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(Co, S, P)-decorated multiwalled carbon nanotubes (MWCNTs) have been synthesized following a hydrothermal route as electrocatalysts to manufacture large surface area air-diffusion cathodes with carbon cloth as substrate. The enhanced electrocatalytic H2O2 production as compared with Co-free MWCNTs cathodes was demonstrated in a 2.5-L pre-pilot plant with either a RuO2-based or boron-doped diamond (BDD) anode, accumulating between 2- and 3-fold greater H2O2 contents with the catalyzed cathode. The good stability of this new material was ensured from the low Co leaching, with less than 9% Co released to solutions upon repeated usage. Aqueous solutions of the brominated organic preservative bronopol with 0.050 M Na2SO4 at pH 3.0 were comparatively treated by electro-oxidation (EO-H2O2), electro-Fenton (EF), UVA-assisted photoelectro-Fenton (PEF) and solar PEF (SPEF) at constant current density. SPEF with BDD anode and the catalyzed cathode showed the best performance, with total bronopol removal at 210 min and 94% mineralization after 360 min at 40 mA cm−2, thanks to the action of OH, BDD( OH) and sunlight. Formic acid was identified as main reaction by-product, whereas Br and N atoms were mainly converted to Br–, BrO3– and NO3–. Some unidentified organic by-product containing Br and N was formed as well.

CoS2/MWCNTs have been previously described as potentially viable catalysts to enhance the classical two-electron H2O2 production from O2 reduction reaction (ORR) for in situ water treatment, but their poor stability still limits their large-scale application. Here, the synthesis and characterization of a novel electrocatalyst made of CoSP nanoparticles supported onto multi-walled carbon nanotubes (MWCNTs) is reported. X-ray diffraction data demonstrated the much higher stability conferred upon partial sulfur substitution by phosphorus. Linear and cyclic voltammograms of CoSP/MWCNTs showed a potential window from 0.9 to 0.1 V for the ORR at pH 3.0, along with greater H2O2 production ability. Large area air-diffusion cathodes were manufactured by depositing the catalyst onto carbon paper, being further used in a pre-pilot filter-press cell containing a boron-doped diamond anode. A stable H2O2 accumulation, with maximum current efficiency of 72.0%, was found upon electrolysis of 2.5 L of 0.050 M Na2SO4 at pH 3.0 and 25 mA cm−2. As a crucial finding, Co leaching was negligible. Solutions with 20 mg L−1 of the herbicide bentazon in the same electrolyte could not be mineralized by electrochemical oxidation, whereas photoelectro-Fenton with an UVA lamp and 0.50 mM Fe2+ led to total removal of the herbicide with 77.0% mineralization.

Pt80Rh20 and Pt60Rh40 alloy catalysts were electrodeposited at constant current density from different electrolytic baths on commercial carbon paper in order to be tested for the ethanol oxidation reaction (EOR) and as anodes in a direct ethanol fuel cell (DEFC). Pt and Rh anodes prepared in the same form were also examined for comparison. As measured by energy-dispersive X-ray microanalyses, the electrodeposited Pt:Rh atomic ratios were the same as those of the precursors in the bath. X-ray diffraction showed the PtRh alloy formation with mean particle sizes of 8.3 and 7.0 nm for Pt80Rh20 and Pt60Rh40, respectively, and a Pt lattice contraction caused by the Rh addition. The X-ray photoelectron spectroscopy analyses suggested a Pt lattice strain due to Rh alloying because the Pt4f binding energies were shifted to higher values with respect to that of pure Pt. The onset potentials of the alloy oxidation, CO stripping and ethanol oxidation in the cyclic and linear sweep voltammograms indicated that Pt60Rh40 was the most active for the CO and the ethanol electrooxidation. The apparent activation energies for the EOR on that alloy were also the lowest one, in agreement with its highest activity. These results were explained by the bifunctional mechanism, assuming that Rh contributed with hydroxylated species to favor the removal of the CO-type adsorbed species on Pt sites, and by the effect of Rh on the Pt electronic structure, the lattice strain being dominating over the charge transfer between Rh and Pt. Tests carried out in single DEFCs showed the feasibility of using the Pt60Rh40 electrodeposited electrodes on carbon as the anode in a real fuel cell environment.

This paper studies the catalytic activity of Pt deposited onto Nb-doped titania supports toward the hydrogen evolution reaction (HER). New catalysts based on Nb-doped TiO2 nanoparticles (nNb-TiO2) and Nb-doped TiO2 nanotubes (nNb-TNTs), with n in the range 3–10 at % (Nb + Ti), were synthesized. The specific surface areas of nNb-TNTs were 250–300 m2g-1, about three times higher than those of nNb-TiO2. X-ray diffraction showed the Nb incorporation into the TiO2 lattice with its consequent lattice expansion. The X-ray photoelectron spectra of Pt deposited onto Nb-doped titania revealed a negative charge accumulation on Pt, thus denoting strong metal-support interaction. The electrochemical characterization in acidic media showed that Pt supported on nNb-TiO2 and nNb-TNTs presented better activity toward the HER than that of Pt deposited onto the un-doped supports and commercial Pt on carbon. The best performance was obtained with a small Nb doping of 3 at %.

[EN] IrO 2 and IrRuO x (Ir:Ru 60:40 at%), supported by 50 wt% onto titania nanotubes (TNTs) and (3 at% Nb) Nb-doped titania nanotubes (Nb-TNTs), as electrocatalysts for the oxygen evolution reaction (OER), were synthesized and characterized by means of structural, surface analytical and electrochemical techniques. Nb doping of titania significantly increased the surface area of the support from 145 (TNTs) to 260 m 2 g −1 (Nb-TNTs), which was significantly higher than those of the Nb-doped titania supports previously re- ported in the literature. The surface analytical techniques showed good dispersion of the catalysts onto the supports. The X-ray photoelectron spectroscopy analyses showed that Nb was mainly in the form of Nb(IV) species, the suitable form to behave as a donor introducing free electrons to the conduction band of titania. The redox transitions of the cyclic voltammograms, in agreement with the XPS results, were found to be reversible. Despite the supported materials presented bigger crystallite sizes than the unsupported ones, the total number of active sites of the former was also higher due to their better cat- alyst dispersion. Considering the outer and the total charges of the cyclic voltammograms in the range 0.1–1.4 V, stability and electrode potentials at given current densities, the preferred catalyst was IrO 2 sup- ported on the Nb-TNTs. The electrode potentials corresponding to given current densities were between the smallest ones given in the literature despite the small oxide loading used in this work and its Nb doping, thus making the Nb-TNTs-supported IrO 2 catalyst a promising candidate for the OER. The good dispersion of IrO 2 , high specific surface area of the Nb-doped supports, accessibility of the electroactive centers, increased stability due to Nb doping and electron donor properties of the Nb(IV) oxide species were considered the main reasons for its good performance., The authors would like to thank to EU FP7 SUSHGEN Network project No. 238678 and project ENE2017-83976-C2-1-R (AEI/FEDER, EU)). The facilities of the Centres Científics i Tecnològics de la Universitat de Barcelona (CCiT-UB) are also acknowledged for the struc- tural and surface analyses.

The potentiostatic deposition mode was used to prepare a catalyst layer of Pd on a gas diffusion substrate (carbon paper) for a polymer electrolyte membrane fuel cell (PEMFC). FE-SEM and TEM analysis revealed that innovative structures are formed on shifting the overpotential deposition from 250 mV to 500 mV: a flower like microstructure with a cubic core evolves to a cubic agglomeration of tiny spherical particles of Pd. At an intermediate overpotential, 400 mV, the deposit exhibits a cubic agglomeration with triangles coming out from their edges. The catalytic activity of these different nanostructures was evaluated towards the oxygen reduction reaction in 0.1 M H 2 SO 4 and 0.1 M HClO 4 solutions. The most active Pd nanostructure, the one obtained at 400 mV overpotential, was tested as a cathode on a H 2 |O 2 feed PEMFC to demonstrate its feasibility in a real fuel cell environment.

This work reports, for the first time, the manufacture and use of an air-diffusion cathode containing CoS2 nanoparticles to enhance the H2O2 electrogeneration. Hydrothermal synthesis allowed the formation of crystalline CoS2 with pyrite structure, either unsupported or supported on carbon nanotubes. Both kinds of catalysts were characterized by X-ray diffraction and FE-SEM combined with energy dispersive X-ray analysis. The use of carbon nanotubes as support led to a remarkable enhancement of the CoS2 stability, as deduced from cyclic voltammetry analysis. The electrochemical activity of the CoS2-based materials towards the oxygen reduction reaction (ORR) in acidic medium was examined by potentiodynamic techniques using a rotating disk electrode. Both catalysts showed activity towards the ORR, being predominant the two-electron pathway to form H2O2 as main product. A novel CoS2-on-carbon nanotubes catalyzed air-diffusion cathode, as well as an uncatalyzed one made for comparison, was manufactured to electrogenerate H2O2 under galvanostatic conditions in an undivided two-electrode cell. A concentration of 56.9 mM was found with the former cathode at constant j of 100 mA cm-2, much greater than 32.0 mM found with the uncatalyzed cathode. This informs about the high performance of the CoS2 nanoparticles to promote the two-electron ORR. Finally, the treatment of aqueous solutions of the anaesthetic tetracaine at pH 3.0 and 100 mA cm-2 by electro-oxidation and photoelectro-Fenton processes demonstrated the viability of the manufactured CoS2-based cathode for water treatment.

An oxygen diffusion cathode for a PEMFC has been prepared by directly depositing the catalyst (pure Pd) on a carbon paper support containing 5% of PTFE through an electroless deposition method. A very low-Pd loading of 0.04 mg Pd cm −2 and a higher one, containing 0.22 mg Pd cm −2 , were obtained. Two different experimental approaches were used to evaluate their catalytic activity towards the oxygen reduction reaction. The overall results revealed that the prepared catalysts exhibit a high catalytic activity, but a low efficiency on the catalyst utilization. PEMFC tests, carried out in a single cell, showed the feasibility of using the novel procedure on the preparation of oxygen diffusion cathodes, and its similar performance to a conventional one prepared by spraying the catalyst ink (Pt black) on a carbon paper support.

The present work is focused on the synthesis of new catalysts of platinum supported on carbon nanofibers and their use in PEMFC electrodes. Carbon nanofibers (CNF) and functionalized carbon nanofibers (CNF-f), synthesized via the thermocatalytic decomposition of CH 4 , were characterized, in the presence and the absence of deposited Pt, by porosimetric, SEM, TPD, and HRTEM analyses, and compared to commercial Vulcan ® XC72R carbon black (CB). CNF and CNF-f show similar BET surface areas, but smaller than that of CB, which have a large quantity of micropores. On the contrary, the microporosity in CNF and CNF-f was negligible, and the mesopores were the dominant pore structure. A single cell characterization of three catalysts Pt/CNF, Pt/CNF-f and Pt/CB was carried out, measuring the relevant kinetic parameters. The power density given by the Pt/CNF catalyst in the cathode catalyst layer was 1.5 times higher than that given by the Pt/CB catalyst at 0.600 V. It is shown when using functionalized carbon nanofibers in the anode catalyst layer, that functionalization by chemically modifying the surface of the nanofibers significantly affects the PEMFC performance.

Ternary PtRu-MoO x catalysts with various Mo compositions have been investigated as anode electrocatalytic materials for a polymer electrolyte fuel cell fed with H 2 /CO mixtures. Electrocatalysts have been prepared using a highly reproducible two step method, which allowed good control over the composition and particle size. All the prepared catalysts record a total metal loading close to 30 wt%, and a Mo load of 0, 1 and 3 wt%, supported on carbon Vulcan XC-72R, keeping the Pt/Ru atomic ratio constant. The incorporation of different amounts of Mo over the PtRu system does not modify structural characteristics such as particle size and crystal phases. However, the surface composition depends largely on the amount of Mo. An increase in the Mo loading to 3 wt% resulted in a decrease of the Pt surface area. The in situ FTIR technique has been used to investigate the CO oxidation process. The extent of CO poisoning was found to be lower for the trimetallic catalysts than for the binary catalyst at a potential below 0.25 V. The fuel cell performance was evaluated at 80 °C in a PEMFC fed with H 2 /CO (10 ppm). Polarization curves for the catalysts show that activity depends heavily on composition, with catalysts with a small amount of Mo (1 wt%) displaying the highest CO tolerance. An increase in Mo loading (3 wt%) decreases activity of the PtRuMo, although it also reduces CO poisoning. The presence of Mo 5+ species must be crucial for reducing the saturation coverage of irreversibly adsorbed CO on Pt surface atoms at very low potentials. However, the surface metal ratio of Pt/Mo (wt%) must be higher than 4, in order to keep the enough surface bare platinum sites, which are required for the dissociative adsorption of molecular H 2 .

This fundamental study deals with the electrochemical stability of several non-conventional carbon based catalyst supports, intended for low temperature proton exchange membrane fuel cell (PEMFC) cathodes. Electrochemical surface oxidation of raw and functionalized carbon nanofibers, and carbon black for comparison, was studied following a potential step treatment at 25.0 °C in acid electrolyte, which mimics the operating conditions of low temperature PEMFCs. Surface oxidation was characterized using cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Cyclic voltammograms clearly showed the presence of the hydroquinone/quinone couple. Furthermore, identification of carbonyl, ether, hydroxyl and carboxyl surface functional groups were made by deconvolution of the XPS spectra. The relative increase in surface oxides on carbon nanofibers during the electrochemical oxidation treatment is significantly smaller than that on carbon black. This suggests that carbon nanofibers are more resistant to the electrochemical corrosion than carbon black under the experimental conditions used in this work. This behaviour could be attributed to the differences found in the microstructure of both kinds of carbons. According to these results, carbon nanofibers possess a high potential as catalyst support to increase the durability of catalysts used in low temperature PEMFC applications.

In the present work, a detailed characterization of the electrochemical behavior of carbon supported Pd–Pt electrocatalysts toward CO and methanol electrooxidation in direct methanol fuel cells is reported. Technical electrodes containing an ionomer in their catalyst layer were prepared for this purpose. CO and methanol electrooxidation reactions were used as test reactions to compare the electrocatalytic behavior of bimetallic supported nanoparticles in acidic liquid electrolyte and in solid polymer electrolyte (real fuel cell operating conditions). Experimental results in both environments are consistent and show that the electrochemical behavior of carbon supported Pd–Pt depends on their composition, giving the best performance in direct methanol single fuel cell with a Pd:Pt atomic ratio of 25:75 in the catalyst.

In this work, the replacement of platinum by palladium in carbon-supported catalysts as anodes for hydrogen oxidation reaction (HOR), in proton exchange membrane fuel cells (PEMFCs), has been studied. Anodes with carbon-supported Pt, Pd, and equiatomic Pt:Pd, with various Nafion® contents, were prepared and tested in H2|O2 (air) PEMFCs fed with pure or CO-contaminated hydrogen. An electrochemical study of the prepared anodes has been carried out in situ, in membrane electrode assemblies, by cyclic voltammetry and CO electrooxidation voltammetry. The analyses of the corresponding voltammograms indicate that the anode composition influences the cell performance. Single cell experiments have shown that platinum could be replaced, at least partially, saving cost with still good performance, by palladium in the hydrogen diffusion anodes of PEMFCs. The performance of the PtPd catalyst fed with CO-contaminated H2 used in this work is comparable to Pt, thus justifying further work varying the CO concentration in the H2 fuel to assert its CO tolerance and to study the effect of the Pt:Pd atomic ratio.

This paper presents, for the first time, a five-cell polymer electrolyte membrane fuel cell (PEMFC) short stack with electrodeposited hydrogen diffusion anodes. The anodes were manufactured by means of galvanostatic pulse electrodeposition and the cathodes by air-brushing. Nafion ® 212 was employed as a solid polymer electrolyte membrane in all cases. The short stack, whose cells had an active geometric area of 14 cm 2 , was assembled and tested under different operating conditions. A peak power of about 11 W was obtained at 50 °C and atmospheric pressure using hydrogen and air feed, whereas a smaller value of 8.6 W was obtained from a five-cell short PEMFC stack with conventional hydrogen diffusion anodes under the same operating conditions. The better performance of the cells described in this paper has been assigned to the higher utilization of the platinum in the electrodeposited anodes compared to the conventional ones.

The effect of gas diffusion layer compositions on the performance of liquid feed direct methanol fuel cell has been investigated. Cathode diffusion layers consisting of carbon paper with different microporous layer compositions have been fabricated. Specifically, we have modified the carbon material used in microporous layers. Morphological and textural properties of different cathode diffusion layers were characterized and related to the performance obtained in single cell experiments. We have found that using a microporous layer made with an acetylene black instead of a furnace carbon black resulted in higher cell voltages in the entire current density region, as well as, higher maximum power density. This was attributed in first instance to the decrease of mass transfer resistance in the oxygen diffusion layer as a consequence of the microstructure of microporous layer.

Carbon nanofibers synthesized via the thermo catalytic decomposition of methane were investigated for the first time as an electrocatalyst support in PEMFC cathodes. Their textural and physical properties make them a highly efficient catalyst support for cathodic oxygen reduction in low temperature PEMFC. Tests performed in MEAs showed that Pt supported on carbon nanofibers exhibited an enhancement of ca. 94% in power density at 0.600 V, in comparison with a commercial catalyst supported on conventional carbon black, Pt/Vulcan XC-72R. Keywords: Carbon nanofibers, Catalyst support, Platinum, Electrocatalyst, Oxygen reduction reaction, PEMFC

A series of novel hybrid proton conducting membranes based on sulfonated naphthalimides and phosphotungstic acid (PTA) were prepared from N-Methyl Pyrrolidone (NMP) solutions. These hybrid organic-inorganic materials, composed of two proton-conducting components, have high ionic conductivities (9.3 × 10−2 S cm−1 at 60 °C, 15% PTA), and show good performance in H2|O2 polymer electrolyte membrane fuel cells (PEMFC), previously reported by us. Moreover, they have low methanol permeability compared to Nafion®112. In this paper we describe, for the first time, the behaviour of these hybrid membranes as electrolyte in a direct methanol fuel cell (DMFC). The maximum power densities achieved with PTA doped sulfonated naphthalimide membrane, operating with oxygen and air, were 34.0 and 12.2 mW cm−2, respectively; about the double and triple higher than those showed by the non-doped membrane at 60 °C.

Pt–Ru electrocatalysts supported on ordered mesoporous carbon (CMK-3) were prepared by the formic acid method. Catalysts were characterized applying energy dispersive X-ray analyses (EDX) and X-ray diffraction (XRD). Methanol and carbon monoxide oxidation was studied electrochemically by cyclic voltammetry, and current–time curves were recorded in a methanol solution in order to establish the activity towards this reaction under potentiostatic conditions. The physicochemical and electrochemical properties of the Pt–Ru catalysts supported on CMK-3 carbon were compared with those of electrocatalysts supported on Vulcan XC-72 and commercial catalyst from E-TEK. Additionally, in order to complete this study, Pt electrocatalysts supported on CMK-3 and Vulcan XC-72 were prepared by the same method and were used as reference. Results showed that the Pt–Ru/CMK-3 catalyst presented the best electrocatalytic activity towards the CO oxidation and, therefore, good perspectives to its application in DMFC anodes. On the other hand, the activity of the Pt–Ru/CMK-3 catalyst towards methanol oxidation was higher than that of the commercial Pt–Ru/C (E-TEK) catalyst on all examined potentials, confirming the potential of the bimetallic catalysts supported on mesoporous carbons.

This paper presents the behavior of ordered mesoporous carbon (OMC)-supported catalysts as anodes for direct methanol fuel cells (DMFC), fed with an aqueous methanol solution. OMC samples were prepared by the nanocasting method from a polymerized furan resin using mesoporous silica as a template. Pt and PtRu nanoparticles were supported on OMC with high dispersion, the particle size being 2.4 nm at PtRu loading of 15 wt.%. The resulting catalysts were analyzed using carbon monoxide stripping voltammetry, cyclic voltammetry, and chronoamperometry in three-electrode experiments and recording cell voltage vs. current density curves in practical DMFC. It was found that PtRu-catalyzed technical electrodes exhibited good activity towards methanol electrooxidation in half-cell experiments under fuel-cell-relevant conditions. Specifically, Pt85Ru15/OMC catalyst showed the highest catalytic enhancement compared to Pt/OMC for the steady-state electrooxidation of methanol at 60 °C and 0.5 V, by a factor of 22 in 2-M MeOH solution. DMFC single cells yielded an open-circuit voltage of 0.625 V at 60 °C. Polarization curves indicate that DMFC with OMC-supported Pt85Ru15 catalyst at the anode exhibited the best performance.

The effect of the cathode gas diffusion layer compositions on the performance of direct methanol fuel cells has been investigated. Morphological and textural properties of different diffusion layers have been characterized. Experiments in a single cell show that the use of a microporous layer (MPL) made with acetylene black instead of furnace carbon black results in higher cell voltages and power densities. This has been explained by a smaller mass-transfer resistance in the cathode diffusion layer due to a more suitable structure of the MPL when using acetylene black.

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