that the prepared electrode has largest catalytic current (148 μA cm⁻²) and exchange current density i₀ (6.3 × 10⁻⁵ A cm⁻²), as well as smallest internal resistance (∼40 Ω). The as-prepared anode exhibited a better conductivity, excellent biocompatibility, good hydrophilicity and superior electrocatalytic activity, which was not only beneficial to the attachment and reproduction of microorganisms, but also promoted extracellular electron transfer between bacteria cells and the anode. This result shows that electrospinning has a promising perspective in fabricating high performance electrodes for microbial fuel cells.     

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.     

Supported bimetallic nanoparticles as anode catalysts for direct methanol fuel cells: A review

Direct methanol fuel cell (DMFC) is an environment friendly energy source that transforms chemical energy of methanol oxidation into electrical energy. The Pt- and non-Pt based bimetallic nanoparticles (BMNPs) with electrocatalyst support materials are employed as anode electrocatalysts for methanol oxidation. These supported BMNPs have drawn prominent consideration due to their incredible physical and chemical properties. This article reviews the advancements in the field of supported BMNPs of varied structures, compositions and morphologies, using innumerable carbonaceous support materials such as carbon black, carbon nanotubes, carbon nanofibers, graphene, mesoporous carbon as well as non-carbonaceous supports like inorganic oxides, graphitic carbon nitride, metal nitrides, conducting polymers and hybrid support materials. The performance of electrocatalysts on the basis of support material, structure, composition and morphology of BMNPs, and pros and cons of various support materials have been discussed.     

Surface modified Ni foam as current collector for syngas solid oxide fuel cells with perovskite anode catalyst

Cu surface modified nickel foam is obtained by heating copper coated nickel foam in a reducing atmosphere. La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCM) perovskite oxide is prepared using a sol–gel combustion method. The modified foams and LSCM powders exhibit excellent resistance to carbon deposition in syngas at high temperatures. Furthermore, Cu modified foams show better mechanical strength compared to bare Ni foam, which readily cracks after exposure to syngas at high temperature. LSCM retains its perovskite structure during exposure to syngas or carbon monoxide at 900 °C for 10 h. Cu surface modified Ni foam current collector demonstrates good chemical compatibility with LSCM in syngas atmosphere at high temperature. Syngas solid oxide fuel cells (SOFCs) are assembled using Cu modified Ni foam anode current collector, LSCM anode catalyst, YSZ electrolyte, and porous Pt cathode. The present fuel cell provides similar power density to one with gold anode current collector and has excellent stability during operation at 900 °C.     

Effect of anode and Boudouard reaction catalysts on the performance of direct carbon solid oxide fuel cells

Tubular electrolyte-supporting solid oxide fuel cells directly operated on carbon fuel were fabricated and tested. Gadolinia doped ceria (GDC) mixed with silver was used as the anode to catalyze the electrochemical oxidation of CO while Fe-based catalyst was loaded on the carbon fuel to enhance the Boudouard reaction. The performance was significantly improved, with a maximum power density of 45 mW cm⁻², 10 times higher than that of the cell without any catalyst. Impedance measurements showed that the polarization resistance was decreased by tens of times through applying catalysts in the cell. An operation life of 10 h was observed at a constant current of 70 mA. The mechanism of the cell reaction was analyzed.     

A new Gd-promoted nickel catalyst for methane conversion to syngas and as an anode functional layer in a solid oxide fuel cell

The effect of lanthanide promoters on a Ni-Al₂O₃ catalyst for methane partial oxidation, steam reforming and CO₂ reforming at 600-850 °C is systematically investigated. The promoters include La₂O₃, CeO₂, Pr₂O₃, Sm₂O₃ and Gd₂O₃. GdNi-Al₂O₃ shows comparable catalytic activity to LaNi-Al₂O₃ and PrNi-Al₂O₃ but higher activity than CeNi-Al₂O₃ and SmNi-Al₂O₃ for all three reactions. The O₂-TPO results show that GdNi-Al₂O₃ possesses the best coke resistance among those tested. It also displays good stability at 850 °C for 300 h. Raman spectroscopy indicates that the addition of lanthanide promoters can reduce the degree of graphitization of the carbon deposited on Ni-Al₂O₃. The GdNi-Al₂O₃ is further applied as an anode functional layer in solid-oxide fuel cells operating on methane. The cell yields peak power densities of 1068, 996 and 986 mW cm⁻² at 850 °C, respectively, for operating on methane-O₂, methane-H₂O and methane-CO₂ gas mixtures, which is comparable to operating on hydrogen fuel. GdNi-Al₂O₃ is promising as a highly coking-resistant catalyst layer for solid-oxide fuel cells.     

The effect of composition of Ni-supported Pt-Ru binary anode catalysts on ethanol oxidation for fuel cells

The effect of the composition of a platinum-ruthenium (Pt-Ru) binary catalyst on a Ni-support for the anodic oxidation of ethanol in aqueous alkaline media has been studied. Co-deposition of nano-crystallites of a Pt-Ru electrocatalyst of varying composition, has been made on Ni-supports by galvanostatic deposition from precursor salt solutions of suitable composition, without using any capping agent. Conjugated scanning electron microscopic-energy dispersion X-ray spectroscopic studies reveal slight alteration of the atomic composition of the electrocatalyst on the electrode surface to that in the deposition bath, as expected. The excellent electrocatalytic activities of the electrodes for the anodic oxidation of ethanol have been found to depend on the mutual variation of composition of the binary catalyst. From cyclic voltammetric, chronopotentiometric, steady state polarization and electrochemical ac impedance studies, it can be inferred that the best catalytic activity of a Pt-Ru binary electrocatalyst on a Ni-support for anodic oxidation of ethanol contains 32–47 at.% of Ru. Moreover, the composition for the best activity within the said range is tilted towards more at.% of Ru when high current density is drawn whereas the composition containing a lower at.% of Ru is favoured when the current density drawn is relatively low.