Abstract: Sodium-ion batteries (SIBs) are regarded as the best alternative to lithium-ion batteries due to their low cost and similar Na+ insertion chemistry. It is still challenging but greatly desired to design and develop novel electrode materials with high reversible capacity, long cycling life, and good rate capability toward high-performance SIBs. This work demonstrates an innovative design strategy and a development of few-layered molybdenum disulfide/sulfur-doped graphene nanosheets (MoS2/SG) composites as the SIB anode material providing a high specific capacity of 587 mA h g−1 calculated based on the total composite mass and an extremely long cycling stability over 1000 cycles at a current density of 1.0 A g−1 with a high capacity retention of ≈85%. Systematic characterizations reveal that the outstanding performance is mainly attributed to the unique and robust composite architecture where few-layered MoS2 and S-doped graphene are intimately bridged at the hetero-interface through a synergistic coupling effect via the covalently doped S atoms. The design strategy and mechanism understanding at the molecular level outlined here can be readily applied to other layered transition metal oxides for SIBs anode and play a key role in contributing to the development of high-performance SIBs.

Abstract: The development of cheap, simple, and green synthetic methods for hierarchically porous nitrogen-doped carbon, especially derived from renewable biomass, such as chitosan, remains a challenging topic. Here, we first synthesized hierarchically porous nitrogen-doped carbon (KIE-8) having graphene-like structure via simple pyrolysis of a chitosan/urea/KOH mixture without any conventional sophisticated treatments, such as freeze-drying, hydrothermal carbonization, and soft or hard templating. On the basis of various analyses of KIE-8, we demonstrated that effect of urea on mesopore formation was insignificant; however, when KOH is used as an activating agent in the presence of urea, a large amount of mesopores can be created along with conventional KOH-derived micropores. In addition, it was revealed that chitosan-derived carbon nanosheets directed by urea are torn into chitosan-derived carbon nanoflakes via KOH activation, and mesopores originate from interstitial voids in aggregates of the carbon nanoflakes...

Abstract: The electron transport layer (ETL) is a key component of perovskite solar cells (PSCs) and must provide efficient electron extraction and collection while minimizing the charge recombination at interfaces in order to ensure high performance. Conventional bilayered TiO2 ETLs fabricated by depositing compact TiO2 (c-TiO2) and mesoporous TiO2 (mp-TiO2) in sequence exhibit resistive losses due to the contact resistance at the c-TiO2/mp-TiO2 interface and the series resistance arising from the intrinsically low conductivity of TiO2. Herein, to minimize such resistive losses, we developed a novel ETL consisting of an ultrathin c-TiO2 layer hybridized with mp-TiO2, which is fabricated by performing one-step spin-coating of a mp-TiO2 solution containing a small amount of titanium diisopropoxide bis(acetylacetonate) (TAA). By using electron microscopies and elemental mapping analysis, we establish that the optimal concentration of TAA produces an ultrathin blocking layer with a thickness of ∼3 nm and ensures that ...

Abstract: In this study, we report self-assembled nitrogen-doped fullerenes (N-fullerene) as non-precious catalysts, which are active for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and thus applicable for energy conversion and storage devices such as fuel cells and metal–air battery systems. We screen the best N-fullerene catalyst at the nitrogen doping level of 10 at%, not at the previously known doping level of 5 or 20 at% for graphene. We identify that the compressive surface strain induced by doped nitrogen plays a key role in the fine-tuning of catalytic activity.

Abstract: The ongoing surge in demand for high-energy/flexible rechargeable batteries relentlessly drives technological innovations in cell architecture as well as electrochemically active materials. Here, a new class of all-nanomat lithium-ion batteries (LIBs) based on 1D building element-interweaved heteronanomat skeletons is demonstrated. Among various electrode materials, silicon (Si, for anode) and overlithiated layered oxide (OLO, for cathode) materials are chosen as model systems to explore feasibility of this new cell architecture and achieve unprecedented cell capacity. Nanomat electrodes, which are completely different from conventional slurry-cast electrodes, are fabricated through concurrent electrospinning (for polymeric nanofibers) and electrospraying (for electrode materials/carbon nanotubes (CNTs)). Si (or rambutan-shaped OLO/CNT composite) powders are compactly embedded in the spatially interweaved polymeric nanofiber/CNT heteromat skeletons that play a crucial role in constructing 3D-bicontinuous ion/electron transport pathways and allow for removal of metallic foil current collectors. The nanomat Si anodes and nanomat OLO cathodes are assembled with nanomat Al2O3 separators, leading to the fabrication of all-nanomat LIB full cells. Driven by the aforementioned structural/chemical uniqueness, the all-nanomat full cell shows exceptional improvement in electrochemical performance (notably, cell-based gravimetric energy density = 479 W h kgCell−1) and also mechanical deformability, which lie far beyond those achievable with conventional LIB technologies.

Abstract: We performed a methane steam reforming (MSR) reaction through a membrane reactor packed with commercial Ni/Al2O3 catalyst and a tubular Pd-Ru membrane deposited on a YSZ modified porous stainless steel support under mild operating conditions: 773 K and a pressure difference range of 100-250 kPa. We prepared the Pd-Ru membrane with thickness of ~6 μm on a tubular stainless steel support (diameter 12.7mm, length 25 cm) using electroless plating, which was observed for the membrane performance using hydrogen and nitrogen. Gas permeation test carried out at 773 K and 31.4 kPa of pressure difference between retentate and permeate sides showed that the hydrogen permeation rate and nitrogen leakage were ~0.1050mol s−1 m−2 and ~0.0018 mol s−1 m−2, respectively. The MSR reaction was under the following conditions: temperature 773 K, pressure 100-250 kPa, gas hourly space velocity (GHSV) 837 h−1, and steam-to-carbon feed ratio (S/C) 3. The MSR reaction result showed that methane conversion was increased with increasing pressure difference and reached ~77.5% at 250 kPa. In this condition, the composition of carbon monoxide was ~2%, meaning that no two series of water gas shift reactors were needed in our membrane reactor system. Longterm stability test carried out for ~100 h showed that methane conversion and the hydrogen yield remained constant.

Abstract: In situ transesterification (direct conversion) of microalgal cells is a promising method to produce biodiesel from microalgae because it integrates the oil extraction and conversion process in one step. Not only biodiesel but also a few biochemicals can be produced through this process because both lipids and carbohydrates are converted under acidic conditions. Levulinic acid ester (levulinate) is one of the byproducts of in situ transesterification, which can be used as an additive in fuels or fragrances. This study investigated the effect of cell composition and reactive variables on the productivity of levulinic acid ester. The cell compositions of microalgal strains were compared between Nannochloropsis and Chlorella , and more levulinate was produced from carbohydrate-rich Chlorella cells. Both reaction temperature and acid concentration highly affected the levulinate yield, whereas the type of alcohols did not have much influence on the yield. Consequently, more than 40 mol% glucose inside the cell was converted to levulinate with a 15 v% sulfuric acid concentration at 130 °C.

Abstract: For the fabrication of high efficiency Cu(In,Ga)Se2 (CIGS) solar cells, a CdS thin film is usually used as the buffer layer. However, since Cd is toxic and also a hazardous material for the environment, Cd-free or Cd-reduced buffer is required for the realization of CIGS solar cells as an environmentally friendly device. We fabricated a Cd-reduced hybrid buffer layer of CdS(Cd-treatment)/Zn(O,S), where CdS was prepared by dipping it into a CdS CBD solution for 2 min and Zn(O,S) was deposited by co-sputtering of ZnO and ZnS. The hybrid buffer provided an improved short circuit current and open circuit voltage and thus high power conversion efficiency. The best CIGS solar cell with the hybrid buffer showed 12.69% cell efficiency compared to the CdS-buffered standard cell with 13.06% cell efficiency. The improved efficiency of the Cd-treated solar cell was found to be a consequence of an enhanced response to blue wavelength photons and surface passivation of the absorber surface by the treatment.

Abstract: The present work introduces spinel oxide nanocrystals self-assembled into mesoporous spheres that are bifunctionally active towards catalyzing both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). The electrochemical evaluation reveals that (Ni,Co)3 O4 demonstrates a significantly positive-shifted ORR onset and half-wave potentials [-0.127 and -0.292 V vs. saturated calomel electrode (SCE), respectively], whereas Co3 O4 results in a negative-shifted OER potential (0.65 V vs. SCE) measured at 10 mA cm-2 . Based on the DFT analysis, the potential at which all oxygen intermediate reactions proceed spontaneously is the highest for (Ni,Co)3 O4 (U=0.66 eV) during ORR, whereas it is the lowest for Co3 O4 (U=2.09 eV) during OER. The high ORR activity of (Ni,Co)3 O4 is attributed to the enhanced electrical conductivity of the spinel lattice, and the high OER activity of Co3 O4 is attributed to relatively weak adsorption energy promoting rapid release of evolved oxygen.

Abstract: A facile improved successive ionic-layer adsorption and reaction (SILAR) sequence is described for the fabrication of Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells (TFSCs) via the selenization of a precursor film. The precursor films were fabricated using a modified SILAR sequence to overcome compositional inhomogeneity due to different adsorptivities of the cations (Cu+, Sn4+, and Zn2+) in a single cationic bath. Rapid thermal annealing of the precursor films under S and Se vapor atmospheres led to the formation of carbon-free Cu2ZnSnS4 (CZTS) and CZTSSe absorber layers, respectively, with single large-grained layers. The best devices based on CZTS and CZTSSe absorber layers showed total area (∼0.30 cm2) power conversion efficiencies (PCEs) of 1.96 and 3.74%, respectively, which are notably the first-demonstrated efficiencies using a modified SILAR sequence. Detailed diode analyses of these solar cells revealed that a high shunt conductance (Gsh), reverse saturation current density (Jo), and ideality fac...

Abstract: Layered perovskite oxides have received enormous attention as prospective cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) due to their high electrical conductivities and fast oxygen kinetics. This study focuses on the structural, electrical, and electrochemical properties of layered perovskites, LnBa0.5Sr0.5Co1.5Fe0.5O5+δ (LnBSCF, Ln = Pr, Sm, and Gd), depending on the lanthanide ions in the A-site as a cathode material for IT-SOFCs. Among the evaluated perovskites, PrBa0.5Sr0.5Co1.5Fe0.5O5+δ(PBSCF) showed the highest electrical conductivity, the highest oxygen content, and the highest values of oxygen bulk diffusion coefficient (D*) and surface exchange coefficient (k) measured by isotope oxygen exchange. The composite cathode of PBSCF and gadolinium doped ceria (GDC) is thus found to be the most suitable cathode material for IT-SOFCs among those investigated materials based on its high electrochemical properties and fast oxygen kinetics.

Abstract: Controlling the surface structure and composition at the atomic level is an effective way to tune the catalytic properties of bimetallic catalysts. Herein, we demonstrate a generalized strategy to synthesize highly monodisperse, surfactant-free octahedral Pt x Ni1−x nanoparticles with tunable surface structure and composition. With increasing the Ni content in the bulk composition, the degree of concaveness of the octahedral Pt x Ni1−x nanoparticles increases. We systematically studied the correlation between their surface structure/composition and their observed oxygen reduction activity. Electrochemical studies have shown that all the octahedral Pt x Ni1−x nanoparticles exhibit enhanced oxygen reduction activity relative to the state-of-the-art commercial Pt/C catalyst. More importantly, we find that the surface structure and composition of the octahedral Pt x Ni1−x nanoparticles have significant effect on their oxygen reduction activity. Among the studied Pt x Ni1−x nanoparticles, the octahedral Pt1Ni1 nanoparticles with slight concaveness in its (111) facet show the highest activity. At 0.90 V vs. RHE, the Pt mass and specific activity of the octahedral Pt1Ni1 nanoparticles are 7.0 and 7.5-fold higher than that of commercial Pt/C catalyst, respectively. The present work not only provides a generalized strategy to synthesize highly monodisperse, surfactant-free octahedral Pt x Ni1−x nanoparticles with tunable surface structure and composition, but also provides insights to the structure-activity correlation.

Abstract: The Er2O3-stabilized Bi2O3 (ESB) exhibits a superior oxygen ion conductivity below 750 oC. However, there is significant conductivity decay due to a cubic-to-rhombohedral phase transformation over time at ~ 600oC. Thus, to enhance the kinetic stability of ESB, we develop a novel double-doped bismuth oxide through additional quadrivalent doping in ESB. Surprisingly, 1 mol.% of Hf-doped ESB shows no conductivity degradation without a phase transition for 1200 h at 600 °C, while the conductivity of pure ESB drops to less than 5% of the initial value within 200 h. Additionally, the stability improvement effect is strongly correlated to the ionic radius of the aliovalent dopant with an optimum value at ~ 0.85A. When the Bi3+ diffusivity in the cation sublattice of ESB is measured using the Boltzmann-Matano method, Hf doping greatly reduces the diffusion coefficient by ~53% compared to pure ESB. This result suggests that the control of the cation interdiffusion coefficient is the key parameter for suppression o...