Because of the problems associated with the generation and storage of hydrogen in portable applications, the use of ammonia has been proposed for on-site production of hydrogen through ammonia decomposition. First, an analysis of the existing systems for ammonia decomposition and the challenges for this technology are presented. Then, the state of the art of the catalysts used to date for ammonia decomposition is described considering the catalysts composed of noble and non-noble metals and their combinations, as well as novel materials such as alkali metal amides and imides. The effect of the supports and promoters used is analyzed in detail, and the catalytic activity obtained is compared. An analysis of the kinetics of the reaction obtained with different catalysts is also presented and discussed, including the reaction mechanism, the determining step of the reaction, and the apparent activation energy. Finally, the structured reactors used to date for the decomposition reaction of ammonia are explored, as well as the possibilities offered by catalytic membrane reactors, which allow the on-site simultaneous production and separation of hydrogen.

Experimental and computed results show a multiband behaviour over five bands for the new fractal Sierpinski antenna. Such a behaviour is based on the self-similarity properties of the antenna's fractal shape, which might open an alternative way for designing new multiband and frequency independent antennas.Introduction: Most antenna designs are highly frequency dependent. The size of the antenna relative to the operating wavelength is the main bandwidth limiting factor. In the early 1960s, some selfscalable structures such as spirals, cones and log-periodic arrays were developed to design frequency independent antennas [2 ~ 51. The common factor is that the shape of all these structures remains invariable under some scaling transformations.

The development of better catalysts is a passionate topic at the forefront of modern science, where operando techniques are necessary to identify the nature of the active sites. The surface of a solid catalyst is dynamic and dependent on the reaction environment and, therefore, the catalytic active sites may only be formed under specific reaction conditions and may not be stable either in air or under high vacuum conditions. The identification of the active sites and the understanding of their behaviour are essential information towards a rational catalyst design. One of the most powerful operando techniques for the study of active sites is near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), which is particularly sensitive to the surface and sub-surface of solids. Here we review the use of NAP-XPS for the study of ceria-based catalysts, widely used in a large number of industrial processes due to their excellent oxygen storage capacity and well-established redox properties.

Hydrogen, produced by water splitting, has been proposed as one of the main green energy vectors of the future if produced from renewable energy sources. However, to substitute fossil fuels, large amounts of pure water are necessary, scarce in many world regions. In this work, we fabricate efficient and earth-abundant electrodes, study the challenges of using real seawater, and propose an electrode regeneration method to face undesired salt deposition. NiÀ MoÀ Fe trimetallic electrocatalyst is deposited on non-expensive graphitic carbon felts both for hydrogen (HER) and oxygen evolution reactions (OER) in seawater and alkaline seawater. Cl À pitting and the chlorine oxidation reaction are suppressed on these substrates and alkalinized electrolyte. Precipitations on the electrodes, mainly CaCO 3 , originating from seawater-dissolved components have been studied, and a simple regeneration technique is proposed to rapidly dissolve undesired deposited CaCO 3 in acidified seawater. Under alkaline conditions, NiÀ MoÀ Fe-based catalyst is found to reconfigure, under cathodic bias, into NiÀ MoÀ Fe alloy with a cubic crystalline structure and Ni : Fe(OH) 2 redeposits whereas, under anodic bias, it is transformed into a follicular Ni: FeOOH structure. High productivities over 300 mA cm À 2 and voltages down to 1.59 V@10 mA cm À 2 for the overall water splitting reaction have been shown, and electrodes are found stable for over 24 h without decay in alkaline seawater conditions and with energy efficiency higher than 61.5 % which makes seawater splitting promising and economically feasible.