First row transition metal catalysts for solar-driven water oxidation produced by electrodeposition

As our reliance on renewable energy resources increases, so will our need to store this energy in the form of chemical fuels to iron-out peaks and troughs in supply. Sunlight, the most plentiful source of renewable energy, is especially problematic in this regard as it is so diffuse. One way to convert solar irradiation to fuels effectively would be to develop large surface area photo-electrochemical devices that could use sunlight directly to split water into H2 and O2. However, in order to be feasible, such an approach requires that these devices (and their components) are extremely cheap. In this review, we will discuss catalysts for the water oxidation half-reaction of electrochemical water splitting that can be produced by electrodeposition (a technique well suited to large-scale, low-cost applications), and that are based on the comparatively plentiful and inexpensive first row transition metals. Special attention will be paid to the electrodeposition conditions used in the various examples given, and structure-function relationships for electrochemical water oxidation for the materials produced by these techniques will be elucidated

Efficient electrocatalytic water oxidation at neutral and high pH by adventitious nickel at nanomolar concentrations

Electrolytic water oxidation using earth-abundant elements is a key challenge in the quest to develop cheap, large surface area arrays for solar-to-hydrogen conversion. There have been numerous studies in this area in recent years, but there remains an imperative to demonstrate that the current densities reported are indeed due to the species under consideration and not due to the presence of adventitious (yet possibly highly active) contaminants at low levels. Herein, we show that adventitious nickel at concentrations as low as 17 nM can act as a water oxidation catalyst in mildly basic aqueous solutions, achieving stable (tens of hours) current densities of 1 mA cm–2 at overpotentials as low as 540 mV at pH 9.2 and 400 mV at pH 13. This nickel was not added to the electrolysis baths deliberately, but it was found to be present in the electrolytes as an impurity by ICP-MS. The presence of nickel on anodes from extended-time bulk electrolysis experiments was confirmed by XPS. In showing that such low levels of nickel can perform water oxidation at overpotentials comparable to many recently reported water oxidation catalysts, this work serves to raise the burden of proof required of new materials in this field: contamination by adventitious metal ions at trace loadings must be excluded as a possible cause of any observed water oxidation activity

An investigation into the unusual linkage isomerization and nitrite reduction activity of a novel tris(2-pyridyl) copper complex

The copper-containing nitrite reductases (CuNIRs) are a class of enzymes that mediate the reduction of nitrite to nitric oxide in biological systems. Metal–ligand complexes that reproduce the salient features of the active site of CuNIRs are therefore of fundamental interest, both for elucidating the possible mode of action of the enzymes and for developing biomimetic catalysts for nitrite reduction. Herein, we describe the synthesis and characterization of a new tris(2-pyridyl) copper complex ([Cu1(NO2)2]) that binds two molecules of nitrite, and displays all three of the common binding modes for NO2−, with one nitrite bound in an asymmetric quasi-bidentate κ2-ONO manner and the other bound in a monodentate fashion with a linkage isomerism between the κ1-ONO and κ1-NO2 binding modes. We use density functional theory to help rationalize the presence of all three of these linkage isomers in one compound, before assessing the redox activity of [Cu1(NO2)2]. These latter studies show that the complex is not a competent nitrite reduction electrocatalyst in non-aqueous solvent, even in the presence of additional proton donors, a finding which may have implications for the design of biomimetic catalysts for nitrite reduction

Investigations into electrochemical water splitting

The work detailed in this thesis is organized in the following manner: In Chapter 1 we discuss electrochemical and photoelectrochemical catalysts in the context of their application for solar-to-hydrogen devices. During this introduction we will give an overview of the current state of the field, discussing the different kinds of materials that are being investigated before giving a brief description of some actual solar-to-hydrogen devices and finishing with a discussion of the current and future challenges in the field. Chapter 2 is a description of the different techniques used throughout this thesis. Once having set the bases, we shall start with the actual research, which corresponds to Chapters 3 to 5. Chapter 3 and 4 deal with the effect of trace metal impurities in electrochemical water splitting. In Chapter 3 we show that adventitious nickel at trace levels can act as a water oxidation catalyst in mildly basic aqueous solutions at overpotentials comparable to many recently-reported water oxidation catalysts, therefore serving to raise the burden of proof required of new materials in this field. Chapter 4 shows how silver ions leaking from Ag/AgCl reference electrodes in aqueous buffers at low pH can deposit on the working electrode as Ag(0) and catalyze the hydrogen evolution reaction, calling into question the validity of any reports using these electrodes that cannot demonstrate significantly superior activity to the baseline we set in this chapter. In Chapter 5 we describe a direct hydrothermal deposition method to prepare Cobalt-doped MoS2 thin films onto transparent Fluorine-doped SnO2 substrate and demonstrate that the obtained films display good activity for the hydrogen evolution reaction from acid solution

La divulgación científica como herramienta para acercar la investigación a los alumnos de Bachillerato

En este trabajo de fin de máster se plantea una propuesta de innovación educativa diseñada para despertar el interés de los alumnos por la investigación científica y conseguir que valoren su importancia para la sociedad. Para ello, se propone una serie de actividades en las que el docente llevará a clase artículos de divulgación científica sobre diferentes temas que pongan en contacto a los alumnos con algunas de las líneas de investigación actuales en Física y Química. El trabajo con los textos se realizará en grupo y se complementará con exposiciones orales y coloquios. La propuesta incluye también actividades dirigidas a combatir la desinformación, con el objetivo de concienciar a los alumnos sobre la necesidad de ser críticos a la hora de buscar información en Internet. Se trata, en definitiva, de generar un interés por la ciencia y sus aplicaciones en la vida cotidiana que acompañe a los alumnos fuera del instituto y les ayude a ser ciudadanos con cultura científica que entiendan la importancia de la investigación y actúen en consecuencia.This Master Thesis presents a teaching innovation proposal aiming to raise students’ interest in scientific research and make them value its importance for society. A series of activities are proposed in order to achieve these goals, in which teachers will bring scientific divulgative articles into the classroom to expose students to current research lines in Physics and Chemistry areas. Students will read the texts and answer related questions in group and then present them to their classmates, leading to a final colloquium. The proposal includes also activities that deal with misinformation, designed to raise awareness of the need to keep a critic approach to sources of scientific information in the Internet. In Summary, this Thesis aims to raise an interest in Science and its applications in real life that students can take with them when they finish High School. This will help them to become citizens with scientific culture who understand the importance of research and are capable to act in consequence.Departamento de Química AnalíticaMáster en Profesor de Educación Secundaria Obligatoria y Bachillerato, Formación Profesional y Enseñanzas de Idioma

Crystal structure of catena-poly[[(μ-6-{[bis­­(pyridin-2-ylmeth­yl)amino]­meth­yl}pyridine-2-carboxyl­ato)copper(II)] perchlorate aceto­nitrile monosolvate]

The crystal structure of the title compound, {[Cu(C19H17N4O2)]ClO4·C2H3N}n, is reported and compared to similar structures in the literature. The compound crystallizes in the monoclinic space group P21. The unit cell contains one complex mol­ecule in addition to perchlorate as the counter-ion and solvent (aceto­nitrile). The crystal packing evinces extended chains whereby the carboxyl­ate moiety on the 6-carboxyl­ato-2-(pyridyl­meth­yl)bis­(pyridin-2-ylmeth­yl)amine ligand bridges between two different copper centers in adjacent mol­ecules. This packing arrangement for the title compound appears to be unique when compared to allied structures in the literature. The perchlorate anion showed signs of disorder and its oxygen atoms were modelled over two sets of partially occupied sites, the occupancy of which was competitively refined to 0.564 (12)/0.436 (12). The crystal studied was refined as a two-component inversion twin

The direct hydrothermal deposition of cobalt-doped MoS2 onto fluorine-doped SnO2 substrates for catalysis of the electrochemical hydrogen evolution reaction

Metal chalcogenides, and doped molybdenum sulfides in particular, have considerable potential as earth-abundant electrocatalysts for the hydrogen evolution reaction. This is especially true in the case of solar-to-hydrogen devices, where an ability to deposit these materials on transparent substrates is therefore desirable. Hydrothermal methods are perhaps the most common route by which metal chalcogenide materials suitable for the hydrogen evolution reaction are produced. Such methods are simple and scalable, but the direct hydrothermal deposition of metal chalcogenides on transparent oxide electrodes has hitherto never been reported. Such an advance would greatly facilitate the expansion of the field by removing the requirement for separate hydrothermal-synthesis and catalyst-deposition steps. In this paper, we show that the ternary chalcogenide Co2Mo9S26 can be synthesised on a fluorine-doped tin oxide substrate by hydrothermal methods directly from solutions of the simple metal salts. These films display good activity for the hydrogen evolution reaction from acid solution, achieving current densities of 10 mA cm−2 at 260 mV overpotential with a Tafel slope of 64 mV per decade. Moreover, the resulting films can be made to be translucent, a very useful property which would allow light to be transmitted through the catalyst to an underlying light-harvesting array in any solar-to-hydrogen device employing this material at the cathode

Polyoxometalates on Functional Substrates: Concepts, Synergies, and Future Perspectives

Polyoxometalates (POMs) are molecular metal oxide clusters that feature a broad range of structures and functionalities, making them one of the most versatile classes of inorganic molecular materials. They have attracted widespread attention in homogeneous catalysis. Due to the challenges associated with their aggregation, precipitation, and degradation under operational conditions and to extend their scope of applications, various strategies of depositing POMs on heterogeneous substrates have been developed. Recent ground-breaking developments in the materials chemistry of supported POM composites are summarized and links between molecular-level understanding of POM-support interactions and macroscopic effects including new or optimized reactivities, improved stability, and novel function are established. Current limitations and future challenges in studying these complex composite materials are highlighted, and cutting-edge experimental and theoretical methods that will lead to an improved understanding of synergisms between POM and support material from the molecular through to the nano- and micrometer level are discussed. Future development in this fast-moving field is explored and emerging fields of research in POM heterogenization are identified

Proton-coupled electron transfer enhances the electrocatalytic reduction of nitrite to NO in a bioinspired copper complex

This work was supported by the EPSRC (Grant No. EP/ K031732/1) and the Royal Society (University Research Fellowship UF150104 to M.D.S.). The data which underpin this work are available at http://dx.doi.org/10.5525/gla. researchdata.590 and are available under a CC-BY licence.The selective and efficient electrocatalytic reduction of nitrite to nitric oxide (NO) is of tremendous importance, both for the development of NO-release systems for biomedical applications and for the removal of nitrogen oxide pollutants from the environment. In nature, this transformation is mediated by (among others) enzymes known as the copper-containing nitrite reductases. The development of synthetic copper complexes that can reduce nitrite to NO has therefore attracted considerable interest. However, there are no studies describing the crucial role of proton-coupled electron transfer during nitrite reduction when such synthetic complexes are used. Herein, we describe the synthesis and characterization of two previously unreported Cu complexes ( 3 and 4 ) for the electrocatalytic reduction of nitrite to NO, in which the role of proton-relaying units in the secondary coordination sphere of the metal can be probed. Complex 4 bears a pendant carboxylate group in close proximity to the copper center, while complex 3 lacks such functionality. Our results suggest that complex 4 is twice as effective an electrocatalyst for nitrite reduction than is complex 3 and that complex 4 is the best copper-based molecular electrocatalyst for this reaction yet discovered. The differences in reactivity between 3 and 4 are probed using a range of electrochemical, spectroscopic, and computational methods, which shed light on the possible catalytic mechanism of 4 and implicate the proton-relaying ability of its pendant carboxylate group in the enhanced reactivity that this complex displays. These results highlight the critical role of proton-coupled electron transfer in the reduction of nitrite to NO and have important implications for the design of biomimetic catalysts for the selective interconversions of the nitrogen oxides.Publisher PDFPeer reviewe