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Summary: The development of highly active, robust and cost‐effective noble metal‐free electrocatalysts for hydrogen evolution reaction (HER) in alkaline solution remains a severe challenge. In this work, a hollow structure CoSe2‐FeSe2 heterojunction electrocatalyst (denoted by "(Co,Fe)Se2") was designed by a simple anion exchange reaction and selenization. Benefiting from the unique hollow structure, the (Co,Fe)Se2 catalyst accelerates diffusion of electrolyte, besides, the CoSe2‐FeSe2 heterojunction could provide rapid interfacial charge transportation and more active sites for the HER reaction. The (Co,Fe)Se2 electrode material exhibits good performance for HER in 1 M KOH electrolyte. It needs an overpotential of 124 mV to obtain a current density of 10 mA cm−2, and the Tafel slope is 65 mV dec−1. Besides, (Co,Fe)Se2 has a smaller charge transfer resistance compared with CoSe2. At the same time, it has relatively large electrochemical active surface area due to the porosity. Most importantly, the (Co,Fe)Se2 electrode displays good stability in alkaline conditions for 15 hours, the linear sweep voltammetry curves are almost coincident before and after 1000 cycles, the overpotential with current density of 10 mA cm−2 increased by only 9.76% after 5000 cycles of CV. It shows great application potential in HER. [ABSTRACT FROM AUTHOR]

In the pursuit of developing highly efficient polymer solar cells, it is indispensable to experimentally determine the molecular electronic and geometrical structures of distributed donor/acceptor bulk heterojunctions for understanding the processes inside the cell. In this article, substrate effect on interface energetics and film morphology of the poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]:[6,6]-phenyl-C70 butyric acid methyl ester (PCDTBT:PC70BM) blends with various blending ratios on various conductive substrates is clarified based on the characterization of photoelectron spectroscopy and atomic force microscope, where the PCDTBT:PC70BM blend film serves as an important model system due to efficient charge generation and transport with low recombination. The energetics of the PCDTBT:PC70BM blend film is demonstrated to be highly dependent on the substrate work function, showing the transition from vacuum level alignment to Fermi level pinning with the variation of PC70BM ratio in the blend film. The resulting morphology is in good agreement with the observed formation of a PCDTBT-rich layer at the top of the PCDTBT:PC70BM blend film irrespective of the variation of the PC70BM blending ratio and annealing temperature. The results show the possibility of tuning the interfacial electronic structures by utilizing the substrate effects and potential applications on performance enhancement in polymer solar cells. [ABSTRACT FROM AUTHOR]

Morphology optimization of donor–acceptor bulk heterojunctions at microscopic scale is critical for improving performance of organic photovoltaic devices. Here, effects of thermal annealing on phase separation processes in small-molecular bulk heterojunctions with different geometrical structures (i.e., PTCDA, TiOPc, CuPc and C 60 ) are investigated with ultraviolet and X-ray photoemission spectroscopies. It was identified that post-annealing treatment caused the different degrees of vertical diffusions at the bulk heterojunctions, leading to non-uniform composition distributions. Variations in phase separations are mainly due to the differences in surface energy of the involved materials, which play a crucial role in the intermolecular interactions and the molecular diffusion. Low-surface-energy materials were found to segregate preferentially on the surface for minimizing total energy of the systems. [ABSTRACT FROM AUTHOR]

The visible-light driven, Pt-free photocatalytic H 2 evolution (PHE) is promising for clean and sustainable H 2 production. The construction of the heterojunction structure with intimate contact and good light adsorption ability is important for realizing the high effective PHE. Here, the core-shell structured MoS 2 /CdS hybrids were constructed through “sequential two-step hydrothermal growth” route for Pt-free PHE. In the synthesis, the hierarchical flower-like MoS 2 was firstly obtained through the reaction of ammonium molybdate and excessive thiourea. Subsequently, without need of centrifugation, the cadmium acetate (Cd source) was added into the cooled MoS 2 solution directly followed by a secondary hydrothermal reaction. In the process, the Cd 2+ could react with partially S 2− in MoS 2 (substituted reaction) and with the excessive S 2− ions in solution to generate CdS, resulting in the formation of CdS shell contacted with MoS 2 core. The micro-structure of the composites (such as the thickness and morphology of CdS shell) could be tuned by changing the amount of Mo source and Cd source. In the composites, the CdS on the outside is convenient to absorb the solar light. The intimate contact of CdS and MoS 2 is beneficial to charge transfer. As a result, the MoS 2 /CdS catalyst showed high catalytic activity for PHE under visible light irradiation (λ > 420 nm). The H 2 evolution rate could reach to 775 μmol h −1 (20 mg catalyst), which is much higher than pure CdS (12 μmol h −1 ) and Pt-CdS (64 μmol h −1 ). The good activity should be related with CdS outside shell beneficial for light adsorption and intimate contact of CdS and MoS 2 for easy charge transfer. A series of experiments demonstrate that the formation of the heterojunction can effectively enhance the charge transfer ability and retard the recombination of electron-hole pairs, thus improving PHE activity and alleviating the photocorrosion of CdS component. [ABSTRACT FROM AUTHOR]

The design of inexpensive bifunctional electrocatalysts with excellent catalytic activity is crucial for the cost reduction from water splitting. As a kind of biomass with hollow tubular structure, Metaplexis japonica fluff is expected to be a natural substrate for the growth of nanostructured electrocatalysts. Herein, nanowire-like NiCo precursors are grown on Metaplexis japonica fluff biomass substrates by hydrothermal method, which are then converted into carbon microtube supported NiCoP-NiS 2 composites (NiCoP-NiS 2 /CMT) by low-temperature phosphorization and sulfidation treatment. As expected, the biomass substrate provides a guiding role for the growth of NiCoP-NiS 2 nanowires, which is conducive to expose more active areas and promote charge transfer during the reaction. As a result, the obtained NiCoP-NiS 2 /CMT exhibits good electrocatalytic performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 M KOH, which only requires overpotentials of 134 and 308 mV at 10 mA cm−2, respectively. In addition, the constructed symmetric water splitting device exhibits a cell voltage of 1.62 V at 10 mA cm−2, and it also displays good stability during the 24 h test. [Display omitted] [ABSTRACT FROM AUTHOR]

Nanocomposite buffer layer based on metal oxide and polymer is merging as a novel buffer layer for organic solar cells, which combines the high charge carrier mobility of metal oxide and good film formation properties of polymer. In this work, a nanocomposite of zinc oxide and a commercialized available polyethylenimine (PEI) was developed and used as the cathode buffer layer (CBL) for the inverted organic solar cells and p-i-n heterojunction perovskite solar cells. The cooperation of PEI in nano ZnO offers a good film forming ability of the composite material, which is an advantage in device fabrication. In addition, power conversion efficiency (PCE) of the ZnO:PEI CBL based device was also improved when compared to that of ZnO-only and PEI-only devices. The highest PCE of P3HT:PC 61 BM and PTB7-Th:PC 61 BM devices reached to 3.57% and 8.16%, respectively. More importantly, there is no obvious device performance loss with the increase of the layer thickness of ZnO:PEI CBL to 60 nm in organic solar cells, which is in contrast to the PEI based devices, whose device performance decreases dramatically when the PEI layer thickness is higher than 6 nm. Such a nano composite material is also applicable in inverted heterojunction perovskite solar cells. A PCE of 11.76% was achieved for the perovskite solar cell with a thick ZnO:PEI CBL (150 nm) CBL, which is around 1.71% higher than that of the reference cell without CBL, or with ZnO CBL. In addition, stability of the organic and perovskite solar cells having ZnO:PEI CBL was also found to be improved in comparison with that of PEI based device. [ABSTRACT FROM AUTHOR]

A novel hierarchical BiOI/Bi 2 MoO 6 composites are prepared by a facile precipitation–deposition method. The prepared photocatalyst was characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectrometer (XPS). The resulting BiOI/Bi 2 MoO 6 composites exhibit excellent photocatalytic activity and stability towards the degradation of methylene blue (MB) and bisphenol A (BPA) in aqueous solution under visible light irradiation. The optimal composite with 25% BiOI content shows the highest photocatalytic activity for MB degradation. The enhanced photocatalytic activity is mainly attributed to the formation of BiOI/Bi 2 MoO 6 heterojunction that can facilitate the separation and transfer of the photo-generated charge carriers. The roles of active species in the photocatalytic process are discussed by using different types of active species scavengers. Meanwhile, combined with the photoluminescence (PL) and electrochemical impedance spectroscopy (EIS), the degradation mechanism of the photocatalysts is proposed. It is hoped that the work could provide valuable information on the design of specific structure materials with more excellent properties and set the foundation for the further industrial application. [ABSTRACT FROM AUTHOR]

Abstract: An efficient inverted polymer solar cell (PSC) is reported by employing an atomic layer deposited (ALD) cadmium sulfide (CdS) film between the indium tin oxide (ITO) cathode and the photoactive layer as the electron collection layer (ECL), on which a active layer is composed of a blended poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester (P3HT:PCBM) bulk heterojunction. As determined by photoelectron spectroscopy, the sulfur vacancy induces an n-type semiconducting property in the ALD-grown CdS films, and suitable energy level alignment at the ITO/CdS/PCBM interface is favorable to electron extraction through CdS to the ITO electrode. With the optimized CdS film thickness, the power conversion efficiency increases to 3.33%, with short-circuit current of 8.94mA/cm2, open-circuit voltage of 0.61V, and fill factor of 61.1% under AM1.5G 100mW/cm2 irradiation. [Copyright &y& Elsevier]