Multielement alloying is an appealing approach for suppressing thermal conductivity of thermoelectric materials. In this study, we synthesized GeTe-based high-entropy alloys with notable (S, Se) substitution at Te sites and (Ag, Sb) at Ge sites. The Ge0.82Ag0.08Sb0.1S0.5Se0.1Te0.4 exhibits an extremely low thermal conductivity of ∼ 0.66 W/m⋅K and a high Seebeck coefficient (>250 μV/K) over a temperature range of 150 – 400 °C. The influence of lattice distortion on phase transformation and transport properties of Ge0.9-2xAg2xSb0.1S0.5Se0.1Te0.4 (x = 0 – 0.06) was investigated.

{Probing and controlling the valley degree of freedom in graphene systems by transport measurements has been a major challenge to fully exploit the unique properties of this two-dimensional material. In this theoretical work, we show that this goal can be achieved by a quantum-wire geometry made of gapped graphene that acts as a valley filter with the following favorable features: (i) all electrical gate control, (ii) electrically switchable valley polarity, (iii) robustness against configuration fluctuation, and (iv) potential for room temperature operation. This valley filtering is accomplished by a combination of gap opening in either bilayer graphene with a vertical electrical field or single layer graphene on h-BN, valley splitting with a horizontal electric field, and intervalley mixing by defect scattering. In addition to functioning as a building block for valleytronics, the proposed configuration makes it possible to convert signals between electrical and valleytronic forms, thus allowing for the integration of electronic and valleytronic components for the realization of electro-valleytronics.}

Abstract Effects of electronic and atomic structures of V-doped 2D layered SnS2 are studied using X-ray spectroscopy for the development of photocatalytic/photovoltaic applications. Extended X-ray absorption fine structure measurements at V K-edge reveal the presence of VO and VS bonds which form the intercalation of tetrahedral OVS sites in the van der Waals (vdW) gap of SnS2 layers. X-ray absorption near-edge structure (XANES) reveals not only valence state of V dopant in SnS2 is ≈4+ but also the charge transfer (CT) from V to ligands, supported by V Lα,β resonant inelastic X-ray scattering. These results suggest V doping produces extra interlayer covalent interactions and additional conducting channels, which increase the electronic conductivity and CT. This gives rapid transport of photo-excited electrons and effective carrier separation in layered SnS2. Additionally, valence-band photoemission spectra and S K-edge XANES indicate that the density of states near/at valence-band maximum is shifted to lower binding energy in V-doped SnS2 compare to pristine SnS2 and exhibits band gap shrinkage. These findings support first-principles density functional theory calculations of the interstitially tetrahedral OVS site intercalated in the vdW gap, highlighting the CT from V to ligands in V-doped SnS2.

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Exploring an efficient platinum group metal (PGM) free electrocatalyst with superior activity and stability for hydrogen evolution reaction (HER) in a wide pH range is desirable for low-cost hydrogen production. Here, we report atomically dispersed cobalt on nitrogen and sulfur co-doped graphene (N-Co-S/G) for HER. Remarkably, the prepared N-Co-S/G electrocatalyst shows a small overpotential of 67.7 mV vs. reversible hydrogen electrode (RHE) at a current density of 10 mA cm−2 and exceptional durability over 100 h at 10 mA cm−2 under acidic conditions. Moreover, we found that the HER activity of N-Co-S/G is close to 20% Pt/C at all pH levels (0–14) and superior activity at high current density (>100 mA cm−2). Experimental and theoretical calculations reveal that the S atom in N-Co-S/G form Co-S bond, resulting new Co-N3S1 active site, which optimizes Gibbs free energy for hydrogen adsorption (∆GH*) close to zero, while water adsorption and dissociation enhanced by S modulation for neutral and basic media HER.

Solar cells based on kesterite Cu2ZnSnSe4 (CZTSe) compounds with earth-abundant elements are highly desirable for the low-cost and high-efficiency production of renewable energy. However, the occurrence of intrinsic defects substantially impairs the photovoltaic properties of CZTSe. Herein, a cation substitution method to control and passivate the defect states in bandgap of kesterite CZTSe by incorporating Ag ions is introduced. Intensity-dependent low-temperature photoluminescence measurements show that Ag incorporation can reduce the density and depth of intrinsic defects in CZTSe. The results reveal that 10% Ag-alloyed CZTSe provides the shallowest defect states and less nonradiative recombination. It is also confirmed by first-principles calculations that Ag incorporation enables the formation and suppresses the beneficial and detrimental defects, respectively. Based on the theoretical results, the observed subband photoluminescence peaks can be assigned to the intrinsic point and cluster defects. The best power conversion efficiency of 10.2% is achieved for the 10% Ag-alloyed CZTSe cell, along with an enhanced open-circuit voltage. These results open up a new avenue for further improving the performances of CZTSe-based device via defect engineering.

Utilization of g-C3N4 as a single photocatalyst material without combination with other semiconductor remains challenging. Herein, we report a facile green method for synthesizing a metal free modified g-C3N4 photocatalyst. The modification process combines four different strategies in a one-pot thermal reaction: non-metal doping, porosity generation, functionalization with amino groups, and thermal oxidation etching. The as-prepared amino-functionalized ultrathin nanoporous boron-doped g-C3N4 exhibited a high specific surface area of 143.2 m2 g−1 which resulted in abundant adsorption sites for CO2 and water molecules. The surface amino groups act as Lewis basic sites to adsorb acidic CO2 molecules, which can also serve as active sites to facilitate hydrogen generation. Besides, the simultaneous use of ammonium chloride as a dynamic gas bubble template along with thermal oxidation etching efficiently boosts the delamination of the g-C3N4 layers to produce ultrathin sheets; this leads to stronger light–matter interactions and efficient charge generation. Consequently, the newly modified g-C3N4 achieved selective gas-phase CO2 reduction into CO with a production yield of 21.95 µmol g-1, in the absence of any cocatalyst. Moreover, a high hydrogen generation rate of 3800 µmol g-1 h-1 and prominent apparent quantum yield of 10.6% were recorded. This work opens up a new avenue to explore different rational modifications of g-C3N4 nanosheets for the efficient production of clean energy.

Cu2ZnSnS4 (CZTS) has demonstrated excellent performance as an anode material for lithium-ion batteries. However, the repeated lithiation and delithiation create a cracking pattern and lead to island formation in the thin-film electrode, resulting in a capacity fading over cycling in lithium-ion batteries (LIB's). In order to control this crack behaviour, we introduce carbon into CZTS thin-films by a hydrothermal method to form CZTS@C composite. CZTS@C significantly reduced the crack pattern formation on the electrode surface as well as improved the conductivity of the CZTS@C electrode. At the early stages of lithiation and delithiation, the volume expansion and contraction of Li–CZTS@C create intra-granular cracking only at the surface level, and it offers a high capacity of about 785 mA h g−1 after 150 cycles at 1000 mA g−1 charging rate, excellent rate capability (942 mA h g−1, 678 mA h g−1 and 435 mA h g−1 at 500 mA g−1, 2000 mA g−1 and 5000 mA g−1), and superior cyclability (925 mA h g−1 even after 200 cycles at 500 mA g−1). The excellent electrochemical performance at high-current rates can be attributed to intra-granular cracking together with carbon coating that provides a short transportation length for both lithium ions and electrons. Moreover, the controlled cracking pattern formation in CZTS@C facilitates faster reaction kinetics, which open up a new solution for the development of high-power thin-film anodes for next-generation LIBs applications.

Layered MoS2 is considered as one of the most promising two-dimensional photocatalytic materials for hydrogen evolution and water splitting; however, the electronic structure at the MoS2-liquid interface is so far insufficiently resolved. Measuring and understanding the band offset at the surfaces of MoS2 are crucial for understanding catalytic reactions and to achieve further improvements in performance. Herein, the heterogeneous charge transfer behavior of MoS2 flakes of various layer numbers and sizes is addressed with high spatial resolution in organic solutions using the ferrocene/ferrocenium (Fc/Fc+) redox pair as a probe in near-field scanning electrochemical microscopy, i.e. in close nm probe-sample proximity. Redox mapping reveals an area and layer dependent reactivity for MoS2 with a detailed insight into the local processes as band offset and confinement of the faradaic current obtained. In combination with additional characterization methods, we deduce a band alignment occurring at the liquid-solid interface.

Abstract Sulfonated polyaryletherketones (SPAEK) bearing four sulfonic acid groups on the phenyl side groups were synthesized. The benzophenone moiety of polymer backbone was further reduced to benzydrol group with sodium borohydride. The membranes were crosslinked by acid-catalyzed Friedel-Crafts reaction without sacrifice of sulfonic acid groups and ion exchange capacity (IEC) values. Crosslinked membranes with the same IEC value but different water uptake could be prepared. The optimal crosslinking condition was investigated to achieve lower water uptake, better chemical stability (Fenton's test), and higher proton conductivity. In addition, the hydrophilic ionic channels from originally course and disordered could be modified to be narrow and continuous by this crosslinking method. The crosslinked membranes, CS4PH-40-PEKOH (IEC = 2.4 meq./g), reduced water uptake from 200 to 88% and the weight loss was reduced from 11 to 5% during the Fenton test compared to uncrosslinked one (S4PH-40-PEK). The membrane showed comparable proton conductivity (0.01?0.19?S/cm) to Nafion 212 at 80°C from low to high relative humidity (RH). Single H2/O2 fuel cell based on the crosslinked SPAEK with catalyst loading of 0.25?mg/cm2 (Pd/C) exhibited a peak power density of 220.3 mW/cm2, which was close to that of Nafion 212 (214.0 mW/cm2) at 80°C under 53% RH. These membranes provide a good option as proton exchange membrane with high ion exchange capacity for fuel cells.