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Potassium ions batteries (PIBs) have been regarded as a promising choice for electrical energy storage technology due to the wide distribution of potassium resources. However, developing low-cost and robust earth-rich anode materials is still a major challenge for the practical and scalable usage of PIBs. Herein, for the first time, we developed nitrogen doped carbon coating CoS2/CuCo2S4 heterostructure (CoS2/CuCo2S4@NCs) hollow spheres and evaluated as anode for PIBs. The CoS2 and CuCo2S4 heterostructure interface could generate a built-in electric field, which can fasten electrons transportation. The nanostructures could shorten the diffusion length of K+ and provide large surface area to contact with electrolytes. Furthermore, the inner hollow sphere morphology along with the carbon layer could accommodate the volume expansion during cycling. What’s more, the N-doped carbon could increase the conductivity of the anodes. Benefitting from the above features, the CoS2/CuCo2S4@NCs displays an outstanding rate capability (309 mAh g−1 at 500 mA g−1 after 250 cycles) and a long-term cycling life (112 mAh g−1 at 1000 mA g−1 after 1000 cycles) in ether-based electrolyte. Conversion reaction mechanism in CoS2/CuCo2S4@NCs anode is also revealed through ex situ XRD characterizations. This work provides a practical direction for investigating metal sulfides as anode for PIBs.

The van der Waals (vdW) integration enables to create heterostructures with intimate contact and bring new opportunities. However, it is not confined to layered materials but can also be generally extended to 3D materials. Multidimensional Bi2O3/BiVO4@graphene oxide (GO) van der Waals heterostructures are synthesized by one-pot wet chemistry method. Bi2O3/BiVO4 composite nanoparticles are self-assembled with GO framework by vdW interaction to form vdW heterostructures, in which GO framework allows short electron transport distance and rapid charge transfer and provides massive reactive sites. Such self-assembled heterostructures show a superior high photoactivity towards oxygen evolution with an enhanced oxygen generation rate of 1828 µmol h−1 g−1, nearly 3 times than that of pure BiVO4, attributed to the accelerated charge separation and transfer processes of Bi2O3/BiVO4@GO vdW heterostructures. This study indicates that our strategy provides a new avenue towards fabricating multi-dimensional vdW heterostructures and inspiring more innovative insights in oxygen evolution field.

TiO2 microtubes with tunable wall thickness have been synthesized by a one-step electrospinning method linked with a calcination process. The wall thickness of TiO2 microtubes can be easily tuned by altering the dosage of liquid paraffin. The influence of the thickness on the light-harvesting ability and separation efficiency of the photogenerated carriers was studied using ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, photoluminescence emission spectroscopy, and photocurrent density measurements. Results show that TiO2 microtubes with an appropriate thickness exhibit enhanced light scattering effect, UV–vis light-harvesting ability, charge separation efficiency, and photocatalytic performance. The degradation rates of rhodamine B and 2,4-dinitrophenol by using TiO2 microtubes synthesized at a dosage of 0.14 g/mL liquid paraffin are 99.9% within 60 min and 97.8% within 40 min, respectively, which are higher than most of the reported values. All these results suggest that our work provides an ideal strategy for adjusting the wall thickness of TiO2 microtubes and new approach to enhance the photocatalytic performance of TiO2.

Potassium-ion batteries (KIBs) have becoming a prospective energy storage technique, due to the abundant potassium resources in the earth crust, approximate redox potential and similar electrochemical behavior of potassium and lithium. However, the insufficient capacity, poor stability and volume expansion of electrode materials during charge and discharge are main factors restricting the further development of KIBs. This work reports an amorphous carbon coated SnO2 nanohseets on hard carbon hollow spheres (AC/SnO2@HCHS) anode with enhanced potassium storage performance. The HCHS acts as a carrier for SnO2 nanosheets, providing high electrical conductivity and stable skeleton. The self-assembled SnO2 nanosheets with high surface area ensures sufficient contact with the electrolyte. Amorphous carbon wrapping can not only relieve SnO2 volume expansion but also provide surface-induced capacitive capacity. As a consequence, the AC/SnO2@HCHS anode presents excellent potassium-ion storage performance with high discharge capacity of 346 mAh g-1 at 0.1 A g-1 over 200 cycles, ultra-long cycling lifetime and outstanding rate capability (236 mAh g-1 at 1 A g-1 over 1000 cycles).

Suitable anode materials for potassium ion batteries (KIBs) with high capacity, good reversibility and stable cycling performances are still in large demand. Here, flexible N doped carbon/bubble-like MoS2 core/sheath framework (MoS2/NCS) is prepared as an anode material for potassium ion batteries. The N doped carbon sponge (NCS) skeleton with good conductivity and high surface area guarantees superior rate capability and high stability of MoS2/NCS anode. The chemical bonds (C Mo) firmly bridge MoS2 and NCS together, which further ensures MoS2/NCS stable cycling performance. More importantly, volume expansion is greatly buffered during cycling by this unique structure: the voids between bubble-like MoS2 sheath and NCS core can effectively buffer volume expansion generated during potassium intercalation/deintercalation; the enlarged interlayer spacing contribute more space to buffer volume change; the ultrathin nanosheets can shorten the charge diffusion distance and buffer volume change. As a consequence, MoS2/NCS delivers a capacity of 374 mAh g−1 over 200 cycles at 50 mA g−1. Even at 1000 mA g−1, a capacity of 212 mAh g−1 can still be obtained over 1000 cycles. We believe this MoS2/NCS structure will highlight the potential of MoS2 in practical KIBs applications.