Energy applications of ionic liquids

Ionic liquids offer a unique suite of properties that make them important candidates for a number of energy related applications. Cation–anion combinations that exhibit low volatility coupled with high electrochemical and thermal stability, as well as ionic conductivity, create the possibility of designing ideal electrolytes for batteries, super-capacitors, actuators, dye sensitised solar cells and thermoelectrochemical cells. In the field of water splitting to produce hydrogen they have been used to synthesize some of the best performing water oxidation catalysts and some members of the protic ionic liquid family co-catalyse an unusual, very high energy efficiency water oxidation process. As fuel cell electrolytes, the high proton conductivity of some of the protic ionic liquid family offers the potential of fuel cells operating in the optimum temperature region above 100 °C. Beyond electrochemical applications, the low vapour pressure of these liquids, along with their ability to offer tuneable functionality, also makes them ideal as CO2 absorbents for post-combustion CO2 capture. Similarly, the tuneable phase properties of the many members of this large family of salts are also allowing the creation of phase-change thermal energy storage materials having melting points tuned to the application. This perspective article provides an overview of these developing energy related applications of ionic liquids and offers some thoughts on the emerging challenges and opportunities

THE STUDY OF PHASE COMPOSITION OF HIGHLY COERCISE ALLOYS WITH Fe-Ni-Al-CO-Ti AS THE BASE BY MEANS OF γ-RESONANCE SPECTROSCOPY

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Towards efficient hydrogen production using water splitting

Although there is no shortage of supply of fossil fuels at the moment, the necessity to reduce green house gas emission and growing difficulties in fossil fuel recovery raise great challenges for the scientific community to develop efficient, low cost alternative energy sources. Hydrogen is sought by many as a way to store and transport energy produced from renewable sources and as a fuel hydrogen produces only water on burning and is not toxic in any way. The main pathways to produce hydrogen can be classified as thermal, electrolytic, and photolytic processes. Most of the hydrogen is currently produced via thermal processes, which use the energy from fossil fuels stored in natural gas, coal or biomass to release hydrogen. Although photolytic processes are very attractive due to the zero greenhouse gas emissions, they can be used for commercial hydrogen production only if limitations related to low efficiency and poor stability can be resolved. State-of-the-art hydrogen producing photoelectrochemical cells have 12.4% efficiency under visible light irradiation and combine several semiconducting materials in a monolithic device. Although efficient, this cell is able to split water only for a few days, making the possibility of commercial application daunting. Thus, the general aim of the project is to develop a novel structure for a stable photo-electrochemical device for water splitting applications. Having high efficiencies for photo electrochemical energy conversion, metal sulfides are promising candidates for use in commercial water splitting systems if their long-term stability can be improved. Cadmium sulfide was chosen for our investigations as a representative of the metal sulfide family, due to its well known properties. In the photo-electrochemical cell developed in this work the light harvester is separated from the electrooxidation and reduction processes that occur in the water splitting cell. The quantum confinement effect observed for semiconducting nanoparticles significantly alters electrical properties of materials that allow for engineering of the desired electrical properties. A range of nanoparticles and nanostructures were prepared in this work in order to investigate the influence of dopant and quantum size effects innanoparticles on the energy structure of the material and their potential to be utilized in the water splitting and electroluminescent applications. In order to address the high costs of production of thin film semiconductors, in this work we have developed a novel method for low cost, efficient deposition of high quality metal sulfide semiconductors and their alloys utilizing electrodeposition from ionic liquids at high temperatures. The structure of the proposed photoelectrochemical cell was created using electrochemical deposition as well as photo-driven electrochemical deposition, which allows in situ deposition of catalyst for water oxidation. It was shown that a multilayered structure of the device based on metal sulfides provides high corrosion resistance of the cell during photo-electrochemical water splitting leading to significant extension of the cell lifetime

Towards efficient hydrogen production using water splitting

Although there is no shortage of supply of fossil fuels at the moment, the necessity to reduce green house gas emission and growing difficulties in fossil fuel recovery raise great challenges for the scientific community to develop efficient, low cost alternative energy sources. Hydrogen is sought by many as a way to store and transport energy produced from renewable sources and as a fuel hydrogen produces only water on burning and is not toxic in any way. The main pathways to produce hydrogen can be classified as thermal, electrolytic, and photolytic processes. Most of the hydrogen is currently produced via thermal processes, which use the energy from fossil fuels stored in natural gas, coal or biomass to release hydrogen. Although photolytic processes are very attractive due to the zero greenhouse gas emissions, they can be used for commercial hydrogen production only if limitations related to low efficiency and poor stability can be resolved. State-of-the-art hydrogen producing photoelectrochemical cells have 12.4% efficiency under visible light irradiation and combine several semiconducting materials in a monolithic device. Although efficient, this cell is able to split water only for a few days, making the possibility of commercial application daunting. Thus, the general aim of the project is to develop a novel structure for a stable photo-electrochemical device for water splitting applications. Having high efficiencies for photo electrochemical energy conversion, metal sulfides are promising candidates for use in commercial water splitting systems if their long-term stability can be improved. Cadmium sulfide was chosen for our investigations as a representative of the metal sulfide family, due to its well known properties. In the photo-electrochemical cell developed in this work the light harvester is separated from the electrooxidation and reduction processes that occur in the water splitting cell. The quantum confinement effect observed for semiconducting nanoparticles significantly alters electrical properties of materials that allow for engineering of the desired electrical properties. A range of nanoparticles and nanostructures were prepared in this work in order to investigate the influence of dopant and quantum size effects innanoparticles on the energy structure of the material and their potential to be utilized in the water splitting and electroluminescent applications. In order to address the high costs of production of thin film semiconductors, in this work we have developed a novel method for low cost, efficient deposition of high quality metal sulfide semiconductors and their alloys utilizing electrodeposition from ionic liquids at high temperatures. The structure of the proposed photoelectrochemical cell was created using electrochemical deposition as well as photo-driven electrochemical deposition, which allows in situ deposition of catalyst for water oxidation. It was shown that a multilayered structure of the device based on metal sulfides provides high corrosion resistance of the cell during photo-electrochemical water splitting leading to significant extension of the cell lifetime

Electrodeposited MnOx films from ionic liquid for electrocatalytic water oxidation

A novel method for the electrodeposition of highly active water oxidation catalysts is described. The manganese oxide (MnOₓ) films are electrodeposited on fluorine tin oxide (FTO) glass substrate at high temperature (120°C) from an ionic liquid electrolyte (ethylammonium nitrate). A range of analytical techniques, including X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), and energy-dispersive X-ray analyzer (EDX), indicate that the valence state of manganese in the deposited films can be controlled by changing the electrolyte composition. Along with the different phase compositions, a number of different morphologies including nanowires, nanoparticles, nanofibers as well as highly open and dense structures are obtained by varying the acidity of the electrolyte. The effect of morphology and chemical composition on the catalytic activity towards water oxidation is investigated. The film composed of Mn₃O₄ shows low catalytic activities, while the films composed of birnessite-like manganese oxide phase and Mn₂O₃ exhibit high catalytic activities for water oxidation. The catalytic activities are also affected by the surface morphology, i.e., a higher surface area and more open structure shows a higher catalytic activity. High rates of oxygen production are observed from MnOₓ films prepared in a neutral electrolyte

Improvement of catalytic water oxidation on MnOₓ films by heat treatment

Manganese oxides (MnOₓ) are considered to be promising catalysts for water oxidation. Electrodeposited MnOₓ films from aqueous electrolytes have previously been shown to exhibit a lower catalytic action than films deposited from ionic liquids when tested in strongly alkaline conditions. In this study, we describe a thermal treatment that converts the MnOₓ films deposited from aqueous electrolytes to highly catalytic films with comparable activity to ionic-liquid-deposited films. The films deposited from aqueous electrolytes show a remarkable improvement in the catalysis of water oxidation after heat treatment at a low temperature (120°C) for 30min. The films were characterised by using XRD and SEM, and energy-dispersive X-ray (EDX), FTIR and Raman spectroscopy, which indicate that dehydration occurs during the heat treatment without significant change to the microstructure or bulk composition. The X-ray absorption spectroscopy (XAS) results show the growth of small amounts (ca. 3-10%) of reduced Mn species (Mn^II or Mn^III) after heat treatment. The dehydration process removes structural water and hydroxyl species to result in a conductivity improvement and a more active catalyst, thereby contributing to the enhancement in water oxidation performance

Phosphorylated manganese oxide electrodeposited from ionic liquid as a stable, high efficiency water oxidation catalyst

Efficient production of hydrogen via water splitting is an important goal that would represent a significant step towards truly sustainable supplies of energy. However, currently available catalysts for water electrolysis are either too low in efficiency or too unstable to be practical in this context. Recognizing the very high stability of manganese phosphate, we describe here a novel catalyst material based on manganese oxide that is both stabilized and sensitized by a surface phosphorylation reaction in an ionic liquid electrodeposition process. XPS and EXAFS data show that the surface of the MnOₓ contains phosphorous at P to Mn ratio of similar to 1:2, indicating that the surface layer contains both phosphate characteristics and oxide characteristics. The catalyst stability was significantly enhanced compared to the previously reported manganese oxide catalysts and more than 25 h of continuous water oxidation is demonstrated