Elucidating structure-property relationships in the design of metal nanoparticle catalysts for the activation of molecular oxygen

A novel synthetic strategy for the design of metal nanoparticles by extrusion of anionic chloride precursors from a porous copper chlorophosphate framework has been devised for the sustainable aerobic oxidation of vanillyl alcohol (4-hydroxy-3-methoxybenzyl alcohol) to vanillin (4-hydroxy-3-methoxybenzaldehyde) using a one-step, base-free method. The precise nature of the Au, Pt, and Pd species has been elucidated for the as-synthesized and thermally activated analogues, which exhibit fascinating catalytic properties when subjected to diverse activation environments. By employing a combination of structural and spectroscopic characterization tools, it has been shown that analogous heat treatments have differing effects on extrusion of a particular metal species. The most active catalysts in this series of materials were the extruded Pt nanoparticles that were generated by reduction in H2, which exhibit enhanced catalytic behavior, when compared to its Au or Pd counterparts, for industrially significant, aerobic oxidation reactions

Catalysis for sustainable energy conversion and storage

Climate change, pollution, unprecedented population growth, geopolitical tensions and rapid technological development are intrinsically connected to the nature, level and availability of global energy, which shapes present and future aspects of human society. Particularly, in a society where global energetic demand is continuously rising and the awareness of the negative impact of fossil fuels on the environment is becoming widespread, the exploitation of renewable sources for the generation of sustainable energy is highly needed. In this regard one key requirement for an effective deployment and expansion of renewable energy in the global energy market is represented by its ability to conveniently convert and store the energy derived from intermittent sources, in order to guarantee a constant supply to the electric grid. The technologies for the energy conversion and storage present various degrees of maturity, each one having specific advantages and disadvantages depending on the type of application and energetic source.This thesis aims to give a tiny contribution to the complex problem of energy conversion and storage, through the design, characterisation and testing of electrocatalytic materials for water electrolysis, photoelectrochemical water splitting and direct methanol fuel cell. It is expected that the first two processes will play an important role in the future as convenient technologies for the conversion of solar and wind power into chemical energy in the form of hydrogen. The third process is regarded as promising way to convert the renewable chemical energy in the form of methanol into electrical energy.At the core of the research lies the design and development of electrocatalysts, which are directly responsible for lowering the reaction overpotentials and ultimately increasing the overall efficiency of the processes. As such, in this thesis three materials were synthesised using straightforward methodologies and evaluated as electrocatalysts for the alkaline hydrogen evolution, the photoelectrochemical oxygen evolution and the alkaline methanol oxidation. Their performances were directly linked to the morphological and structural properties which in turn significantly affected the nature of active sites. For the first work reported in Chapter 3, a material based on a mixed cobalt nickel sulphide nanoparticles supported onto Ni foam showed high activity toward the hydrogen evolution reaction, with a required small overpotentials of 163 mV at a current density of 10 mA/cm2 in 1.0 M KOH electrolyte. This value compares well with the best existing hydrogen evolution reaction electrocatalysts based on non-noble elements. Moreover the catalyst showed good durability which was tested under chronoamperometric conditions, maintaining an optimal performance for 72 hours. The origin of such high activity was attributed to the existence of an optimal nickel-cobalt sulphide ratio at the surface of the electrode, which was obtained by selecting the appropriate temperature and time of thermal annealing of the material. This optimal presence of the biphasic nickel-cobalt sulphide nanoparticles led to high electrochemically active surface area and small charge transfer resistance, as evidenced by the extensive characterisation analysis carried out on these materials. For the second work reported in Chapter 4, a WO3/Co3O4 photoanode was successfully synthesised via a facile sol-gel method and tested for the photoelectrochemical oxygen evolution. It was found that the degree of crystallinity of the cocatalyst influenced heavily the photoelectrochemical activity towards the oxygen evolution. In particular, a poorly crystalline structure of Co3O4 led to an improvement of up to 40% in photocurrent generation compared to the bare WO3. Interestingly, the highly crystalline Co3O4 significantly suppressed the photocurrent generation, as a result of the creation of an unfavourable band alignment, with a dramatic increase in the charge recombination at the interface. Finally, for the third and last work reported in Chapter 5, ultra-small Pt nanoparticles embedded on a 3D structure composed of CeO2, NiO and Ni foam was synthesised and tested as electrocatalyst for the alkaline methanol oxidation reaction. The generated catalyst showed extremely high activity for the alkaline methanol oxidation, with mass and geometric current density values of 1160 mA/mgPt and 202 mA/cm2, whose values are among the highest ever reported for Pt-based materials. It was demonstrated that the unique morphological architecture and existence of a synergistic effect between Pt and adjacent CeO2 nanoparticles contributed decisively to the observed high performance. Particularly the presence of defective and poorly crystalline CeO2 nanoparticles was beneficial to the efficient oxidative removal of the CO from the Pt active sites which resulted in a higher durability of the electrocatalyst. Moreover, the concomitant presence of the superficial Ni(OH)2 was thought to contribute to the supply of OH species to the Pt, which act as reactants for the CO removal. The most active electrocatalyst was subjected to stability test, retaining 40 % of the initial geometric current density after 6 hours, and quite surprisingly the activity could be totally restored through straightforward CV scans in 1.0 M NaOH electrolyte

Ex-ante life cycle assessment of polyethylenefuranoate (PEF) from bio-based monomers synthesized via a novel electrochemical process

An ex-ante Life Cycle Assessment was conducted to assess the cradle-to-factory gate environmental impact of polyethylenefuranoate (PEF). The two monomers used to synthesize a 100% bio-based PEF, namely 2,5- furan dicarboxylic acid (2,5-FDCA) and mono ethylene glycol (MEG), are synthesized simultaneously from a novel electrochemical reactor using bio-based raw materials. The technology is currently at a low Technological Readiness Level (TRL 2–3), and was scaled up to a theoretical TRL4 using process design. The purposes of this study are two folds: 1) to identify the significant environmental issues at an early development stage and 2) to gain insights into and experience of ex-ante assessment for a low-TRL bio-based innovation. The electrochemical technology investigated offers the opportunity of electrification of the chemical sector in the future. Ex-ante LCA was applied based on recently suggested TRL-frameworks. Primary data from the foreground system, covering the electrochemical reactor and the downstream purification processes, were obtained from lab-scale experiments and conceptual design. Five environmental indicators were assessed: namely, climate change, non-renewable energy use (NREU), acidification, eutrophication and land use. The results show that the electricity demand from the electrochemical reactor is the most important contributor of the environmental impacts, yet downstream processes contribute significantly as well. Future scenarios show that a carbon neutral electricity in 2050 could help to significantly reduce the climate change impact (by up to 60%). As a proof-of-concept, the assessed electrochemical reactor shows its important potential of the electrification of the chemical sector for monomer and polymer production, provided that a zero emission electricity in the future can be achieved

Ex-ante life cycle assessment of polyethylenefuranoate (PEF) from bio-based monomers synthesized via a novel electrochemical process

An ex-ante Life Cycle Assessment was conducted to assess the cradle-to-factory gate environmental impact of polyethylenefuranoate (PEF). The two monomers used to synthesize a 100% bio-based PEF, namely 2,5- furan dicarboxylic acid (2,5-FDCA) and mono ethylene glycol (MEG), are synthesized simultaneously from a novel electrochemical reactor using bio-based raw materials. The technology is currently at a low Technological Readiness Level (TRL 2–3), and was scaled up to a theoretical TRL4 using process design. The purposes of this study are two folds: 1) to identify the significant environmental issues at an early development stage and 2) to gain insights into and experience of ex-ante assessment for a low-TRL bio-based innovation. The electrochemical technology investigated offers the opportunity of electrification of the chemical sector in the future. Ex-ante LCA was applied based on recently suggested TRL-frameworks. Primary data from the foreground system, covering the electrochemical reactor and the downstream purification processes, were obtained from lab-scale experiments and conceptual design. Five environmental indicators were assessed: namely, climate change, non-renewable energy use (NREU), acidification, eutrophication and land use. The results show that the electricity demand from the electrochemical reactor is the most important contributor of the environmental impacts, yet downstream processes contribute significantly as well. Future scenarios show that a carbon neutral electricity in 2050 could help to significantly reduce the climate change impact (by up to 60%). As a proof-of-concept, the assessed electrochemical reactor shows its important potential of the electrification of the chemical sector for monomer and polymer production, provided that a zero emission electricity in the future can be achieved

Ex-ante life cycle assessment of polyethylenefuranoate (PEF) from bio-based monomers synthesized via a novel electrochemical process

An ex-ante Life Cycle Assessment was conducted to assess the cradle-to-factory gate environmental impact of polyethylenefuranoate (PEF). The two monomers used to synthesize a 100% bio-based PEF, namely 2,5- furan dicarboxylic acid (2,5-FDCA) and mono ethylene glycol (MEG), are synthesized simultaneously from a novel electrochemical reactor using bio-based raw materials. The technology is currently at a low Technological Readiness Level (TRL 2–3), and was scaled up to a theoretical TRL4 using process design. The purposes of this study are two folds: 1) to identify the significant environmental issues at an early development stage and 2) to gain insights into and experience of ex-ante assessment for a low-TRL bio-based innovation. The electrochemical technology investigated offers the opportunity of electrification of the chemical sector in the future. Ex-ante LCA was applied based on recently suggested TRL-frameworks. Primary data from the foreground system, covering the electrochemical reactor and the downstream purification processes, were obtained from lab-scale experiments and conceptual design. Five environmental indicators were assessed: namely, climate change, non-renewable energy use (NREU), acidification, eutrophication and land use. The results show that the electricity demand from the electrochemical reactor is the most important contributor of the environmental impacts, yet downstream processes contribute significantly as well. Future scenarios show that a carbon neutral electricity in 2050 could help to significantly reduce the climate change impact (by up to 60%). As a proof-of-concept, the assessed electrochemical reactor shows its important potential of the electrification of the chemical sector for monomer and polymer production, provided that a zero emission electricity in the future can be achieved

A highly active hydrogen evolution electrocatalyst based on a cobalt–nickel sulfide composite electrode

A novel Co9S8–NixSy/Ni foam composite material was synthesized through the thermal decomposition of a cobalt–thiourea molecular precursor onto a 3D metallic support. The obtained electrode exhibited good activity toward the hydrogen evolution reaction in an alkaline medium, requiring a small overpotential of 163 mV at a current density of 10 mA cm?2, which is one of the lowest ever reported among transition metal sulfide materials

Elucidating structure-property relationships in the design of metal nanoparticle catalysts for the activation of molecular oxygen

© 2015 American Chemical Society. A novel synthetic strategy for the design of metal nanoparticles by extrusion of anionic chloride precursors from a porous copper chlorophosphate framework has been devised for the sustainable aerobic oxidation of vanillyl alcohol (4-hydroxy-3-methoxybenzyl alcohol) to vanillin (4-hydroxy-3-methoxybenzaldehyde) using a one-step, base-free method. The precise nature of the Au, Pt, and Pd species has been elucidated for the as-synthesized and thermally activated analogues, which exhibit fascinating catalytic properties when subjected to diverse activation environments. By employing a combination of structural and spectroscopic characterization tools, it has been shown that analogous heat treatments have differing effects on extrusion of a particular metal species. The most active catalysts in this series of materials were the extruded Pt nanoparticles that were generated by reduction in H2, which exhibit enhanced catalytic behavior, when compared to its Au or Pd counterparts, for industrially significant, aerobic oxidation reactions.Link_to_subscribed_fulltex

The effect of crystallinity on photocatalytic performance of Co3O4 water-splitting cocatalysts

Cocatalysts, when loaded onto a water splitting photocatalyst, accelerate the gas evolution reaction and improve the efficiency of the photocatalyst. In this paper, we report that the efficiency of the photocatalyst is enhanced using an amorphous cobalt oxide cocatalyst. The WO3 film, when loaded with amorphous or nanocrystalline Co3O4, shows an improvement of up to 40% in photocurrent generation and 34% in hydrogen gas evolution. The effect of cocatalyst crystallinity on performance was systematically studied, and we found that the photocurrent deteriorates with the conversion of the cocatalyst to a highly crystalline phase at an annealing temperature of 500 degrees C. The mechanism of this effect was studied in detail using electrochemical impedance spectroscopy, and the enhancement effect produced by the amorphous cocatalyst is attributed to the large density of unsaturated catalytically active sites in the amorphous material