Carbon nitride (CNx) films supported on fluorine-doped tin oxide (FTO) glass are prepared by radio frequency magnetron sputtering, in which the film thicknesses are 90–100 nm, and the element components in the CNx films are in the range of x = 0.15–0.25. The as-prepared CNx is for the first time used as counter electrode for dye-sensitized solar cells (DSSCs), and show a preparation-temperature dependent electrochemical performance. X-ray photoelectron spectroscopy (XPS) demonstrates that there is a higher proportion of sp2 CC and sp3 CN hybridized bonds in CNx-500 (the sample treated at 500 °C) than in CNx-RT (the sample without a heat treatment). It is proposed that the sp2 CC and sp3 C–N hybridized bonds in the CNx films are helpful for improving the electrocatalytic activities in DSSCs. Meanwhile, Raman spectra also prove that CNx-500 has a relatively high graphitization level that means an increasing electrical conductivity. This further explains why the sample after the heat treatment has a higher electrochemical performance in DSSCs. In addition, the as-prepared CNx counter electrodes have a good light transmittance in the visible light region. The results are meaningful for developing low-cost metal-free transparent counter electrodes for DSSCs.Download high-res image (438KB)Download full-size imageMagnetron sputtered transparent carbon nitride is used as counter electrode in DSSCs, and the electrochemical performance and light transmittance is controllable by preparation temperature.

Carbon materials have attracted extensive attention as the host materials of sulfur for lithium–sulfur battery, especially those with 3D architectural structure. Here, a novel 3D graphene nanosheet–carbon nanotube (GN–CNT) matrix is obtained through a simple one-pot pyrolysis process. The length and density of CNTs can be readily tuned by altering the additive amount of carbon source (urea). Specifically, CNTs are in situ introduced onto the surface of the graphene nanosheets (GN) and show a stable covalent interaction with GN. Besides, in the GN–CNT matrix, cobalt nanoparticles with different diameters exist as being wrapped in the top of CNTs or scattering on the GN surface, and abundant heteroatoms (N, O) are detected, both of which can help in immobilizing sulfur species. Such a rationally designed 3D GN–CNT matrix makes much more sense in enhancing the electrochemical performance of the sulfur cathode for rapid charge transfer and favorable electrolyte infiltration. Moreover, the presence of dispersed cobalt nanoparticles is beneficial for trapping lithium polysulfides by strong chemical interaction, and facilitating the mutual transformation between the high-order polysulfides and low-order ones. As a result, the S/GN–CNT composite presents a high sulfur utilization and large capacity on the basis of the S/GN–CNT composite as active material.

•A solar rechargeable battery is proposed based on hydrogen storage mechanism.•The hydrogen storage alloy acts as counter electrode and anode in the battery.•The battery shows a new solution of energy conversion, storage and utilization.Solar water splitting is an effective approach to hydrogen production and application of solar energy. However, the photo-generated hydrogen should be initially stored in high pressure cylinder and subsequently applied in hydrogen-oxygen fuel cells. Herein, a solar rechargeable battery is proposed based mainly on hydrogen storage mechanism in dual-phase electrolyte. Specifically, the hydrogen production, storage and utilization are integrated into a hybrid system of the dye-sensitized solar cell and electrochemical cell with the dye-sensitized TiO2 as photo-anode, LiI as the cathode active material in organic electrolyte, AB5-type hydrogen storage alloy as anode in alkaline solution, and PEDOT-modified Nafion membrane as separator. Here, the photo-generated electrons in organic electrolyte pass to the AB5-type hydrogen storage alloy to split water in alkaline aqueous electrolyte for generating hydrogen, which is in situ stored into AB5-type hydrogen storage alloy. Subsequently, the hydrogen stored in the AB5-type hydrogen storage alloy can be oxidized by electrochemical way to generate electricity, coupled with LiI cathode in organic electrolyte. The solar rechargeable battery demonstrates a new solution of the solar energy conversion, hydrogen production, storage, and utilization, achieving the new energy conversion and storage from solar energy to chemical energy, and further to electrical energy.Download high-res image (250KB)Download full-size image

Molybdenum disulfide attracts additional attention due to its layered structure which allows transformation into a two-dimensional morphology, like graphene. In this paper, three kinds of molybdenum disulfides with distinguishable morphologies, i.e. multilayers, a few layers and nanoparticles, are prepared and used as counter electrode materials for dye-sensitized solar cells (DSSCs). The characterization results from X-ray diffraction (XRD) and transmission electron microscopy (TEM) demonstrate that the molybdenum disulfides have an obviously different edge area to basal-plane ratio, with the order: synthesized MoS2 nanoparticles (MoS2-NPs) > multilayered MoS2 (ML-MoS2) > few-layered MoS2 (FL-MoS2). It is interesting that the MoS2 counter electrodes show the same order as above in the energy conversion efficiency measurements of the corresponding DSSCs. Electrochemical impedance spectra (EIS) show that the MoS2-NPs electrode has the minimum charge-transfer resistance, while the FL-MoS2 electrode provides the maximum. Combined with the results from triiodine ion adsorption experiences and N2-adsorption measurements, it is proposed that the catalytically active sites of molybdenum disulfide lie on the edges of the typical layered material, but not on the basal planes. In addition, the transparency of the FL-MoS2 electrode is obviously higher than that of the other MoS2 and Pt electrodes.

•Group VIIIB metal sulfides thin films are prepared by a solution-process strategy.•The sulfide electrodes achieve optical transparency and high electrochemical activity.•The DSSC using nickel sulfide shows a higher efficiency than using Pt electrode.Dye-sensitized solar cells (DSSCs) have obtained exciting progress in improving energy conversion efficiency and cutting material cost in recent years. It is found that many kinds of inorganic compounds have promising potential to replace platinum as counter electrode materials for DSSCs. Actually, to a thin film electrode, preparation of the thin film is the same important as choice of active materials, because quality of the films has a direct effect on electrochemical and optical performance of the final counter electrodes. In this paper, a general strategy is developed to prepare transparent and high-efficient metal sulfide counter electrodes. In the route, the Group VIIIB metal sulfides are formed as compact, homogenous and stable films on fluorine-doped tin oxide conductive glass from a precursor organic solution by spin coating, and the film thickness can be readily converted to reach the balance between optical transparency and electrochemical activity. Among the Group VIIIB metal sulfides, the nickel sulfide film with the thickness of 100 nm shows the high transparency and energy conversion efficiency of 7.37%, higher than that of the DSSC using platinum electrode. The results provide a new and facile alternative to prepare high-efficient and transparent sulfide counter electrodes for DSSCs.

Li4Ti5O12/carbon composites have shown promising high rate capability as anode materials for lithium ion batteries. In this paper, unique effects of graphene in Li4Ti5O12/carbon composites on electrochemical performances are focused by means of comparing Li4Ti5O12/graphene with Li4Ti5O12/conductive carbon black (CCB) and Li4Ti5O12. The investigated anode materials are synthesized by a facile hydrothermal method. The amount of graphene or CCB in the Li4Ti5O12/carbon composites is about 3 wt% measured by thermogravimetric (TG) analysis. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that Li4Ti5O12/graphene consists of small sized Li4Ti5O12 nanocrystals supported on graphene nanosheets, while Li4Ti5O12/CCB comprises Li4Ti5O12 nanocrystal aggregates coated nearly by graphited carbon. The electrochemical performances of these samples as anode materials for lithium ion batteries are investigated by galvanostatic charge–discharge method. Li4Ti5O12/graphene provides a superior rate capability. At the high current density of 1600 mA g−1, the reversible capacity after 200 cycles is still more than 120 mAh g−1, which is about 40% higher than that of Li4Ti5O12/CCB. Cyclic voltammetry (CV) demonstrates that stronger pseudocapacitive effect occurs on Li4Ti5O12/graphene than on Li4Ti5O12/CCB. This derived from the structure features that graphene-supported small Li4Ti5O12 nanocrystals provide more surface active sites for the lithium ion insertion/extraction. The strong pseudocapacitive effect is responsible for the improvements of capacity and high-rate capability. Further, electrochemical impedance spectra (EIS) show that Li4Ti5O12/graphene electrode have lower charge transfer resistance and smaller diffusion impedance, indicating the obvious advantages in electrode kinetics over Li4Ti5O12 and Li4Ti5O12/CCB. The results clarify the positive effects of graphene in Li4Ti5O12/carbon composites as anode materials for lithium ion batteries.

As a counter electrode for dye-sensitized solar cells (DSSCs), MoN presents a high intrinsic electrocatalytic activity for the reduction of triiodide ions. However, the photovoltaic performance of DSSCs with a MoN counter electrode is hindered by the large diffusion impedance of the MoN electrode. In response to this problem, a MoN–carbon nanotube (CNT) composite is prepared by nitridation of the precursor MoO2–CNTs, fabricated via a hydrothermal reaction of ammonium molybdate and carboxyl-functionalized CNTs. In the composite, MoN nanoparticles are well and stably dispersed on the surface of the CNTs, with a particle size of several tens of nanometers. Employing the composite as a counter electrode, the DSSC shows an energy conversion efficiency of 6.74%, which is much higher than that (5.57%) of the DSSC using pure MoN nanoparticles. The improvement is mainly attributed to a synergistic effect between the MoN nanoparticles and CNTs on ion diffusion and electrocatalysis. Electrochemical impedance spectra (EIS) indicate that the MoN–CNTs electrode has a lower ion diffusion impedance. It is believed that the smaller size of the MoN nanoparticles and the abundant porous structure in the MoN–CNTs composite are able to shorten the ion diffusion path and improve ion diffusion flux.

Usually, perovskite solar cells employ gold or silver as counter electrode materials. The use of the precious metals is a serious obstacle to the practical application of perovskite solar cells. In this work, low-cost non-precious transition metals are investigated to replace gold or silver as counter electrode materials in perovskite solar cells. Under optimized conditions, perovskite solar cells with Cu, Ni, W, and Mo films, prepared by magnetron sputtering deposition, present satisfactory performance with the power conversion efficiency of 13.04, 12.18, 12.38, and 11.38%, respectively, as compared with that (15.97%) of the perovskite solar cell with Ag counter electrode. Even though a slightly loss in efficiency, these non-precious transition metals are the promising candidates to the counter electrode of perovskite solar cells on the aspect of the practicality and cost performance ratio.Perovskite solar cells with non-precious metal (Cu, Ni, W, and Mo) films as low-cost counter electrode materials present satisfactory performance with the power conversion efficiency.Download high-res image (163KB)Download full-size image

Molybdenum disulfide attracts additional attention due to its layered structure which allows transformation into a two-dimensional morphology, like graphene. In this paper, three kinds of molybdenum disulfides with distinguishable morphologies, i.e. multilayers, a few layers and nanoparticles, are prepared and used as counter electrode materials for dye-sensitized solar cells (DSSCs). The characterization results from X-ray diffraction (XRD) and transmission electron microscopy (TEM) demonstrate that the molybdenum disulfides have an obviously different edge area to basal-plane ratio, with the order: synthesized MoS2 nanoparticles (MoS2-NPs) > multilayered MoS2 (ML-MoS2) > few-layered MoS2 (FL-MoS2). It is interesting that the MoS2 counter electrodes show the same order as above in the energy conversion efficiency measurements of the corresponding DSSCs. Electrochemical impedance spectra (EIS) show that the MoS2-NPs electrode has the minimum charge-transfer resistance, while the FL-MoS2 electrode provides the maximum. Combined with the results from triiodine ion adsorption experiences and N2-adsorption measurements, it is proposed that the catalytically active sites of molybdenum disulfide lie on the edges of the typical layered material, but not on the basal planes. In addition, the transparency of the FL-MoS2 electrode is obviously higher than that of the other MoS2 and Pt electrodes.

As a counter electrode for dye-sensitized solar cells (DSSCs), MoN presents a high intrinsic electrocatalytic activity for the reduction of triiodide ions. However, the photovoltaic performance of DSSCs with a MoN counter electrode is hindered by the large diffusion impedance of the MoN electrode. In response to this problem, a MoN–carbon nanotube (CNT) composite is prepared by nitridation of the precursor MoO2–CNTs, fabricated via a hydrothermal reaction of ammonium molybdate and carboxyl-functionalized CNTs. In the composite, MoN nanoparticles are well and stably dispersed on the surface of the CNTs, with a particle size of several tens of nanometers. Employing the composite as a counter electrode, the DSSC shows an energy conversion efficiency of 6.74%, which is much higher than that (5.57%) of the DSSC using pure MoN nanoparticles. The improvement is mainly attributed to a synergistic effect between the MoN nanoparticles and CNTs on ion diffusion and electrocatalysis. Electrochemical impedance spectra (EIS) indicate that the MoN–CNTs electrode has a lower ion diffusion impedance. It is believed that the smaller size of the MoN nanoparticles and the abundant porous structure in the MoN–CNTs composite are able to shorten the ion diffusion path and improve ion diffusion flux.