Chemical kinetics in solar to chemical energy conversion: The photoelectrochemical oxygen transfer reaction

After introducing the basic aspects of the photoelectrochemical processes for the oxygen transfer reaction, we present the simplest kinetics models that have been built to represent the dynamics of light-induced redox reactions. Additionally, we discuss the basic chemical kinetics formalism usedin photocatalysis and photoelectrochemistry, where interplay between the oxidation process and nonequilibrium adsorbed states is considered. We also comment about the experimental developments related to the treatment of wastewater with electricity or H2 generation. Finally, we discuss the need to measure reaction rates to determine and compare the physicochemical parameters describing thechemical interactions during photoelectrochemical processes, in order to understand these reactive systems and apply them to new challenges related to the environment and energy.Fil: Vargas Balda, Ronald Eduardo. Universidad Simon Bolivar.; Venezuela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Carvajal, David. Universidad Simon Bolivar.; VenezuelaFil: Madriz Ruiz, Lorean Mercedes. Universidad Simon Bolivar.; Venezuela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Scharifker, Benjamín R.. Universidad Simon Bolivar.; Venezuela. Universidad Metropolitana.; Venezuel

Diffuse neutron reflectivity and AFM study of interface morphology of an electro-deposited Ni/Cu film

We present a detailed study of the interface morphology of an electro-deposited (ED) Ni/Cu bilayer film by using off-specular (diffuse) neutron reflectivity technique and Atomic Force Microscopy (AFM). The Ni/Cu bilayer has been electro-deposited on seed layers of Ti/Cu. These two seed layers were deposited by magnetron sputtering. The depth profile of density in the sample has been obtained from specular neutron reflectivity data. AFM image of the air-film interface shows that the surface is covered by globular islands of different sizes. The AFM height distribution of the surface clearly shows two peaks [Fig. 3] and the relief structure (islands) on the surface in the film can be treated as a quasi-two-level random rough surface structure. We have demonstrated that the detailed morphology of air-film interfaces, the quasi-two level surface structure as well as morphology of the buried interfaces can be obtained from off-specular neutron reflectivity data. We have shown from AFM and off-specular neutron reflectivity data that the morphologies of electro-deposited surface is distinctly different from that of sputter-deposited interface in this sample. To the best of our knowledge this is the first attempt to microscopically quantify the differences in morphologies of metallic interfaces deposited by two different techniques viz. electro-deposition and sputtering

Three-dimensional nucleation with diffusion controlled growth: a comparative study of electrochemical phase formation from aqueous and deep eutectic solvents

The nucleation of Ag onto vitreous carbon from aqueous 3 M NaCl or 0.6 M NaClO4 and deep eutectic solvent (DES) 1:2 M mixture of choline chloride:urea solutions containing Ag+, has been studied analyzing the chronoamperometric response to single potential steps. From the coordinates of the maxima observed in the current responses, the nucleation frequencies A (s(-1)) and number densities of nucleation sites N-0 (cm(-2)) were obtained from the standard model of nucleation with diffusion-controlled three-dimensional growth. Analysis of the overpotential dependence of nucleation frequencies using the classical electrochemical nucleation theory allowed to calculate the Gibbs free energy of nucleation Delta(G) over tilde (n(c)) and critical nucleus size n(c) as well as the exchange current density j(o), transfer coefficient alpha and surface tension sigma of silver nuclei. The kinetics of Ag+ reduction is two orders of magnitude slower in DES compared to both aqueous systems studied, and values of alpha << 0.5 where found in both aqueous and DES media, indicating either that the intermediate state for metal ion reduction is located close to the initial state, i.e., the solvated or complexed metal ion in solution, or that the metal ion is specifically adsorbed on the surface and the symmetry factor involved requires an alternative electron transfer formalism. The low Delta(G) over tilde (n(c)) and n(c) values observed indicate that the discharge of a single Ag ion on the surface already becomes a supercritical nucleus, involving a very low Gibbs energy barrier, characteristic of a non-activated process. (C) 2016 Elsevier B.V. All rights reserved

Rendimiento de las celdas solares de heterounión ZnO/Cu2O modificadas con óxido de grafeno

[EN] We report the fabrication of ZnO/Cu2O heterojunction solar cells by means of the electrodeposition technique. The effect of electrolyte medium for the ZnO deposition, annealing treatment and interface modification with graphene oxide (GO) layer on the photoelectrical properties was analyzed. The electrochemical results indicated a markedly dependent Cu2O film electrodeposition on the GO-modified ZnO films. The modification of ZnO/Cu2O interface with GO nanosheets and annealing treatment results in improved interface properties, varying morphology and defects in ZnO lattice that further lead to enhanced performance of the proposed heterojunction solar cells. While the obtained results indicate that the properties of GO coating need to be tailored for improved performance, a synergetic effect of the GO addition and annealing treatment on the photoelectric properties of the electrodeposited heterojunction is achieved. (C) 2019 SECV. Published by Elsevier Espana, S.L.U.[ES] Se presenta la fabricación de celdas solares de heterounión de ZnO/Cu2O obtenidas mediante la técnica de electrodeposición. Se analizó el efecto del electrolito utilizado para la deposición de ZnO, el tratamiento térmico aplicado y la modificación de la interfaz con una capa de óxido de grafeno (GO) sobre las propiedades fotoeléctricas. Los resultados electroquímicos indicaron que existe una marcada dependencia de electrodeposición de capa de Cu2O sobre las películas de ZnO modificadas con GO. La modificación de la interfaz ZnO/Cu2O con nanohojas de GO y el tratamiento térmico dan como resultado mejoras en las propiedades de la interfaz, una morfología variable y defectos en la red de ZnO que conducen a un mejor rendimiento de las celdas solares de heterounión propuestas. Si bien los resultados obtenidos indican que las propiedades del recubrimiento de GO deben adaptarse para mejorar el rendimiento, se logra un efecto sinérgico del tratamiento de adición y térmico de GO aplicados sobre las propiedades fotoeléctricas de la heterounión electrodepositada.Financial support from Escuela Politécnica Nacional (project number PIMI 15-09), Secretaría de Educación Superior, Ciencia, Tecnología e Innovación (SENESCYT) of Ecuador, Romanian National Authority for Scientific Research and Innovation CNCS ¿ UEFISCDI (project number PN-III-P1-1.1-TE-2016-1544), Spanish government MINECO (projects MAT2016-75586-C4-2-P and MAT2015-71070-REDC) and from Generalitat Valenciana (project PROMETEO 2018/123 ¿ EFIMAT) is gratefully acknowledged. In addition, authors would like to thank to the Microscopy Service of UPV and Dr. David Busquets-Mataix for useful advice.Rosas-Laverde, NM.; Pruna, AI.; Cembrero Gil, J.; Orozco-Messana, J.; Manjón, F. (2019). 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Fabrication of vertically aligned Pd nanowire array in AAO template by electrodeposition using neutral electrolyte

A vertically aligned Pd nanowire array was successfully fabricated on an Au/Ti substrate using an anodic aluminum oxide (AAO) template by a direct voltage electrodeposition method at room temperature using diluted neutral electrolyte. The fabrication of Pd nanowires was controlled by analyzing the current–time transient during electrodeposition using potentiostat. The AAO template and the Pd nanowires were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) methods and X-Ray diffraction (XRD). It was observed that the Pd nanowire array was standing freely on an Au-coated Ti substrate after removing the AAO template in a relatively large area of about 5 cm2, approximately 50 nm in diameter and 2.5 μm in length with a high aspect ratio. The nucleation rate and the number of atoms in the critical nucleus were determined from the analysis of current transients. Pd nuclei density was calculated as 3.55 × 108 cm−2. Usage of diluted neutral electrolyte enables slower growing of Pd nanowires owing to increase in the electrodeposition potential and thus obtained Pd nanowires have higher crystallinity with lower dislocations. In fact, this high crystallinity of Pd nanowires provides them positive effect for sensor performances especially