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Las celdas solares sensibilizadas con colorante (DSSCs), o celdas de Grätzel, son dispositivos fotovoltaicos prometedores para la generación de energía eléctrica, debido a su bajo coste y su simplicidad de fabricación. Las DSSCs están formadas por un fotoánodo basado en una película de colorante y óxido de titanio, un electrolito que contiene pares redox yoduro/triyoduro y un contraelectrodo basado en una película delgada de platino. El rol del contraelectrodo es catalizar la reacción de reducción de yodo a yoduro del electrolito. Los materiales carbonosos se han postulado como un sustituto prometedor del platino, gracias a su elevada área superficial y conductividad eléctrica, lo que permitiría reducir el coste de fabricación de las DSSC. En este trabajo se han investigado xerogeles de carbono (CXGs) dopados con nitrógeno (N-CXG) o azufre (S-CXG) como contraelectrodos de DSSCs y se ha evaluado su comportamiento electroquímico.

In this work, carbon xerogels (CXGs) doped with nitrogen or sulfur have been investigated as DSSC counter electrodes. CXGs have been prepared by a sol–gel method from resorcinol and formaldehyde and subsequent carbonization. Nitrogen doping has been carried out by introducing melamine into the synthesis process along with resorcinol and formaldehyde, while sulfur has been incorporated by direct reaction of the carbon material with elemental sulfur. The counter electrodes for DSSCs have been prepared by airbrushing on conductive glass (fluorine-doped tin oxide, FTO), and their electrochemical behavior has been evaluated, observing that the introduction of heteroatoms such as nitrogen or sulfur leads to an improvement in efficiency compared to the undoped material thanks to a decrease in charge transfer resistance.

The only strategy for reducing fossil fuel-based energy sources is to increase the use of sustainable ones. Among renewable energy sources, solar energy can significantly contribute to a sustainable energy future, but its discontinuous nature requires a large storage capacity. Due to its ability to be produced from primary energy sources and transformed, without greenhouse gas emissions, into mechanical, thermal, and electrical energy, emitting only water as a by-product, hydrogen is an effective carrier and means of energy storage. Technologies for hydrogen production from methane, methanol, hydrocarbons, and water electrolysis using non-renewable electrical power generate CO2. Conversely, employing photoelectrochemistry to harvest hydrogen is a sustainable technique for sunlight-direct energy storage. Research on photoelectrolysis is addressed to materials, prototypes, and simulation studies. From the latter point of view, models have mainly been implemented for aqueous-electrolyte cells, with only one semiconductor-based electrode and a metal-based counter electrode. In this study, a novel cell architecture was numerically modelled. A numerical model of a tandem cell with anode and cathode based on metal oxide semiconductors and a polymeric membrane as an electrolyte was implemented and investigated. Numerical results of 11% solar to hydrogen conversion demonstrate the feasibility of the proposed novel concept.

In order to decrease the cost of direct methanol fuel cells (DMFCs), allowing the market penetration of these devices, it is necessary to reduce the costs of the components, in particular the cathode catalysts based on platinum. Another issue of these fuel cells is related to methanol crossover through the polymeric membrane, which creates a mixed potential at the cathode and decreases the overall efficiency. For this reason the development of methanol-tolerant cathode catalysts that are cheaper than Pt are of great importance in this field. In this chapter a short review analysis on Pt-free catalysts, mainly based on Pd and platinum group metal-free compounds with the general formula M–N–C (M being a transition metal such as Fe or Co) for the cathode, with good methanol-tolerance characteristics, has been carried out. Preparation procedures for the catalysts and physicochemical characteristics are reported and discussed in correlation with the DMFC performance.

It has recently been established that 1-octanethiol in the electrolyte can allow iron electrodes to be discharged at higher rates. However, the effect of thiol additives on the air electrode has not yet been studied. The effect of solvated thiols on the surface positive electrode reaction is of prime importance if these are to be used in an iron-air battery. This work shows that the air-electrode catalyst is poisoned by the presence of octanethiol, with the oxygen reduction overpotential at the air electrode increasing with time of exposure to the solution and increased 1-octanethiol concentration in the range 0–0.1 mol dm−3. Post-mortem XPS analyses were performed over the used air electrodes suggesting the adsorption of sulphur species over the catalyst surface, reducing its performance. Therefore, although sulphur-based additives may be suitable for nickel-iron batteries, they are not recommended for iron-air batteries except in concentrations well below 10 × 10−3 mol dm−3.

The oxygen reduction reaction (ORR) is one of the most important reactions in renewable energy conversion and storage devices. The full deployment of these devices depends on the development of highly active, stable, and low‐cost catalysts. Herein, a new hybrid material consisting of Na2Ta8O21−x/Ta2O5/Ta3N5 nanocrystals grown on N‐doped reduced graphene oxide is reported. This catalyst shows a significantly enhanced ORR activity by ≈4 orders of magnitude in acidic media and by ≈2 orders of magnitude in alkaline media compared to individual Na2Ta8O21−x on graphene. Moreover, it has excellent stability in both acid and alkaline media. It also has much better methanol tolerance than the commercial Pt/C, which is relevant to methanol fuel cells. The high ORR activity arises not only from the synergistic effect among the three Ta phases, but also from the concomitant nitrogen doping of the reduced graphene oxide nanosheets. A correlation between ORR activity and nitrogen content is demonstrated. Deep insights into the mechanism of the synergistic effect among these three Ta‐based phases, which boosts the ORR's kinetics, are acquired by combining specific experiments and density functional theory calculations.

Iron-based aqueous batteries, such as the iron-air and nickel-iron chemistries, are limited by passivation and hydrogen evolution at the iron anode, especially at high current densities. In this paper, strategies to minimise these issues are investigated with iron electrodes composed of 20–50 nm Fe2O3 nanoparticles produced by the Adams and Oxalate methods. The strategies include ball milling the Fe2O3 with Ketjenblack carbon to improve conductivity, addition of bismuth sulphide to the electrode and 1-octanethiol to the electrolyte, and addition of potassium carbonate as a pore-forming agent. The ratio of Fe/C in the electrode and the 1-octanethiol additive have the greatest impact on the electrode capacity. The Fe/C ratio should be below 2.0 to ensure conductivity of the discharged electrode. The presence of 1-octanethiol can protect the electrodes from passivation during discharge; at very high 2C discharge rates adding 1-octanethiol increases the electrode specific capacity from 17 to 171 mAh/gFe. The synthesis method and use of pore former do not have a significant effect on the capacity. In all electrodes, the Fe2O3 nanoparticles are in the same crystalline phase after cycling and do not undergo significant crystal growth and passivation, demonstrating the stability and suitability of these materials for iron-based batteries.

Graphene oxide nanomaterials, specifically reduced few-layer graphene oxide (rFLGO) sheets and reduced graphene oxide quantum dots (rGOQD), were explored as active and cost-effective counter electrodes for dye-sensitized solar cells (DSSCs). The synthesis strategy adopted in this work for these materials is based on an economic and easily scalable route of exfoliation of multi-wall carbon nanotubes (Top-Down approach). This allows the easy tailoring of rFLGO/rGOQD size and oxidation degree for their use as bulk material in counter electrodes, having a significant influence on the photovoltaic performance and stability. Despite the slower kinetics of carbon for the reduction of triiodide compared to platinum, they are characterized by low cost and promising stability. The electrochemical performance of DSSC assembled with either rFLGO or rGOQD at the counter electrode is correlated to their most important physico-chemical features. The domain size of graphene sheets had an important effect on the performance at the counter electrode, with quantum dots performing 13% higher efficiency than rFLGO, correlated with a higher density of active sites. Both graphene nanostructures exhibited a better stability behavior upon electrochemical cycling and seasoning of the cells as compared to Pt counter electrode.

Dye-sensitized solar cells (DSSCs) are well known as potentially low-cost photovoltaic devices [1] and are attracting great attention for their capability to provide low cost power. DSSC components include a photoanode composed of a dye-sensitized wide-bandgap semiconductor, a redox electrolyte (e.g. iodide/triiodide), and a counter electrode (CE) for reducing oxidized species in the electrolyte, generally based on a noble metal thin film. The CE collects the electrons from the external circuit to reduce the redox species used as a mediator in regenerating the sensitizer after electron injection into the photoanode. Platinum is well known as benchmark CE due to its high catalytic activity [2]. Efforts are nowadays directed to decrease the fabrication cost through alternative CE formulations. Metal-Nitrogen-Carbon (M-N-C) materials represent an attractive alternative to platinum in DSSC counter electrodes to contribute to an efficient conversion of solar energy into electricity. Despite the slower kinetics of these carbon-based materials for the reduction of triiodide compared to platinum, they are characterized by low cost. Various Fe-N-C catalysts were prepared by the so-called sacrificial support method (SSM) [3], consisting of the use of a templating agent based on silica, which is removed by hydrofluoric acid (HF) after a thermal treatment. The influence of the Fe-precursor, used for the synthesis, on the electrochemical behavior as counter electrodes in DSSC is analysed. The fabricated DSSCs were investigated by polarization experiments and electrochemical impedance spectroscopy, and compared with a cell equipped with a benchmark CE.

Las energías renovables son actualmente el modo más sostenible y limpio de producción de energía. Sin embargo, su naturaleza intermitente es uno de los factores limitantes para su mayor expansión e implementación en las redes de suministro eléctrico. Las baterías recargables son óptimas candidatas para el almacenamiento de dicha energía debido a su elevada eficiencia, su escalabilidad y flexibilidad1, siendo las baterías de flujo redox o las de plomo-ácido las más empleadas, junto con las baterías de ion litio, utilizadas principalmente en vehículos y dispositivos eléctricos. En las últimas décadas, la investigación en dispositivos de almacenamiento de energía se centra en desarrollar baterías de nueva generación con mayor potencia, mayor densidad energética y cuyos materiales sean seguros, económicos y abundantes. Las baterías metal-aire (MABs) pertenecen a esta nueva generación de baterías: con densidades de energía teóricas entre 1000 y 11000 Wh/kg (frente a los 250 Wh/kg aprox. de las baterías de ion litio), menores costes, y el uso de materiales abundantes, reciclables y sin los problemas de seguridad del litio 2. Las MABs generan electricidad a través de una reacción redox entre el metal (electrodo negativo) y el oxígeno del aire (que reacciona en el electrodo positivo), que, al no estar directamente almacenado en la celda, hace estas baterías mucho más ligeras. Existen diversos tipos de MABs, según sea el metal que empleen en el electrodo negativo: Zn, Al, Mg, Li, Na o Fe. De entre todos ellos, el sistema Fe-aire es uno de los más atractivos. El Fe es el cuarto elemento más abundante de la corteza terrestre, se produce en todo el mundo, su producción posee la menor huella de carbono de todos los metales, y, además, es fácilmente reciclable. Las baterías hierro-aire (FAB), con un voltaje de celda de 1,28 V, presentan hasta 764 Wh/kg de densidad de energía, así como la reversibilidad de la electroquímica del hierro, la simplicidad del diseño, y una gran durabil

Transition‐metal‐based materials are among the most active and durable catalysts for the effective electrocatalysis of oxygen‐related reactions. Herein, we present a study on bifunctional catalysts as air electrodes aimed at metal‐air batteries based on nickel and cobalt spinel (NiCo2O4) supported on electrospun carbon nanofibers. The physicochemical features of these transition‐metal‐based catalysts are essential for the understanding of their electrochemical activity. Results show that the major presence of oxidized Ni and Co species (Ni3+ and Co3+) produces higher activity for the oxygen evolution reaction (OER), whereas lower oxidation states of the metals (Ni2+, Co2+, Ni0 and Co0) together with the presence of N‐doped carbon lead to enhanced oxygen reduction reaction (ORR) performance. This study highlights the importance of designing catalysts in terms of crystallographic structure and proper oxidation states of the elements for maximizing their performance.

The large-scale application of polymer electrolyte membrane fuel cells (PEMFCs) requires a reduction of the costs and an improvement in performance and stability. Particularly, the automotive market needs the PEMFC works under harsh conditions (high temperature, low relative humidity, etc.), maintaining a good performance level and low degradation. These operating conditions permit to mitigate the constraints concerning the thermal and water management allowing both a simplification and a volume reduction of the system inside the car with a strong impact on costs and reliability. However, PEMFCs require the development of the components such as catalysts, ionomers and membranes with a proper stability. In this work, PtCo/KB and Pt/KB electrocatalysts were investigated with the aim of verifying the performance and stability, coupling them with an innovative reinforced Aquivion® membrane. An optimization of the catalytic ink composition was carried out, according to the different ionomers characteristics to be used in the catalytic layer in order to reduce the degradation level. The stability is assessed by considering the variations of the performance and electrochemical parameters, such as electrochemical surface area (ECSA) and mass activity (jm), at the beginning and end of accelerated stress test procedures.

Homemade non-critical raw materials such as Ni or NiCu co-catalysts were added at the photocathode of a tandem cell, constituted by photoelectrodes made of earth-abundant materials, to generate green solar hydrogen from photoelectrochemical water splitting. Oxygen evolving at the Ti-and-P-doped hematite/TCO-based photoanode and hydrogen at the cupric oxide/GDL-based photocathode are separated by an anion exchange polymer electrolyte membrane placed between them. The effect of the aforementioned co-catalysts was studied in a complete PEC cell in the presence of the ionomer dispersion and the anionic membrane to evaluate their impact under practical conditions. Notably, different amounts of Ni or NiCu co-catalysts were used to improve the hydrogen evolution reaction (HER) kinetics and the overall solar-to-hydrogen (STH) efficiency of the photoelectrochemical cells. At −0.6 V, in the bias-assisted region, the photocurrent density reaches about 2 mA cm−2 for a cell with 12 µg cm−2 of Ni loading, followed by 1.75 mA cm−2 for the cell configuration based on 8 µg cm−2 of NiCu. For the best-performing cell, enthalpy efficiency at −0.4 V reaches a first maximum value of 2.03%. In contrast, the throughput efficiency, which is a ratio between the power output and the total power input (solar + electric) provided by an external source, calculated at −1.225 V, reaches a maximum of 10.75%. This value is approximately three times higher than the best results obtained in our previous studies without the use of co-catalysts at the photocathode.