The development of efficient noble-metal-free hydrogen evolution catalysts is quite appealing with the aim of providing cost-competitive hydrogen. Herein, nickel sulfides (NiS x ) with tunable ...NiS/Ni3S4 molar ratios were synthesized via a simple hydrothermal method. Detailed electrochemical studies under neutral conditions indicated that the electrocatalytic property of NiS x catalysts was determined by the composition. Notably, the NiS x sample with the NiS/Ni3S4 molar ratio of 1.0 exhibited the lowest overpotential and charge-transfer resistance. As analyzed from the Tafel plots, the rate-determining step of NiS x catalysts for hydrogen generation was the Volmer step, in which the proton adsorption played a key role. Theoretical calculation revealed that NiS and Ni3S4 exhibited the metallic behaviors with different work functions. Consequently, the NiS x sample with the NiS/Ni3S4 molar ratio of 1.0 owned the most adsorbed protons, which led to the highest electrocatalytic property. Meanwhile, NiS x was demonstrated to be efficient cocatalysts to promote photocatalytic hydrogen generation. NiS x /CdS with the NiS/Ni3S4 molar ratio of 1.0 showed the best photocatalytic activity with the apparent quantum efficiency of 56.5% at 420 nm. This result was in good agreement with the electrocatalytic activities of NiS x samples, indicating the intrinsic property for efficient hydrogen generation.
Precursor types play crucial factors for synthesizing high-efficiency graphitic carbon nitrides (GCNs). Herein, biuret was employed as a new precursor to prepare a disordered nitrogen-defect-rich ...porous GCN (BCN). The crystallinity, structure and performance properties for BCN were explored by making systematic comparisons with other commonly available GCNs which were derived from conventional precursors under the identical conditions. Biuret could be the optimal choice for the preparation of high-performance GCN according to the reports so far. BCN not only possessed long-range atomic disordered structure, but also contained numerous nitrogen defects embedded into the in-planes of the disordered GCN networks, leading to extended visible-light absorption (absorption edge at 525 nm), improved separation of photoexcited charge carriers, and rich available reactive sites. The large surface area and high porosity of BCN also provided plenty of reactive sites. Consequently, ultrahigh photocatalytic H2 production and excellent O2 production performance were achieved for BCN, the AQY for H2 production achieved 45.5% at 420 nm, which was one of the highest values for GCN-based photocatalysts.
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•Graphitic carbon nitride was prepared by direct thermal polymerization of a kind of new precursor–biuret.•Biuret-derived graphitic carbon nitride (BCN) possessed disordered structure with nitrogen vacancies and cyano groups.•BCN behaved favorable visible-light absorption ability with the absorption edge at about 525 nm, the bandgap was 2.45 eV.•BCN behaved ultrahigh photocatalytic H2 production performance, and the AQY achieved 45.5% at 420 nm.
CdS is a promising visible light response photoanode of photoelectrochemical (PEC) water splitting, but it remains a great challenge for practical application, due to the photohole‐induced ...self‐corrosion, and sulfide/sulfite ions as hole scavengers are always necessary for stable solar hydrogen generation. Herein, a CdS/SnSx nanorods/nanosheets hierarchical heterostructure with novel phase‐engineered band alignment is rationally designed via a two‐step solution reaction route for PEC water splitting. In the Na2SO4 aqueous electrolyte without any hole scavengers, compared with the pristine CdS, the CdS/SnSx photoanode achieves a remarkably enhanced photocurrent density of 1.59 mA cm−2 and a considerable stability at bias potential 1.23 V versus reversible hydrogen electrode (RHE) under simulated sunlight. It is proposed that the deposited SnSx nanosheets not only act as protective layers to restrain the photocorrosion of CdS, but also facilitate the charge separation in CdS by the virtue of the Type II heterojunction formed between CdS and SnSx.
CdS/SnSx 1D/2D hierarchical heterostructure photoanodes are successfully constructed via a two‐step process and rationally improved with engineered band alignment by tuning the crystal phase of SnSx. Compared with pristine CdS, the optimal heterostructure achieves a greatly enhanced photocurrent density of 1.59 mA cm−2 with considerable stability in neutral Na2SO4 aqueous electrolyte without any hole scavengers.
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‐C3N4) and sodium borohydride in an inert atmosphere, boron dopants and nitrogen defects are simultaneously introduced into g‐C3N4. The resultant boron‐doped and nitrogen‐deficient g‐C3N4 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‐C3N4. 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‐C3N4, 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‐C3N4 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.
Boron dopants and nitrogen defects are simultaneously introduced into g‐C3N4 through a simple NaBH4 thermal treatment approach. With exceptionally modulated band structures for effective optical absorption and increased water‐oxidation driving force, as well as engineered electronic structure for efficient electron excitation and facilitated charge transport, the resultant boron‐doped and nitrogen‐deficient g‐C3N4 exhibits excellent activity for photocatalytic oxygen evolution.
The charge carrier separation and surface catalytic redox reactions are of primary importance as elementary steps in photocatalytic hydrogen evolution. In this study, both of these two processes in ...photocatalytic hydrogen evolution over graphitic carbon nitride (g-C3N4) were greatly promoted with the earth-abundant ferrites (Co, Ni)Fe2O4 modification. CoFe2O4 was further demonstrated to be a better modifier for g-C3N4 as compared to NiFe2O4, due to the more efficient charge carrier transfer as well as superior surface oxidative catalytic activity. When together loading CoFe2O4 and reductive hydrogen production electrocatalyst Pt onto g-C3N4, the obtained Pt/g-C3N4/CoFe2O4 photocatalyst achieved visible-light (λ > 420nm) hydrogen production rate 3.5 times as high as Pt/g-C3N4, with the apparent quantum yield reaching 3.35% at 420nm.
Sodium-ion batteries (SIBs) have attracted much attention for their high energy densities and low cost. However, the unstable solid-liquid interphase seriously restricts the development and ...application of SIBs. Herein, Ca(ClO4)2 as a new-type electrolyte additive is developed to engineer the solid-liquid interphase of carbon-coated anodes. In the electrolyte with an appropriate concentration of Ca(ClO4)2, Ca2+ can insert into the carbon coating and form a passivation layer during the first cycle, reducing the irreversible sodium-ion capture in the carbon coating and the electrolyte decomposition at the solid-liquid interface. Thus, the carbon-coated anode with a thin and stable solid electrolyte interphase (SEI) layer formed realizes the superior sodium storage performance with enhanced sodium-ion diffusion kinetics. Specifically, after adding 0.015 M Ca(ClO4)2 into the electrolyte, the reversible capacity of carbon-coated TiO2 anode could be greatly improved from 271.2 mAh g−1 to 335.1 mAh g−1 at 50 mA g−1, with the initial coulombic efficiency increasing from 41.2 % to 48.7 %. This study provides an alternative strategy to optimizing the SEI layer of carbon-coated TiO2 anode for superior sodium storage property, which also can be applied to other carbon-coated anodes for SIBs.
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•Ca(ClO4)2 is developed to optimize the SEI layer of carbon-coated TiO2 anode.•Ca2+ can be inserted into the carbon coating with a passivation layer formed.•Ca(ClO4)2 suppresses electrolyte decomposition and irreversible Na+ capture.•A thin and stable SEI layer realizes a superior sodium storage performance.
A novel insight is elucidated to explain the excellent sodium storage capability of ultra-small TiO2 nanoparticles embedded in carbon nanosheets.
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•TCNS is prepared by a facile method ...and reveals excellent high-rate capability.•The (101) plane of anatase serves as the active plane for sodium storage.•A structure distortion happens to anatase TiO2 during the initial sodium insertion.•This twisted crystal structure effectively promotes the sodium diffusion rate.
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 (101) 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.
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.
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•N3−/Nb4+ co-doped Ca2NaNb4O13- nanosheets has been synthesized via a nitridation-exfoliation process.•N3-and Nb4+ co-doping narrowed bandgap for enhanced visible light absorption.•Excellent oxygen evolution was observed for optimized N3-and Nb4+ co-doping in Ca2NaNb4O13- nanosheets.
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 ...potential nonmetal photocatalyst owing to its low cost, earth abundance, and narrow bandgap. Herein, RP nanosheets were synthesized and tightly combined with carbon nitride (CN) framework nanosheets to form RP/CN van der Waals (vdW) heterostructure. CN nanosheets could act as a substrate to generate RP nanosheets through a “confinement effect”. This hybrid photocatalyst could utilize the incident light with the wavelength longer than 620 nm for pure water splitting, with hydrogen production activity of 367.0 μmol h–1g–1 under full arc illustration and 239.8 μmol h–1g–1 under visible light irradiation. The improved photocatalytic property was ascribed to the wide light absorption and intimate electronic coupling between 2D RP and 2D CN for accelerated charge transfer. Instead of O2, water was oxidized into H2O2 via a two-electron pathway, which could avoid the potential explosion by producing H2 and O2 simultaneously. This work proved the great potential of RP-based vdW heterostructures for solar-driven water splitting.
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.
