Z-scheme photocatalytic systems, consisting of semiconductor/semiconductor heterostructures, mimic the natural photosynthesis and enhance the photocatalytic activity dramatically. Herein, we have for the first time synthesized unique all-solid-state Z-scheme ternary heterostructures by growing CdS nano-hemispheres radially assembled with nanorods as the core and CoS hexagonal nanoflakes as the shell on graphene sheets (CdS/Co9S8-RGO) through a facile one-pot hydrothermal method and subsequent annealing treatment. Furthermore, the growth mechanism is explored and analyzed by monitoring the intermediates in terms of structure and composition. The heterostructures form three paths available for charge carrier transfer and separation, wherein a redox-mediator-free Z-scheme constitutes CdS and Co9S8 and upgrades to an all-solid-state Z-scheme system by combination with RGO. Moreover, due to the excellent photon capture capability and electric conductivity, RGO also made great contribution to the effective separation and transfer of photogenerated carriers. Benefiting from efficient charge transfer and separation, CdS/Co9S8-RGO exhibits a H2 evolution rate up to 4.82 mmol h−1 g−1 and remarkable activity stability even after 20 h of photocatalytic reaction. We believe that the design philosophy via the plain synthesis merges multiple structural interfaces and transfer paths in a system reported here, shedding an insight into the design of other photocatalysts.
Na Wang,Wenjing Hou,Yunzhen Chang,Hua Song,Honggang Li,Yanping Li,Gaoyi Han
Flexible energy storage devices attracted extensive attention due to their application in personal wearable electronic products. However, the applications of flexible energy storage devices, especially supercapacitors are limited by their low energy density, because anode materials with large capacitance are scarce for the devices based on aqueous electrolyte. Therefore, developing high-performance anode is an effective way to break through the low energy density of flexible devices. Herein, the electroless plating method was used to prepare a flexible cobalt metal substrate based on carbon cloth (CC). The composite of Co 9 S 8 and reduced oxide graphene (rGO/Co 9 S 8 (rGO)/CC) is prepared by one-step hydrothermal method as a flexible anode with outstanding performance. Benefiting from the high hydrogen storage capacity of rGO/Co 9 S 8 (rGO), only a small amount of anode materials are needed to match the capacity of the cathode material of rGO/Ni 3 S 2 (rGO). The optimized flexible device assembled by using rGO/Co 9 S 8 (rGO) as negative electrode and rGO/Ni 3 S 2 (rGO) as positive electrode shows a high specific capacitance of 192.4 mAh g −1 at the current density of 4.0 A g −1 , large energy density (168.1 Wh kg −1 at 3.5 kW kg −1 ). Furthermore, the network structure of the electrode can provide enough space for the expansion and contraction of the electrode materials during the repeated charging and discharging process, so the device exhibits good cycle stability (the capacitance of the device can retain 84.3% after 6000 cycles). Moreover, the device also exhibits remarkable flexibility. These results reveal that this kind of electrochemical hydrogen storage material can be developed as a promising anode in flexible energy storage devices.
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