Optimization hydrogen production over visible light-driven titania-supported bimetallic photocatalyst from water photosplitting in tandem photoelectrochemical cell

Solar hydrogen production was investigated over a Cu-Ni doped TiO₂ photocatalyst from water photosplitting in a tandem photoelectrochemical cell, which was made up by connecting a modified photoelectrochemical cell to dye solar cell in a series. A mathematical representation for preparation parameters for hydrogen production was successfully generated. Optimization of hydrogen production was conducted with varying preparation parameters of Cu-Ni doped TiO₂ photocatalyst including molar ratios of water, acetic acid and Cu to titanium tetraisopropoxide. The optimum preparation parameters of photocatalyst was obtained at molar ratios of water, acetic acid and Cu to titanium tetraisopropoxide of 32, 4.9, and 5.9, respectively. Physical and photoelectrochemical characterization revealed that low content of water and Cu decreased the charge transfer resistance and charge carrier recombination rate on Cu-Ni/TiO₂ surface. This is attributed to the better crystallinity and less degree of agglomeration which led to obtain optimum particle size at this condition. Maximum hydrogen production rate of 2.12 mL/cm². h was achieved under the optimum condition using the tandem photoelectrochemical cell in the aqueous KOH and glycerol solution under visible light irradiation (λ > 400 nm).     

Oligothiophene-based small molecules with 3,3′-difluoro-2,2′-bithiophene central unit for solution-processed organic solar cells

Two new oligothiophene-based small molecules, namely DRCN6T-F and DRCN8T-F, with 3,3′-difluoro-2,2′-bithiophene as the central building block and 2-(1,1-dicyanomethylene)-rhodanine as end groups, were designed and synthesized. Compared to their non-fluorinated counterparts DRCN6T and DRCN8T, DRCN6T-F and DRCN8T-F exhibit enhanced intermolecular interactions and lower HOMO energy levels. However, PCEs of 2.26% and 5.07% were obtained for DRCN6T-F and DRCN8T-F based optimized devices, respectively, lower than those of non-fluorinated molecules DRCN6T and DRCN8T. The relatively poor performance for the DRCN6T-F and DRCN8T-F were mainly caused by their low short-circuit current densities, due to their unfavorable morphologies and low charge carrier mobilities.     

Kinetics of ultrasonic extraction of polyphenols,anthocyanins and tannins from five different New Zealand grape pomaces

Polyphenols were extracted from five kinds of New Zealand grape pomace (Sauvignon Blanc, Pinot Gris, Gerwurztraminer, Merlot and Pinot Noir) at 30, 50 and 70 °C in an ultrasonic generator. The extraction kinetics for total phenol, anthocyanin and tannin were determined. The results of dynamics study showed that the extraction of total polyphenols, anthocyanin and tannin followed first-order reaction kinetics during the extraction at 30, 50 and 70 °C. The total phenolic content, anthocyanin conten, and tannin content of water–ethanol extracts from grape pomaces were compared, and the parameters in the extraction kinetics equations were determined. The extraction results showed that the Pinot Noir pomace extract had the highest total phenolic content of 59.95 mg GAE g⁻¹ pomace and tannin content of 79.93 mg EE g⁻¹ pomace. The anthocyanin content in Merlot pomace extract was the highest, which was 4.50 CE g⁻¹ pomace. The results might be of great significance for the development of grape pomace or its polyphenol and/or anthocyanin components as an antioxidant source with natural and inexpensive benefits.     

X-ray computed tomography reconstruction and analysis of polymer electrolyte membrane fuel cell porous transport layers

A commercially available porous transport layer (SGL carbon group Sigracet^® GDL 30BA), is investigated using X-ray computed tomography reconstruction. A novel aspect of this study is an investigation of the effects of non-homogeneous compression of the GDL 30BA sample including effective transport properties. Non-homogeneous compression is typical in polymer electrolyte fuel cells as the flow field plates consist of a series of lands and channels which apply an uneven loading to the porous transport layers. The X-ray computed tomography technique provides input data for the computer reconstruction procedures integrating image post-processing and iso-surface reconstruction. The resulting tomographic and surface reconstruction is converted into the computational volume/grid for microstructural and computational fluid dynamics (CFD) analysis. The heterogeneous compression effects on effective geometric and transport properties are investigated for various compression levels and effective transport properties are compared to theoretical studies such as Bruggeman [1] and Tomadakis and Sotirchos [2]. The effects of non-homogeneous compression are significant, with the transport properties differing by a factor of about 2 between the land and the channel regions. It is found that the effective transport properties are significantly lower than predicted by commonly used relations, with the lowest values representing only 15% of the predictions from the Bruggeman relation.     

Understanding CO2 electrochemical reduction kinetics of mixed-conducting cathodes by the electrical conductivity relaxation method

Electrochemical reduction reaction is an important approach to utilize CO₂ and convert it into valuable products. Exceptional reaction kinetics at a high temperature of solid oxide electrolysis cells (SOECs) attracts particular attention. In this work, we propose to investigate CO₂-RR kinetics using a new theoretical method based on the electrical conductivity relaxation (ECR) technique on a typical mixed-conducting Sr₂Fe_1.5Mo_0.5O_6-δ (SFM) electrode. Three kinetic parameters that are commonly adopted in the typical electrochemical test experiments consisting of overpotential, current density and area-specific resistance (ASR) are derived. The overpotential resulted from the difference in the oxygen partial pressure is caused by the change of CO₂ partial pressure, while current density from the surface reaction rate constant. Accordingly, area-specific resistance, as well as overpotential-current density relationship, can be derived. We believe that this work brings a new method to study the kinetic process of CO₂ electrolysis and to evaluate the electrocatalyst activity of developed new electrode materials as well as to benefit the designing of novel electrode electrocatalysts for highly efficient solid oxide electrolysis cells.     

Perovskite materials for highly efficient catalytic CH4 fuel reforming in solid oxide fuel cell

SOFC (solid oxide fuel cell, SOFC) is recognized to be efficient green energy technology in the 21st century. However, when hydrocarbons are directly used as fuel, carbon deposition is easy to occur in Ni-based anode, thus losing electrochemical catalytic activity. Fuel pre-reforming is also called on-cell reforming of hydrocarbons, which has been a promising solution for alleviating the carbon deposition problem in cermet anodes to varying degrees. And the key factor is to find an efficient and stable fuel reforming catalyst. Perovskite oxides have stable structure, highly catalytic activity and adjustable thermal expansion coefficient for using on the cells, showing great potentials of application for fuel reforming. In this paper, we summarize the application of perovskite catalyst in CH₄ fuel reforming based on the research of our group and other scholars, and puts forward the corresponding views and perspective, especially in perovskite catalyst with Ni exsolution.     

Investigation of the copper concentration on photocurrent collection of CuInSe2 solar cells

In this study, CuInSe₂ (CISe) thin films were prepared from thermally evaporated Cu/In precursors, having various Cu/In atomic ratio, under the same selenization conditions. The precursors were converted into CISe absorber by annealing in a quartz tube furnace in the selenium vapours at substrate temperature of 500 °C. We developed four CISe films with Cu/In atomic ratio of 0.81–1.19, denoted as Cu‐very rich, Cu‐rich, Cu‐poor, and Cu‐very poor CISe thin films respectively. The effects of Cu/In atomic ratio on grain size, surface morphology, micro‐structure and defect formation of the resulting CISe films were examined. It has been found that the photovoltaic properties were strongly related to Cu concentration, as well as carrier transport mechanism. Defects at the surface and in the bulk of CISe thin films were observed using X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy, Raman spectroscopy, energy dispersive X‐ray spectroscopy and scanning electron microscopy. Moreover, XRD revealed that the CISe film surface had a preferred orientation along the (112) plane. The XRD intensity and full width at half maximum of the (112) plane of CISe varied according to the Cu/In atomic ratio. Our experimental results show that the Cu‐rich solar cell achieves conversion efficiency of 4.55% and exhibits an exceptional high short‐circuit current density. Copyright © 2016 John Wiley & Sons, Ltd.     

Determination of the electrical characteristics and thermal behaviour of a c-Si cell under transient conditions for various concentration ratios

An extended study of c-Si cell performance under transient conditions for various concentration ratios, C, between 0.6 and 12.25 is presented. PV cell temperature, T_c, open-circuit voltage, V_oc, and short-circuit current, I_sc, were measured using an experimental set-up based on a solar light simulator. The dependence of V_oc, I_sc, dV_oc/dT_c, dI_sc/dT_c and r_s on T_c was investigated against C. A model was developed to predict T_c. Generalised formulae were proposed for prediction of V_oc and I_sc. Theoretically obtained T_c and V_oc profiles were compared with the measured ones. A good agreement was observed. The time constants of V_oc and T_c profiles were determined experimentally for various C values and lie within ±5% from theoretically predicted time constants. The coefficient dV_oc/dT_c was determined for various C values. The results show a decrease in the absolute value of dV_oc/dT_c against C. A partial recovery of PV cell performance through a ventilation process was tried.