Vladimir L. Kuznetsov

Turning carbon dioxide into fuel.

Our present dependence on fossil fuels means that, as our demand for energy inevitably increases, so do emissions of greenhouse gases, most notably carbon dioxide (CO2). To avoid the obvious consequences on climate change, the concentration of such greenhouse gases in the atmosphere must be stabilized. But, as populations grow and economies develop, future demands now ensure that energy will be one of the defining issues of this century. This unique set of (coupled) challenges also means that science and engineering have a unique opportunity—and a burgeoning challenge—to apply their understanding to provide sustainable energy solutions. Integrated carbon capture and subsequent sequestration is generally advanced as the most promising option to tackle greenhouse gases in the short to medium term. Here, we provide a brief overview of an alternative mid- to long-term option, namely, the capture and conversion of CO2, to produce sustainable, synthetic hydrocarbon or carbonaceous fuels, most notably for transportation purposes. Basically, the approach centres on the concept of the large-scale re-use of CO2 released by human activity to produce synthetic fuels, and how this challenging approach could assume an important role in tackling the issue of global CO2 emissions. We highlight three possible strategies involving CO2 conversion by physico-chemical approaches: sustainable (or renewable) synthetic methanol, syngas production derived from flue gases from coal-, gas- or oil-fired electric power stations, and photochemical production of synthetic fuels. The use of CO2 to synthesize commodity chemicals is covered elsewhere (Arakawa et al. 2001 Chem. Rev. 101, 953–996); this review is focused on the possibilities for the conversion of CO2 to fuels. Although these three prototypical areas differ in their ultimate applications, the underpinning thermodynamic considerations centre on the conversion—and hence the utilization—of CO2. Here, we hope to illustrate that advances in the science and engineering of materials are critical for these new energy technologies, and specific examples are given for all three examples. With sufficient advances, and institutional and political support, such scientific and technological innovations could help to regulate/stabilize the CO2 levels in the atmosphere and thereby extend the use of fossil-fuel-derived feedstocks.

Dopant-induced bandgap shift in Al-doped ZnO thin films prepared by spray pyrolysis

A series of 1 at. % Al-doped ZnO (AZO) films were deposited onto glass substrates by a spray pyrolysis technique. We find that the observed blue shift in the optical bandgap of 1% AZO films is dominated by the Burstein Moss effect. The Fermi level for an 807u2009nm thick AZO film rose by some 0.16u2009eV with respect to the edge of the conduction band. By controlling the film thickness, all AZO films exhibit the same lattice strain values. The influence of strain-induced bandgap shift was excluded by selecting films with nearly the same level of bandgap volume-deformation potentials, and the differences in out-plain strain and in-plain stress remained effectively constant.

Highly conducting and optically transparent Si-doped ZnO thin films prepared by spray pyrolysis

We report the fabrication and investigation of highly conducting and optically transparent ZnO thin films prepared by the spray pyrolysis technique. Undoped and Si-doped ZnO thin films were deposited on glass substrates at deposition temperatures between 250 °C and 500 °C from a precursor solution containing zinc acetylacetonate and silicon tetraacetate. X-ray diffraction analysis confirms that the deposited films have the wurtzite ZnO structure with individual crystallite sizes varying between 65 and 122 nm. The optical transparency of the films in the visible range is in the range of 80–85%. The effect of deposition temperature and Si dopant concentration on structural, optical and electrical properties of Si-doped films was investigated. For 3% Si-doped ZnO films the electrical resistivity and carrier concentration reached values of 3.7 × 10−3 Ωcm and 1.7 × 1020 cm−3, respectively. The temperature dependence of the electrical transport properties were measured across the range of 77–350 K. The carrier concentration for all the films is practically temperature independent, illustrating that the samples are degenerate semiconductors. Interestingly, a temperature-activated Hall mobility is observed for the thin films over the whole temperature range of measurements. This is attributed to the thermionic emission of free electrons across potential barriers formed between grains. Si-doped ZnO thin films prepared by a vacuum-free solution-based technique can provide cost-effective transparent conducting layers for optoelectronic and energy applications.

Functional Materials for Sustainable Energy Technologies: Four Case Studies

The critical topic of energy and the environment has rarely had such a high profile, nor have the associated materials challenges been more exciting. The subject of functional materials for sustainable energy technologies is demanding and recognized as a top priority in providing many of the key underpinning technological solutions for a sustainable energy future. Energy generation, consumption, storage, and supply security will continue to be major drivers for this subject. There exists, in particular, an urgent need for new functional materials for next-generation energy conversion and storage systems. Many limitations on the performances and costs of these systems are mainly due to the materials intrinsic performance. We highlight four areas of activity where functional materials are already a significant element of world-wide research efforts. These four areas are transparent conducting oxides, solar energy materials for converting solar radiation into electricity and chemical fuels, materials for thermoelectric energy conversion, and hydrogen storage materials. We outline recent advances in the development of these classes of energy materials, major factors limiting their intrinsic functional performance, and potential ways to overcome these limitations.

Microwave treatment in oil refining

In this paper, we discuss the potential of using microwave techniques in the refinement of heavy fraction of petroleums such as bunker oil. After discussing the fundamental issues associated with conversion of microwave energy into heat, we present measurements of the dielectric properties of heavy oils at 2.45xa0GHz using a highly sensitive resonant cavity method, and also over a broader frequency range (100xa0MHz to 8xa0GHz) using a coaxial probe technique. We find that the dielectric loss is very small even in these heavy oils, but still may be sufficiently large to provide efficient conversion of microwave energy into heat on untreated samples, and could be massively enhanced by means of a microwave-absorbing additive (e.g., carbon black). We conclude by discussing the design of a suitable microwave actuator for heavy oil cracking within a flow process.

Sir Humphry Davy: Boundless Chemist, Physicist, Poet and Man of Action

The years 2007 and 2008 mark the bi-centenary of two brilliant discoveries by Sir Humphry Davy: the isolation of sodium and potassium (1807) and the subsequent first observation (1808) of the beautiful blue and bronze colours now known to be characteristic of the solvated electron(1) in potassium-ammonia systems. In celebration of these dazzling discoveries, we reflect on Davys many extraordinary contributions to science, technology and poetry. Humphry Davy, a truly great man, of Cornish spirit, brought immeasurable benefits to humankind.

UV-induced improvement in ZnO thin film conductivity: a new in situ approach†

We report a long-lasting enhancement in electrical properties occurs when zinc oxide (ZnO) thin films prepared by spray pyrolysis in a nitrogen atmosphere are treated with UV prior to the films first exposure to air (here termed “in situ irradiation”). Carrier mobilities as high as 44.3 cm2 V−1 s−1 – the highest values yet reported for any ZnO thin films made by spray pyrolysis – are exhibited by samples deposited at ca. 376 °C. In fact, such mobility values compare favorably with results that have been obtained using more complex, vacuum-based deposition techniques. The results of electrical, chemical, and microstructural characterization as a function of irradiation and deposition temperature indicate that the improved electrical properties stem from a modification of the relative populations of donor and acceptor defects at the grain boundaries of these polycrystalline films, allowing parallels to be drawn to the well-known phenomenon of “persistent” photoconductivity in ZnO. Finally, we consider how these observations about the interaction of ZnO with UV light relate to factors that limit the electrical performance of practical, transparent conducing oxide thin films.

Electronic conduction in amorphous and polycrystalline zinc-indium oxide films

We report on the electronic properties of both amorphous and polycrystalline zinc-indium oxide thin films with similar degenerate electron concentrations just above the insulator-to-metal transition. The highest electron mobilities occur in amorphous oxide films deposited at 100u2009°C; for these, structural disorder is on a spatial scale much smaller than the characteristic electron wavelength (∼3u2002nm) of the conduction electron gas. For polycrystalline films fabricated at 200–300u2009°C enhanced electron scattering occurs at evolving grain boundaries when the grain size is comparable to the electron wavelength. Larger, highly crystalline grains form for deposition at 500u2009°C with concomitant higher carrier mobilities.

Dry reforming of methane over ZrO2-supported Co–Mo carbide catalyst

The process of dry reforming of methane has the potential to be an effective route for CO2 utilization via syn-gas production. In the present study, ZrO2-supported Co–Mo bimetallic carbide catalysts were prepared via a co-precipitation method through a combined reduction and carburization procedure employing a CH4/H2 (20/80xa0%) mixture. All of the as-synthesized materials were tested at 850°, under atmospheric pressure and a CO2:CH4 ratio of 1. The importance of the ZrO2 support became immediately apparent when it exhibited a higher conversion than the corresponding low-surface-area bulk Mo2C catalyst, which we attribute to lewis acid and base active sites on the surface of ZrO2. From catalytic tests and pre-and post-reaction X-ray diffraction (XRD) patterns, we observed that different dispersions of the monometallic carbides, caused by varying the pre-heating temperatures on ZrO2, did not significantly affect conversion or yield. In contrast, incorporation of cobalt atoms into the Mo2C lattice significantly enhanced the conversion, yield and stability of the catalysts. Post-reaction XRD patterns indicated that the bimetallic carbide had enhanced the resistance to the oxidation effect that is known to deactivate Mo2C catalysts. In addition, increasing the Co loading in the mixed metal carbides was seen to enhance the resistance of the catalyst to the reverse water gas shift reaction, leading to improved stability of the H2 yields.

The Electronic Structure and Properties of Solids

We review some of the important concepts and models relating to the metallic, nonmetallic (insulating), and superconducting states of matter. We focus on the underlying physics and chemistry of various states, rather than on elaborate mathematical devices, and highlight important mechanisms influencing the transition between each state. We link the physical properties of these states with key aspects of the chemistry of materials, since both disciplines are fundamentally important for the 21st century of the Science of Materials.