scispace - formally typeset
Search or ask a question

Showing papers in "Energy and Environmental Science in 2009"


Journal ArticleDOI
TL;DR: In this paper, the authors introduce the principles and present status of bulk nanostructured materials, then describe some of the unanswered questions about carrier transport and how current research is addressing these questions.
Abstract: Thermoelectrics have long been recognized as a potentially transformative energy conversion technology due to their ability to convert heat directly into electricity. Despite this potential, thermoelectric devices are not in common use because of their low efficiency, and today they are only used in niche markets where reliability and simplicity are more important than performance. However, the ability to create nanostructured thermoelectric materials has led to remarkable progress in enhancing thermoelectric properties, making it plausible that thermoelectrics could start being used in new settings in the near future. Of the various types of nanostructured materials, bulk nanostructured materials have shown the most promise for commercial use because, unlike many other nanostructured materials, they can be fabricated in large quantities and in a form that is compatible with existing thermoelectric device configurations. The first generation of these materials is currently being developed for commercialization, but creating the second generation will require a fundamental understanding of carrier transport in these complex materials which is presently lacking. In this review we introduce the principles and present status of bulk nanostructured materials, then describe some of the unanswered questions about carrier transport and how current research is addressing these questions. Finally, we discuss several research directions which could lead to the next generation of bulk nanostructured materials.

1,742 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present a review and ranking of energy-related solutions to global warming, air pollution mortality, and energy security while considering other impacts of the proposed solutions, such as on water supply, land use, wildlife, resource availability, thermal pollution, water chemical pollution, nuclear proliferation, and undernutrition.
Abstract: This paper reviews and ranks major proposed energy-related solutions to global warming, air pollution mortality, and energy security while considering other impacts of the proposed solutions, such as on water supply, land use, wildlife, resource availability, thermal pollution, water chemical pollution, nuclear proliferation, and undernutrition. Nine electric power sources and two liquid fuel options are considered. The electricity sources include solar-photovoltaics (PV), concentrated solar power (CSP), wind, geothermal, hydroelectric, wave, tidal, nuclear, and coal with carbon capture and storage (CCS) technology. The liquid fuel options include corn-ethanol (E85) and cellulosic-E85. To place the electric and liquid fuel sources on an equal footing, we examine their comparative abilities to address the problems mentioned by powering new-technology vehicles, including battery-electric vehicles (BEVs), hydrogen fuel cell vehicles (HFCVs), and flex-fuel vehicles run on E85. Twelve combinations of energy source-vehicle type are considered. Upon ranking and weighting each combination with respect to each of 11 impact categories, four clear divisions of ranking, or tiers, emerge. Tier 1 (highest-ranked) includes wind-BEVs and wind-HFCVs. Tier 2 includes CSP-BEVs, geothermal-BEVs, PV-BEVs, tidal-BEVs, and wave-BEVs. Tier 3 includes hydro-BEVs, nuclear-BEVs, and CCS-BEVs. Tier 4 includes corn- and cellulosic-E85. Wind-BEVs ranked first in seven out of 11 categories, including the two most important, mortality and climate damage reduction. Although HFCVs are much less efficient than BEVs, wind-HFCVs are still very clean and were ranked second among all combinations. Tier 2 options provide significant benefits and are recommended. Tier 3 options are less desirable. However, hydroelectricity, which was ranked ahead of coal-CCS and nuclear with respect to climate and health, is an excellent load balancer, thus recommended. The Tier 4 combinations (cellulosic- and corn-E85) were ranked lowest overall and with respect to climate, air pollution, land use, wildlife damage, and chemical waste. Cellulosic-E85 ranked lower than corn-E85 overall, primarily due to its potentially larger land footprint based on new data and its higher upstream air pollution emissions than corn-E85. Whereas cellulosic-E85 may cause the greatest average human mortality, nuclear-BEVs cause the greatest upper-limit mortality risk due to the expansion of plutonium separation and uranium enrichment in nuclear energy facilities worldwide. Wind-BEVs and CSP-BEVs cause the least mortality. The footprint area of wind-BEVs is 2–6 orders of magnitude less than that of any other option. Because of their low footprint and pollution, wind-BEVs cause the least wildlife loss. The largest consumer of water is corn-E85. The smallest are wind-, tidal-, and wave-BEVs. The US could theoretically replace all 2007 onroad vehicles with BEVs powered by 73 000–144 000 5 MW wind turbines, less than the 300 000 airplanes the US produced during World War II, reducing US CO2 by 32.5–32.7% and nearly eliminating 15 000/yr vehicle-related air pollution deaths in 2020. In sum, use of wind, CSP, geothermal, tidal, PV, wave, and hydro to provide electricity for BEVs and HFCVs and, by extension, electricity for the residential, industrial, and commercial sectors, will result in the most benefit among the options considered. The combination of these technologies should be advanced as a solution to global warming, air pollution, and energy security. Coal-CCS and nuclear offer less benefit thus represent an opportunity cost loss, and the biofuel options provide no certain benefit and the greatest negative impacts.

1,299 citations


Journal ArticleDOI
TL;DR: In this article, the main achievements obtained with photocatalyst alternatives to TiO2 in the three main niches for this technology are summarized, with an historical perspective, in order to assess which of the photoactive materials are best for each particular application.
Abstract: Since the early development of this technology in the 1970s, TiO2 constitutes the archetypical photocatalyst due to its relatively high efficiency, low cost and availability. However, during the last decade a considerable number of new photocatalytic materials, either semiconductor or not, have been proposed as potential substitutes of TiO2, particularly in the case of solar applications, for which this standard photocatalyst is not very suitable because of its wide band gap. Semiconductors based on cations with d0 configuration such Ta5+ or Nb5+, as well as oxides or nitrides of d10 elements such as Bi3+, In3+ or Ga3+ are among the most successful novel photocatalysts, but non-semiconductor solids like cation-interchanged zeolites also produce interesting results. In addition, some classical semiconductors like ZnO or CdS, initially discarded as a consequence of their poor stability under irradiation, have been reconsidered as feasible photocatalysts for particular applications. This growing body of data requires new analysis of the challenges and opportunities facing photocatalysis in order to assess which of the photoactive materials are best for each particular application. In this review, we summarize, with an historical perspective, the main achievements obtained with photocatalyst alternatives to TiO2 in the three main niches for this technology: water splitting for hydrogen production, decontamination and disinfection processes, and organic synthesis.

1,119 citations


Journal ArticleDOI
TL;DR: Carbon nanotubes (CNTs) are a candidate material for use in lithium ion batteries due to their unique set of electrochemical and mechanical properties as mentioned in this paper, and the incorporation of CNTs as a conductive additive at a lower weight loading than conventional carbons, like carbon black and graphite, presents a more effective strategy to establish an electrical percolation network.
Abstract: Lithium ion batteries are receiving considerable attention in applications, ranging from portable electronics to electric vehicles, due to their superior energy density over other rechargeable battery technologies. However, the societal demands for lighter, thinner, and higher capacity lithium ion batteries necessitate ongoing research for novel materials with improved properties over that of state-of-the-art. Such an effort requires a concerted development of both electrodes and electrolyte to improve battery capacity, cycle life, and charge–discharge rates while maintaining the highest degree of safety available. Carbon nanotubes (CNTs) are a candidate material for use in lithium ion batteries due to their unique set of electrochemical and mechanical properties. The incorporation of CNTs as a conductive additive at a lower weight loading than conventional carbons, like carbon black and graphite, presents a more effective strategy to establish an electrical percolation network. In addition, CNTs have the capability to be assembled into free-standing electrodes (absent of any binder or current collector) as an active lithium ion storage material or as a physical support for ultra high capacity anode materials like silicon or germanium. The measured reversible lithium ion capacities for CNT-based anodes can exceed 1000 mAh g−1 depending on experimental factors, which is a 3× improvement over conventional graphite anodes. The major advantage from utilizing free-standing CNT anodes is the removal of the copper current collectors which can translate into an increase in specific energy density by more than 50% for the overall battery design. However, a developmental effort needs to overcome current research challenges including the first cycle charge loss and paper crystallinity for free-standing CNT electrodes. Efforts to utilize pre-lithiation methods and modification of the single wall carbon nanotube bundling are expected to increase the energy density of future CNT batteries. Other progress may be achieved using open-ended structures and enriched chiral fractions of semiconducting or metallic chiralities that are potentially able to improve capacity and electrical transport in CNT-based lithium ion batteries.

1,018 citations


Journal ArticleDOI
TL;DR: In this paper, a comparison of binary and ternary platinum-based catalysts and non-platinum based catalysts for low-temperature fuel cells is presented, showing that the performance of Pd and Pd-containing catalysts can be improved with the addition of a suitable metal such as Co or Fe.
Abstract: Carbon supported platinum is commonly used as anode and cathode electrocatalyst in low-temperature fuel cells fuelled with hydrogen or low molecular weight alcohols. The cost of Pt and the limited world supply are significant barriers to the widespread use of these types of fuel cells. Moreover, platinum used as anode material is readily poisoned by carbon monoxide, present in the reformate gas used as H2 carrier in the case of polymer electrolyte fuel cells, and a byproduct of alcohol oxidation in the case of direct alcohol fuel cells. In addition, Pt alone does not present satisfactory activity for the oxygen reduction reaction when used as cathode material. For all these reasons, binary and ternary platinum-based catalysts and non-platinum-based catalysts have been tested as electrode materials for low temperature fuel cells. Palladium and platinum have very similar properties because they belong to the same group in the periodic table. The activity for the oxygen reduction reaction (ORR) of Pd is only slightly lower than that of Pt, and by addition of a suitable metal, such as Co or Fe, the ORR activity of Pd can overcome that of Pt. Conversely, the activity for the hydrogen oxidation reaction (HOR) of Pd is considerably lower than that of Pt, but by adding of a very small amount (5 at%) of Pt, the HOR activity of Pd attains that of pure Pt. This paper presents an overview of Pd and Pd-containing catalysts, tested both as anode and cathode materials for low-temperature fuel cells.

963 citations


Journal ArticleDOI
TL;DR: In this paper, the authors focus on the recent developments of nanostructured TiO2 and Sn-based anode materials, including rutile, anatase, coated TiO 2, and pristine SnO2, and SnO 2/C, Sn(M)/C composites.
Abstract: It is expected that the market dominance of lithium-ion batteries will continue for at least another decade as there are currently no competing alternatives with the versatility of lithium-ion batteries for powering mobile and portable devices; and for buffering the fluctuating supply of intermittent energy sources such as wind and solar. While the pursuit of higher energy density and higher power density materials constitute the bulk of current interest, there is increasing interest in durable active battery materials that can be produced with minimum environmental impact. It is with these considerations that TiO2- and Sn-based anode materials are most interesting candidates for fulfilling future green energy storage materials. This review will focus on the recent developments of nanostructured TiO2 and Sn-based anode materials, including rutile, anatase, TiO2 (B), and coated TiO2, and pristine SnO2, and SnO2/C, Sn(M)/C composites.

818 citations


Journal ArticleDOI
TL;DR: In this paper, the potential of single and tandem solar cells, the main experimental achievements reported in the literature so far, and design rules for efficient material combinations in bulk-heterojunction organic tandem solar cell are presented.
Abstract: In this article some brief theoretical considerations addressing the potential of single and tandem solar cells, the main experimental achievements reported in the literature so far and finally some design rules for efficient material combinations in bulk-heterojunction organic tandem solar cells are presented.

752 citations


Journal ArticleDOI
TL;DR: In this article, the authors discuss how the specific properties of biomass pose new requirements on the processes and on the solids that are used as catalysts for their conversion, and focus mostly on the desired properties of solid catalysts.
Abstract: The discovery and investigation of novel and efficient pathways for the conversion of biomass into fuels and chemicals are among the big challenges facing heterogeneous catalysis nowadays. However, not all experience gained in the transformation of hydrocarbons over the last 100 years can directly be transferred to biomass conversion. In this article, we will discuss how the specific properties of biomass pose new requirements on the processes and on the solids that are used as catalysts for their conversion. Due to the importance of lignocellulosic materials, which constitute ca. 95% of the total plant biomass, we will focus mostly on the desired properties of solid catalysts for the conversion of these polymeric biomolecules. Research in this field is very intense presently and novel transformations and catalysts are being discovered at a high rate. This paper thus focuses on the concepts that govern biomass transformation instead of giving a complete and comprehensive survey of the literature, which would be outdated within a short time.

651 citations


Journal ArticleDOI
TL;DR: In this article, a brief account of the most recent developments observed in the application of ZnO nanostructured materials in excitonic solar cells (organic, hybrid and dye sensitized solar cells).
Abstract: This work is a brief account of the most recent developments observed in the application of ZnO nanostructured materials in excitonic solar cells (organic, hybrid and dye sensitized solar cells). Special emphasis is made to one-dimensional (1D), vertically-aligned nanostructures (nanowires NW, nanorods NR) of ZnO semiconductor oxide and the extensive research work invested in recent years for its application as an electron acceptor material in solar cells. Our aim is to give the reader a broad overview of this semiconductor oxide and to understand the causes, advantages and disadvantages, for its application in a well-aligned nanostructure form. We briefly describe the most applied methodologies for its synthesis as well as the effect on surface area, electron transport and charge recombination when it is applied as an electron transport material in excitonic solar cells (XSCs). The importance of low-cost and easy-scalable synthesis techniques, as well as stability issues on these solar cells are discussed. Finally, we include a brief analysis of the possible future trends for the application of this interesting semiconductor oxide in XSCs.

650 citations


Journal ArticleDOI
TL;DR: A review of the current knowledge of the chemical physics of CO2 photoreduction on titania (TiO2)-based catalysts and Ti-species in porous materials is presented in this paper.
Abstract: This article is a review of the current knowledge of the chemical physics of carbon dioxide (CO2) conversion to fuels using light energy and water (CO2 photoreduction) on titania (TiO2)-based catalysts and Ti-species in porous materials. Fairly comprehensive literature reviews of CO2 photoreduction are available already. However, this article is focused on CO2 photoreduction on Ti-based catalysts, and incorporates fundamental aspects of CO2 photoreduction, knowledge from surface science studies of TiO2 and the surface chemistry of CO2. Firstly, the current state of development of this field is briefly reviewed, followed by a description of and insights from surface state and surface site approaches. Using examples such as metal-doping of TiO2, dye-sensitization, oxygen vacancies in TiO2 and isolated-Ti centers in microporous/mesoporous materials, the utility of these approaches to understand photoinduced reactions involved in CO2activation is examined. Finally, challenges and prospects for further development of this field are presented. Enhanced understanding of the CO2 : TiO2 system, with a combination of computational and experimental studies is required to develop catalysts exhibiting higher activity towards CO2 photoreduction.

646 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used Electrochemical impedance spectroscopy (EIS) to study the internal resistance of microbial fuel cells (MFCs), electrode materials, catalyst coatings on electrodes, biofilm development and electrochemical reactions on the anodes and the cathodes of MFCs.
Abstract: Electrochemical impedance spectroscopy (EIS) is a powerful nondestructive technique that can act as a beneficial addition to the current techniques for studying microbial fuel cells (MFCs). Its application in MFC research should be further explored in the analysis of the internal resistance of MFCs, electrode materials, catalyst coatings on electrodes, biofilm development and electrochemical reactions on the anodes and the cathodes of MFCs.

Journal ArticleDOI
TL;DR: In this paper, five approaches for changing the fatty acid profile of biodiesel fuel have been discussed, including physical means, genetic modification of the feedstock or use of alternative feedstocks with different fatty acid profiles.
Abstract: Biodiesel is an alternative to petroleum-derived diesel fuel composed of alkyl esters of vegetable oils, animal fats or other feedstocks such as used cooking oils. The fatty acid profile of biodiesel corresponds to that of its feedstock. Most common feedstocks possess fatty acid profiles consisting mainly of five C16 and C18 fatty acids, namely, palmitic (hexadecanoic), stearic (octadecanoic), oleic (9(Z)-octadecenoic), linoleic (9(Z),12(Z)-octadecadienoic) and linolenic (9(Z),12(Z),15(Z)-octadecatrienoic) acids, with the exception of a few oils such as coconut oil, which contains high amounts of saturated acids in the C12–C16 range or others. While in many respects biodiesel possesses advantages or is competitive with petroleum-derived diesel fuel, virtually all biodiesel fuels, typically the methyl esters, produced from these oils have performance problems such as poor low-temperature properties or insufficient oxidative stability. Considerable research has focused on solving or alleviating these problems and five approaches have been developed. Besides the approach of using additives, changing the fatty ester composition by either varying the alcohol or the fatty acid profile of the oil have been studied. Changing the fatty acid profile can be achieved by physical means, genetic modification of the feedstock or use of alternative feedstocks with different fatty acid profiles. In some cases approaches may overlap. This article briefly summarizes the five approaches currently used with an emphasis on those dealing with changing the fatty ester composition of a biodiesel fuel.

Journal ArticleDOI
TL;DR: In this article, the epitaxial growth of multijunction cells is considered to maximize light absorption and minimize I2R losses in the gridlines and the semiconductor sheet.
Abstract: Concerns about the changing environment and fossil fuel depletion have prompted much controversy and scrutiny. One way to address these issues is to use concentrating photovoltaics (CPV) as an alternate source for energy production. Multijunction solar cells built from III–V semiconductors are being evaluated globally in CPV systems designed to supplement electricity generation for utility companies. The high efficiency of III–V multijunction concentrator cells, with demonstrated efficiency over 40% since 2006, strongly reduces the cost of CPV systems, and makes III–V multijunction cells the technology of choice for most concentrator systems today. In designing multijunction cells, consideration must be given to the epitaxial growth of structures so that the lattice parameter between material systems is compatible for enhancing device performance. Low resistance metal contacts are crucial for attaining high performance. Optimization of the front metal grid pattern is required to maximize light absorption and minimize I2R losses in the gridlines and the semiconductor sheet. Understanding how a multijunction device works is important for the design of next-generation high efficiency solar cells, which need to operate in the 45%–50% range for a CPV system to make better economical sense. However, the survivability of solar cells in the field is of chief concern, and accelerated tests must be conducted to assess the reliability of devices during operation in CPV systems. These topics are the focus of this review.

Journal ArticleDOI
TL;DR: Due to their unusual sets of properties, ionic liquids have many important applications in devices and processes for the production, storage and efficient use of energy and other resources as mentioned in this paper, and they have been used in many applications.
Abstract: Due to their unusual sets of properties, ionic liquids have many important applications in devices and processes for the production, storage and efficient use of energy and other resources.

Journal ArticleDOI
TL;DR: In this paper, the authors present an overview of the computation approach aimed at designing better electrode materials for lithium ion batteries and show how each relevant property can be related to the structural component in the material and can be computed from first principles.
Abstract: First principles computation methods play an important role in developing and optimizing new energy storage and conversion materials. In this review, we present an overview of the computation approach aimed at designing better electrode materials for lithium ion batteries. Specifically, we show how each relevant property can be related to the structural component in the material and can be computed from first principles. By direct comparison with experimental observations, we hope to illustrate that first principles computation can help to accelerate the design and development of new energy storage materials.

Journal ArticleDOI
TL;DR: In this article, cyclic voltammetry (CV) of wild type (WT) and mutant G. sulfurreducens strains was used to demonstrate the use of bound extracellular electron transfer mediators by Geobacter biofilms and the distinct roles of OmcB and OmcZ.
Abstract: Geobacteracea are distinct for their ability to reduce insoluble oxidants including minerals and electrodes without apparent reliance on soluble extracellular electron transfer (ET) mediators. This property makes them important anode catalysts in new generation microbial fuel cells (MFCs) because it obviates the need to replenish ET mediators otherwise necessary to sustain power. Here we report cyclic voltammetry (CV) of biofilms of wild type (WT) and mutant G. sulfurreducens strains grown on graphite cloth anodes acting as electron acceptors with acetate as the electron donor. Our analysis indicates that WT biofilms contain a conductive network of bound ET mediators in which OmcZ (outer membranec-type cytochrome Z) participates in homogeneous ET (through the biofilm bulk) while OmcB mediates heterogeneous ET (across the biofilm/electrode interface); that type IV pili are important in both reactions; that OmcS plays a secondary role in homogenous ET; that OmcE, important in Fe(III) oxide reduction, is not involved in either reaction; that catalytic current is limited overall by the rate of microbial uptake of acetate; that protons generated from acetate oxidation act as charge compensating ions in homogenous ET; and that homogenous ET, when accelerated by fast voltammetric scan rates, is limited by diffusion of protons within the biofilm. These results provide the first direct electrochemical evidence substantiating utilization of bound ET mediators by Geobacter biofilms and the distinct roles of OmcB and OmcZ in the extracellular ET properties of anode-reducing G. sulfurreducens.

Journal ArticleDOI
TL;DR: In this article, a review of photocatalysis for water splitting by various kinds of metal oxides and nitrides such as ferroelectric metal oxide, different kinds of titanates with d0 (Ti4+) electronic configuration as a core metal ion, and various typical metal oxide with d10 (In3+, Ga3+, Ge4+, Sn4+, Sb5+) configuration, and d10(Ga3+) metal nitride, together with d 10s2 (Pb2+) and d0f0 (Ce4+) metal oxided
Abstract: This article reviews photocatalysis for water splitting by various kinds of metal oxides and nitrides such as ferroelectric metal oxides, different kinds of titanates with d0 (Ti4+) electronic configuration as a core metal ion, and various typical metal oxides with d10 (In3+, Ga3+, Ge4+, Sn4+, Sb5+) configuration, and d10 (Ga3+) metal nitride, together with d10s2 (Pb2+) and d0f0 (Ce4+) metal oxides. Ferroelectric metal oxides with single domain structure showed anomalous photovoltaic effects that controlled the behavior of photoexcited electrons. Various metal oxides involving ionic alkaline metal/alkaline earth metal ions showed good correlation between photocatalytic activity and the distortion of octahedral XO6/tetrahedral XO4 (X = core metal ion). When the metal oxides involved covalent metal ions such as Zn2+ and Pb2+, the activity was invoked even in distortion-free structures: this is due to strong electronic effects that affect the band structure. The activity of d10 metal oxides and nitrides is associated with conduction bands of hybridized sp orbitals with large dispersion that are able to generate photoexcited electrons with large mobility. A feature of the photocatalytically active metal oxides and nitrides discovered so far, which is their closed shell electronic structures is discussed.

Journal ArticleDOI
TL;DR: The central role of heterogeneous catalysis in biomass conversion is discussed and the science of catalysis and the different routes to make biofuels are reviewed.
Abstract: Lignocellulosic biofuels have a tremendous potential to reduce problems caused by our dependence on fossil fuels. The current roadblock with biofuels is the lack of economical conversion technologies. Heterogeneous catalysis offers immense potential in helping to make lignocellulosic biofuels a commercial reality. In this article we discuss the central role of heterogeneous catalysis in biomass conversion. We review the science of catalysis and the different routes to make biofuels. During the last several decades multiple new spectroscopic, theoretical, and synthesis tools are available that allow us to study catalysis at a molecular level. These new tools will allow us to rapidly develop new catalytic processes for the production of cost-efficient lignocellulosic biofuels.

Journal ArticleDOI
TL;DR: In this article, the authors focus on an important set of solar, thermal, and electrochemical energy conversion, storage, and conservation technologies specifically related to recent and prospective advances in nanoscale science and technology that offer high potential in addressing the energy challenge.
Abstract: The creation of a sustainable energy generation, storage, and distribution infrastructure represents a global grand challenge that requires massive transnational investments in the research and development of energy technologies that will provide the amount of energy needed on a sufficient scale and timeframe with minimal impact on the environment and have limited economic and societal disruption during implementation. In this opinion paper, we focus on an important set of solar, thermal, and electrochemical energy conversion, storage, and conservation technologies specifically related to recent and prospective advances in nanoscale science and technology that offer high potential in addressing the energy challenge. We approach this task from a two-fold perspective: analyzing the fundamental physicochemical principles and engineering aspects of these energy technologies and identifying unique opportunities enabled by nanoscale design of materials, processes, and systems in order to improve performance and reduce costs. Our principal goal is to establish a roadmap for research and development activities in nanoscale science and technology that would significantly advance and accelerate the implementation of renewable energy technologies. In all cases we make specific recommendations for research needs in the near-term (2–5 years), mid-term (5–10 years) and long-term (>10 years), as well as projecting a timeline for maturation of each technological solution. We also identify a number of priority themes in basic energy science that cut across the entire spectrum of energy conversion, storage, and conservation technologies. We anticipate that the conclusions and recommendations herein will be of use not only to the technical community, but also to policy makers and the broader public, occasionally with an admitted emphasis on the US perspective.

Journal ArticleDOI
TL;DR: In this paper, the use of semiconductors, more specifically CdS-based semiconductor, which are able to absorb photons in the visible region of the spectrum, is discussed.
Abstract: The demand for hydrogen over the coming decade is expected to grow for both traditional uses (ammonia, methanol, refinery) and running fuel cells. At least in the near future, this thirst for hydrogen will be quenched primarily through the reforming of fossil fuels. However, reforming fossil fuels emits huge amounts of carbon dioxide. One approach to reduce carbon dioxide emissions, which is considered first in this review, is to apply reforming methods to alternative renewable materials. Such materials might be derived from plant crops, agricultural residues, woody biomass, etc. Clean biomass is a proven source of renewable energy that is already used for generating heat, electricity, and liquid transportation fuels. Clean biomass and biomass-derived precursors such as ethanol and sugars are appropriate precursors for producing hydrogen through different conversion strategies. Virtually no net greenhouse gas emissions result because a natural cycle is maintained, in which carbon is extracted from the atmosphere during plant growth and released during hydrogen production. The second option explored here is hydrogen production from water splitting by means of the photons in the visible spectrum. The sun provides silent and precious energy that is distributed fairly evenly all over the earth. However, its tremendous potential as a clean, safe and economical energy source cannot be exploited unless it is accumulated or converted into more useful forms of energy. Finally, this review discusses the use of semiconductors, more specifically CdS and CdS-based semiconductors, which are able to absorb photons in the visible region of the spectrum. The energy stored within a semiconductor as electronic energy (electrons and holes) can be used to split water molecules by simultaneous reactions into H2 and O2. This conversion of solar energy into a clean fuel (H2) is perhaps the greatest challenge for scientists in the 21st century.

Journal ArticleDOI
TL;DR: In this article, the authors reviewed salient features of electrochemical capacitors employing hydrogel-polymer electrolytes and showed that they have a wide potential window of ca. 4 V and hence can provide high energy-density.
Abstract: Electrochemical capacitors are electrochemical devices with fast and highly reversible charge-storage and discharge capabilities. The devices are attractive for energy storage particularly in applications involving high-power requirements. Electrochemical capacitors employ two electrodes and an aqueous or a non-aqueous electrolyte, either in liquid or solid form; the latter provides the advantages of compactness, reliability, freedom from leakage of any liquid component and a large operating potential-window. One of the classes of solid electrolytes used in capacitors is polymer-based and they generally consist of dry solid-polymer electrolytes or gel-polymer electrolyte or composite-polymer electrolytes. Dry solid-polymer electrolytes suffer from poor ionic-conductivity values, between 10−8 and 10−7 S cm−1 under ambient conditions, but are safer than gel-polymer electrolytes that exhibit high conductivity of ca. 10−3 S cm−1 under ambient conditions. The aforesaid polymer-based electrolytes have the advantages of a wide potential window of ca. 4 V and hence can provide high energy-density. Gel-polymer electrolytes are generally prepared using organic solvents that are environmentally malignant. Hence, replacement of organic solvents with water in gel-polymer electrolytes is desirable which also minimizes the device cost substantially. The water containing gel-polymer electrolytes, called hydrogel-polymer electrolytes, are, however, limited by a low operating potential-window of only about 1.23 V. This article reviews salient features of electrochemical capacitors employing hydrogel-polymer electrolytes.

Journal ArticleDOI
TL;DR: In this paper, the authors suggest that more complex nanostructures, both in the form of hierarchically branching/hyperbranching nanowire structures and in the case of multi-component nanowires of diverse materials, are potentially even more interesting for solar energy harvesting and conversion.
Abstract: Nanoscience and nanotechnology can provide many benefits to photovoltaic and photoelectrochemical applications by combining novel nanoscale properties with processability and low cost. Taking advantage of high quality, high efficiency, yet low cost nanomaterials could potentially provide the new and transformative approaches to enable the proposed generation-III solar technologies. Nanowires are interesting because they have a long axis to absorb incident sunlight yet with a short radial distance to separate the photogenerated carriers. In this perspective, we further suggest that more “complex” nanostructures, both in the form of hierarchically branching/hyperbranching nanowire structures and in the form of multi-component nanowire heterostructures of diverse materials, are potentially even more interesting for solar energy harvesting and conversion. The common bottom-up synthetic techniques to induce branching in nanowires to form hierarchical nanowire structures are reviewed. Several potential strategies for their incorporation into solar conversion devices are discussed and some fundamental issues and future directions are identified.

Journal ArticleDOI
TL;DR: In this article, the authors compared the performance of boron hydrides in hydrogen and fuel cell applications and concluded that there are many similarities between SB and AB in their features and applications.
Abstract: Since the late 1990s, sodium borohydride (NaBH4, denoted SB) is presented as a promising hydrogen storage material and an attractive fuel (aqueous solution) of the direct fuel cell (or direct liquid-feed fuel cell). In 2007, the U.S. Department of Energy recommended a no-go for SB for vehicular applications and suggested work on ammonia borane (AB), another promising hydrogen storage material, which is also considered as a fuel for the direct fuel cell. Both boron hydrides in hydrogen and fuel cell applications are the topics of the present paper. The basics, issues, solutions to the issues and state-of-the-art are tackled but the discussion aims to compare the hydrides for either application. It is shown that there are many similarities between SB and AB in their features and applications. Nevertheless SB and AB as hydrogen storage materials do not compete. Rather, SB is intended more to portable technologies while AB to vehicular applications. Otherwise, when these hydrides are utilised as fuels of direct fuel cell, one question arises: what can be the advantage of developing the AB-powered fuel cell when it seems to be less effective, practical, and more complex than the SB-powered fuel cell? These aspects are discussed. However that may be, it is concluded that both SB and AB are not mature enough for the applications considered.

Journal ArticleDOI
TL;DR: The creation of a Synechocystis sp.
Abstract: Development of renewable energy is rapidly being embraced by our society and industry to achieve the nation's economic growth goals and to help address the world's energy and global warming crises. Currently most of the bioethanol production is from the fermentation of agricultural crops and residues. There is much debate concerning the cost effectiveness and energy efficiency of such biomass based ethanol production processes. Here, we report the creation of a Synechocystis sp. PCC 6803 strain that can photoautotrophically convert CO2 to bioethanol. Transformation was performed using a double homologous recombination system to integrate the pyruvate decarboxylase (pdc) and alcohol dehydrogenase II (adh) genes from obligately ethanol producing Zymomonas mobilis into the Synechocystis PCC 6803 chromosome under the control of the strong, light driven psbAII promoter. PCR based assay and ethanol production assay were used to screen for stable transformants. A computerized photobioreactor system was established for the experimental design and data acquisition for the analysis of the cyanobacterial cell cultures and ethanol production. The system described here shows an average yield of 5.2 mmol OD730 unit−1 litre−1 day−1 with no required antibiotic/selective agent.

Journal ArticleDOI
TL;DR: In this article, a passive-type biofuel cell was developed, which achieved a power density of 1.45 ± 0.24 mW cm−2 at 0.3 V. This performance was achieved by introducing three technologies: (1) Enzymes and mediator are densely entrapped on carbon-fiber electrodes with the enzymatic activity retained, (2) the concentration of buffer in electrolyte solution was optimized for the immobilized enzymes, and (3) the cathode structure was designed to supply O2 efficiently.
Abstract: Biofuel cells are a next-generation energy device because they use renewable fuels with high energy density and safety. We have developed passive-type biofuel cell units, which generate a power over 100 mW (80 cm3, 39.7 g). Our biofuel cell, in which two-electron oxidation of glucose and four-electron reduction of O2 occurs at pH 7 in mediated bioelectrochemical processes under quiescent conditions, accomplished the maximum power density of 1.45 ± 0.24 mW cm−2 at 0.3 V. This performance was achieved by introducing three technologies: (1) Enzymes and mediator are densely entrapped on carbon-fiber electrodes with the enzymatic activity retained, (2) the concentration of buffer in electrolyte solution was optimized for the immobilized enzymes, and (3) the cathode structure was designed to supply O2 efficiently. The cell units with a multi-stacked structure successfully operate a radio-controlled car (16.5 g), which demonstrates the potential of biofuel cells in practical applications.

Journal ArticleDOI
TL;DR: In this paper, high-dispersed Ru nanoparticles loaded on a TiO2 support (Ru/TiO2(B)), which affects the hydrogenation of CO2 to CH4 (methanation), were prepared by employing a "dry" modification method using a barrel-sputtering instrument.
Abstract: Highly dispersed Ru nanoparticles loaded on a TiO2 support (Ru/TiO2(B)), which affects the hydrogenation of CO2 to CH4 (methanation), were prepared by employing a “dry” modification method using a barrel-sputtering instrument. The loaded Ru nanoparticles exhibited a narrow particle-size distribution with a mean diameter of ca. 2.5 nm. Methanation of CO2 on the Ru/TiO2(B) catalyst produced a 100% yield at ca. 160 °C, which is more than 200 °C below that required for Ru/TiO2 prepared by a conventional “wet” impregnation method. In addition, the methanation reaction over Ru/TiO2(B) proceeded at temperatures as low as room temperature with a reaction rate of 0.04 µmol min−1 g−1.

Journal ArticleDOI
TL;DR: In this article, a review deals with recent progress in the fabrication, microstructure, and energy storage performance of different carbon nanotube arrays (CNTAs) electrodes and their composites in electrochemical capacitors and lithium-ion batteries.
Abstract: One of the greatest challenges for our society is to provide powerful electrochemical energy conversion and storage devices. Electrochemical capacitors and lithium-ion batteries are among the most promising candidates in terms of power- and energy-densities. The choice of electrode material is key to improving the performance of these energy conversion devices. Carbon nanotube arrays (CNTAs) and their composites show good capacity, excellent rate performance, and long cycle life when used as electrode materials because they present superior electronic conductivity, high surface area, developed porous structure, and robust properties. This review deals with recent progress in the fabrication, microstructure, and energy storage performance of different CNTA electrodes and their composites in electrochemical capacitors and lithium-ion batteries. In particular, representative examples of our CNTA-based electrodes are highlighted.

Journal ArticleDOI
TL;DR: In this paper, the bisthienothiophene conjugated linker along with a hydrophobic triphenylamine electron-donor and a hyphilic cyanoacrylic acid electron-acceptor was employed to construct a high molar extinction coefficient organic photosensitizer, exhibiting a power conversion efficiency of 8.0% measured under irradiation of air mass 1.5 global (AM 1 5G) full sunlight.
Abstract: We employed the bisthienothiophene conjugated linker along with a hydrophobic triphenylamine electron-donor and a hydrophilic cyanoacrylic acid electron-acceptor to construct a high molar extinction coefficient organic photosensitizer, exhibiting a power conversion efficiency of 8.0% measured under irradiation of air mass 1.5 global (AM 1.5G) full sunlight.

Journal ArticleDOI
TL;DR: In this paper, a validated and thermodynamically consistent kinetic model for the coupling of degradation and the catalyst particle size distribution was developed, showing that crossover hydrogen changes the surface area loss mechanism from coarsening to platinum loss through dissolution and precipitation off of the carbon support.
Abstract: This work demonstrates the essential role of particle size and crossover hydrogen on the degradation of platinum polymer electrolyte membrane fuel cell (PEMFC) cathodes. One of the major barriers to implementation of practical PEMFCs is the degradation of the cathode catalyst under operating conditions. This work combines both experimental and theoretical techniques to develop a validated and thermodynamically consistent kinetic model for the coupling of degradation and the catalyst particle size distribution. Our model demonstrates that, due to rapid changes in the Gibbs–Thomson energy, particle size effects dominate degradation for ∼2 nm particles but play almost no role for ∼5 nm particles. This result can help guide synthesis of more stable distributions. We also identify the effect of hydrogen molecules that cross over from the anode, demonstrating that in the presence of this crossover hydrogen surface area loss is greatly enhanced. We demonstrate that crossover hydrogen changes the surface area loss mechanism from coarsening to platinum loss through dissolution and precipitation off of the carbon support.

Journal ArticleDOI
TL;DR: In this article, block copolymers, which naturally self-assemble into periodic ordered nanostructures, can be utilized in diverse ways to control morphology, ranging from active layers to structure directors to a combination of these methodologies.
Abstract: Photovoltaic energy conversion is arguably the most promising option for supplying renewable, carbon-neutral energy on a global scale. In order to reach grid parity, however, costs must be reduced substantially. Inexpensive materials generally exhibit efficiencies too low for practical application, but by controlling the morphology on the nanoscale there are opportunities to achieve significant improvements in this area. Block copolymers, which naturally self-assemble into periodic ordered nanostructures, can be utilized in diverse ways to control morphology, ranging from active layers to structure directors to a combination of these methodologies.