Iron-nitrogen on carbon (Fe-N/C) catalysts have emerged as promising nonprecious metal catalysts (NPMCs) for oxygen reduction reaction (ORR) in energy conversion and storage devices. It has been ...widely suggested that an active site structure for Fe-N/C catalysts contains Fe-Nx coordination. However, the preparation of high-performance Fe-N/C catalysts mostly involves a high-temperature pyrolysis step, which generates not only catalytically active Fe-Nx sites, but also less active large iron-based particles. Herein, we report a general "silica-protective-layer-assisted" approach that can preferentially generate the catalytically active Fe-Nx sites in Fe-N/C catalysts while suppressing the formation of large Fe-based particles. The catalyst preparation consisted of an adsorption of iron porphyrin precursor on carbon nanotube (CNT), silica layer overcoating, high-temperature pyrolysis, and silica layer etching, which yielded CNTs coated with thin layer of porphyrinic carbon (CNT/PC) catalysts. Temperature-controlled in situ X-ray absorption spectroscopy during the preparation of CNT/PC catalyst revealed the coordination of silica layer to stabilize the Fe-N4 sites. The CNT/PC catalyst contained higher density of active Fe-Nx sites compared to the CNT/PC prepared without silica coating. The CNT/PC showed very high ORR activity and excellent stability in alkaline media. Importantly, an alkaline anion exchange membrane fuel cell (AEMFC) with a CNT/PC-based cathode exhibited record high current and power densities among NPMC-based AEMFCs. In addition, a CNT/PC-based cathode exhibited a high volumetric current density of 320 A cm-3 in acidic proton exchange membrane fuel cell. We further demonstrated the generality of this synthetic strategy to other carbon supports.
Oxygen functionalization of carbon supports has been a widely used strategy to enhance catalytic performance of carbon supported Pt (Pt/C) catalysts. However, the effect of oxidative ...functionalization on the catalytic performance of Pt/C catalysts for the oxygen reduction reaction (ORR) has rarely been investigated. We report the impact of oxygen functionalization of carbon black (CB) supports on the activity and durability of CB supported Pt catalysts for the ORR. Pristine and mildly oxygen-functionalized CB supported Pt catalysts (Pt/CB and Pt/CB_O, respectively) show nearly identical structural parameters, including surface areas and pore volumes of the CB support, and supported Pt particle sizes. The Pt/CB_O catalyst shows higher electrochemically active surface area and ORR activity than Pt/CB catalyst, which is likely caused by differing interfacial structure between the carbon support and Pt nanoparticles in the two catalysts. In ORR durability tests, Pt/CB exhibits significantly higher stability than Pt/CB_O. Spectroscopic characterizations reveal that oxygen functionalization in the Pt/CB_O catalyst partially oxidizes the Pt nanoparticles, triggering facile dissolution and Ostwald ripening of Pt nanoparticles, which accelerates the decline of the ORR activity of Pt CB_O.
Plastics, including poly(ethylene terephthalate) (PET), possess many desirable characteristics and thus are widely used in daily life. However, non-biodegradability, once thought to be an advantage ...offered by plastics, is causing major environmental problem. Recently, a PET-degrading bacterium, Ideonella sakaiensis, was identified and suggested for possible use in degradation and/or recycling of PET. However, the molecular mechanism of PET degradation is not known. Here we report the crystal structure of I. sakaiensis PETase (IsPETase) at 1.5 Å resolution. IsPETase has a Ser-His-Asp catalytic triad at its active site and contains an optimal substrate binding site to accommodate four monohydroxyethyl terephthalate (MHET) moieties of PET. Based on structural and site-directed mutagenesis experiments, the detailed process of PET degradation into MHET, terephthalic acid, and ethylene glycol is suggested. Moreover, other PETase candidates potentially having high PET-degrading activities are suggested based on phylogenetic tree analysis of 69 PETase-like proteins.
Tin sulfide (SnS) is one of the most promising solar cell materials, as it is abundant, environment friendly, available at low cost, and offers long‐term stability. However, the highest efficiency of ...the SnS solar cell reported so far remains at 4.36% even using the expensive atomic layer deposition process. This study reports on the fabrication of SnS solar cells by a solution process that employs rapid thermal treatment for few seconds under Ar gas flow after spin‐coating a precursor solution of SnCl2 and thiourea dissolved in dimethylformamide onto a nanostructured thin TiO2 electrode. The best‐performing cell exhibits power conversion efficiency (PCE) of 3.8% under 1 sun radiation conditions (AM1.5G). Moreover, secondary treatment using SnCl2 results in a significant improvement of 4.8% in PCE, which is one of the highest efficiencies among SnS‐based solar cells, especially with TiO2 electrodes. The thin film properties of SnS after SnCl2 secondary treatment are analyzed using grazing‐incidence wide‐angle X‐ray scattering, and high‐resolution transmittance electron microscopy.
Herein, the fabrication of a high‐efficiency heterojunction solar cell with a tin sulfide (SnS) thin film formed on a nanostructured TiO2 electrode by combining a solution process and rapid thermal annealing under Ar flow is reported. The secondary thermal treatment of the SnS thin film with SnCl2 improves the efficiency by up to 5%.
Electroactive actuators have received enormous interest for a variety of biomimetic technologies ranging from robotics and microsensors to artificial muscles. Major challenges towards practically ...viable actuators are the achievement of large electromechanical deformation, fast switching response, low operating voltage and durable operation. Here we report a new electroactive actuator composed of self-assembled sulphonated block copolymers and ionic liquids. The new actuator demonstrated improvements in actuation properties over other polymer actuators reported earlier, large generated strain (up to 4%) without any signs of back relaxation. In particular, the millimetre-scale displacements obtained for the actuators, with rapid response (<1 s) at sub-1-V conditions over 13,500 cycles in air, have not been previously reported in the literature. The key to success stems from the evolution of the unique hexagonal structure of the polymer layer with domain size gradients beneath the cathode during actuation, which promotes the bending motion of the actuators.
Iron- and nitrogen-codoped carbon (Fe–N/C) catalysts have emerged as promising alternatives to Pt-based catalysts for the oxygen reduction reaction (ORR) owing to their prominent ORR activity among ...nonprecious metal catalysts (NPMCs). This high ORR activity originates from atomically dispersed Fe coordinated with nitrogen atoms (Fe–N x site). However, the rational design of Fe–N/C catalysts with abundant Fe–N x active sites remains a challenge. In this work, we demonstrate that a silica-coating-mediated synthetic strategy enables the preparation of Fe–N/C catalysts enriched with active Fe–N x sites while mitigating the formation of less active Fe and Fe3C species. The silica-coating-mediated strategy was generally applicable to various types of Fe and N precursors, including iron porphyrin, iron acetate/1,10-phenanthroline, and iron chloride/polyaniline. This strategy was also effective in the preparation of Fe–N/C catalysts with various carbon supports and a wide range of Fe contents and pyrolysis temperatures. The strategy could be further extended to S- or P-doped Fe–N/C catalysts, in which the formation of inactive FeS and Fe2P species was suppressed. As a result, Fe–N/C catalysts prepared with the silica coating exhibited improved ORR activity up to a factor of 11 compared to silica-uncoated counterparts. Significantly, the S-doped Fe–N/C catalyst exhibited very high ORR activity with half-wave potential at 0.91 V (vs RHE) in alkaline media. In anion-exchange membrane fuel cell (AEMFC) tests, the S-doped Fe–N/C-based cathode showed a current density of 977 mA cm–2 at 0.6 V, which is the highest performance among reported AMEFCs with NPMC-based cathodes. The S-doped Fe–N/C-based cathode also demonstrated promising volumetric current density in an acidic proton exchange membrane fuel cell. Thus, the silica-coating-mediated strategy is generally effective in preparing atomically dispersed catalytic entities and may be applicable to other catalytic reactions whereby monatomic catalysts exhibit high catalytic activities.
Ambipolar polymer semiconductors are highly suited for use in flexible, printable, and large-area electronics as they exhibit both n-type (electron-transporting) and p-type (hole-transporting) ...operations within a single layer. This allows for cost-effective fabrication of complementary circuits with high noise immunity and operational stability. Currently, the performance of ambipolar polymer semiconductors lags behind that of their unipolar counterparts. Here, we report on the side-chain engineering of conjugated, alternating electron donor–acceptor (D–A) polymers using diketopyrrolopyrrole-selenophene copolymers with hybrid siloxane-solubilizing groups (PTDPPSe-Si) to enhance ambipolar performance. The alkyl spacer length of the hybrid side chains was systematically tuned to boost ambipolar performance. The optimized three-dimensional (3-D) charge transport of PTDPPSe-Si with pentyl spacers yielded unprecedentedly high hole and electron mobilities of 8.84 and 4.34 cm2 V–1 s–1, respectively. These results provide guidelines for the molecular design of semiconducting polymers with hybrid side chains.
Abstract
Hematite has a great potential as a photoanode for photoelectrochemical (PEC) water splitting by converting solar energy into hydrogen fuels, but the solar-to-hydrogen conversion efficiency ...of state-of-the-art hematite photoelectrodes are still far below the values required for practical hydrogen production. Here, we report a core-shell formation of gradient tantalum-doped hematite homojunction nanorods by combination of hydrothermal regrowth strategy and hybrid microwave annealing, which enhances the photocurrent density and reduces the turn-on voltage simultaneously. The unusual bi-functional effects originate from the passivation of the surface states and intrinsic built-in electric field by the homojunction formation. The additional driving force provided by the field can effectively suppress charge–carrier recombination both in the bulk and on the surface of hematite, especially at lower potentials. Moreover, the synthesized homojunction shows a remarkable synergy with NiFe(OH)
x
cocatalyst with significant additional improvements of photocurrent density and cathodic shift of turn-on voltage. The work has nicely demonstrated multiple collaborative strategies of gradient doping, homojunction formation, and cocatalyst modification, and the concept could shed light on designing and constructing the efficient nanostructures of semiconductor photoelectrodes in the field of solar energy conversion.
We report here a strategy for influencing the phase and lattice of the inverse mesophases of a single branched‐linear block copolymer (BCP) in solution which does not require changing the structure ...of the BCP. The phase of the self‐assembled structures of the block copolymer can be controlled ranging from bilayer structures of positive curvature (polymersomes) to inverse mesophases (triply periodic minimal surfaces and inverse hexagonal structures) by adjusting the solvent used for self‐assembly. By using solvent mixtures to dissolve the block copolymer we were able to systematically change the affinity of the solvent toward the polystyrene block, which resulted in the formation of inverse mesophases with the desired lattice by self‐assembly of a single branched‐linear block copolymer. Our method was also applied to a new solution self‐assembly method for a branched‐linear block copolymer on a stationary substrate under humidity, which resulted in the formation of large mesoporous films. Our results constitute the first controlled transition of the inverse mesophases of block copolymers by adjusting the solvent composition.
The phase and lattice of the inverse mesophases of a single branched‐linear block copolymer (BCP) in solution can be influenced without changing the BCP structure. The phase of the self‐assembled structures of the BCP can be controllably shifted from bilayer structures of positive curvature to inverse mesophases by adjusting the interaction parameter of the solvent used for self‐assembly.
PDF
