Black phosphorus (BP) is an interesting two‐dimensional material with low‐cost and abundant metal‐free properties and is used as one cocatalyst for photocatalytic H2 production. However, the BP quantum dot (BPQD) is not studied. Herein, for the first time, BPQD is introduced as a hole‐migration cocatalyst of layered g‐C3N4 for visible‐light‐driven photocatalytic hydrogen generation. A high‐vacuum stirring method is developed for BPQD loading without the dissociation of BP. The layered BPQD is coupled on the layered g‐C3N4 surface to form a heterojunction structure. The 7% BPQD–C3N4 samples show similar time‐resolved photoluminescence curves as 0.5% Pt–C3N4. The optimum hydrogen rates of the modified sample (7% BPQD–C3N4) are 190, 133, 90, and 10.4 µmol h−1 under simulated sunlight, LED‐405, LED‐420, and LED‐550 nm irradiation, respectively, which are 3.5, 3.6, and 3 times larger than that of the pristine g‐C3N4. Such low‐cost layered system not only optimizes the optical, electrical, and texture properties of the hybrid materials for photocatalytic water splitting to generate hydrogen but also provides ideas for designing novel or easily oxidized candidates by incorporating different available materials with given carriers.
Sodium‐ion batteries are a promising large‐scale electrochemical energy storage system because of their excellent cost advantage compared with lithium‐ion batteries. However, the lack of high safety, low cost, and long service life anode materials hinder its actual development. Here, a sodium titanate/titanium dioxide/C (C‐NTC) heterostructure composite is reported with oxygen vacancies (OVs) that delivers a high specific capacity of 92.6 mAh g‐1 at 5 A g‐1 after 35 000 cycles (100% capacity retention) and excellent rate performance of 54 mAh g‐1 at 20 A g‐1 when tested in combination with a Na‐metal anode. Moreover, sodium‐ion full batteries assembled with C‐NTC as the anode and Na3V2(PO4)3@C‐BN as the cathode demonstrates a high specific capacity after 5500 cycles. Electrochemical kinetic tests and density functional theory measurements confirm that the synergistic effect of heterostructure and OVs accelerate the ion/electron transfer kinetics, the stable frame structure, and solid electrolyte interphase layer ensuring the long cycle life. Ex‐situ X‐ray photon spectroscopy reveals that the generation of Ti0 by disproportionation reactions may be responsible for the degradation of Ti‐based oxide performance, which provides unique insight and guidance for the design of titanium‐based electrodes with ultra‐long cycle life.
Titanates have been widely reported as anode materials for sodium-ion batteries (SIBs). However, their wide temperature suitability and cycle life remain fundamental issues that hinder their practical application. Herein, a novel hollow Na 2 Ti 3 O 7 microsphere (H-NTO) with a unique chemically bonded NTO/C(N) interface is reported. Theoretical calculations demonstrated that the NTO/C(N) interface stabilizes the crystal structure, and the optimized interface enables the H-NTO anode to stably operate for 80 000 cycles in a conventional ester electrolyte with negligible capacity loss. Optimizing the electrolyte allows the H-NTO electrode to cycle stably for 200 calendar days without capacity degradation at −40 °C. The excellent cycling stability is attributed to the NTO/C(N) interface and the stable solid electrolyte interphase formed by the highly adaptable electrolyte/electrode interface. Titanate exhibits solvent co-intercalation behavior in ether-based electrolytes, and its robust structure ensures that it can adapt to large volume changes at low temperatures. This study provides a unique perspective on the long-cycle mechanism of titanate anodes and highlights the critical importance of manipulating the interfacial chemistry in SIBs, including the material and electrode/electrolyte interfaces.
Selenium (Se), with its high specific volume capacity and high electronic and superior kinetics, is considered a promising electrode material with promising applications. However, the solvation and shuttle effects of polyselenides hinder their further application. The selenium/nitrogen-doped hollow porous carbon spheres (Se/NHPCs) are obtained using the sacrificial template and in situ gas-phase selenization methods. The Se species are doped into carbon matrixes in an adjustable amount to form Se-C(N) bonds during this process. Density functional theory calculations show that the Se-C(N) bond enhances the charge transfer between Na 2 Se and carbon matrix and binding energy, which improves rate performance and cycling stability. As expected, Se/NHPCs electrode exhibit high reversible capacity (480 mAh g -1 at 0.5 A g -1 after 200 cycles) and rate performance (311 mAh g -1 at 5 A g -1 ) as the anode for sodium-ion batteries. A series of ex situ characterization results show that Cu 2 Se produced by copper current collector induction is effective in the adsorption of polyselenides while enhancing the electrode conductivity. Since the lattice structures of Cu 2 Se and Na 2 Se are similar, this displacement reaction that does not involve lattice reconfiguration provides an effective strategy for the preparation of high-performance and low-cost electrode materials.
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