Hydrogen from wet air and sunlight in a tandem photoelectrochemical cell

A solid-state photoelectrochemical (SSPEC) cell is an attractive approach for solar water splitting, especially when it comes to monolithic device design. In a SSPEC cell the electrodes distance is minimized, while the use of polymer-based membranes alleviates the need for liquid electrolytes, and at the same time they can separate the anode from the cathode. In this work, we have made and tested, firstly, a SSPEC cell with a Pt/C electrocatalyst as the cathode electrode, under purely gaseous conditions. The anode was supplied with air of 80% relative humidity (RH) and the cathode with argon. Secondly, we replaced the Pt/C cathode with a photocathode consisting of 2D photocatalytic g-C₃N₄, which was placed in tandem with the photoanode (tandem-SSPEC). The tandem configuration showed a three-fold enhancement in the obtained photovoltage and a steady-state photocurrent density. The mechanism of operation is discussed in view of recent advances in surface proton conduction in absorbed water layers. The presented SSPEC cell is based on earth-abundant materials and provides a way towards systems of artificial photosynthesis, especially for areas where water sources are scarce and electrical grid infrastructure is limited or nonexistent. The only requirements to make hydrogen are humidity and sunlight.     

Mining citizen emotions to estimate the urgency of urban issues

Crowdsourcing technology offers exciting possibilities for local governments. Specifically, citizens are increasingly taking part in reporting and discussing issues related to their neighborhood and problems they encounter on a daily basis, such as overflowing trash-bins, broken footpaths and lifts, illegal graffiti, and potholes. Pervasive citizen participation enables local governments to respond more efficiently to these urban issues. This interaction between citizens and municipalities is largely promoted by civic engagement platforms, such as See-Click-Fix, FixMyStreet, CitySourced, and OpenIDEO, which allow citizens to report urban issues by entering free text describing what needs to be done, fixed or changed. In order to develop appropriate action plans and priorities, government officials need to figure out how urgent are the reported issues. In this paper we propose to estimate the urgency of urban issues by mining different emotions that are implicit in the text describing the issue. More specifically, a reported issue is first categorized according to the emotions expressed in it, and then the corresponding emotion scores are combined in order to produce a final urgency level for the reported issue. Our experiments use the SeeClickFix hackathon data and diverse emotion classification algorithms. They indicate that (i) emotions can be categorized efficiently with supervised learning algorithms, and (ii) the use of citizen emotions leads to accurate urgency estimates. Further, using additional features such as the type of issue or its author leads to no further accuracy gains.     

Enhanced electrocatalytic performance of Cu0.02S0.01/rGO hybrid for oxygen reduction reaction in alkaline medium at low temperature

Graphene, is a carbon allotrope, which is widely used as a substrate for various catalysts due to its interesting physicochemical properties. In the present study, graphene oxide sheets were prepared from graphite, then, the graphene oxide surface was modified by a low-temperature method using sulfur and copper atoms to obtain pseudo-enzyme Cu/S/Graphene prosthetic group. The current density passing through Cu/S/Graphene catalyst was four times higher than that passing through graphite. The novel copper-based catalyst had an extraordinary performance for oxygen reduction reaction (ORR) due to the unique bio-inspired and stoichiometric structure. The results of Raman and Dispersive X-ray spectroscopy confirmed the presence of ultra-low content of copper (2%) and sulfur (1%) atoms on the graphene surface. Thermogravimetric analysis indicated a strong interaction between nanoparticles and graphene layers. The number of electrons transferred for ORR varied from 3.98 to 4.16 in a wide range of over-potentials indicating an effective 4-electron pathway form O₂ to H₂O. The Tafel slopes indicated insignificant amount of formed copper oxide on the catalyst surface. The catalyst showed excellent electrochemical durability and its half-wave potential (E_1/2) was exhibited a negative shift only 8.2 mV after 10000 cycles.     

Macaroon-like FeCo2O4 modified activated carbon anode for enhancing power generation in direct glucose fuel cell

Macaroon-like FeCo₂O₄ nanomaterial was prepared and used as electrocatalyst in direct glucose alkaline fuel cell (DGAFC), which exhibited high catalytic activity towards glucose oxidation reaction. Maximum power density of 35.91 W m⁻² was achieved in the DGAFC equipped with a FeCo₂O₄ modified activated carbon (AC) anode, which was almost 151% higher than the control. Physical and electrochemical characterizations were performed to provide further understanding of the origin of its high activity. Our results show that the introduction of FeCo₂O₄ into the AC anode remarkably increase the exchange current density and reduce the charge transfer resistance. It is supposed that there is a synergistic effect between Fe (III) and Co (III), which accelerates electron transfer from glucose to external circuits. This study will promote the development of cost effective and environmentally benign catalysts for electrochemical energy applications.     

Synthesis of a new “green” sponge via transesterification of dimethyl carbonate with polyvinyl alcohol and foaming approach

In this article, the low toxicity of polyvinyl alcohol (PVA) and dimethyl carbonate (DMC) were used to synthesize polyvinyl alcohol carbonate (PVAC) sponge via a simple transesterification-foaming approach, and the structure and morphology of PVAC sponge were characterized; moreover, the influence of dosage of K₂CO₃, PVA, distilled water and n-pentane on the water retention capacity of PVAC sponge were investigated, and the influence of reaction temperature and reaction time on the water retention capacity of PVAC sponge were also surveyed. Based on those, it was confirmed that 9.00 g PVA and 5.00 mL DMC in the presence of 2.00 g K₂CO₃ and 50.00 mL water could be used to synthesize PVAC polymer at 75?°C and for 2.5 h via the transesterification approach, and PVAC polymer in the presence of 5.00 mL n-pentane could be used to synthesize PVAC sponge at 55?°C and for 10 h via the foaming approach, and PVAC sponge owned the structure of six-membered lactone ring and the polyporous morphology, and the maximal water retention capacity was 21.50 g/g.     

Systematic optimization of low bandgap polymer/[6,6]-phenyl C70 butyric acid methyl ester blend photodiode via structural engineering

Synthetic approaches for optimizing polymer-based organic photodiodes (OPDs) by systematically analyzing the effects of the hole-blocking layer, the electron-blocking layer, and the thickness and morphology of the active layer with respect to the dark current and detectivity have been reported. PBDTT-DPP with a repeating alkylthienylbenzodithiophene (BDTT) and diketopyrrolopyrrole (DPP) units is used as a p-type polymer for achieving both broadband absorption and a high absorption coefficient in conjunction with n-type [6,6]-phenyl C₇₀ butyric acid methyl ester (PC₇₀BM) for constructing photoactive layers. Through systematic investigations of various interfacial layers, we found that the thickness of the active layer and the energy level of the hole/electron blocking layer were critical for minimizing the dark current of OPDs. By changing the deposition method of the PBDTT-DPP/PC₇₀BM blend and using post treatment, we discovered that the morphology of the active layer was directly related to the photocurrent of OPDs. Furthermore, we conducted a comparative study between a bulk heterojunction and a planar heterojunction (PHJ) to demonstrate the effectiveness of the PHJ for suppressing the dark current. Consequently, we realized a high detectivity of 5.3 × 10¹² Jones with an optimized device architecture and morphology. This work shows the importance of a synthetic approach for optimizing OPDs that requires both a high photocurrent and a low dark current in the reverse saturation regime.     

Modeling iron-catecholates binding to NGAL protein

Neutrophil gelatinase associated lipocalin (NGAL) protein is attracting a great interest because of its antibacterial properties played upon modulating iron content in competition against iron acquisition processes developed by pathogenic bacteria that bind selective ferric iron chelators (siderophores). Besides its known high affinity to enterobactin, the most important siderophore, it has been recently shown that NGAL is able to bind Fe(III) coordinated by catechols. The selective binding of Fe(III)-catechol ligands to NGAL is here studied by using iron coordination structures with one, two, and three catecholate ligands. By means of a computational approach that consists of B3LYP/6-311G(d,p) quantum calculations for geometries, electron properties and electrostatic potentials of ligands, protein–ligand flexible docking calculations, analyses of protein–ligand interfaces, and Poisson–Boltzmann electrostatic potentials for proteins, we study the binding of iron catecholate ligands to NGAL as a central member of the lipocalin family of proteins. This approach provides a modeling basis for exploring in silico the selective binding of iron catecholates ligands giving a detailed picture of their interactions in terms of electrostatic effects and a network of hydrogen bonds in the protein binding pocket.     

Cleavage resistance of plastically deformed natural diamonds revealed by dissolved planar features

We describe here diamonds with planar segments of limited lateral extension, some of which have dissolved to form flat etch channels. We have documented such features only in diamonds which show otherwise lamellae of brown or pink color due to plastic deformation along (111) planes, called “colored graining lamellae”. The planar segments are identified as cleavage segments. We suggest that the extension of the etch channels is controlled by the geometry of the pre-existing cleavage segments, as dissolution happens preferentially at sites offering a high available surface. These cleavage segments (indifferently dissolved as flat etch channels or not) are laterally limited by colored graining lamellae along another set of (111) planes. This indicates that plastically deformed diamond is “cleavage resistant”. Further, it reveals that plastic deformation may induce different types of defects–either cleavage or colored graining lamellae–along different sets of octahedral planes in the same crystal.     

Preparation of rutile (TiO<Subscript>2</Subscript>) nanostructured materials at low temperature from TiCl<Subscript>4</Subscript> aqueous solution

The synthesis of rutile (TiO₂) nanostructured materials at low temperature from TiCl₄ aqueous solution was described. TiO₂ coatings on polystyrene (PS) particles were prepared by layer-by-layer assembly technique. The samples were characterized by DTA-TG, SEM, XPS, TEM and XRD techniques. The experimental results showed that pure rutile-TiO₂ coatings with nanocrystal structure were synthesized at 100 °C. On the surface of PS particles, sphere-type TiO₂ coatings exhibited uniform shape and a narrow size distribution. The amount of TO₂ (wt%) and shell thickness of particles increased with the adding of coating layers. Hollow TiO₂ spheres were obtained by calcination at 450 °C. TiO₂/PS with 2 coating layers showed higher degradation rate. The photocatalytic activity of hollow TiO₂ spheres was higher than that of TiO₂/PS.