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AbstractDye-sensitized solar cells (DSSCs) rely heavily on the counter electrode for their performance, which is responsible for collecting and transferring electrons generated at the photoanode. While platinum (Pt) has traditionally been used as a counter-electrode material, its cost, limited availability, and environmental concerns make it an unsuitable option for large-scale implementation. Iron–nitrogen––carbon (Fe–N–C) catalysts are receiving increasing attention due to their high catalytic activity and low cost. This study aims to investigate the performance of Fe–N–C materials as counter electrodes in DSSCs and assess their potential as a sustainable alternative to currently used platinum. Two different Fe–N–C-based materials have been synthesized using different carbon and nitrogen sources, and their electrochemical behavior has been assessed using current–voltage curves and impedance spectroscopy. The catalyst comprised a higher amount of iron and nitrogen shows higher efficiency and lower charge-transfer resistance due to improved iodide reaction kinetics and proper stability under potential cycling. However, this catalyst shows lower stability under a passive ageing procedure, which requires further clarification. Results provide new insights into the performance of Fe–N–C-based materials in DSSCs and aid in the further development of this promising technology.

Carbon xerogels represent nowadays an outstanding alternative to carbon blacks for the preparation of efficient fuel cell electrocatalysts, due to their easily tunable and well developed mesoporous structure. To further improve both activity and durability of Pt/C catalysts, the introduction of heteroatoms (such as O, N, S, P, B, etc.) in the structure of carbon materials has been proposed. In the present work, highly mesoporous carbon xerogels (CXGs) have been subjected to a sulfurization process with elemental sulfur. The insertion of S into the carbon matrix does not compromise their mesoporous structure. Pt catalysts supported on sulfurized carbon xerogels show enhanced catalytic activity towards both the methanol electro-oxidation and the oxygen electro-reduction reactions, exceeding not only the performance of the catalyst supported on the bare xerogel, but also of the catalyst supported on a commercial carbon black. The sulfurization treatment is also effective in improving the resistance of Pt/CXG catalysts towards corrosion phenomena occurring at the fuel cell cathode. The authors wish to thank the Spanish Ministry of Economy and Competitiveness (Secretaría de Estado de I+D+I) and FEDER for financial support under the project CTQ2011-28913-C02-01. Peer reviewed

9 páginas.- 1 tabla.- 18 figuras. Several graphite-based electrodes are investigated for vanadium flow battery applications. These materials are characterized both as-received and after chemical or electrochemical treatments in order to vary the content of oxygen functional groups on the electrode surface. The surface properties of the samples are investigated by X-ray photoelectron spectroscopy. Electrochemical performance is evaluated by cyclic voltammetry and electrochemical impedance spectroscopy measurements in a three electrode half-cell. The chemical treatment with HNO3 causes a cleaning of the electrode surface from adsorbed oxygen species or labile bonded functional groups in highly graphitic samples. Whereas, carbonaceous materials characterized by smaller graphitic domains or a higher degree of amorphous carbon show an increase of oxygen functional groups upon chemical and electrochemical pre-treatments. In both cases, an increase of oxygen species content on the surface above 5% causes a decrease of electrochemical performance for the redox battery determined by an increase of ohmic and charge transfer resistance Authors from CNR-ITAE acknowledge the financial support from “Ministero dello Sviluppo Economico – Accordo di Programma MSE-CNR per la Ricerca del Sistema elettrico Nazionale”. Peer reviewed

In recent decades, significant efforts have been focused on the direct electrochemical oxidation of alcohol and hydrocarbon fuels. Organic liquid fuels are characterized by high energy density and the electromotive force associated with their electrochemical combustion to CO2 is comparable to that of hydrogen combustion to water. Among the liquid organic fuels, methanol and ethanol have promising characteristics in terms of reactivity at low temperatures, storage and handling. Compared with ethanol, methanol has the significant advantage of faster reaction kinetics and higher selectivity to CO2 formation for the electrochemical oxidation process. Highly dispersed carbon-supported bimetallic PtRu and PtSn alloy catalysts are widely recognized among the most performing anode formulations for these processes. Alloying Pt with Ru and Sn promotes oxidation of methanol and ethanol by the adsorption of OH species at considerably lower overpotentials and, thus, favoring the occurrence of a bifunctional mechanism. Furthermore, the electronic effect caused by a second metal on the neighboring Pt atoms affects the strength of CO adsorption on the catalyst surface. This causes a decrease of the coverage of poisoning CO intermediate species. Catalysts characterized by a high degree of alloying and metallic behavior on the surface appear to be very active towards methanol oxidation. However, beside the alloyed catalysts, noble metal oxides (IrOx, RuOx) and valve metal oxides (SnOx, TiOx and VOx) can be suitable promoters for methanol and ethanol oxidation in acidic environment. An effective use of such oxide promoters in combination with the alloy catalysts can provide a multifunctional catalytic system. Recent studies carried out in our laboratory have shown that IrOx can give rise to a significant promoting effect, even larger than that of RuOx, both in the case of methanol and ethanol oxidation. Whereas, the electrocatalytic enhancement produced by the valve metal oxides is generally lower than IrOx and RuOx but well evident. These results are interpreted in terms of the different water displacement mechanisms for the various oxides and the related effects on adsorbed CO removal. The effect of temperature is also discussed with reference to the coverage of adsorbed methanolic residues or change in selectivity in the case of ethanol electro-oxidation. For the ethanol oxidation process, anode catalyst selectivity towards CO2, acetic acid and acetaldehyde reaction products is discussed in relation to the alloy and oxide content in the catalyst. In particular, SnOx species on the surface of Sn-rich Pt-Sn-based electrocatalyst appear to assist the further oxidation of ethanolic adsorbates, leading to larger yields of acetic acid and CO2. In addition to the enhancement of reaction rates, there is an effect of the promoter on the stability of the bimetallic alloy as evidenced by accelerated stress tests. All these evidences seem to indicate that a multifunctional catalyst may represent a valid route to enhance performance and reliability of methanol and ethanol electro-oxidation processes at low temperature.

Xerogel–nanofiber carbon composites (XNCCs) have been easily synthesized by using a Ni catalyst supported on carbon xerogel (CXG), growing randomly oriented carbon nanofibers (CNFs) within the coralline-like structure of the xerogel (CXG). This novel composite combines the advantages of xerogel and fiber nanostructures. The interactions between these phases as well as their effect as a support on Pt electrocatalysts for the oxygen reduction reaction (ORR) have been investigated. Platinum catalysts supported on different XNCCs (varying in terms of CXG and CNF contents) as well as on bare CXG and CNFs have been synthesized using a microemulsion route. They have been characterized in terms of structure, morphology and porosity and investigated for the ORR in a half-cell configuration. The catalyst supported on the XNCC with a 44% CNF content shows the best electrochemical behavior. This catalyst formulation leads to a catalytic activity 5 times higher than that obtained on a Vulcan-based catalyst at low overpotential and 2.5 times higher at large overpotential. Accelerated degradation tests also show better stability for the composite support-based catalyst. Compared to bare CNF and CXG supports, a stabilization effect is envisaged by the presence of highly graphitic CNFs within the composite structure. CNR-ITAE authors acknowledge the financial support through the PRIN 2010-11 project “Advanced nanocomposite membranes and innovative electrocatalysts for durable polymer electrolyte membrane fuel cells (NAMED-PEM)”. CSIC-ICB authors gratefully acknowledge financial support given by the Ministry of Economy and Competitiveness through the Project CTQ2011-28913-CO2-01. Peer reviewed

A PtCu electrocatalyst was synthesized using a galvanic displacement route obtaining nanoparticles with a semi-spherical morphology and an average size of 4 nm, supported on carbon black (Vulcan). The crystallographic characterization by X-ray diffraction showed a certain degree of Pt-Cu alloying. The electrocatalytic activity of the prepared electrocatalyst for the electro-oxidation of ethanol in alkaline media was investigated. A 2-fold increase of the peak current density and a negative shift of the potential were recorded in half-cell experiments for the bimetallic catalyst compared to a commercial Pt/C. The presence of Cu promotes ethanol oxidation in alkaline electrolyte by hindering the Pt-H adsorption at low overpotentials. Additionally, the PtCu electrocatalyst was used as anode in an anion-exchange-membrane direct ethanol fuel cell (AEM-DEFC) exhibiting about 2-fold higher power density than the benchmark Pt/C.

Fuel cells are very promising technologies for efficient electrical energy generation. The development of enhanced system components and new engineering solutions is fundamental for the large-scale deployment of these devices. Besides automotive and stationary applications, fuel cells can be widely used as auxiliary power units (APUs). The concept of a direct methanol fuel cell (DMFC) is based on the direct feed of a methanol solution to the fuel cell anode, thus simplifying safety, delivery, and fuel distribution issues typical of conventional hydrogen-fed polymer electrolyte fuel cells (PEMFCs). In order to evaluate the feasibility of concrete application of DMFC devices, a cost analysis study was carried out in the present work. A 200 W-prototype developed in the framework of a European Project (DURAMET) was selected as the model system. The DMFC stack had a modular structure allowing for a detailed evaluation of cost characteristics related to the specific components. A scale-down approach, focusing on the model device and projected to a mass production, was used. The data used in this analysis were obtained both from research laboratories and industry suppliers specialising in the manufacturing/production of specific stack components. This study demonstrates that mass production can give a concrete perspective for the large-scale diffusion of DMFCs as APUs. The results show that the cost derived for the DMFC stack is relatively close to that of competing technologies and that the introduction of innovative approaches can result in further cost savings.