Ion-Electron Transduction Layer of the SnS2-MoS2 Heterojunction to Elevate Superior Interface Stability for All-Solid Sodium-Ion Selective Electrode

The high selectivity and fast ion response of all-solid sodium ion selective electrodes were widely applied in human sweat analysis. However, the potential drift due to insufficient interfacial capacitance leads to the deterioration of its stability and ultimately affects the potential accuracy of ion analysis. Designing a novel ion-electron transduction layer between the electrode and the ion selective membrane is an effective method to stabilize the interfacial potential. Herein, the SnS2-MoS2 heterojunction material was constructed by doping Sn in MoS2 nanosheets and used as the ion electron transduction layers of an all-solid sodium ion selective electrode for the first time, achieving the stable and efficient detection of Na+ ions. The proposed electrode exhibited a Nernst slope of 57.86 mV/dec for the detection of Na+ ions with a detection limit of 10-5.7 M in the activity range of 10-6-10-1 M. Via the electronic interaction at the heterojunction interfaces between SnS2 and MoS2 materials, the micro-nanostructure of the SnS2-MoS2 heterojunction was changed and SnS2-MoS2 as the ion-electron transduction layer acquired excellent capacitance (699 μF) and hydrophobicity (132°), resulting in a long-term potential stability of 1.37 μV/h. It was further proved that the large capacitance and high hydrophobicity of the ion-electron transduction layer are primary reasons for the excellent stability of the all-solid sodium ion selective electrode toward Na+ ions.

Three-Dimensional (3D) Ordered Macroporous Bimetallic (Mn,Fe) Selenide/Carbon Composite with Heterojunction Interface for High-Performance Sodium Ion Batteries

Transition-metal selenides have captured significant research attention as anode materials for sodium ion batteries (SIBs) due to their high theoretical specific capacities and excellent electronic conductivity. However, volumetric expansion and inferior cycle life still hinder their practical application. Herein, a three-dimensional (3D) ordered macroporous bimetallic (Mn,Fe) selenide modified by a carbon layer (denoted as 3DOM-MnFeSex@C) composite containing a heterojunction interface is fabricated through selenizing a 3D ordered macroporous Mn-based Prussian Blue analogue single crystal. The 3DOM-MnFeSex@C exhibits hierarchically porous architecture with enhanced mass-transfer efficiency; MnSe and FeSe2 particles are encapsulated into macroporous carbon framework, which can significantly promote the electronic conductivity and maintain the structural integrity. The density functional theory calculation indicates that the heterojunction interface between MnSe and FeSe2 has been successfully engineered so that Na+ can be readily adsorbed and rapidly converted, thus promoting the reaction kinetics and extending the cyclic life. As expected, the 3DOM-MnFeSex@C composite delivers excellent rate performance (277.6 mA h g-1 at 10 A g-1), and prolonged cycling life (191.6 mA h g-1 even after 1000 cycles at 2 A g-1) as a sodium storage anode. The sodium storage mechanism of the composite was further investigated by in situ X-ray diffraction and ex situ high-resolution transmission electron microscopy characterization techniques.

Exploring the Effects of Crystal Facet Orientation at the Heterojunction Interface on Charge Separation for Photoanodes

As one of the most effective strategies to promote the spatial separation of charges, constructing heterojunction has received extensive attention in recent years. However, it remains unclear whether the crystal facet orientation (CFO) at the heterojunction interface is contributory to charge separation. Herein, three types of TiO₂/CdS heterojunction films with different CFOs at the heterojunction interface were produced by adjusting the CdS CFO through in situ conversion. Among them, the TiO₂/CdS film with a mixed CdS CFO showed the maximum photocurrent density and charge separation efficiency. In contrast, the TiO₂/CdS film with a uniform CdS (100) (CdS-100) performed worst. According to the results of experimentation and DFT calculation, these three types of TiO₂/CdS films varied significantly in electron transport time. This is attributable to the different Fermi levels of CdS CFO and the formation of different built-in electric fields upon coupling with TiO₂. The rise in the Fermi level of CdS can increase the driving force required for charge migration at the heterojunction interface. Additionally, a stronger built-in electric field is conducive to charge separation. To sum up, these results highlight the significant impact of CFO at the heterojunction interface on charge separation.

Activating a TiO2/BiVO4 Film for Photoelectrochemical Water Splitting by Constructing a Heterojunction Interface with a Uniform Crystal Plane Orientation

The construction of a heterojunction has been considered one of the most effective strategies to improve the photoelectrochemical (PEC) performance of photoanodes; however, most researchers only focus on the design and preparation of a novel and efficient heterojunction photoelectrode, and the investigation on the effect of the heterojunction interface structure on PEC performance is ignored. In this work, a TiO₂/BiVO₄ photoanode with a uniform crystal plane orientation in the heterojunction interface (TiO₂-110/BiVO₄-202) was prepared by an in situ transformation method. We found that the PEC activity of the TiO₂/BiVO₄ photoanode can be activated by constructing such a heterojunction interface. Compared with a TiO₂/BiVO₄ photoanode with a random crystal plane orientation prepared by a simple soaking-calcining method (S-TiO₂/BiVO₄, 0.04 mA/cm² at 1.23 V_RHE), the TiO₂/BiVO₄ photoanode prepared by the in situ transformation method (I-TiO₂/BiVO₄) exhibits a significantly better PEC performance, and the photocurrent density of I-TiO₂/BiVO₄ is about 2.2 mA/cm² at 1.23 V_RHE under visible light irradiation without a cocatalyst. This is mainly attributed to the fact that I-TiO₂/BiVO₄ has a faster electron transfer rate in the heterojunction interface according to the results of PEC analysis. Furthermore, density functional theory (DFT) calculations show that the BiVO₄-202 surface has a higher Fermi energy level, thereby expediting the photogenerated carrier transport in the heterojunction interface. This work corroborates and strengthens the view that the heterojunction interface structure has a significant effect on the PEC performance.

Minimal TiO2 Coupled with Conductive Polymer-Stimulated Synergistic Effect on Fast and Reversible Sodium-Ion Storage for Bismuth Sulfide

Designing multiphase composition is believed to availably boost the structural integrity and electrochemical properties of sodium-ion battery anodes. Herein, a conceive of nanoflowers, assembled with Bi₂S₃ nanorods, is demonstrated to construct the multiphase composition involving TiO₂ coating and polypyrrole (PPy) encapsulation. Bi₂S₃ acted as the dominating active material, in consideration of the low content of TiO₂, which ensured the high capacity of the composite. The dual-structural restrain of the TiO₂ and PPy coatings can effectively alleviate volume variation based on the pseudo-"zero-strain" effect of TiO₂ and high flexibility of PPy shells. Meanwhile, the heterointerface greatly enhanced the coupling effect between Bi₂S₃ and TiO₂ and thus improved the electrochemical performance, which was proved by the results of density functional theory calculation and electrochemical tests. Combining the regulation from the Bi₂S₃/TiO₂ heterojunction and the dual-structural restrain effect, the Bi₂S₃/TiO₂@PPy electrode exhibited excellent rate performance and superior cycle stability (275.8 mA h g^-1 over 500 cycles at 10 A g^-1). This study indicates that designing multiphase composition can be very promising and provides a structural insight to construct high stability in electrodes for sodium-ion batteries.

Conduction Band Energy-Level Engineering for Improving Open-Circuit Voltage in Antimony Selenide Nanorod Array Solar Cells

Antimony selenide (Sb2 Se3 ) nanorod arrays along the [001] orientation are known to transfer photogenerated carriers rapidly due to the strongly anisotropic one-dimensional crystal structure. With advanced light-trapping structures, the Sb2 Se3 nanorod array-based solar cells have excellent broad spectral response properties, and higher short-circuit current density than the conventional planar structured thin film solar cells. However, the interface engineering for the Sb2 Se3 nanorod array-based solar cell is more crucial to increase the performance, because it is challenging to coat a compact buffer layer with perfect coverage to form a uniform heterojunction interface due to its large surface area and length-diameter ratio. In this work, an intermeshing In2 S3 nanosheet-CdS composite as the buffer layer, compactly coating on the Sb2 Se3 nanorod surface is constructed. The application of In2 S3 -CdS composite buffers build a gradient conduction band energy configuration in the Sb2 Se3 /buffer heterojunction interface, which reduces the interface recombination and enhances the transfer and collection of photogenerated electrons. The energy-level regulation minimizes the open-circuit voltage deficit at the interfaces of buffer/Sb2 Se3 and buffer/ZnO layers in the Sb2 Se3 solar cells. Consequently, the Sb2 Se3 nanorod array solar cell based on In2 S3 -CdS composite buffers achieves an efficiency of as high as 9.19% with a VOC of 461 mV.

Synergistic Effect of Charge Generation and Separation in Epitaxially Grown BiOCl/Bi2S3 Nano-Heterostructure

Nano-heterostructures are widely used in the field of optoelectronic devices, and an optimal proportion usually exists between the constituents that make up the structures. Investigation on the mechanism underlying the optimal ratio is instructive for fabricating nano-heterostructures with high efficiency. In this work, BiOCl/Bi₂S₃ type-II nano-heterostructures with different Bi₂S₃/BiOCl ratios have been prepared via epitaxial growth of Bi₂S₃ nanorods on BiOCl nanosheets with solvothermal treatment at different sulfuration temperatures (110-180 °C) and their photoelectrochemical (PEC) performances as photoanodes have been studied. Results indicate that the Bi₂S₃ content increases with the sulfuration temperature. BiOCl/Bi₂S₃-170 (i.e., sulfurized@170 °C) exhibits the highest PEC performance under visible-light illumination, whereas BiOCl/Bi₂S₃-180 with the maximum Bi₂S₃ content shows the highest visible-light absorption, i.e., possessing the best potential for charge generation. Further analysis indicates that the BiOCl/Bi₂S₃ heterojunction interface is also crucial in determining the PEC performance of the obtained heterostructures by influencing the charge separation process. With increasing Bi₂S₃ content, the interface area in the BiOCl/Bi₂S₃ nano-heterostructures increases first and then decreases due to the mechanical fragility of the nanosheet-nanorod structure and the structural instability in the [010] direction of Bi₂S₃ with higher Bi₂S₃ content. Therefore, the increasing content of the Bi₂S₃ does not necessarily correspond to higher heterojunction area. The optimal performance of BiOCl/Bi₂S₃-170 results from the maximum of the synthetic coordination of the charge generation and separation. This is the first time ever to figure out the detailed explanation of the optimal property in the nano-heterostructures. The result is inspiring in designing high-performance nano-heterostructures from the point of synthesizing morphological mechanically robust heterostructure and structurally stable constituents to reach a high interfacial area, as well as high light-absorption ability.