Showing papers in "Energy and Environmental Science in 2010"
TL;DR: Density functional theory calculations explain copper's unique ability to convert CO2 into hydrocarbons, which may open up (photo-)electrochemical routes to fuels as mentioned in this paper, which may lead to new energy sources.
Abstract: Density functional theory calculations explain copper's unique ability to convert CO2 into hydrocarbons, which may open up (photo-)electrochemical routes to fuels.
2,420 citations
TL;DR: In this paper, the authors review and validate best practice test methods that accurately predict a material's performance, yet are flexible and quick enough to accommodate a wide range of material sample types and amounts.
Abstract: Ultracapacitors are rapidly being adopted for a wide range of electrical energy storage applications. While ultracapacitors are able to deliver high rates of charge and discharge, they are limited in the amount of energy stored. The capacity of ultracapacitors is largely determined by the electrode material and as a result research to improve the performance of electrode materials has dramatically increased. While test methods for packaged ultracapacitors are well developed, it is often impractical for the materials scientist to assemble full sized, packaged cells to test electrode materials. Methodology to reliably measure a material's performance for use as an ultracapacitor electrode is not well standardized with various techniques yielding widely varying results. In this manuscript, we review and validate best practice test methods that accurately predict a material's performance, yet are flexible and quick enough to accommodate a wide range of material sample types and amounts.
1,891 citations
TL;DR: In this paper, the authors present a review of CO2, its synthetic reactions and their possible role in future CO2 mitigation schemes that have to match the scale of man-made CO2 in the atmosphere, which rapidly approaches 1 teraton.
Abstract: The increase in atmospheric carbon dioxide is linked to climate changes; hence there is an urgent need to reduce the accumulation of CO2 in the atmosphere. The utilization of CO2 as a raw material in the synthesis of chemicals and liquid energy carriers offers a way to mitigate the increasing CO2 buildup. This review covers six important CO2 transformations namely: chemical transformations, photochemical reductions, chemical and electrochemical reductions, biological conversions, reforming and inorganic transformations. Furthermore, the vast research area of carbon capture and storage is reviewed briefly. This review is intended as an introduction to CO2, its synthetic reactions and their possible role in future CO2 mitigation schemes that has to match the scale of man-made CO2 in the atmosphere, which rapidly approaches 1 teraton.
1,771 citations
TL;DR: Three of the leading options for large scale CO2 capture are reviewed from a technical perspective, including solvent-based chemisorption techniques, carbonate looping technology, and the so-called oxyfuel process.
Abstract: In this paper, three of the leading options for large scale CO2 capture are reviewed from a technical perspective. We consider solvent-based chemisorption techniques, carbonate looping technology, and the so-called oxyfuel process. For each technology option, we give an overview of the technology, listing advantages and disadvantages. Subsequently, a discussion of the level of technological maturity is presented, and we conclude by identifying current gaps in knowledge and suggest areas with significant scope for future work. We then discuss the suitability of using ionic liquids as novel, environmentally benign solvents with which to capture CO2. In addition, we consider alternatives to simply sequestering CO2—we present a discussion on the possibility of recycling captured CO2 and exploiting it as a C1 building block for the sustainable manufacture of polymers, fine chemicals, and liquid fuels. Finally, we present a discussion of relevant systems engineering methodologies in carbon capture system design.
1,349 citations
TL;DR: In this paper, a sulfur-carbon sphere composite was proposed to enhance the long stability of sulfur cathode for a high energy lithium-sulfur battery system by encapsulating sulfur into micropores of carbon spheres.
Abstract: To enhance the long stability of sulfur cathode for a high energy lithium–sulfur battery system, a sulfur–carbon sphere composite was prepared by encapsulating sulfur into micropores of carbon spheres by thermal treatment of a mixture of sublimed sulfur and carbon spheres. The elemental sulfur exists as a highly dispersed state inside the micropores of carbon spheres with a large surface area and a narrow pore distribution, based on the analyses of the X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), thermogravimetry (TG) and local element line-scanning. It is demonstrated from galvanostatic discharge–charge process, cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) that the sulfur–carbon sphere composite has a large reversible capacity and an excellent high rate discharge capability as cathode materials. In particular, the sulfur–carbon sphere composite with 42 wt% sulfur presents a long electrochemical stability up to 500 cycles, based on the constrained electrochemical reaction inside the narrow micropores of carbon spheres due to strong adsorption. Therefore, the electrochemical reaction constrained inside the micropores proposed here would be the dominant factor for the enhanced long stability of the sulfur cathode. The knowledge acquired in this study is important not only for the design of efficient new electrode materials, but also for understanding the effect of the micropores on the electrochemical cycle stability.
1,202 citations
TL;DR: The main conclusions are that the biochemical composition of the biomass influences the economics, in particular, increased lipid content reduces other valuable compounds in the biomass; the “biofuel only” option is unlikely to be economically viable; and among the hardest problems in assessing the economics are the cost of the CO2 supply and uncertain nature of downstream processing.
Abstract: Following scrutiny of present biofuels, algae are seriously considered as feedstocks for next-generation biofuels production. Their high productivity and the associated high lipid yields make them attractive options. In this review, we analyse a number aspects of large-scale lipid and overall algal biomass production from a biochemical and energetic standpoint. We illustrate that the maximum conversion efficiency of total solar energy into primary photosynthetic organic products falls in the region of 10%. Biomass biochemical composition further conditions this yield: 30 and 50% of the primary product mass is lost on producing cell protein and lipid. Obtained yields are one third to one tenth of the theoretical ones. Wasted energy from captured photons is a major loss term and a major challenge in maximising mass algal production. Using irradiance data and kinetic parameters derived from reported field studies, we produce a simple model of algal biomass production and its variation with latitude and lipid content. An economic analysis of algal biomass production considers a number of scenarios and the effect of changing individual parameters. Our main conclusions are that: (i) the biochemical composition of the biomass influences the economics, in particular, increased lipid content reduces other valuable compounds in the biomass; (ii) the “biofuel only” option is unlikely to be economically viable; and (iii) among the hardest problems in assessing the economics are the cost of the CO2 supply and uncertain nature of downstream processing. We conclude by considering the pressing research and development needs.
1,128 citations
TL;DR: It is argued that a large, collaborative international research programme is necessary to fully develop the potential of electrochemical capacitors.
Abstract: Electrochemical capacitors, also known as supercapacitors, are becoming increasingly important components in energy storage, although their widespread use has not been attained due to a high cost/performance ratio. Fundamental research is contributing to lowered costs through the engineering of new materials. Currently the most viable materials used in electrochemical capacitors are biomass-derived and polymer-derived activated carbons, although other carbon materials are useful research tools. Metal oxides could result in a step change for electrochemical capacitor technology and is an exciting area of research. The selection of an appropriate electrolyte and electrode structure is fundamental in determining device performance. Although there are still many uncertainties in understanding the underlying mechanisms involved in electrochemical capacitors, genuine progress continues to be made. It is argued that a large, collaborative international research programme is necessary to fully develop the potential of electrochemical capacitors.
985 citations
TL;DR: In this paper, the factors that affect charge recombination and electron injection efficiency systematically discussed in order to formulate basic guidelines and strategies for improving open circuit voltage and the overall performance of DSCs is reviewed.
Abstract: The dye-sensitized solar cell (DSC) has been regarded as one of the most promising next-generation solar cells. Tremendous research efforts have been invested to improve the efficiency of solar energy conversion which is generally determined by the light harvesting efficiency, electron injection efficiency and undesirable charge recombination degree. Recently, charge recombination and electron injection efficiency, that are correlated with the open circuit voltage (Voc), have received more and more attention for their crucial roles in the further improvement of the efficiency of DSCs. In this review article, the factors that affect charge recombination and electron injection efficiency systematically discussed in order to formulate basic guidelines and strategies for improving Voc and the overall performance of DSCs is reviewed.
689 citations
TL;DR: In this paper, the utilization of carbon dioxide and formic acid for hydrogen storing is discussed, and the problem of storing appropriate amounts of hydrogen is addressed in the context of a hydrogen economy.
Abstract: In search for future energy supplies the application of hydrogen as an energy carrier is seen as a prospective issue. However, the implementation of a hydrogen economy is suffering from several unsolved problems. Particularly challenging is the storage of appropriate amounts of hydrogen. In this context the utilization of carbon dioxide–formic acid for hydrogen storing is discussed.
615 citations
TL;DR: A critical review of novel achievements in the modification of N-TiO2 photocatalytic systems aimed at enhancing TiO2 applications in the areas of energy conversion and environmental clean-up is presented in this article.
Abstract: This paper presents a critical review of novel achievements in the modification of N–TiO2 photocatalytic systems aimed at enhancing TiO2 applications in the areas of energy conversion and environmental clean-up. Herein we studied the synthesis, physical properties, as well as synergism of modified N-doped TiO2. Based on the studies reported in the literature, metal, nonmetal and metal oxide modified N–TiO2 are very effective systems to extend the activating spectra to the visible range. Therefore, modified N–TiO2 play an important role in the development of efficient photocatalysts for future perspectives.
585 citations
TL;DR: In this article, the nitrogen functional groups introduced into a carbon support appear to influence at least three aspects of the catalyst/support system: modified nucleation and growth kinetics during catalyst nanoparticle deposition, which results in smaller catalyst particle size and increased catalyst particle dispersion, increased support/catalyst chemical binding (or "tethering"), and catalyst particle electronic structure modification, which enhances intrinsic catalytic activity.
Abstract: Insufficient catalytic activity and durability are key barriers to the commercial deployment of low temperature polymer electrolyte membrane (PEM) and direct-methanol fuel cells (DMFCs). Recent observations suggest that carbon-based catalyst support materials can be systematically doped with nitrogen to create strong, beneficial catalyst-support interactions which substantially enhance catalyst activity and stability. Data suggest that nitrogen functional groups introduced into a carbon support appear to influence at least three aspects of the catalyst/support system: 1) modified nucleation and growth kinetics during catalyst nanoparticle deposition, which results in smaller catalyst particle size and increased catalyst particle dispersion, 2) increased support/catalyst chemical binding (or “tethering”), which results in enhanced durability, and 3) catalyst nanoparticle electronic structure modification, which enhances intrinsic catalytic activity. This review highlights recent studies that provide broad-based evidence for these nitrogen-modification effects as well as insights into the underlying fundamental mechanisms.
TL;DR: In this article, a review of recent advances in the research field of high energy density electrode materials with focus on multi-electron reaction chemistry of light-weight elements and compounds is presented.
Abstract: The need for high energy density batteries becomes increasingly important for the development of new and clean energy technologies, such as electric vehicles and electrical storage from wind and solar power. The search for new energetic materials of primary and secondary batteries with higher energy density has been highlighted in recent years. This review surveys recent advances in the research field of high energy density electrode materials with focus on multi-electron reaction chemistry of light-weight elements and compounds. In the first section, we briefly introduce the basic strategies for enhancement of the energy density of primary batteries based on multi-electron reactions. The following sections present overviews of typical electrode materials with multi-electron chemistry and their secondary battery applications in aqueous and non-aqueous electrolytes. Finally, the challenges and ongoing research strategies of these novel electrode materials and battery systems for high density energy storage and conversion are discussed.
TL;DR: In this article, a semi-transparent flexible polymer solar cells were manufactured in a full roll-to-roll process under ambient conditions and encapsulation was printed onto the back side of the polymer solar cell module followed by sheeting and application of discrete components and vias.
Abstract: Semitransparent flexible polymer solar cells were manufactured in a full roll-to-roll process under ambient conditions. After encapsulation a silver based circuit was printed onto the back side of the polymer solar cell module followed by sheeting and application of discrete components and vias. The discrete components were white light LEDs, a blocking diode, a lithium ion battery, vias and button contacts in two adjacent corners. The completed lamp has outside dimensions of 22.5 × 30.5 cm, a weight of 50 g and a very flat outline. The battery and components were the thickest elements and measured < 1 mm. A hole with a ring was punched in one corner to enable mechanical fixation or tying. The lamp has two states. In the charging state it has a completely flat outline and will charge the battery when illuminated from either side while the front side illumination is preferable. When used as a lamp two adjacent corners are joined via button contacts whereby the device can stand on a horizontal surface and the circuit is closed such that the battery discharges through the LEDs that illuminate the surface in front of the lamp. Several different lamps were prepared using the same solar cell and circuitry while varying the amount of white LEDs employed and by variation of the number of batteries and the individual battery capacity. The lamp prototype was developed through two early prototypes and the final and serially produced prototype was subjected to field tests in Zambia. Some of the lamps were recovered and the experiences gained with the prototype are presented allowing for further development that takes systemic factors such as the immediate response and spontaneous handling of the lamp by someone with no prior knowledge of the lamp or its workings.
TL;DR: In this paper, the results of all-inorganic materials for catalytic water oxidation reported recently from other laboratories, in particular electrodeposits generated from Co phosphate solutions, a molecular water oxidation catalyst based on a polyoxotungstate featuring a Co oxide core, and Mn oxide materials with incorporated Ca ions are reviewed.
Abstract: Recent development of new methods of preparing cobalt oxide and manganese oxide clusters has led to oxygen evolving catalysts that operate under mild conditions and modest overpotentials at rates approaching practical utility. Synthesis of nanostructured Co3O4 and Mn oxide clusters in mesoporous silica scaffolds affords catalysts with very high densities of surface metal sites per projected area, with the silica environment providing stability in terms of dispersion of the clusters and prevention of restructuring of catalytic surface sites. Stacking of the nanoclusters of these earth abundant, durable oxide catalysts in the scaffold results in turnover frequencies per projected area that are sufficient for keeping up with the photon flux at high solar intensity. Opportunities for expanding the metal oxide/silica interface approach to heterogeneous water oxidation catalysis to a more general approach for multi-electron catalyst designs based on core/shell constructs are discussed. The results are reviewed in the context of all-inorganic materials for catalytic water oxidation reported recently from other laboratories, in particular electrodeposits generated from Co phosphate solutions, a molecular water oxidation catalyst based on a polyoxotungstate featuring a Co oxide core, and Mn oxide materials with incorporated Ca ions.
TL;DR: In this article, the authors review the range of Enhanced Oil Recovery techniques, broadly classified into either thermal or non-thermal methods, and their applicability to the extraction of heavy oils and bitumens.
Abstract: With World oil demand increasing in the face of limited supplies, increasing attention is turning towards non-conventional oil sources as a means to relieve the pressure exerted on conventional stocks. However, non-conventional oils are hard to extract, process and transport. Several technologies are already at work with differing levels of success, recovery ranging from as low as 5% through to more than 70%. This paper reviews the range of Enhanced Oil Recovery techniques, broadly classified into either thermal or non-thermal methods, and their applicability to the extraction of heavy oils and bitumens. Advantages and disadvantages are presented in terms of their recovery factors, requirements, limitations and economics. The potential benefits of additional downhole catalytic upgrading of heavy oils are also explored.
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TL;DR: In this article, the advantages and limitations of using a fuel cell as an energy converter for electric vehicles are discussed. And an outlook is given that addresses cost targets and infrastructure opportunities as well as requirements.
Abstract: The energy storage system is of decisive importance for all types of electric vehicles, in contrast to the case of vehicles powered by a conventional fossil fuel or bio-fuel based internal combustion engine. Two major alternatives exist and need to be discussed: on the one hand, there is the possibility of electrical energy storage using batteries, whilst on the other hand there is the storage of energy in chemical form as hydrogen and the application of a fuel cell as energy converter. The advantages and limitations, and also the impact of both options are described. To do so, existing GM concept vehicles and mass production vehicles are presented. Eventually, an outlook is given that addresses cost targets and infrastructure opportunities as well as requirements.
TL;DR: In this article, the role of both the promoter and support play on the catalysts' activity is reviewed, and the role that both the promoters and support plays on the catalyst's activity is discussed.
Abstract: The impact that anthropogenic CO2 is having on the environment has been thoroughly documented over the last 20 years. Many different technologies have been proposed to reduce its impact on global warming such as geological sequestration. However, an interesting and attractive alternative would be the recycling of the gas into energy-rich molecules. Iron rather than cobalt catalysts, based on the Fischer–Tropsch technology, have shown the greatest promise in converting CO2 to value-added hydrocarbons. The addition of co-catalysts is, however, essential to fine tune the product distribution to the more desired alkene products. The role that both the promoter and support play on the catalyst's activity is reviewed.
TL;DR: An overview of the opportunities, progresses, and challenges in the rapidly accelerating field of nanopiezoelectrics suggests a rich platform for a host of exciting avenues in fundamental research and novel applications.
Abstract: The development of a method for efficiently harvesting energy from the human body could enable extraordinary advances in biomedical devices and portable electronics. Being electromechanically coupled, nanopiezoelectrics represent a promising new materials paradigm for scavenging otherwise wasted energy, with the ultimate goal of replacing or augmenting batteries. Of particular interest is developing biomechanical energy nanogenerators that are highly efficient, but with flexible form factors for wearable or implantable applications. This perspective presents an overview of the opportunities, progresses, and challenges in the rapidly accelerating field of nanopiezoelectrics. The combination of new nanomaterial properties, novel assembly strategies, and breakthrough device performance metrics suggests a rich platform for a host of exciting avenues in fundamental research and novel applications.
TL;DR: In this paper, a new approach of tailoring the properties of metal hydrides through size restriction at the nanoscale is discussed, which already shows great promise in leading to further breakthroughs because both thermodynamics and kinetics can be effectively controlled at molecular levels.
Abstract: Storing hydrogen in materials is based on the observation that metals can reversibly absorb hydrogen. However, the practical application of such a finding is found to be rather challenging especially for vehicular applications. The ideal material should reversibly store a significant amount of hydrogen under moderate conditions of pressures and temperatures. To date, such a material does not exist, and the high expectations of achieving the scientific discovery of a suitable material simultaneously with engineering innovations are out of reach. Of course, major breakthroughs have been achieved in the field, but the most promising materials still bind hydrogen too strongly and often suffer from poor hydrogen kinetics and/or lack of reversibility. Clearly, new approaches have to be explored, and the knowledge gained with high-energy ball milling needs to be exploited, i.e. size does matter! Herein, progress made towards the practical use of magnesium as a hydrogen store and the barriers still remaining are reviewed. In this context, the new approach of tailoring the properties of metal hydrides through size restriction at the nanoscale is discussed. Such an approach already shows great promise in leading to further breakthroughs because both thermodynamics and kinetics can be effectively controlled at molecular levels.
TL;DR: In this article, a working direct urea and direct urine fuel cell has been developed to generate electricity directly from urea or urine, which is the first time such a system has been used.
Abstract: For the first time, a working direct urea and direct urine fuel cell has been developed to generate electricity directly from urea or urine.
TL;DR: In this paper, the authors investigated the use of an air-cathode microbial desalination cell (MDC) as an RO pre-treatment method using a new type of air cathode MDC containing three equally sized chambers.
Abstract: A microbial desalination cell (MDC) is a new method to reduce the salinity of one solution while generating electrical power from organic matter and bacteria in another (anode) solution. Substantial reductions in the salinity can require much larger volumes of the anode solution than the saline water, but any reduction of salinity will benefit the energy efficiency of a downstream reverse osmosis (RO) desalination system. We investigated here the use of an MDC as an RO pre-treatment method using a new type of air-cathode MDC containing three equally sized chambers. A single cycle of operation using a 1 g L−1 acetate solution reduced the conductivity of salt water (5 g L−1 NaCl) by 43 ± 6%, and produced a maximum power density of 480 mW m−2 with a coulombic efficiency of 68 ± 11%. A higher concentration of acetate (2 g L−1) reduced solution conductivity by 60 ± 7%, and a higher salt concentration (20 g L−1 NaCl) reduced solution conductivity by 50 ± 7%. The use of membranes with increased ion exchange capacities further decreased the solution conductivity by 63 ± 2% (20 g L−1 NaCl). These results demonstrate substantial (43–67%) desalination of water is possible using equal volumes of anode solution and salt water. These results show that MDC treatment could be used to substantially reduce salt concentrations and thus energy demands for downstream RO processing, while at the same time producing electrical power.
TL;DR: In this article, the authors assess the current knowledge on biomass resource potentials and interrelated factors such as water availability, biodiversity, food demand, energy demand and agricultural commodity markets.
Abstract: The growing use of bioenergy goes hand in hand with a heated public debate, in which conflicting claims are made regarding the amount of biomass that can be sustainably used for this purpose. This article assesses the current knowledge on biomass resource potentials and interrelated factors such as water availability, biodiversity, food demand, energy demand and agricultural commodity markets. A sensitivity analysis of the available information narrows the range of biomass potentials from 0–1500 EJ/yr to approximately 200–500 EJ/yr in 2050. In determining the latter range, water limitations, biodiversity protection and food demand are taken into consideration. Key factors are agricultural efficiency and crop choice. In principle, global biomass potentials could meet up to one third of the projected global energy demand in 2050.
TL;DR: In this article, a simple approach for the synthesis of mesoporous TiO2 anatase using a soft-template method, which shows superior storage performance without such conductive surface layers.
Abstract: Micrometre-sized mesoporous materials have characteristic grains as well as pores nearly in the same scale. Electrodes of mesoporous materials for lithium batteries have short transport lengths for Li+ ions due to their nano-sized grains (10–20 nm), and easy access for electrolytes due to their nanopores (5–10 nm). Such mesoporous materials have high packing densities unlike nanopowders, nanowires, nanorods and nanotubes. Despite such advantages, electronic conduction over micrometre-sized particles limits the rate performance of mesporous materials. Occasionally counductive thin layers (2–5 nm) of carbon or RuO2 have been used to overcome such kinetic limitations and to achieve high storage performances. In this manuscript, we present a simple approach for the synthesis of mesoporous TiO2 anatase using a soft-template method, which shows superior storage performance without such conductive surface layers. Various cationic surfactants with different chain lengths have been selected for this investigation to assist the formation of the mesoporous TiO2 structure. Among these, cetyl trimethylammoniumbromide templated C16-TiO2 has the highest surface area of 135 m2 g−1 and reversible capacity of 288, 220, 138,134 and 107 mAh g−1 at 0.2, 1, 5, 10 and 30C respectively. The storage performance of the as-synthesized mesoporous TiO2 is nearly five times better than the commercially available TiO2 nanopowder. The packing density of meso-TiO2 is found to be 6.6 times higher than the TiO2 nanopowder. In addition, battery testing using mesoporous TiO2 electrodes without the 15% carbon additive exhibits nearly the same performance at low rate as the meso-TiO2 with carbon additives. These exciting results suggest a facile conduction path for electrons, a unique character of micrometre-sized mesoporous TiO2 with highly interconnected nanograins of 15–20 nm.
TL;DR: Amorphous carbon bearing sulfonic acid groups, a new type of solid Bronsted acid catalyst, was investigated for potential application to environmentally benign biodiesel production and cellulose saccharification as discussed by the authors.
Abstract: Amorphous carbon bearing sulfonic acid groups, a new type of solid Bronsted acid catalyst, was investigated for potential application to environmentally benign biodiesel production and cellulose saccharification. The carbon material exhibits much higher catalytic performance for the esterification of higher fatty acids, transesterification of triglycerides and the hydrolysis of cellulose than conventional solid acid catalysts.
TL;DR: In this article, the current status of the long-term stability of dye solar cells and factors affecting it are reviewed, and the authors conclude that techniques giving chemical information are needed for the stability investigations of DSCs to reveal possible ways to improve their lifetime.
Abstract: The current status of the long-term stability of dye solar cells (DSCs) and factors affecting it is reviewed. The purpose is to clarify present knowledge of degradation phenomena and factors in these cells by critically separating the assumptions from the solid experimental evidence reported in the literature. Important degradation processes such as dye desorption, decrease in the tri-iodide concentration, degradation at the photoelectrode and counter electrode, affect of ultraviolet light and moisture, and issues related to the sealing, are covered. It is concluded that techniques giving chemical information are needed for the stability investigations of DSCs to reveal possible ways to improve their lifetime. In this regard, experimental methods suitable for separating degradation mechanisms in complete cells during long-term testing are proposed employing specifically designed sealed cell structures, called segmented cells, that provide windows to measure specific cell components without being obscured by the others.
TL;DR: In this paper, the authors review the recent state of the art development of bulk heterojunction hybrid solar cells and highlight the critical factors limiting the solar cell device performance and strategies for further device improvement.
Abstract: Emerging alternative photovoltaic technologies such as dye sensitized solar cells (DSSCs) and organic solar cells (OSCs) have recently gained much attention as well as maturity and are on the step of being commercialized. Bulk heterojunction hybrid solar cells containing inorganic nanoparticles and semiconducting polymers are still lagging behind in respect of device performance although they have theoretically the potential to exhibit better performances than devices containing solely organic compounds. In this article we review the recent state of the art development of bulk heterojunction hybrid solar cells. Critical factors limiting the solar cell device performance are highlighted and strategies for further device improvement are demonstrated by giving recent examples from literature.
TL;DR: In this article, an economic assessment of the Fischer-Tropsch (F-T) co-electrolysis process is performed through process modelling and sensitivity analysis. But it is not yet technologically mature, and the high-temperature steam/CO2 co-decomposition process offers potentially a feasible and environmentally benign way to convert carbon-free or low-carbon electrical energy into chemical energy stored in syngas with a desired H2 to CO ratio for further processing.
Abstract: Although it is not yet technologically mature, the high-temperature steam/CO2 co-electrolysis process offers potentially a feasible and environmentally benign way to convert carbon-free or low-carbon electrical energy into chemical energy stored in syngas with a desired H2 to CO ratio for further processing. An attractive application is to convert the as-produced syngas further into synthetic liquid fuels through the Fischer–Tropsch (F-T) process. The synfuel can be used as alternative fuels in the transportation sector while keeping the existing infrastructure and motor engine technology unchanged. The combination of the high-temperature steam/CO2 co-electrolysis process and the F-T process thus offers an efficient way to store electricity in transportation fuels. The implementation of such a quasi carbon-neutral process depends on its economic competitiveness. In the present paper, an economic assessment of this process is performed through process modelling and sensitivity analysis. As an energy-intensive process, the availability of cost-effective electricity is crucial for its economic competitiveness. Preferred electricity sources are probably nuclear power and surplus wind power, with which synthetic fuels could be produced at a cost comparable to BTL (Biomass to Liquid) process. The present process is biomass-independent, and can also be located in regions where solar energy is abundant.
TL;DR: In this article, the authors review recent efforts to improve PEC efficiencies by modification of semiconductor photoanode surfaces with water-oxidation catalysts that can operate at low overpotentials.
Abstract: Photoelectrochemical (PEC) water splitting is an attractive approach to capturing and storing the earth's abundant solar energy influx. The challenging four-electron water-oxidation half-cell reaction has hindered this technology, giving rise to slow water oxidation kinetics at the photoanode surfaces relative to competitive loss processes. In this perspective, we review recent efforts to improve PEC efficiencies by modification of semiconductor photoanode surfaces with water-oxidation catalysts that can operate at low overpotentials. This approach allows separation of the tasks of photon absorption, charge separation, and surface catalysis, allowing each to be optimized independently. In particular, composite photoanodes marrying nanocrystalline and molecular/non-crystalline components provide flexibility in adjusting the properties of each component, but raise new challenges in interfacial chemistries.
TL;DR: In this paper, a simple solvothermal method has been described to synthesize carbon coated LFP (LFP/C) nanoplates with varying thickness from 20 to 500 nm by using different iron precursors.
Abstract: Lithium iron phosphate, LiFePO4 (LFP), is considered to be a potential cathode material for lithium-ion batteries but its rate performance is significantly restricted by sluggish kinetics of electrons and lithium ions. A simple solvothermal method has been described in this article to synthesize carbon coated LFP (LFP/C) nanoplates with varying thickness from 20 to 500 nm by using different iron precursors. The influence of solvents on the morphology of the LFP in the solvothermal synthesis is also investigated. A uniform carbon coverage at the surfaces has been achieved by a selective chelating carbonising source, D-gluconic acid lactone. The smallest dimension of the nanoplates has been found to be the b-axis where the Li+ ion diffuses quickly. The overall capacity and rate performance have, in general, been found to increase with the decrease of thickness of the nanoplates. Hierarchical LFP/C with ∼30 nm thickness shows the best electrochemical performance of 167 mA h g−1, followed by spindle (<20 nm thickness but aggregated, 121 mA h g−1), plates (200–300 nm thickness, 110 mA h g−1) and diamond shaped LFP/C (300–500 nm thickness, 82 mA h g−1) at a current rate of 17mA g−1 (0.1C rate). The spindle shaped LFP/C shows unexpected electrochemical performance since the nanoplates are heavily agglomerated in the bulk which prevents access for the liquid electrolyte, as well as additive Super P carbon, between neighbouring nanoplates during the fabrication of the composite electrodes. Hence, only the peripheral plates of the spindle are actively involved in the insertion/extraction of Li+, while the core of the spindle shaped LFP/C is almost inactive, resulting in moderate storage behaviour.
TL;DR: In this article, the authors summarize and discuss the efforts of fabricating nanostructures, modifying surface chemistry and manipulating crystallinity to achieve enhanced lithium ion intercalation capacities, rate capabilities and cyclic stability, as well as the direct fabrication of binderless film electrodes with desirable nano- and microstructures.
Abstract: Lithium ion batteries have been one of the major power supplies for small electronic devices since the last century. However, with the rapid advancement of electronics and the increasing demand for clean sustainable energy, newer lithium ion batteries with higher energy density, higher power density, and better cyclic stability are needed. In addition, newer generations of lithium ion batteries must meet the requirements of low and easy fabrication cost and be free of toxic materials. There have been many novel approaches to gain high energy storage capacities and charge/discharge rates without sacrificing the battery cyclic life. Nanostructured electrodes are seemingly the most promising candidate for future lithium ion batteries. Modification of the electrode surface chemistry and the control of appropriate crystallinity are also reported to improve the electrode intercalation capabilities. The study of appropriately designed nanostructures, interfaces and crystallinity has also promoted and is accompanied with the development of thin film electrodes without the addition of binders and conductive carbon that are typically used in the fabrication of traditional lithium ion battery electrodes, simplifying the electrode fabrication process and enhancing electrode storage density. In this perspective, we summarize and discuss the efforts of fabricating nanostructures, modifying surface chemistry and manipulating crystallinity to achieve enhanced lithium ion intercalation capacities, rate capabilities and cyclic stability, as well as the direct fabrication of binderless film electrodes with desirable nano- and microstructures.