Showing papers in "International Journal of Energy Research in 2015"

A review on clean energy solutions for better sustainability

Abstract: Summary This paper focuses on clean energy solutions in order to achieve better sustainability, and hence discusses opportunities and challenges from various dimensions, including social, economic, energetic and environmental aspects. It also evaluates the current and potential states and applications of possible clean-energy systems. In the first part of this study, renewable and nuclear energy sources are comparatively assessed and ranked based on their outputs. By ranking energy sources based on technical, economic, and environmental performance criteria, it is aimed to identify the improvement potential for each option considered. The results show that in power generation, nuclear has the highest (7.06/10) and solar photovoltaic (PV) has the lowest (2.30/10). When nonair pollution criteria, such as land use, water contamination, and waste issues are considered, the power generation ranking changes, and geothermal has the best (7.23/10) and biomass has the lowest performance (3.72/10). When heating and cooling modes are considered as useful outputs, geothermal and biomass have approximately the same technical, environmental, and cost performances (as 4.9/10), and solar has the lowest ranking (2/10). Among hydrogen production energy sources, nuclear gives the highest (6.5/10) and biomass provides the lowest (3.6/10) in ranking. In the second part of the present study, multigeneration systems are introduced, and their potential benefits are discussed along with the recent studies in the literature. It is shown that numerous advantages are offered by renewable energy-based integrated systems with multiple outputs, especially in reducing overall energy demand, system cost and emissions while significantly improving overall efficiencies and hence output generation rates. Copyright © 2015 John Wiley & Sons, Ltd.

Vanadium redox flow batteries: a technology review

Abstract: Summary Flow batteries have unique characteristics that make them especially attractive when compared with conventional batteries, such as their ability to decouple rated maximum power from rated energy capacity, as well as their greater design flexibility. The vanadium redox flow batteries (VRFB) seem to have several advantages among the existing types of flow batteries as they use the same material (in liquid form) in both half-cells, eliminating the risk of cross contamination and resulting in electrolytes with a potentially unlimited life. Given their low energy density (when compared with conventional batteries), VRFB are especially suited for large stationary energy storage, situations where volume and weight are not limiting factors. This includes applications such as electrical peak shaving, load levelling, UPS, and in conjunction with renewable energies (e.g. wind and solar). The present work thoroughly reviews the VRFB technology detailing their genesis, the basic operation of the various existing designs and the current and future prospects of their application. The main original contribution of the work was the addressing of a still missing in-depth review and comparison of existing, but dispersed, peer reviewed publications on this technology, with several original and insightful comparison tables, as well as an economic analysis of an application for storing excess energy of a wind farm and sell it during peak demand. The authors have also benefited from their background in electric mobility to carry out original and insightful discussions on the present and future prospects of flow batteries in mobile (e.g. vehicle) and stationary (e.g. fast charging stations) applications related to this field, including a case study. Vanadium redox flow batteries are currently not suitable for most mobile applications, but they are among the technologies which may enable, when mature, the mass adoption of intermittent renewable energy sources which still struggle with stability of supply and lack of flexibility issues.Copyright © 2014 John Wiley & Sons, Ltd.

A review on coke management during dry reforming of methane

Abstract: Summary The dry (CO2) reforming of methane is a great promising technology, particularly because of its dual advantages of natural gas valorization and mitigating global warming via carbon dioxide sequestration. However, coke management is the most difficult problem in commercialization of the process. We have therefore examined in this paper the various catalytic systems being evaluated for the dry reforming with emphasis on operating parameters, activity, and coke deposition. Other factors such as the catalyst promoter, the reactor system, and the periodical regeneration were also critically reviewed. The benefits of utilizing methane from natural gas and other sources, where carbon dioxide is considered as an impurity component, are emphasized. Structured basic catalysts, with periodic regeneration certainties, are strong candidates for industrial applications. Therefore, efforts to build commercial scales for the benefit of global energy industries were highlighted. Copyright © 2015 John Wiley & Sons, Ltd.

A review of large‐scale electrical energy storage

Abstract: Summary This paper gives a broad overview of a plethora of energy storage technologies available on the large-scale complimented with their capabilities conducted by a thorough literature survey. According to the capability graphs generated, thermal energy storage, flow batteries, lithium ion, sodium sulphur, compressed air energy storage, and pumped hydro storage are suitable for large-scale storage in the order of 10's to 100's of MWh; metal air batteries have a high theoretical energy density equivalent to that of gasoline along with being cost efficient; compressed air energy storage has the lowest capital energy cost in comparison to other energy storage technologies; flywheels, super conducting magnetic storage, super capacitors, capacitors, and pumped hydro storage have very low energy density; compressed air energy storage, cryogenic energy storage, thermal energy storage, and batteries have relatively high energy density; high efficiencyin tandem with high energy density results in a cost efficient storage system; and power density pitted against energy density provides a clear demarcation between power and energy applications. This paper also provides a mathematical model for thermal energy storage as a battery. Furthermore, a comprehensive techno-economic evaluation of the various energy storage technologies would assist in the development of an energy storage technology roadmap. Copyright © 2015 John Wiley & Sons, Ltd.

Review on processing of metal–organic framework (MOF) materials towards system integration for hydrogen storage

Abstract: SUMMARY Development of safe and effective hydrogen storage systems is critical for further implementation of hydrogen in fuel cell technologies. Amongst the various approaches to improve the performance of such systems, porous materials-based adsorptive hydrogen storage is envisaged as a long-term solution because of the excellent reversibility, good kinetics and the possibility to store hydrogen at low pressures. Metal–organic frameworks (MOFs) have attracted much attention as porous hydrogen storage materials in the transition from the laboratory to commercial applications. However, MOF materials are often obtained as loose powders with low packing densities and low thermal conductivities. Therefore, to facilitate this transition and enable the MOF materials to form part of a practical hydrogen storage system, knowledge of the ‘processing’ techniques to improve the properties of the powders is essential. However, the processing routes of MOF materials towards system integration are rarely reviewed in the literature although this is of great significance in their proper assessment and potential use for hydrogen storage on a commercial scale. In this review, we begin by introducing the general requirements of an MOF materials-based hydrogen storage system and present how these requirements translate into desired characteristics for further processing. Then, an overview of MOF materials processing towards system integration is provided with an emphasis on improving selected properties including (i) structural stability, (ii) thermal conductivity and (iii) hydrogen storage properties. Copyright © 2014 John Wiley & Sons, Ltd.

Exoelectrogens in microbial fuel cells toward bioelectricity generation: a review

Abstract: Summary Exoelectrogens are catalytic microorganisms competent to shuttle electrons exogenously to the electrode surface without utilizing artificial mediators. Diverse microorganisms acting as exoelectrogens in the fluctuating ambience of microbial fuel cells (MFCs) propose unalike metabolic pathways and incompatible, specific proteins or genes for their inevitable performance toward bioelectricity generation. A pivotal mechanism known as quorum sensing allows bacterial population to communicate and regulates the expression of biofilm-related genes. Moreover, it has been found that setting the anode potential affects the metabolism of the exoelectrogens and hence the output of MFCs. Microscopic, spectrometry investigations and gene deletion studies have confirmed the expression of certain genes for outer-membrane multiheme cytochromes and conductive pili, and their potential roles in the exoelectrogenic activity. Further, cyclic voltammetry has suggested the role of multifarious redox-active compounds secreted by the exoelectrogens in direct electron transport mechanisms. Besides, it also explores the various mechanisms of exoelectrogens with genetic and molecular approaches, such as biofilm formation, microbial metabolism, bioelectrogenesis, and electron transfer mechanisms from inside the exoelectrogens to the electrodes and vice versa. Copyright © 2015 John Wiley & Sons, Ltd.

A review on biomass-based hydrogen production for renewable energy supply

Abstract: This article gives an overview of the state-of-the-art biomass-based hydrogen production technologies Various biological and thermochemical processes of biomass are taken into consideration to find the most economical method of hydrogen production Biohydrogen generated by biophotolysis method, photo-fermentation and dark fermentation is studied with respect to various feedstocks in Malaysia The fermentation approaches of biohydrogen production have shown great potential to be a future substitute of fossil fuels Dark fermentation method is a simple biological hydrogen production method that uses a variety of substrate and does not require any light as a source of energy A promising future for biohydrogen production is anticipated by this process both industrially and commercially Feasibility of hydrogen production from pyrolysis and water gasification of various biomass feedstock confirm that supercritical water gasification (SCWG) of biomass is the most cost-effective thermochemical process Highly moisturized biomass could be employed directly in SCWG without any high-cost drying process Indeed, a small amount of energy is required to pressurize hydrogen in the storage tank because of highly pressurized SCWG process The cost of hydrogen produced by SCWG of biomass is about US$3/GJ (US$035/kg), which is extremely lower than biomass pyrolysis method (in the range of US$886/GJ to US$1552/GJ) and wind-electrolysis systems and PV-electrolysis systems (US$202/GJ and US$418/GJ, respectively) The best feedstock for biomass-based hydrogen production is identified based on the availability, location of the sources, processes required for the preparation of the feedstock and the total cost of acquiring the feedstock The cheapest and most abundantly available biomass source in Malaysia is the waste of palm industry Hydrogen production from palm oil mill effluent and palm solid residue could play a crucial role in the energy mix of Malaysia Malaysia has this great capability to supply about 40% of its annual energy demand by hydrogen production from SCWG of palm solid waste © 2015 John Wiley & Sons, Ltd

Fabrication of flexible polypyrrole/graphene oxide/manganese oxide supercapacitor

Abstract: Summary A flexible polypyrrole/graphene oxide/manganese oxide-based supercapacitor was prepared via an electrodeposition process. The polypyrrole, graphene oxide, and manganese oxide were deposited onto a flexible and highly porous nickel foam, which acted as a current collector to enhance the electrochemical performances. The good coverage of the polypyrrole, graphene oxide, and manganese oxide onto the scaffold of the nickel foam was evidenced using field emission scanning electron microscopy and X-ray diffraction. The manganese species, which were present in the oxidation states of Mn3+ and Mn4+, were shown using X-ray photoelectron spectroscopy. The presence of Mn2O3 and MnO2 polymorphs was detected using Fourier transform infrared and Raman spectroscopies. The cyclic stability of the ternary supercapacitor was consistent regardless of its geometry and curvature. In contrast, an activated carbon supercapacitor possesses limited energy storage capability compared to a ternary supercapacitor, which suppresses the electrochemical performances of activated carbon. The ternary as-fabricated supercapacitor could retain a specific capacitance of 96.58% after 1000 cycles, and the as-synthesized energy storage device was able to light up a light emitting diode. Copyright © 2014 John Wiley & Sons, Ltd.

Impact assessment and efficiency evaluation of hydrogen production methods

Abstract: Summary In this study, we investigate the economic, environmental and social impacts of various hydrogen production methods, based on fossil fuel and renewable energy resources with a special emphasis on hybrid photoelectrochemical systems perform comparative assessments of these methods for applications. The sources considered for hydrogen production in this study are water, fossil hydrocarbons, and biomass. Furthermore, the primary energy sources considered in this study are natural gas, coal, biomass, wind and solar. In order to address sustainability, the relationship between efficiency and environmental impact is also investigated. The results show that solar based hydrogen production options (photocatalysis, photoelectrolysis, and photoelectrochemical methods) provide near zero global warming potentials and air pollutants, while coal gasification has the highest ones. In regards to the exergy efficiencies, biomass gasification gives the highest exergy efficiency, while photoelectrochemical method ends up with the lowest one. Copyright © 2015 John Wiley & Sons, Ltd.

Performance of OWC wave energy converters: influence of turbine damping and tidal variability

Abstract: We investigate the different factors affecting the performance of an OWC chamber. We carry out a comprehensive campaign of physical model tests (387 in total). The turbine damping is the main factor, taking precedence over the wave conditions. The wave period is far more important than the wave height. The tidal level plays a significant role under certain wave conditions.

Strategic optimization of forest residues to bioenergy and biofuel supply chain

Abstract: Summary Forest residues are renewable materials for bioenergy conversion that have the potential to replace fossil fuels beyond electricity and heat generation. A challenge hindering the intensified use of forest residues for energy production is the high cost of their supply chain. Previous studies on optimal design of forest residue supply chains focused on biofuel or bioenergy production separately, mostly with a single time period approach. We present a multi-period mixed integer linear programming model that optimizes the supply chain of forest residues for the production of bioenergy and biofuels simultaneously. The model determines (i) the location, type and size of the technologies to install and the period to install them, (ii) the mix of biofuel and bioenergy products to generate, (iii) the type and amount of forest residues to acquire and the sourcing points, (iv) the amount of forest residues to transport from sources to facilities and (v) the amount of product to transport from facilities to markets. The objective of the model is to maximize the net present value of the supply chain over a 20-year planning horizon with yearly time steps. We applied the model to a case study in British Columbia, Canada, to investigate the production of heat, electricity, pellets and pyrolysis bio-oil from available forest harvesting residues and sawmill wastes. Based on current energy generation costs in the region and the predicted operating costs of new conversion plants, the results of our model recommended the installation of small biomass boilers coupled with steam turbines for electricity production (0.5 and 5 MW) and pyrolysis plants with a capacity of 200 and 400 odmt day−1. We performed a sensitivity analysis to evaluate the sensitivity of the optimal result to changes in the demand and price of products, as well as the availability and cost of forest residues. Copyright © 2014 John Wiley & Sons, Ltd.

Perturbative methods for maximum power point tracking (MPPT) of photovoltaic (PV) systems: a review

Abstract: Summary Over the past few decades, the world demand for energy has risen steadily, forcing the world communities to look for alternative sources. Photovoltaic (PV) is seen as the most promising solution for this demand. However, the PV system is popularly known to suffer from low-energy harvesting due to the change of environment conditions. An inexpensive and practical solution to extract the energy from the PV is by improving the maximum power point tracking (MPPT) controller technique. An ideal MPPT should be able to track the true maximum power operating point accurately under all circumstances and overcome all nonlinearities in the characteristic I-V curves. This paper presents an updated review of the techniques based on the perturbative MPPT methods, both using the conventional and soft computing methods. The working principles of the techniques, parameter effects, and their limitations are discussed. The focus of this review is to direct the readers to the new direction of MPPT using the artificial intelligence and evolutionary computation techniques. Besides serving as a comprehensive source of information, the paper also provides a critical review on the relative performance of the selected MPPT methods. This includes the module dependency, tracking performance, and the ability to handle the partial shading conditions. Copyright © 2015 John Wiley & Sons, Ltd.

Quantification of the European industrial heat demand by branch and temperature level

Abstract: We present the first comprehensive estimate of the final energy demand for heat in all EU28 member states for the reference year 2012, differentiated by temperature levels, comparing two different approaches. Two different calculation approaches based on different data sets yielded estimates of the total final energy demand for heat in the EU28 of 8150 PJ and 8518 PJ in 2012, respectively. Approach 1 distinguishes between three different process heat (PH) temperature levels and results in final energy demand for heat 400°C: 3859 PJ. The second approach distinguishes between low temperature space heat and hot water (<100°C: 1161 PJ) and four different PH temperature levels with a resulting energy demand of 1000°C: 2865 PJ. The high share of high-temperature heat illustrates the limits to the potential decarbonisation of industrial thermal processes with renewable energy sources such as (non-concentrating) solar thermal, geothermal or environmental heat. Therefore specific information on required temperature levels is of the essence. This, in turn, points out the relevance of renewable electricity and synthetic fuels based on renewable power for a significant reduction of CO2 emissions from the industry sector in Europe. Considering current data quality, it is recommended to develop a consistent, comprehensive methodology to significantly improve the data basis on industrial heat demand.

A generic demand-side management model for smart grid

Abstract: The demand-side management (DSM) is one of the most important aspects in future smart grids: towards electricity generation cost by minimizing the expensive thermal peak power plants. The DSM greatly affects the individual users’ cost and per unit cost. The main objective of this research article is to develop a generic demand-side management (G-DSM) model for residential users to reduce peak-to-average ratio (PAR), total energy cost, and waiting time of appliances (WTA) along with fast execution of the proposed algorithm. We propose a system architecture and mathematical formulation for total energy cost minimization, PAR reduction, and WTA. The G-DSM model is based on genetic algorithm (GA) for appliances scheduling and considers 20 users having a combination of appliances with different operational characteristics. Simulation results show the effectiveness of G-DSM model for both single and multiple user scenarios. Copyright © 2015 John Wiley & Sons, Ltd.

Supporting security and adequacy in future energy systems: The need to enhance long-term energy system models to better treat issues related to variability

Abstract: As the shares of variable renewable generation in power systems increase, so does the need for, inter alia, flexible balancing mechanisms. These mechanisms help ensure the reliable operation of the electricity system by compensating for fluctuations in supply or demand. However, a focus on short-term balancing is sometimes neglected when assessing future capacity expansions with long-term energy system models. Developing heuristics that can simulate short-term system issues is one way of augmenting the functionality of such models. To this end, we present an extended functionality to the Open Source Energy Modelling System (OSeMOSYS), which captures the impacts of short-term variability of supply and demand on system adequacy and security. Specifically, we modelled the system adequacy as the share of wind energy is increased. Further, we enable the modelling of operating reserve capacities required for balancing services. The dynamics introduced through these model enhancements are presented in an application case study. This application indicates that introducing short-term constraints in long-term energy models may considerably influence the dispatch of power plants, capacity investments, and, ultimately, the policy recommendations derived from such models.

Graphene-based materials for flexible electrochemical energy storage

Abstract: Summary Sustainable development of renewable energy sources is one of the most important themes that humanity faces in this century. Wide use of renewable energy sources will require a drastically increased ability to store electrical energy. Electrochemical energy storage devices are expected to play a key role. With the increased demand in flexible energy resource for wearable electronic devices, great efforts have been devoted to developing high-quality flexible electrodes for advanced energy storage and conversion systems. Because of its high specific surface area, good chemical stability, high mechanical flexibility, and outstanding electrical properties, graphene, a special allotrope of carbon with two-dimensional mono-layered network of sp2 hybridized carbon, have been showing great potential in next-generation energy conversion and storage devices. This review presents the latest advances on the flexible graphene-based materials for the most vigorous electrochemical energy storage devices, that is, supercapacitors and lithium-ion batteries. Copyright © 2014 John Wiley & Sons, Ltd.

Electrochemical properties of free‐standing polypyrrole/graphene oxide/zinc oxide flexible supercapacitor

Abstract: SUMMARY We report the preparation of a polypyrrole/graphene oxide/zinc oxide nanocomposite on a nickel foam using a simple and rapid single-step electrochemical deposition process under ambient conditions. A free-standing flexible supercapacitor was fabricated by sandwiching a polyvinyl alcohol hydrogel polymer electrolyte between two layers of the as-prepared ternary nanocomposite electrodes. The electrochemical properties of the free-standing supercapacitor were analyzed using a two-electrode system. The supercapacitor achieved a specific capacitance of 123.8 F/g at 1 A/g, which was greater than its single (39.1 F/g) and binary (81.3 F/g) counterparts. This suggests that ZnO acts as a spacer and support that hinders the ternary structure from collapsing and subsequently enhances the diffusion of ions within the matrix. The flexible supercapacitor exhibited remarkable electrochemical stability when subjected to bending at various angles. The cycling stability of the ternary nanocomposite showed a favorable specific capacitance retention of more than 90% after 1000 cycles for mild alkaline electrolytes compared with strong alkali electrolytes. The presence of glycerin in the polymer electrolyte enabled the supercapacitor to perform better under the vigorous cycling condition. The potential of the as-fabricated supercapacitor for real applications was manifested by its ability to light up a light-emitting diode after being charged. Copyright © 2014 John Wiley & Sons, Ltd.

Thermodynamic analysis of H2 production from CaO sorption‐enhanced methane steam reforming thermally coupled with chemical looping combustion as a novel technology

Abstract: Summary In this novel paper, a technique for hydrogen production route of CaO sorption-enhanced methane steam reforming (SEMSR) thermally coupled with chemical looping combustion (CLC) was presented (CLC-SEMSR), which perceived as an improvement of previous methane steam reforming (MSR) thermally coupled with CLC technology (CLC-MSR). The application of CLC instead of furnace achieves the inherent separation of CO2 from flue gas without extra energy required. The required heat for the reformer is provided by thermally coupling CLC. The addition of CaO sorbents can capture CO2 as it is formed from the reformer gas to the solid phase, displacing the normal MSR equilibrium restrictions and obtaining higher purity of H2. The Aspen Plus was used to simulate this novel process on the basis of thermodynamics. The performances of this system examined included the composition of reformer gas, yield of reformer gas (YRg), methane conversion (αM), the overall energy efficiency (η), and exergy efficiency (φ) of this process. The effects of the molar ratio of CaO to methane for reforming (Ca/M) in the range of 0–1.2, the molar ratio of methane for combustion to methane for reforming (M(fuel)/M) in the range of 0.1–0.3, and the molar ratio of NiO to methane for reforming (Ni/M) in the range of 0.4–1.2 were investigated. It has been found to be favored by operating under the conditions of Ca/M = 1, M(fuel)/M = 0.2, and Ni/M = 0.8. The most excellent advantage of CLC-SEMSR was that it could obtain higher purity of H2 (95%) at lower operating temperature (655 °C), as against H2 purity of 77.1% at higher temperature (900 °C) in previous CLC-MSR. In addition, the energy efficiency of this process could reach 83.3% at the optimal conditions. Copyright © 2014 John Wiley & Sons, Ltd.

A review on the use of carbon nanostructured materials in electrochemical capacitors

Abstract: Summary Sustainable and renewable energy resources, as well as energy storage systems (ESSs), are amongst the current and critical global requirements. A comparative discussion on batteries, fuel cells and electrochemical capacitors (ECs) is presented. The mechanisms involved in various classes of ECs are also elaborated. Additionally, a historical background highlighting some of the major steps associated with EC development over the years is discussed in this review. In particular, carbon nanostructured materials have high potential in the development of ESSs, and hence this review presents an insight on the current ESSs with a strong bias towards these materials as ECs. The current status of carbon nanomaterials, such as carbon nanotubes, nanofibers, nano-onions, nanorods, fullerenes and graphene nanosheets, in ECs is reviewed. The associated effects of nanostructural parameters, such as pore sizes and specific electro-active areas, amongst others, in terms of energy storage capabilities are also discussed. Typical physicochemical characterisation techniques, which enrich understanding of their characteristics, are also reviewed. The discussion views set platforms for a variety of unique carbon nanomaterial designs with high prospective specific capacitance. Key porosity tailoring protocols, such as chemical activation, introduction of heteroatoms in carbon nanostructures and template synthesis methods, are also reviewed. The effects of other device components, such as electrolyte ion size and solvent system, electrode design and use of binders, to the overall capability of EC, are also discussed. Copyright © 2015 John Wiley & Sons, Ltd.

Solar hydrogen generation from spinel ZnFe2O4 photocatalyst: effect of synthesis methods

Abstract: Summary This paper investigates solar radiation-induced photocatalytic hydrogen generation using spinel ZnFe2O4 (ZFO) photocatalysts fabricated using different routes, viz., solid state reaction (SSR), polymer complex (PC), microwave sintering (μW) and self-propagating combustion (SPC) method. The physicochemical properties of the photocatalysts like crystallinity, surface area, band gap and band energetics is studied as it influences their photochemical behavior. The study reveals a high crystallinity of the ZFO photocatalysts, those are synthesized using SSR, PC and μW methods, where SSR method yields the larger dimension crystallites of ~53 nm. The nanoparticles obtained from SPC methodology exhibit a relatively large surface area and a smaller crystallite size of around ~18 nm. Monodispersed particles with comparatively large surface area are obtained in the case of PC method. ZFO obtained from μW synthesis exhibits enhanced optical properties, thus favoring high absorption of solar photons. A relatively more negative flat band potential is displayed by the μW samples (−0.543 vs normal hydrogen electrode) as estimated from the electrochemical measurements. Consequently, these samples yield a higher quantum yield (0.19%) for hydrogen evolution even without co-catalyst loading. On the contrary, the photocatalysts obtained by SSR and PC methods did display an enhancement in the quantum yield as compared to the μW samples but only after Pt co-catalyst loading. Copyright © 2015 John Wiley & Sons, Ltd.

Co-culture strategies for increased biohydrogen production

Abstract: SUMMARY Biological hydrogen production from organic wastes is a less expensive, less energy-demanding, and environmentalfriendly process. Pure monoculture delivers low H2 content and low yield; these limitations are overcome by a defined co-culture system, which outperforms mixed cultures with increased H2 yield. The strategies used in co-culture systems for increasing H2 production have been discussed in this review. The strategies include hydrolysis of a variety of complex substrates, such as cellulose, molasses, crude glycerol, and algal biomass into simple fermentable sugars for increased H2 yield by eliminating the use of exogenous enzymes. The strategies can bring geographically distant isolated microorganisms from different sources to coexist for simultaneous utilization of substrate and end metabolites into H2 production of 99.99% purity without the expenses of reducing agents. In the case of maximum hydrogen production using co-culture strategies, Clostridium, Enterobacter, and photo-fermenting bacteria in a consolidated bioprocess system will result in increased H2 yield. A co-culture system is more feasible to achieve theoretical H2 yield with high conversion efficiency of organic wastes, enhance the economic viability of H2 production, provide better effluent treatment quality, and concurrently address the limitations of H2 production. Copyright © 2015 John Wiley & Sons, Ltd.

Insights into the production potential and trends of China's rural biogas

Abstract: Summary China, one of the countries in the world abundant in agricultural wastes, has a great potential for rural biogas production. As a strategy for building a new socialist countryside and sustainable agriculture in rural China, the development of biogas is an important means to convert agricultural wastes to clean and safe energy, thereby reducing the need for fossil fuel and alleviating environmental pollution. This study presents an assessment of the biogas production potential, its current development state, and perspectives of agricultural wastes in rural China. Estimated data show that annual biogas potential from agricultural wastes is approximately (3350.58 ± 669.28) × 108 m3 (equal to 239.22 ± 47.78 million tons of equivalent standard coal); such potential has been underutilized in the past. By analyzing and summarizing the direction for future development and various benefits of rural biogas in China, we present burning questions and countermeasures for biogas development and recommend that the future development of rural biogas in China should focus on both household-scale and large-scale development, giving priority to the establishment of large-scale biogas engineering and biogas plants, improvement of biogas comprehensive utilization level, and construction of a reticular model of systemized green agricultural engineering linked with biogas to solve completely the problem of agricultural waste accumulation and improve the living conditions in rural China. Copyright © 2015 John Wiley & Sons, Ltd.

Thermodynamic study on solar thermochemical fuel production with oxygen permeation membrane reactors

Abstract: Thermodynamic analysis is performed on a conceptual oxygen permeation membrane reactor driven by concentrated solar energy (heat) for isothermal H2O splitting for the purpose of solar fuel derivation. By way of a plug-flow reactor model, kinetic and thermodynamic factors responsible for conversion rate, reactor dimension, and solar-to-fuel efficiency are analyzed for the case of pump-assisted and methane-assisted scenarios. The pump-assisted case achieves the same solar-to-fuel efficiency (2.9% at 1500 degrees C) as isothermal solar thermochemical cycling, while the methane-assisted case attains much higher efficiencies at much lower temperatures, whose net solar-to-fuel efficiency reaches 63% at around 900 degrees C. The theoretical framework developed in this study can be applied to the solar thermochemical splitting of other gases such as CO2 and can be further extended to the co-splitting of H2O and CO2 for syngas production driven by solar energy only (i.e., without the participation of hydrocarbon fuels). Copyright (c) 2015 John Wiley & Sons, Ltd.

Reduced graphene oxide–titania nanocomposite-modified photoanode for efficient dye-sensitized solar cells

Abstract: Summary We report the successful application of reduced graphene oxide–titania (rGO–TiO2) nanocomposite as an efficient photoanode for dye-sensitized solar cell (DSSC). The DSSC assembled with the rGO–TiO2-modified photoanode demonstrated an enhanced solar to electrical energy conversion efficiency of 4.74% compared with the photoanode of DSSC composed with unmodified TiO2 (2.19%) under full sunlight illumination (100 mW/cm2, AM 1.5G) as a result of the better charge collection efficiency of rGO, which reduced the back electron transfer process. Influence of the rGO content on the overall efficiency was also investigated, and the optimal rGO content for TiO2 was 0.5 mg. Further, the modification of rGO–TiO2 on the compact layer TiO2 surface led to an increase in efficiency to 5.83%. The superior charge collection and enhanced solar energy conversion efficiency of the rGO–TiO2 nanocomposite makes it to be used as a promising alternative to conventional photoanode-based DSSCs. Copyright © 2015 John Wiley & Sons, Ltd.

Research progress of solar thermochemical energy storage

Abstract: Summary Solar thermal power generation technology has great significance to alleviate global energy shortage and improve the environment. Solar energy must be stored to provide a continuous supply because of the intermittent and instability nature of solar energy. Thermochemical storage (TCS) is very attractive for high-temperature heat storage in the solar power generation because of its high energy density and negligible heat loss. To further understand and develop TCS systems, comprehensive analyses and studies are very necessary. The basic principle and main components of a solar TCS system are described in this paper. Besides, recent progress and existing problems of several promising reaction systems are introduced. Further research directions are pointed out considering the technical, economic, and environmental issues that existed in the wide application of TCS. Copyright © 2014 John Wiley & Sons, Ltd.

Capturing and using CO2 as feedstock with chemical looping and hydrothermal technologies

Abstract: Summary Chemical looping technology for capturing and hydrothermal processes for conversion of carbon are discussed with focused and critical assessments. The fluidized and stationary reactor systems using solid, including biomass, and gaseous fuels are considered in chemical looping combustion, gasification, and reforming processes. Sustainability is emphasized generally in energy technology and in two chemical looping simulation case studies using coal and natural gas. Conversion of captured carbon to formic acid, methanol, and other chemicals is also discussed in circulating and stationary reactors in hydrothermal processes. This review provides analyses of the major chemical looping technologies for CO2 capture and hydrothermal processes for carbon conversion so that the appropriate clean energy technology can be selected for a particular process. Combined chemical looping and hydrothermal processes may be feasible and sustainable in carbon capture and conversion and may lead to clean energy technologies using coal, natural gas, and biomass. Copyright © 2014 John Wiley & Sons, Ltd.

Microencapsulation of n-hexadecanol by in situ polymerization of melamine-formaldehyde resin in emulsion stabilized by styrene-maleic anhydride copolymer

Abstract: Summary Microcapsules with high thermal energy storage density were synthesized by in situ polymerization using melamine–formaldehyde resin as shell and n-hexadecanol as core. Styrene–maleic anhydride (SMA) copolymer was synthesized by solution polymerization and hydrolyzed by NaOH to enhance its water solubility. This negatively charged SMA molecular copolymer self-assembles on the surface of n-hexadecanol droplets and facilitates the precipitation of positively charged melamine–formaldehyde prepolymer onto the droplet surface electrostatically. The morphology, chemical structure, composition, and thermal properties were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, and gas chromatography, respectively. The results show that the obtained microencapsulated phase-change material (MePCM) dispersed individually with a spherical shape. Amount of emulsifier, ratio of shell–core material, and pH value of solution have a significant effect on the microencapsulation. Under optimum condition of 8% SMA to core material, 3.3:10 of shell–core material in feed, and polymerization under pH 4.0, spherical n-hexadecanol MePCMs with core content of 79.1% and melting enthalpy of 171 J g−1 at around 51°C were prepared. In situ polymerization based on SMA-stabilized emulsion opens up a route to prepare a variety of microcapsules with aliphatic alcohol as core material. Copyright © 2014 John Wiley & Sons, Ltd.

Effect of surface modification of anode with surfactant on the performance of microbial fuel cell

Abstract: Summary Surface modification of anode using surfactant has great influence on the electrical performance of a microbial fuel cell (MFC). In this study, the effect of surface-modified exfoliated graphite used for anode fabrication on a cube-type MFC batch reactor was examined. The surface exfoliated graphite was modified with 5-mM anionic surfactant, sodium dodecyl sulfate. Anaerobic sludge used as inoculum containing 70% (v/v) of artificial wastewater and 30% (v/v) of seed sludge in an anode chamber and air cathode was used in cathode side. Anode modification was explored as an approach to enhance the start-up and improve the performance of the reactor. Scanning electron microscopy was used to evaluate the morphology and activity of electrochemically active bacteria. In the study, the start-up time of MFC required to approach stable voltage was substantially reduced, and the maximum stable voltage was higher than the control. In addition, the activation resistance of the MFC was considerably reduced, and the maximum power density (1640 mW/m2) was 20% higher than control. However, when the surface of exfoliated graphite was modified with over 10-mM anionic surfactant, some negative effects on start-up time, activation resistance and maximum power density were observed. This modification also enhanced the bacterial attachment and biofilm formation on the modified anode surface. The result suggested that surface modification anode with surfactant is effective for electrical responses achieved in the MFC. Copyright © 2015 John Wiley & Sons, Ltd.