Abstract: Using first-principles calculations, we demonstrated that high lithium storage capacity and fast kinetics are achieved for Ti3C2O2 by preintercalating organic molecules. As a proof-of-concept, two different quinone molecules, namely 1,4-benzoquinone (C6H4O2) and tetrafluoro-1,4-benzoquinone (C6F4O2) were selected as the molecular linkers to demonstrate the feasibility of this interlayer engineering strategy for energy storage. As compared to Ti3C2O2 bilayer without linker molecules, our pillared structures facilitate a much faster ion transport, promising a higher charge/discharge rate for Li. For example, while the diffusion barrier of a single Li ion within pristine Ti3C2O2 bilayer is at least 1.0 eV, it becomes 0.3 eV in pillared structures, which is comparable and even lower than that of commercial materials. At high Li concentrations, the calculated diffusion barriers are as low as 0.4 eV. Out-of-plane migration of Li ions is hindered due to large barrier energy with a value of around 1-1.35 eV. Concerning storage capacity, we can only intercalate one monolayer of Li within pristine Ti3C2O2 bilayer. In contrast, pillared structures offer significantly higher storage capacity. Our calculations showed that at least two layers of Li can be intercalated between Ti3C2O2 layers without forming bulk Li and losing the pillared structure upon Li loading/unloading. A small change in the in-plane lattice parameters (<0.5%) and volume (<1.0%) and ab initio molecular dynamics simulations prove the stability of the pillared structures against Li intercalation and thermal effects. Intercalated molecules avoid the large contraction/expansion of the whole structure, which is one of the key problems in electrochemical energy storage. Pillared structures allow us to realize electrodes with high capacity and fast kinetics. Our results open new research paths for improving the performance of not only MXenes but also other layered materials for supercapacitor and battery applications.

Abstract: The hydrogen evolution properties of CZTS heterostructure photocathodes are reported with graphene oxide (GO) as a co-catalyst layer coated by a drop-cast method and an Al2O3 protection layer fabricated using atomic layer deposition. In the CZTS absorber, a minor deviation from stoichiometry across the cross section of the thin film results in nanoscale growth of spurious phases, but the kesterite phase remains the dominant phase. We have investigated the band alignment parameters such as the band gap, work function, and Fermi level position that are crucial for making kesterite-based heterostructure devices. The photocurrent density in the photocathode CZTS/CdS/ZnO is found to be improved to -4.71 mAmiddotcm(-2) at -0.40 V-RHE, which is 3 times that of the pure CZTS. This enhanced photoresponse can be attributed to faster carrier separation at p-n junction regions driven by upward band bending at CZTS grain boundaries and the ZnO layer. GO as a co-catalyst over the heterostructure photocathode significantly improves the photocurrent density to -6.14 mAmiddotcm(-2) at -0.40 V-RHE by effective charge migration in the CZTS/CdS/ZnO/GO configuration, but the onset potential shifts only after application of the Al2O3 protection layer. Significant photocurrents of -29 mAmiddotcm(-2) at -0.40 V-RHE and -8 mAmiddotcm(-2) at 0 V-RHE are observed, with an onset potential of 0.7 V-RHE in CZTS/CdS/ZnO/GO/Al2O3. The heterostructure configuration and the GO co-catalyst reduce the charge-transfer resistance, while the Al2O3 top layer provides a stable photocurrent for a prolonged time (similar to 16 h). The GO co-catalyst increases the flat band potential from 0.26 to 0.46 V-RHE in CZTS/CdS/ZnO/GO, which supports the bias-induced band bending at the electrolyte-electrode interface.

Abstract: Using density-functional theory in combination with the nonequilibrium Green's function formalism, we study the effect of iodide/chloride and iodide/bromide mixing on the electronic transport in lead based organometallic perovskite CH3NH3PbI3, which is known to be an effective tool to tune the electronic and optical properties of such materials. We found that depending on the level and position of the halide mixing, the electronic transport can be increased by more than a factor of 4 for a given voltage biasing. The largest current is observed for small concentration of bromide substitutions located at the equatorial sites. However, full halide substitution has a negative effect on the transport properties of this material: the current drops by an order of magnitude for both CH3NH3PbCl3 and CH3NH3PbBr3 samples. (C) 2015 Elsevier B.V. All rights reserved.

Abstract: Conversion of solar energy into thermal energy helps reducing consumption of non-renewable energies. Cermets (ceramicmetal composites) are versatile materials suitable, amongst other applications, for solar selective absorbers. Although the presence of metallic Ni particles in the dielectric matrix is a prerequisite for efficient solar selective absorption in NiCrOx cermets, no clear evidence of such particles is reported so far. By combining comprehensive chemical and structural analyses, we reveal the presumed nanostructure which is at the origin of the remarkable optical properties of this cermet material. Using sputtered NiCrOx layers in a solar absorber multilayer stack on aluminium substrate allows us to achieve solar absorptance as high as α=96.1% while keeping thermal emissivity as low as ε=2.2%, both values being comparable to best values recorded so far. With the nanostructure of sputtered NiCrOx cermets eventually revealed, further optimization of solar absorbers can be anticipated and technological exploitation of cermet materials in other applications can be foreseen.

Abstract: Er3+Yb3+ co-doped transparent glass-ceramics with varying Er/Yb content and ratio have been prepared. High quantum yields for up- and down-conversion luminescence by energy transfer from Yb3+ to Er3+ and from Er3+ to Yb3+, respectively, have been detected and optimized with respect to the Er/Yb content and ratio, and proposed in particular for up- and down-conversion of solar spectrum for enhancement of the efficiency of solar cells. The rise and decay kinetics for the population of the excited levels of Er3+ and Yb3+ have been studied and fit. Based on these experimental data, the mechanisms for the energy transfers have been suggested with emphasis on the optimized Er/Yb content and ratio for enhancement of the efficiency of the Er3+↔Yb3+ energy transfers.

Abstract: Second-generation biofuels, starting from lignocellulosic biomass, are considered as a renewable alternative for fossil fuels with lower environmental impact and potentially higher supply and energy security. The economic and environmental performance of second-generation bioethanol production from corn stover in the European Union (EU) is studied, starting in Belgium as base case. A comparative environmental techno-economic assessment has been conducted, with process simulations in Aspen Plus and corn stover availability data in thirteen EU countries to calculate minimum ethanol selling prices (MESP) and Greenhouse gas emissions (GHGe). In this analysis, the emphasis is on the comparison of different pretreatment technologies, namely (i) dilute acid, (ii) alkaline, (iii) steam explosion and (iv) liquid hot water. Dilute acid showed the best economic and environmental performance for the base case scenario. Within the EU, Hungary and Romania presented the lowest MESP for the steam explosion model at 0.39 and 0.43 EUR/L respectively. Poland showed the lowest GHGe, at 0.46 kg CO2eq/L for the alkaline model, mainly due to the avoided product allocation on electricity and its high carbon intensity in the electricity generation sector. The second lowest GHGe were obtained in France for the dilute acid model and are attributed to its low agricultural emissions intensity. This study identifies a location-dependence of the economic and environmental performance of pretreatment technologies, which can be extrapolated from the EU to other large regions around the world and should be taken into consideration by decision-makers.

Abstract: Companies dealing with chemical products have to cope with large amounts of waste and environmental risk due to the use and production of toxic substances. Against this background, increasing attention is being paid to green chemistry and the translation of this concept into biobased chemicals. Given the multitude of economic, environmental and societal impacts that the production and use of biobased chemicals have on sustainability, assessment approaches need to be developed that allow for measurement and comparison of these impacts. To evaluate sustainability in the context of policy and decision-making, indicators are generally accepted means. However, sustainability indicators currently predominantly exist for low-value applications in the bioeconomy, like bioenergy and biofuels. In this paper, a review of the state-of-the-art sustainability indicators for biobased chemicals is conducted and a gap analysis is performed to identify indicator development needs. Based on the analysis, a clear hierarchy within the concept of sustainability is found where the environmental aspect dominates over economic and social indicators. All one-dimensional indicator-sets account for environmental impacts (50%), whereas two-dimensional sets complement the environmental issues with economic indicators (34%). Moreover, even the sets encompassing all three sustainability dimensions (16%) do not account for the dynamics and interlinkages between the environment, economy and society. Using results from the literature review, an indicator list is presented that captures all indicators currently used within sustainability assessment of biobased chemicals. Finally, a framework is proposed for future indicator selection using a stakeholder survey to obtain a prioritized list of sustainability indicators for biobased chemicals.

Abstract: Biomass is expected to play an increasingly significant role in the greening of energy supply. Nevertheless, concerns are rising about the sustainability of large-scale energy crop production. Impacts must be assessed carefully before deciding whether and how this industry should be developed, and what technologies, policies and investment strategies should be pursued. There is need for a comprehensive and reliable sustainability assessment tool to evaluate the environmental, social and economic performance of biomass energy production. This paper paves the way for such a tool by analysing and comparing the performance and applicability of a selection of existing tools that are potentially useful for sustainability assessment of bioenergy systems. The selected tools are: Criteria And Indicators (C&I), Life Cycle Assessment (LCA), Environmental Impact Assessment (EIA), Cost Benefit Analysis (CBA), Exergy Analysis (EA) and System Perturbation Analysis (SPA). To evaluate the tools, a framework was constructed that consists of four evaluation levels: sustainability issues, tool attributes, model structure, area of application. The tools were then evaluated using literature data and with the help of a Delphi panel of experts. Finally, a statistical analysis was performed on the resulting data matrix to detect significant differences between tools. It becomes clear that none of the selected tools is able to perform a comprehensive sustainability assessment of bioenergy systems. Every tool has its particular advantages and disadvantages, which means that trade-offs are inevitable and a balance must be found between scientific accuracy and pragmatic decision making. A good definition of the assessment objective is therefore crucial. It seems an interesting option to create a toolbox that combines procedural parts of C&I and EIA, supplemented with calculation algorithms of LCA and CBA for respectively environmental and economic sustainability indicators. Nevertheless, this would require a more comprehensive interdisciplinary approach to align the different tool characteristics and focuses.

Abstract: Organic photovoltaics (OPV) have developed into a vast research area. Progress in various directions has made it difficult to monitor the technology's precise development state. We offer a patent landscape analysis over all OPV devices, their substrates and encapsulation materials to provide an overview of patenting activity from a historical, organizational, geographical and technological point of view. Such an exercise is instrumental for private companies and research institutes aiming at both internal or external technology creation. We discuss our findings in the context of the Industrial Life Cycle model and find OPV still residing in the fluid technology development phase. Technology development is still following an exponential growth path, with the majority of patents coming from the Asian continent and in general private companies. For devices, the main technological focus can be traced back to the “H01L-031” international patent classification (IPC) main group. For the queried substrates, the most attention has gone to glass, but paper and textile have drawn significant interest too. Finally, encapsulation is found to be a less mature research field given the smaller number of patent families. The latter shows that the technology has not matured to the level where processing is carried out on a commercial scale. (C) 2013 Elsevier Ltd. All rights reserved.

Abstract: Piezoelectricity is considered to be one of the key functionalities in biomaterials to boost bone tissue regeneration, however, integrating biocompatibility, biodegradability and 3D structure with pronounced piezoresponse remains a material challenge. Herein, novel hybrid biocompatible 3D scaffolds based on biodegradable poly(3-hydroxybutyrate) (PHB) and reduced graphene oxide (rGO) flakes have been developed. Nanoscale insights revealed a more homogenous distribution and superior surface potential values of PHB fibers (33 +/- 29 mV) with increasing rGO content up to 1.0 wt% (314 +/- 31 mV). The maximum effective piezoresponse was detected at 0.7 wt% rGO content, demonstrating 2.5 and 1.7 times higher out-of-plane and in-plane values, respectively, than that for pure PHB fibers. The rGO addition led to enhanced zigzag chain formation between paired lamellae in PHB fibers. In contrast, a further increase in rGO content reduced the alpha-crystal size and prevented zigzag chain conformation. A corresponding model explaining structural and molecular changes caused by rGO addition in electrospun PHB fibers is proposed. In addition, finite element analysis revealed a negligible vertical piezoresponse compared to lateral piezoresponse in uniaxially oriented PHB fibers based on alpha-phase (P2(1)2(1)2(1) space group). Thus, the present study demonstrates promising results for the development of biodegradable hybrid 3D scaffolds with an enhanced piezoresponse for various tissue engineering applications.

Abstract: In this work, we employed first-principles density functional theory (DFT) calculations to investigate the dynamical and thermal stability of graphene-like ZnX (X = N, P, As) nanosheets. We moreover analyzed the electronic, mechanical and optical properties of these novel two-dimensional (2D) systems. Acquired phonon dispersion relations reveal the absence of imaginary frequencies and thus confirming the dynamical stability of predicted monolayers. According to ab-initio molecular dynamics results however only ZnN and ZnP exhibit the required thermally stability. The elastic modulus of ZnN, ZnP and ZnAs are estimated to be 31, 21 and 17 N/m, respectively, and the corresponding tensile strengths values are 6.0, 4.9 and 4.0 N/m, respectively. Electronic band structure analysis confirms the metallic electronic character for the predicted monolayers. Results for the optical characteristics also indicate a reflectivity of 100% at extremely low energy levels, which is desirable for photonic and optoelectronic applications. According to our results, graphene-like ZnN and ZnP nanosheets can yield high capacities of 675 and 556 mAh/g for Li-ion storage, respectively. Acquired results confirm the stability and acceptable strength of ZnN and ZnP nanosheets and highlight their attractive application prospects in optical and energy storage systems.

Abstract: Nanoconfined magnesium hydride can be simultaneously protected and thermodynamically destabilized when interfaced with materials such as Ti and Fe. We study the hydrogenation of thin layers of Mg (<14 nm) nanoconfined in one dimension within thin film Fe/Mg/Fe/Pd multilayers by the optical technique Hydrogenography. The hydrogenation of nanosized magnesium layers in Fe/Mg/Fe multilayers surprisingly shows the presence of multiple plateau pressures, whose nature is thickness dependent. In contrast, hydrogen desorption occurs via a single plateau which does not depend on the Mg layer thickness. From structural and morphological analyses with X-ray diffraction/reflectometry and cross-section TEM, we find that the Mg layer roughness is large when deposited on Fe and furthermore contains high-angle grain boundaries (GB's). When grown on Ti, the Mg layer roughness is low and no high-angle GB's are detected. From a Ti/Mg/Fe multilayer, in which the Mg layer is flat and has little or no GB's, we conclude that MgH2 is indeed destabilized by the interface with Fe. In this case, both the ab- and desorption plateau pressures are increased by a factor two compared to the hydrogenation of Mg within Ti/Mg/Ti multilayers. We hypothesize that the GB's in the Fe/Mg/Fe multilayer act as diffusion pathways for Pd, which is known to greatly alter the hydrogenation behavior of Mg when the two materials share an interface. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Abstract: We present a combined study of experimental and computational work for a dielectric barrier discharge (DBD) used for CH4 conversion into H2. More specifically, we investigated the influence of N2 as an impurity (150,000 ppm) and as additive gas (199%) on the CH4 conversion and H2 yield. For this purpose, a zero-dimensional chemical kinetics model is applied to study the plasma chemistry. The calculated conversions and yields for various gas mixing ratios are compared to the obtained experimental values, and good agreement is achieved. The study reveals the significance of the View the MathML source and View the MathML source metastable states for the CH4 conversion into H2, based on a kinetic analysis of the reaction chemistry.

Abstract: Demand response (DR) can aid with grid integration of renewables, ensuring security of supply, and reducing generation costs. However, not enough is known about how residential customers’ perceptions of DR shape their response to such programs. This paper offers a deeper understanding of – and reveals the heterogeneity in – this relationship by conducting a quantile regression analysis of a Belgian DR trial, combining data on response with information on household attitudes towards smart appliances. Results overall suggest that improving response requires subtle shifts in electricity consumption behaviour, which can be achieved through changes in user perceptions. Specifically, if customers are inclined to be flexible, a stronger perception of smart appliances as being beneficial can greatly improve response. With those who are less flexible, the cost of smart appliances is a bigger concern. Thus, when designing DR programs, policymakers should aim to promote modest behaviour changes – so as to minimise inconvenience – in customers, by improving awareness on the benefits of smart appliances. Uptake of such DR programs may be improved by explaining the financial benefits or offering incentives to less flexible population segments. Lastly, improving response among older population segments will require a deeper investigation into their concerns.

Abstract: This paper assesses unintentional interference between different public policies promoting energy efficiency and renewable energy. The paper develops a methodology to study the interference by analysing the economic and technical behaviour of a hybrid energy system. The hybrid energy system in this case consists of an existing cogeneration unit extended with a new installation of thermal solar panels. This puts two complementary heating technologies in juxtaposition. The two technologies are supported with distinct regional support instruments in each region. The design and operation of the energy system is optimised from the point of view of the investor according to the different support instruments. The optimal configuration is analysed as well as its effect on reduced CO2-emissions during the lifetime of the project. The methodology is applied to a case-study for two neighbouring regions, the Netherlands and Flanders. The policies in the Netherlands show a beneficial synergy. In Flanders, the hybrid energy system is not interesting, indicating unbalanced high support for cogeneration in this case. From the point of view of the authorities, a more balanced regional policy as in the Netherlands provides a larger CO2-emission reduction for a smaller cost. (C) 2012 Elsevier Ltd. All rights reserved.