Showing papers in "Energy and Environmental Science in 2013"
TL;DR: In this paper, a variety of electrode materials including cathodes and anodes as well as electrolytes for room-temperature stationary sodium-ion batteries are briefly reviewed and compared the difference in storage behavior between Na and Li in their analogous electrodes and summarize the sodium storage mechanisms in available electrode materials.
Abstract: Room-temperature stationary sodium-ion batteries have attracted great attention particularly in large-scale electric energy storage applications for renewable energy and smart grid because of the huge abundant sodium resources and low cost. In this article, a variety of electrode materials including cathodes and anodes as well as electrolytes for room-temperature stationary sodium-ion batteries are briefly reviewed. We compare the difference in storage behavior between Na and Li in their analogous electrodes and summarize the sodium storage mechanisms in the available electrode materials. This review also includes some new results from our group and our thoughts on developing new materials. Some perspectives and directions on designing better materials for practical applications are pointed out based on knowledge from the literature and our experience. Through this extensive literature review, the search for suitable electrode and electrolyte materials for stationary sodium-ion batteries is still challenging. However, after intensive research efforts, we believe that low-cost, long-life and room-temperature sodium-ion batteries would be promising for applications in large-scale energy storage system in the near future.
2,687 citations
TL;DR: In this paper, the bulk absorber layer of CH3NH3PbI3−xClx perovskite solar cells was reduced from 500 to <150 °C and achieved power conversion efficiency up to 12.3%.
Abstract: We have reduced the processing temperature of the bulk absorber layer in CH3NH3PbI3−xClx perovskite solar cells from 500 to <150 °C and achieved power conversion efficiencies up to 12.3%. Remarkably, we find that devices with planar thin-film architecture, where the ambipolar perovskite transports both holes and electrons, convert the absorbed photons into collected charge with close to 100% efficiency.
1,524 citations
TL;DR: In this paper, a state-of-the-art update on the most recent developments concerning the advanced heteroatom doping of carbon that goes beyond nitrogen is given, with respect to their boron-, sulphur-and phosphorus-doping.
Abstract: Heteroatom doped carbon materials represent one of the most prominent families of materials that are used in energy related applications, such as fuel cells, batteries, hydrogen storage or supercapacitors. While doping carbons with nitrogen atoms has experienced great progress throughout the past decades and yielded promising material concepts, also other doping candidates have gained the researchers' interest in the last few years. Boron is already relatively widely studied, and as its electronic situation is contrary to the one of nitrogen, codoping carbons with both heteroatoms can probably create synergistic effects. Sulphur and phosphorus have just recently entered the world of carbon synthesis, but already the first studies published prove their potential, especially as electrocatalysts in the cathodic compartment of fuel cells. Due to their size and their electronegativity being lower than those of carbon, structural distortions and changes of the charge densities are induced in the carbon materials. This article is to give a state of the art update on the most recent developments concerning the advanced heteroatom doping of carbon that goes beyond nitrogen. Doped carbon materials and their applications in energy devices are discussed with respect to their boron-, sulphur- and phosphorus-doping.
1,490 citations
TL;DR: In this paper, a review of recent developments and future perspectives in carbon dioxide usage for sustainable production of energy and chemicals and to reduce global warming is presented, focusing on the design of metal electrodes to improve their performance and recent developments of alternative approaches such as the application of ionic liquids as electrolytes and microorganisms as co-catalysts.
Abstract: This review highlights recent developments and future perspectives in carbon dioxide usage for the sustainable production of energy and chemicals and to reduce global warming. We discuss the heterogeneously catalysed hydrogenation, as well as the photocatalytic and electrocatalytic conversion of CO2 to hydrocarbons or oxygenates. Various sources of hydrogen are also reviewed in terms of their CO2 neutrality. Technologies have been developed for large-scale CO2 hydrogenation to methanol or methane. Their industrial application is, however, limited by the high price of renewable hydrogen and the availability of large-volume sources of pure CO2. With regard to the direct electrocatalytic reduction of CO2 to value-added chemicals, substantial advances in electrodes, electrolyte, and reactor design are still required to permit the development of commercial processes. Therefore, in this review particular attention is paid to (i) the design of metal electrodes to improve their performance and (ii) recent developments of alternative approaches such as the application of ionic liquids as electrolytes and of microorganisms as co-catalysts. The most significant improvements both in catalyst and reactor design are needed for the photocatalytic functionalisation of CO2 to become a viable technology that can help in the usage of CO2 as a feedstock for the production of energy and chemicals. Apart from technological aspects and catalytic performance, we also discuss fundamental strategies for the rational design of materials for effective transformations of CO2 to value-added chemicals with the help of H2, electricity and/or light.
1,368 citations
TL;DR: In this article, a review of 3D carbon-based nanostructures for advanced supercapacitor applications is presented, which includes CNTs-based networks, graphene-based architectures, hierarchical porous carbon-bimodal structures, and other even more complex 3D configurations.
Abstract: Supercapacitors have attracted intense attention due to their great potential to meet the demand of both high energy density and power density in many advanced technologies. Various carbon-based nanocomposites are currently pursued as supercapacitor electrodes because of the synergistic effect between carbon (high power density) and pseudo-capacitive nanomaterials (high energy density). This feature article aims to review most recent progress on 3D (3D) carbon based nanostructures for advanced supercapacitor applications in view of their structural intertwinement which not only create the desired hierarchical porous channels, but also possess higher electrical conductivity and better structural mechanical stability. The carbon nanostructures comprise of CNTs-based networks, graphene-based architectures, hierarchical porous carbon-based nanostructures and other even more complex carbon-based 3D configurations. Their advantages and disadvantages are compared and summarized based on the results published in the literature. In addition, we also discuss and view the ongoing trends in materials development for advanced supercapacitors.
1,346 citations
TL;DR: In this paper, a theoretical model for contact-mode TENGs was constructed based on the theoretical model, its real-time output characteristics and the relationship between the optimum resistance and TENG parameters were derived.
Abstract: A theoretical model for contact-mode TENGs was constructed in this paper. Based on the theoretical model, its real-time output characteristics and the relationship between the optimum resistance and TENG parameters were derived. The theory presented here is the first in-depth interpretation of the contact-mode TENG, which can serve as important guidance for rational design of the TENG structure in specific applications.
1,246 citations
TL;DR: In this paper, an overview of organic electrode materials, including their fundamental knowledge, development history and perspective applications, is provided. And the authors elaborate in detail various organics with different structures, including conducting polymers, organodisulfides, thioethers, nitroxyl radical polymers and conjugated carbonyl compounds.
Abstract: As an alternative to conventional inorganic intercalation electrode materials, organic electrode materials are promising candidates for the next generation of sustainable and versatile energy storage devices. In this paper we provide an overview of organic electrode materials, including their fundamental knowledge, development history and perspective applications. Based on different organics including n-type, p-type and bipolar, we firstly analyzed their working principles, reaction mechanisms, electrochemical performances, advantages and challenges. To understand the development history and trends in organic electrode materials, we elaborate in detail various organics with different structures, including conducting polymers, organodisulfides, thioethers, nitroxyl radical polymers and conjugated carbonyl compounds. The high electrochemical performance, in addition with the unique features of organics such as flexibility, processability and structure diversity, provide them great perspective in various energy storage devices, including rechargeable Li/Na batteries, supercapacitors, thin film batteries, aqueous rechargeable batteries, redox flow batteries and even all-organic batteries. It is expected that organic electrode materials will show their talents in the “post Li-ion battery” era, towards cheap, green, sustainable and versatile energy storage devices.
1,156 citations
TL;DR: In this paper, the authors review the recent accumulated experience, understandings, new strategies and materials, in the continuous R&D process of non-aqueous Mg batteries.
Abstract: The first working Mg rechargeable battery prototypes were ready for presentation about 13 years ago after two breakthroughs. The first was the development of non-Grignard Mg complex electrolyte solutions with reasonably wide electrochemical windows in which Mg electrodes are fully reversible. The second breakthrough was attained by demonstrating high-rate Mg cathodes based on Chevrel phases. These prototypes could compete with lead–acid or Ni–Cd batteries in terms of energy density, very low self-discharge, a wide temperature range of operation, and an impressive prolonged cycle life. However, the energy density and rate capability of these Mg battery prototypes were not attractive enough to commercialize them. Since then we have seen gradual progress in the development of better electrolyte solutions, as well as suggestions of new cathodes. In this article we review the recent accumulated experience, understandings, new strategies and materials, in the continuous R&D process of non-aqueous Mg batteries. This paper provides a road-map of this field during the last decade.
1,138 citations
TL;DR: In this article, the authors present the results of a technical and economic feasibility analysis conducted for four hypothetical, centralized, large-scale hydrogen production plants based on this technology, including a single bed particle suspension system, a dual-bed particle suspension systems, a fixed panel array, and a tracking concentrator array.
Abstract: Photoelectrochemical water splitting is a promising route for the renewable production of hydrogen fuel. This work presents the results of a technical and economic feasibility analysis conducted for four hypothetical, centralized, large-scale hydrogen production plants based on this technology. The four reactor types considered were a single bed particle suspension system, a dual bed particle suspension system, a fixed panel array, and a tracking concentrator array. The current performance of semiconductor absorbers and electrocatalysts were considered to compute reasonable solar-to-hydrogen conversion efficiencies for each of the four systems. The U.S. Department of Energy H2A model was employed to calculate the levelized cost of hydrogen output at the plant gate at 300 psi for a 10 tonne per day production scale. All capital expenditures and operating costs for the reactors and auxiliaries (compressors, control systems, etc.) were considered. The final cost varied from $1.60–$10.40 per kg H2 with the particle bed systems having lower costs than the panel-based systems. However, safety concerns due to the cogeneration of O2 and H2 in a single bed system and long molecular transport lengths in the dual bed system lead to greater uncertainty in their operation. A sensitivity analysis revealed that improvement in the solar-to-hydrogen efficiency of the panel-based systems could substantially drive down their costs. A key finding is that the production costs are consistent with the Department of Energy's targeted threshold cost of $2.00–$4.00 per kg H2 for dispensed hydrogen, demonstrating that photoelectrochemical water splitting could be a viable route for hydrogen production in the future if material performance targets can be met.
1,058 citations
TL;DR: In this paper, a functionalized three-dimensional hierarchical porous carbon (THPC) is prepared via a facile modified chemical activation route with polypyrrole microsheets as precursor and KOH as activating agent.
Abstract: Functionalized three-dimensional hierarchical porous carbon (THPC) is prepared via a facile modified chemical activation route with polypyrrole microsheets as precursor and KOH as activating agent. The as-obtained THPC presents a large specific surface area (2870 m2 g−1), high-level heteroatom doping (N: 7.7 wt%, O: 12.4 wt%), excellent electrical conductivity (5.6 S cm−1), and hierarchical porous nano-architecture containing macroporous frameworks, mesoporous walls and microporous textures. Such unique features make the THPC an ideal electrode material for electrochemical energy storage. As the electrode material for a supercapacitor, the THPC exhibits a high capacitance, excellent rate performance and long-term stability in both aqueous and organic electrolytes.
1,029 citations
TL;DR: In this article, the authors discuss the routes, opportunities and barriers in increasing the share of renewable energy by using CO2 reaction and their impact on the chemical and energy value chains.
Abstract: Replacement of part of the fossil fuel consumption by renewable energy, in particular in the chemical industry, is a central strategy for resource and energy efficiency. This perspective will show that CO2 is the key molecule to proceed effectively in this direction. The routes, opportunities and barriers in increasing the share of renewable energy by using CO2 reaction and their impact on the chemical and energy value chains are discussed after introducing the general aspects of this topic evidencing the tight integration between the CO2 use and renewable energy insertion in the value chain of the process industry. The focus of this perspective article is on the catalytic aspects of the chemistries involved, with an analysis of the state-of-the-art, perspectives and targets to be developed. The reactions discussed are the production of short-chain olefins (ethylene, propylene) from CO2, and the conversion of carbon dioxide to syngas, formic acid, methanol and dimethyl ether, hydrocarbons via Fischer–Tropsch synthesis and methane. The relevance of availability, cost and environmental footprints of H2 production routes using renewable energies is addressed. The final part discusses the possible scenario for CO2 as an intermediary for the incorporation of renewable energy in the process industry, with a concise roadmap for catalysis needs and barriers to reach this goal.
TL;DR: In this paper, a grey metallic luster has been fabricated for the first time, by a convenient one-step method on a large scale, where the assembly of graphene oxide dispersion into ordered paper occurs simultaneously with the chemical reduction of the oxide to graphene.
Abstract: Free-standing graphene paper with a grey metallic luster has been fabricated for the first time, by a convenient one-step method on a large scale. Herein, the assembly of graphene oxide dispersion into ordered paper occurs simultaneously with the chemical reduction of graphene oxide to graphene. The graphene paper presents the advantages of good flexibility, low weight (0.2 g cm−3) and high electrical conductivity (15 Ω sq−1). Moreover, the size and shape of the graphene paper are freely exchanged for those of the Teflon substrate used. The flexible graphene–PANI paper subsequently exhibits excellent supercapacitor performance with an enhanced specific capacitance (763 F g−1) and good cycling stability by electropolymerization of PANI nanorods on the above graphene paper. The method presented here shows great promise for the development of low-cost electrode materials in potential energy storage devices.
TL;DR: In this article, a review focusing on recent developments of some promising photoelectrode materials, such as BiVO4, a-Fe2O3, TaON, and Ta3N5 for solar hydrogen production is presented.
Abstract: Harnessing solar energy for the production of clean hydrogen fuels by a photoelectrochemical (PEC) cell represents a very attractive but challenging alternative This review focuses on recent developments of some promising photoelectrode materials, such as BiVO4, a-Fe2O3, TaON, and Ta3N5 for solar hydrogen production Some strategies have been developed to improve PEC performances of the photoelectrode materials, including: (i) doping for enhancing visible light absorption in the wide bandgap semiconductor or promoting charge transport in the narrow bandgap semiconductor, respectively; (ii) surface treatment for removing segregation phase or surface states; (iii) electrocatalysts for decreasing the overpotentials; (iv) morphology control for enhancing the light absorption and shortening transfer distance of minority carriers; (v) other methods, such as sensitization, passivating layer, and band structure engineering using heterojunction structures, and so on Photochemical durability of the photoelectrodes is also discussed, since any potential PEC technology must balance efficiency against cost and photochemical durability Photochemical durability may be amended by optimizing the photoelectrode, electrocatalyst, and electrolyte at the same time In addition, solar seawater splitting is briefly introduced because it has received attention recently Finally, trends in research in PEC cells for solar hydrogen production are detailed
TL;DR: A group of first-row transition metal dichalcogenides (ME2, M = Fe, Co, Ni; E = S, Se) were introduced as non-precious HER catalysts in an acidic electrolyte.
Abstract: A group of first-row transition metal dichalcogenides (ME2, M = Fe, Co, Ni; E = S, Se) are introduced as non-precious HER catalysts in an acidic electrolyte. They exhibit excellent catalytic activity especially in their nanoparticle form. These compounds expand and enrich the family of high performance HER catalysts.
TL;DR: In this article, the structure of mesoporous cellular foam with egg white-derived proteins was used to obtain hierarchically mesophorous (pores centered at ∼4 nm and at 20-30 nm) partially graphitized carbons with a surface area of 805.7 m2 g−1 and a bulk N content of 10.1 wt%.
Abstract: In this work we demonstrate that biomass-derived proteins serve as an ideal precursor for synthesizing carbon materials for energy applications. The unique composition and structure of the carbons resulted in very promising electrochemical energy storage performance. We obtained a reversible lithium storage capacity of 1780 mA h g−1, which is among the highest ever reported for any carbon-based electrode. Tested as a supercapacitor, the carbons exhibited a capacitance of 390 F g−1, with an excellent cycle life (7% loss after 10 000 cycles). Such exquisite properties may be attributed to a unique combination of a high specific surface area, partial graphitization and very high bulk nitrogen content. It is a major challenge to derive carbons possessing all three attributes. By templating the structure of mesoporous cellular foam with egg white-derived proteins, we were able to obtain hierarchically mesoporous (pores centered at ∼4 nm and at 20–30 nm) partially graphitized carbons with a surface area of 805.7 m2 g−1 and a bulk N-content of 10.1 wt%. When the best performing sample was heated in Ar to eliminate most of the nitrogen, the Li storage capacity and the specific capacitance dropped to 716 mA h g−1 and 80 F g−1, respectively.
TL;DR: A Ni3S2 nanorods/Ni foam composite electrode is prepared as a high-performance catalyst for the oxygen evolution reaction (OER), which exhibits excellent OER activity with a small overpotential of ∼157 mV based on the onset of catalytic current as discussed by the authors.
Abstract: A Ni3S2 nanorods/Ni foam composite electrode is prepared as a high-performance catalyst for the oxygen evolution reaction (OER), which exhibits excellent OER activity with a small overpotential of ∼157 mV based on the onset of catalytic current.
TL;DR: In this paper, the authors provide a general overview of the current and most innovative uses of food supply chain waste, providing a range of worldwide case-studies from around the globe.
Abstract: Increasing demand for fuels and chemicals, driven by factors including over-population, the threat of global warming and the scarcity of fossil resources, strains our resource system and necessitates the development of sustainable and innovative strategies for the chemical industry. Our society is currently experiencing constraints imposed by our resource system, which drives industry to increase its overall efficiency by improving existing processes or finding new uses for waste. Food supply chain waste emerged as a resource with a significant potential to be employed as a raw material for the production of fuels and chemicals given the abundant volumes globally generated, its contained diversity of functionalised chemical components and the opportunity to be utilised for higher value applications. The present manuscript is aimed to provide a general overview of the current and most innovative uses of food supply chain waste, providing a range of worldwide case-studies from around the globe. These studies will focus on examples illustrating the use of citrus peel, waste cooking oil and cashew shell nut liquid in countries such as China, the UK, Tanzania, Spain, Greece or Morocco. This work emphasises 2nd generation food waste valorisation and re-use strategies for the production of higher value and marketable products rather than conventional food waste processing (incineration for energy recovery, feed or composting) while highlighting issues linked to the use of food waste as a sustainable raw material. The influence of food regulations on food supply chain waste valorisation will also be addressed as well as our society's behavior towards food supply chain waste. “There was no ways of dealing with it that have not been known for thousands of years. These ways are essentially four: dumping it, burning it, converting it into something that can be used again, and minimizing the volume of material goods – future garbage – that is produced in the first place.” William Rathje on waste (1945–2012) – Director of the Tucson Garbage project.
TL;DR: In this paper, the feasibility of two novel energy storage systems: Na-aqueous batteries and Na-O2 technology is explored, and new advances on nonaqueous Na-ion systems are summarized.
Abstract: This work presents an up-to-date information on Na-based battery materials. On the one hand, it explores the feasibility of two novel energy storage systems: Na-aqueous batteries and Na–O2 technology. On the other hand, it summarises new advances on non-aqueous Na-ion systems. Although all of them can be placed under the umbrella of Na-based systems, aqueous and oxygen-based batteries are arising technologies with increasing significance in energy storage research, while non-aqueous sodium-ion technology has become one of the most important research lines in this field. These systems meet different requirements of energy storage: Na-aqueous batteries will have a determining role as a low cost and safer technology; Na–O2 systems can be the key technology to overcome the need for high energy density storage devices; and non-aqueous Na-ion batteries have application in the field of stationary energy storage.
TL;DR: In this paper, a supercapacitor-battery hybrid energy storage device was designed and fabricated, which combines an electrochemical double layer capacitance (EDLC) type positive electrode with a Li-ion battery type negative electrode.
Abstract: In pursuing higher energy density with no sacrifice of power density, a supercapacitor-battery hybrid energy storage device—combining an electrochemical double layer capacitance (EDLC) type positive electrode with a Li-ion battery type negative electrode—has been designed and fabricated. Graphene is introduced to both electrodes: an Fe3O4/graphene (Fe3O4/G) nanocomposite with high specific capacity as negative electrode material, and a graphene-based three-dimensional porous carbon material (3DGraphene) with high surface area (∼3355 m2 g−1) as positive electrode material. The Fe3O4/G nanocomposite shows a high reversible specific capacity exceeding 1000 mA h g−1 at 90 mA g−1 and remaining at 704 mA h g−1 at 2700 mA g−1, as well as excellent rate capability and improved cycle stability. Meanwhile the 3DGraphene positive electrode also displays great electrochemical performance. With these two graphene-enhanced electrode materials and using the best recommended industry evaluation method, the hybrid supercapacitor Fe3O4/G//3DGraphene demonstrates an ultrahigh energy density of 147 W h kg−1 (power density of 150 W kg−1), which also remains of 86 W h kg−1 even at high power density of 2587 W kg−1, so far the highest value of the reported hybrid supercapacitors. Furthermore, the energy density of the hybrid supercapacitor is comparable to lithium ion batteries, and the power density also reaches that of symmetric supercapacitors, indicating that the hybrid supercapacitor could be a very promising novel energy storage system for fast and efficient energy storage in the future.
TL;DR: In this article, molybdenum carbide (β-Mo2C) nanoparticles are prepared by in situ carburization of ammonium molydate on carbon nanotubes and XC-72R carbon black without using any gaseous carbon source.
Abstract: In an attempt to tailor low-cost, precious-metal-free electrocatalysts for water electrolysis in acid, molybdenum carbide (β-Mo2C) nanoparticles are prepared by in situ carburization of ammonium molybdate on carbon nanotubes and XC-72R carbon black without using any gaseous carbon source. The formation of Mo2C is investigated by thermogravimetry and in situ X-ray diffraction. X-ray absorption analysis reveals that Mo2C nanoparticles are inlaid or anchored into the carbon supports, and the electronic modification makes the surface exhibit a relatively moderate Mo–H bond strength. It is found that carbon nanotube-supported Mo2C showed superior electrocatalytic activity and stability in the hydrogen evolution reaction (HER) compared to the bulk Mo2C. An overpotential of 63 mV for driving 1 mA cm−2 of current density was measured for the nanotube-supported Mo2C catalysts; this exceeds the activity of analogous Mo2C catalysts. The enhanced electrochemical activity is facilitated by unique effects of the anchored structure coupled with the electronic modification.
TL;DR: In this paper, a review of recent and significant advances in the development of metal-organic frameworks for clean energy applications are reviewed, and special emphases are shown to the applications of MOFs as platforms for hydrogen production and storage, fuel cells, Li-ion rechargeable batteries, supercapacitors and solar cells.
Abstract: In order to void environmental pollution and an energy shortage, the application of clean and renewable energy, such as solar, instead of fossil fuel is foreseen as a prospective issue. It is urgent and important to develop and optimize various energy storage and conversion technologies and materials aimed at utilization of different clean energy sources. Metal–organic frameworks (MOFs), a new class of porous crystalline materials, act as an outstanding candidate in this field based on their high surface areas, controllable structures and excellent electrochemical properties. Here, selected recent and significant advances in the development of MOFs for clean energy applications are reviewed, and special emphases are shown to the applications of MOFs as platforms for hydrogen production and storage, fuel cells, Li-ion rechargeable batteries, supercapacitors and solar cells.
TL;DR: In this article, the authors show that the kinetics of oxygen reduction reaction are influenced by catalysts at small discharge capacities, but not at large Li2O2 thicknesses, yielding insights into the governing processes during discharge.
Abstract: Rechargeable energy storage systems with high energy density and round-trip efficiency are urgently needed to capture and deliver renewable energy for applications such as electric transportation Lithium–air/lithium–oxygen (Li–O2) batteries have received extraordinary research attention recently owing to their potential to provide positive electrode gravimetric energies considerably higher (∼3 to 5×) than Li-ion positive electrodes, although the packaged device energy density advantage will be lower (∼2×) In light of the major technological challenges of Li–O2 batteries, we discuss current understanding developed in non-carbonate electrolytes of Li–O2 redox chemistry upon discharge and charge, oxygen reduction reaction product characteristics upon discharge, and the chemical instability of electrolytes and carbon commonly used in the oxygen electrode We show that the kinetics of oxygen reduction reaction are influenced by catalysts at small discharge capacities (Li2O2 thickness less than ∼1 nm), but not at large Li2O2 thicknesses, yielding insights into the governing processes during discharge In addition, we discuss the characteristics of discharge products (mainly Li2O2) including morphological, electronic and surface features and parasitic reactivity with carbon On charge, we examine the reaction mechanism of the oxygen evolution reaction from Li2O2 and the influence of catalysts on bulk Li2O2 decomposition These analyses provide insights into major discrepancies regarding Li–O2 charge kinetics and the role of catalyst In light of these findings, we highlight open questions and challenges in the Li–O2 field relevant to developing practical, reversible batteries that achieve the anticipated energy density advantage with a long cycle life
TL;DR: In this article, a functional microporous conducting carbon with a high surface area of about 1230 m2 g−1 is synthesized by single-step pyrolysis of dead plant leaves (dry waste, ground powder) without any activation and studied for supercapacitor application.
Abstract: Functional microporous conducting carbon with a high surface area of about 1230 m2 g−1 is synthesized by single-step pyrolysis of dead plant leaves (dry waste, ground powder) without any activation and studied for supercapacitor application. We suggest that the activation is provided by the natural constituents in the leaves composed of soft organics and metals. Although the detailed study performed and reported here is on dead Neem leaves (Azadirachta indica), the process is clearly generic and applicable to most forms of dead leaves. Indeed we have examined the case of dead Ashoka leaves as well. The comparison between the Neem and Ashoka leaves brings out the importance of the constitution and composition of the bio-source in the nature of carbon formed and its properties. We also discuss and compare the cases of pyrolysis of green leaves as well as un-ground dead leaves with that of ground dead leaf powder studied in full detail. The concurrent high conductivity and microporosity realized in our carbonaceous materials are key to the high energy supercapacitor application. Indeed, our synthesized functional carbon exhibits a very high specific capacitance of 400 F g−1 and an energy density of 55 W h kg−1 at a current density of 0.5 A g−1 in aqueous 1 M H2SO4. The areal capacitance value of the carbon derived from dead (Neem) plant leaves (CDDPL) is also significantly high (32 μF cm−2). In an organic electrolyte the material shows a specific capacitance of 88 F g−1 at a current density of 2 A g−1.
TL;DR: In this paper, the authors demonstrate that the HER exchange current density in alkaline solutions can be correlated with calculated hydrogen binding energy (HBE) on the metal surfaces via a volcano type of relationship.
Abstract: The slow reaction kinetics of the hydrogen evolution and oxidation reactions (HER/HOR) on platinum in alkaline electrolytes hinders the development of alkaline electrolysers, solar hydrogen cells and alkaline fuel cells. A fundamental understanding of the exchange current density of the HER/HOR in alkaline media is critical for the search and design of highly active electrocatalysts. By studying the HER on a series of monometallic surfaces, we demonstrate that the HER exchange current density in alkaline solutions can be correlated with the calculated hydrogen binding energy (HBE) on the metal surfaces via a volcano type of relationship. The HER activity varies by several orders of magnitude from Pt at the peak of the plot to W and Au located on the bottom of each side of the plot, similar to the observation in acids. Such a correlation suggests that the HBE can be used as a descriptor for identifying electrocatalysts for HER/HOR in alkaline media, and that the HER exchange current density can be tuned by modifying the surface chemical properties.
TL;DR: In this paper, the authors proposed integration of MFCs with other treatment technologies to form an MFC-centered treatment scheme based on thoroughly analyzing the challenges and opportunities, and discuss future efforts to be made for realizing sustainable wastewater treatment.
Abstract: Microbial fuel cells (MFCs) have been conceived and intensively studied as a promising technology to achieve sustainable wastewater treatment. However, doubts and debates arose in recent years regarding the technical and economic viability of this technology on a larger scale and in a real-world applications. Hence, it is time to think about and examine how to recalibrate this technology's role in a future paradigm of sustainable wastewater treatment. In the past years, many good ideas/approaches have been proposed and investigated for MFC application, but information is scattered. Various review papers were published on MFC configuration, substrates, electrode materials, separators and microbiology but there is lack of critical thinking and systematic analysis of MFC application niche in wastewater treatment. To systematically formulate a strategy of (potentially) practical MFC application and provide information to guide MFC development, this perspective has critically examined and discussed the problems and challenges for developing MFC technology, and identified a possible application niche whereby MFCs can be rationally incorporated into the treatment process. We propose integration of MFCs with other treatment technologies to form an MFC-centered treatment scheme based on thoroughly analyzing the challenges and opportunities, and discuss future efforts to be made for realizing sustainable wastewater treatment.
TL;DR: In this article, the authors showed that lignin can be selectively cleaved into propylguaiacol and propylsyringol with total selectivity >90% at a lignins conversion of about 50%.
Abstract: Valorization of native birch wood lignin into monomeric phenols over nickel-based catalysts has been studied. High chemoselectivity to aromatic products was achieved by using Ni-based catalysts and common alcohols as solvents. The results show that lignin can be selectively cleaved into propylguaiacol and propylsyringol with total selectivity >90% at a lignin conversion of about 50%. Alcohols, such as methanol, ethanol and ethylene glycol, are suitable solvents for lignin conversion. Analyses with MALDI-TOF and NMR show that birch lignin is first fragmented into smaller lignin species consisting of several benzene rings with a molecular weight of m/z ca. 1100 to ca. 1600 via alcoholysis reaction. The second step involves the hydrogenolysis of the fragments into phenols. The presence of gaseous H2 has no effect on lignin conversion, indicating that alcohols provide active hydrogen species, which is further confirmed by isotopic tracing experiments. Catalysts are recycled by magnetic separation and can be reused four times without losing activity. The mechanistic insights from this work could be helpful in understanding native lignin conversion and the formation of monomeric phenolics via reductive depolymerization.
TL;DR: In this article, a comparative overview of the major developments in the area of positive and negative electrode materials in both Li-ion and Na-ion batteries in the past decade is provided.
Abstract: We discuss the similarities and dissimilarities of sodium- and lithium-ion batteries in terms of negative and positive electrodes. Compared to the comprehensive body of work on lithium-ion batteries, research on sodium-ion batteries is still at the germination stage. Since both sodium and lithium are alkali metals, they share similar chemical properties including ionicity, electronegativity and electrochemical reactivity. They accordingly have comparable synthetic protocols and electrochemical performances, which indicates that sodium-ion batteries can be successfully developed based on previously applied approaches or methods in the lithium counterpart. The electrode materials in Li-ion batteries provide the best library for research on Na-ion batteries because many Na-ion insertion hosts have their roots in Li-ion insertion hosts. However, the larger size and different bonding characteristics of sodium ions influence the thermodynamic and/or kinetic properties of sodium-ion batteries, which leads to unexpected behaviour in electrochemical performance and reaction mechanism, compared to lithium-ion batteries. This perspective provides a comparative overview of the major developments in the area of positive and negative electrode materials in both Li-ion and Na-ion batteries in the past decade. Highlighted are concepts in solid state chemistry and electrochemistry that have provided new opportunities for tailored design that can be extended to many different electrode materials for sodium-ion batteries.
TL;DR: In this article, a depleted hole conductor free CH3NH3PbI3/TiO2 heterojunction solar cell using a thick CH3NHPbII3 film was presented, which formed large crystals which function simultaneously as light harvesting and hole transport materials.
Abstract: Lead halide perovskite is an excellent candidate for use as a light harvester in solar cells. Our work presents a depleted hole conductor free CH3NH3PbI3/TiO2 heterojunction solar cell using a thick CH3NH3PbI3 film. The CH3NH3PbI3 formed large crystals which function simultaneously as light harvesters and as hole transport materials. We performed capacitance voltage measurements, which show a depletion region which extends to both n and p sides. The built-in field of the depletion region assists in the charge separation and suppresses the back reaction of electrons from the TiO2 film to the CH3NH3PbI3 film. This depleted hole conductor free CH3NH3PbI3/TiO2 heterojunction solar cell provides a power conversion efficiency of 8% with a current density of 18.8 mA cm−2, the highest efficiency achieved to date for perovskite based solar cells without a hole conductor.
TL;DR: In this paper, the authors provide an overview of recent research progress in graphene-based materials as electrodes for electrochemical energy storage, including the use of graphene for improving the performance of lithium-sulfur and lithium-oxygen batteries.
Abstract: The ever-increasing demands for energy and environmental concerns due to burning fossil fuels are the key drivers of today's R&D of innovative energy storage systems. This paper provides an overview of recent research progress in graphene-based materials as electrodes for electrochemical energy storage. Beginning with a brief description of the important properties of single-layer graphene, methods for the preparation of graphene and its derivatives (graphene oxide and reduced graphene oxide) are summarized. Then, graphene-based electrode materials for electrochemical capacitors and lithium-ion batteries are reviewed. The use of graphene for improving the performance of lithium–sulfur and lithium–oxygen batteries is also presented. Future research trend in the development of high-power-density and high-energy-density electrochemical energy storage devices is analysed.
TL;DR: In this article, a critical overview of all advances in the field of homogeneous and heterogeneous catalysis and recognises a great potential of some of these chemocatalytic approaches to produce and transform lactic acid as well as some other promising α-hydroxy acids.
Abstract: Upcoming bio-refineries will be at the heart of the manufacture of future transportation fuels, chemicals and materials. A narrow number of platform molecules are envisioned to bridge nature's abundant polysaccharide feedstock to the production of added-value chemicals and intermediate building blocks. Such platform molecules are well-chosen to lie at the base of a large product assortment, while their formation should be straightforward from the refined biomass, practical and energy efficient, without unnecessary loss of carbon atoms. Lactic acid has been identified as one such high potential platform. Despite its established fermentation route, sustainability issues – like gypsum waste and cost factors due to multi-step purification and separation requirements – will arise as soon as the necessary orders of magnitude larger volumes are needed. Innovative production routes to lactic acid and its esters are therefore under development, converting sugars and glycerol in the presence of chemocatalysts. Moreover, catalysis is one of the fundamental routes to convert lactic acid into a range of useful chemicals in a platform approach. This contribution attempts a critical overview of all advances in the field of homogeneous and heterogeneous catalysis and recognises a great potential of some of these chemocatalytic approaches to produce and transform lactic acid as well as some other promising α-hydroxy acids.