A facile and controllable strategy, which combines solvothermal treatment with ex situ nitrogen doping by using urea saturated alcohol solution or monoethanolamine as nitrogen source, is used to prepare flexible, freestanding, and compact nitrogen‐doped delaminated Ti3C2 (abbreviated N‐Ti3C2) film electrodes for symmetric electrochemical capacitors (ECs). Compared with the N sites from in situ N solid solution doping, those of ex situ N solvothermal doping enable larger contributions to the capacitance through regulating nitrogen species and content. As a result, the urea‐assisted N‐Ti3C2 (UN‐Ti3C2) film exhibits an ultrahigh volumetric capacitance of 2836 F cm−3 (927 F g−1) at 5 mV s−1 in 3 m H2SO4 solution. This value surpasses the all previously reported volumetric performance of MXenes. A large capacitance of 2643 F cm−3 (786 F g−1) is also obtained for the monoethanolamine‐assisted N‐Ti3C2 film. In addition, the symmetric electrochemical capacitor fabricated from the binder‐free UN‐Ti3C2 film exhibits a high volumetric energy density of 76 Wh L−1, which is the highest value achieved compared to those of MXenes so far. This work presents the effects of nitrogen species and solvothermal treatment on the electrochemical performance of MXene, and opens up an exciting opportunity for fabricating highly flexible and integrated ECs.
Nitrides MAX have attracted ever-growing interest owing to its unique metallic and ceramic characteristics and properties. Here, we report on the synthesis of highly purified Ti2AlN and Ti4AlN3 powders from Ti, Al and TiN powders by a facile atmosphere sintering method. The obtained nitrides show highly pure phase and excellent layered structure. Except for the composition difference of raw materials, both the nitrides can be sintered and obtained by same sintering temperature and holding time, which thus makes less processing time and less usage of synthesis parameters as compared to previously synthesis methods. To our knowledge, present work is one of the few reports on synthesis of Ti4AlN3 and Ti2AlN using atmosphere sintering method. Furthermore, the lattice changes of the layered structure of Ti2Al[Formula: see text] ([Formula: see text]) were studied by changing the composition of [Formula: see text] position from the synthesis of Ti2AlCN and Ti2AlC, and the optimal formulation and synthesis mechanism of Ti4AlN3 were also studied.
A perovskite solar cell (PSC) featuring a mesoporous architecture can facilitate perovskite layer formation over a large area via increasing the number of heterogeneous nucleation sites. The morphology of the electron transport layer (ETL) and its interface with the perovskite layer is one of the key factors to boost the performance of a PSC. Tin dioxide (SnO2) is considered as a promising ETL in PSCs owing to its high carrier mobility, good transmittance, deep conduction band level, and efficient photoelectron extraction. Generally, the mesoporous SnO2 (m-SnO2) ETL has a higher surface-to-volume ratio compared to a compact SnO2 layer. Herein, we report on an m-SnO2 ETL prepared by anodizing a metallic tin film on a fluorine-doped tin oxide (FTO) substrate in NaOH solution under an ambient atmosphere. In particular, we developed a bilayer architecture of the m-SnO2 ETL based on the fabrication of two consecutive m-SnO2 layers. The morphology of each layer was controlled by varying the anodization voltage and time at a constant solution concentration during the growth process. This unique approach enabled the deposition of an m-SnO2 ETL with sufficient coverage of the FTO substrate, which is difficult to achieve with a single layer of m-SnO2. In particular, the scanning electron and atomic force microscopy analyses confirmed that the m-SnO2 layer covers completely the FTO substrate. The device fabricated with this bilayer m-SnO2 ETL achieved a 27% improvement in power conversion efficiency compared to that with a single layer of m-SnO2.
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