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Developing active photocatalysts using wide-spectrum light is crucial to promote the application of photocatalytic water splitting. Elemental red phosphorus (RP) has attracted much attention as a p...

Sodium ion batteries have a huge potential for large-scale energy storage for the low cost and abundance of sodium resources. In this work, a novel structure of ultrafine polycrystalline TiO2 nanofibers is prepared on nickel foam/carbon cloth by a simple vapor deposition method. The as-prepared TiO2 nanofibers show excellent performance when used as anodes for sodium-ion batteries. Specifically, the TiO2 nanofibers@nickel foam electrode delivers a high reversible capacity of 263.2 mAh g−1 at 0.2 C and maintains a considerable capacity of 144.2 mAh g−1 at 10 C. The TiO2 nanofibers@carbon cloth electrode also shows excellent high-rate capability, sustaining a capacity of 148 mAh g−1 after 2000 cycles at 10 C. It is believed that the novel nanofibrous structure increases the contact area with the electrolyte and greatly shortens the sodium ion diffusion distance, and meanwhile, the polycrystalline nature of nanofibers exposes more intercalation sites for sodium storage. Furthermore, the density functional theory calculations exhibit strong ionic interactions between the exposed TiO2 (101) facets and sodium ions, leading to a preferable sodiation/desodiation process. The unique structural features endow the TiO2 nanofibers electrodes great advantages in rapid sodium storage with an outstanding high-rate capability.

To address the bottlenecks of sluggish sodium-ion transfer processes, the electrode materials of sodium-ion battery (SIB) are always designed from the viewpoints of sodium-ion diffusion kinetics or reaction thermodynamics for high-performance sodium storage. Herein, starting with spongiform TiO2/C composite derived from zinc alginate, a NH4Cl-assisted annealing strategy is developed to prepare chlorine-doped spongiform TiO2/C composite (ZATC-Cl). Acting as the anode of SIBs, the obtained ZATC-Cl delivers excellent sodium storage performance with a high reversible capacity of 352.4 mAh g−1 at 50 mA g−1, a superior rate capability of 246.8 mAh g−1 at 2 A g−1 and a considerable high-rate cycling performance of 248.5 mAh g−1 at 2 A g−1 for 1000 cycles. It is believed that the unique spongiform structure and ultra-small sized TiO2 particles in ZATC-Cl can achieve fast sodium-ion insertion/extraction, realizing rapid sodium-ion diffusion kinetics. Moreover, as well evidenced by experiment results and theoretical calculations, the Cl dopants introduced in ZATC-Cl can provide more active sites for robust sodium-ion chemical adsorption, optimizing sodium-ion reaction thermodynamics. This study demonstrates an alternative approach to improve the sodium storage capability of TiO2 anodes by the synergistically engineering the morphological and structural properties and manipulating the surface active sites, from both kinetic and thermodynamic viewpoints of sodium storage processes.

The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (nos. 51961165103 and 51672210) and the National Key Research and Development Program of China (2018YFB1502003 and 2017YFE0193900). S.S. is supported by the National Program for Support of Top-notch Young Professionals and “The Youth Innovation Team of Shaanxi Universities.”

With the properties of high theoretical capacity and excellent structural stability, TiO2 has been widely studied as anode material for sodium-ion batteries (SIBs). In this work, a composite structure of ultra-small TiO2 nanoparticles embedded in carbon nanosheets (TCNS) is obtained by annealing polyvinylpyrrolidone coated Zn-Ti layered double hydroxide under inert atmosphere, with zinc species removed by hydrochloric acid. As sodium-ion battery anode, the resultant TCNS shows a high reversible capacity of 271.2 mAh g−1 at 50 mA g−1 and considerable cycling stability (maintaining 196.7 mAh g−1 after 2000 cycles at 2 A g−1). Ex-situ XRD and TEM investigations clearly illustrate the structure changes of anatase during the sodium storage process. Specifically, ultra-small TiO2 nanoparticles in TCNS show obvious crystal distortion as triggered by the initial insertion of sodium ions, with the reversible sodium storage happening at the (1 0 1) active plane of anatase. As experimentally and theoretically evidenced, the twisted crystal structure is maintained in the subsequent cycles, which can effectively promote the sodium diffusion rate in anatase, resulting in the excellent rate and cycle performances of TCNS anode. This study provides informative guidance to explore high-performance TiO2 anodes for SIBs, with novel insights into the sodium ion insertion/extraction mechanism comprehensively elucidated during reversible sodium storage process.

Electronic structure greatly determines the band structures and the charge carrier transport properties of semiconducting photocatalysts and consequently their photocatalytic activities. Here, by simply calcining the mixture of graphitic carbon nitride (g-C3 N4 ) and sodium borohydride in an inert atmosphere, boron dopants and nitrogen defects are simultaneously introduced into g-C3 N4 . The resultant boron-doped and nitrogen-deficient g-C3 N4 exhibits excellent activity for photocatalytic oxygen evolution, with highest oxygen evolution rate reaching 561.2 µmol h-1 g-1 , much higher than previously reported g-C3 N4 . It is well evidenced that with conduction and valence band positions substantially and continuously tuned by the simultaneous introduction of boron dopants and nitrogen defects into g-C3 N4 , the band structures are exceptionally modulated for both effective optical absorption in visible light and much increased driving force for water oxidation. Moreover, the engineered electronic structure creates abundant unsaturated sites and induces strong interlayer C-N interaction, leading to efficient electron excitation and accelerated charge transport. In the present work, a facile approach is successfully demonstrated to engineer the electronic structures and the band structures of g-C3 N4 with simultaneous introduction of dopants and defects for high-performance photocatalytic oxygen evolution, which can provide informative principles for the design of efficient photocatalysis systems for solar energy conversion.

光生载流子分离和表面催化反应是光催化分解水制氢过程的2个主要步骤,协同提高这两步速率必然能极大促进催化剂的制氢效率。本文以g-C3N4为研究对象,通过负载铁酸盐CoFe2O4或NiFe2O4,g-C3N4的光催化制氢性能得到大幅提高。研究结果表明,(Co, Ni)Fe2O4不仅能够有效地促进g-C3N4中的光生载流子的分离,而且能够有效地促进表面催化氧化半反应;与此同时,负载Pt作为产氢助催化剂,能促进表面催化还原产氢半反应。在光催化反应中,g-C3N4中的光生电子和空穴分别流向Pt和(Co, Ni)Fe2O4,电子在Pt上还原反应产生氢气,而空穴转移到(Co, Ni)Fe2O4上与牺牲剂反应。进一步研究结果发现,CoFe2O4对g-C3N4的载流子分离与氧化半反应催化效果均优于NiFe2O4。通过CoFe2O4和Pt共负载,Pt/g-C3N4/CoFe2O4光催化剂的催化制氢量子效率在420 nm处达到3.35 %,在可见光区(λ > 420 nm)的光催化制氢速率是未负载铁酸盐的Pt/g-C3N4的3.5倍。

The article describes a robust method for the facile polyol synthesis of high-quality CuS nanocrystals with a controlled hierarchical nanoplate structure. The success of this method relies on manipulating the reaction kinetics with different sulfur precursors. In particular, with a medium releasing rate of S2−, we are able to produce CdS hierarchical spherical nanoflowers composed with multi-layered nanoplates, while a slow or fast release of S2− gives the monodispersed hexagonal nanoplates or disordered nanoplate complexes, respectively. Benefitting from its large surface area and the hierarchical structure for light reflection, the CuS nanoflower with a hierarchical plate structure showed the best electrocatalytic and photocatalytic performances when benchmarking its activity with the well-shaped nanoplate and the disordered nanoplate complex.

The present study combines the advantages of chemical exfoliation and elemental doping to have enhanced surface area, better charge carrier separation and extended light absorption in N3−/Nb4+ co-doped nanosheets, which were employed for the first time to study their O2 evolution response. The Dion-Jacobson phase, KCa2NaNb4O13 perovskite was calcined under NH3 environment at various reaction durations (5 hr, 6 hr, 7 hr) to yield N3−/Nb4+ co-doped layered structures and subsequently exfoliated into ultrathin nanosheets. The N3−/Nb4+ co-doped nanosheets realized superior visible light absorption and bandgap narrowing as determined from UV–visible spectroscopy profiles. The synthesis of bulk materials and ultrathin morphology of exfoliated nanosheets were confirmed through XRD, SEM and AFM. The chemical states of the elements were examined by XPS measurements. The optimized N3−/Nb4+ co-doped CNNO--6hr nanosheets demonstrated excellent O2 evolution of 903 μmol g-1 after 4 h compared to N3−/Nb4+ co-doped CNNO--5hr (510 μmol g-1), N3−/Nb4+ co-doped CNNO--7hr (528 μmol g-1) and non-doped CNNO- nanosheets (381 μmol g-1). Our study paves a way on the feasibility of combining various chemical strategies for advanced photocatalyst design.

To gain high photocatalytic activity for hydrogen evolution, both charge separation efficiency and surface reaction kinetics must be improved, and together would be even better. In this study, the visible light photocatalytic hydrogen production activity of graphitic carbon nitride (g-C3N4) was greatly enhanced with MgFe2O4 modification. It was demonstrated that MgFe2O4 could not only extract photoinduced holes from g-C3N4, leading to efficient charge carrier separation at the g-C3N4/MgFe2O4 interface, but also act as an oxidative catalyst accelerating the oxidation reaction kinetics at g-C3N4 surface. This dual function of MgFe2O4 thus contributed to the great improvement (up to three-fold) in photocatalytic activity for hydrogen generation over g-C3N4/MgFe2O4 as compared to pristine g-C3N4, after loading Pt by photoreduction method. It was revealed that in the Pt/g-C3N4/MgFe2O4 system, the photoinduced electrons and holes were entrapped by Pt and MgFe2O4, respectively, giving rise to the promoted charge separation; moreover, as evidenced by electrochemical analysis, the electrocatalysis effect of MgFe2O4 benefited the oxidation reaction at g-C3N4 surface.