The water oxidation half-reaction is considered to be a bottleneck for achieving highly efficient solar-driven water splitting due to its multiproton-coupled four-electron process and sluggish kinetics. Herein, a triadic photoanode consisting of dual-sized CdTe quantum dots (QDs), Co-based layered double hydroxide (LDH) nanosheets, and BiVO4 particles, that is, QD@LDH@BiVO4, was designed. Two sets of consecutive Type-II band alignments were constructed to improve photogenerated electron-hole separation in the triadic structure. The efficient charge separation resulted in a 2-fold enhancement of the photocurrent of the QD@LDH@BiVO4 photoanode. A significantly enhanced oxidation efficiency reaching above 90% in the low bias region (i.e., E < 0.8 V vs RHE) could be critical in determining the overall performance of a complete photoelectrochemical cell. The faradaic efficiency for water oxidation was almost 90%. The conduction band energy of QDs is ∼1.0 V more negative than that of LDH, favorable for the electron injection to LDH and enabling a more efficient hole separation. The enhanced photon-to-current conversion efficiency and improved water oxidation efficiency of the triadic structure may result from the non-negligible contribution of hot electrons or holes generated in QDs. Such a band-matching and multidimensional triadic architecture could be a promising strategy for achieving high-efficiency photoanodes by sufficiently utilizing and maximizing the functionalities of QDs.

The rational design of advanced structures consisting of multiple components with excellent electrochemical capacitive properties is one of the crucial hindrances to be overcome for high‐performance supercapacitors (SCs). Herein, a superfast and facile synthesis of flower‐like NiMn‐layered double hydroxides (NiMn‐LDH) with high SC performance using an electrodeposition process on nickel foam is proposed. Oxygen vacancies are then modulated via mild H2O2 treatment for the first time, significantly promoting the electrochemical energy storage performance. The oxygen‐vacancy abundant NiMn‐LDH (Ov‐LDH) reaches a maximum specific capacity of 1183 C g−1 at the current density of 1 A g−1 and retains a high capacity retention of 835 C g−1 even at a current density of up to 10 A g−1. Furthermore, the assembled asymmetric SC device achieves a high specific energy density of 46.7 Wh kg−1 at a power density of 1.7 kW kg−1. Oxygen vacancies are proven to play a vital role in the improvement of electrochemistry performance of LDH based on experimental and theoretical studies. This vacancy engineering strategy provides a new insight into SC active materials and should be beneficial for the design of the next generation of energy storage devices.

In the past few years, attention has been focused on the research field of one-dimensional nanostructural materials, both because of their fundamental importance and because of the wide range of potential applications in nanodevices.[1±12] Many attempts have been made to fabricate onedimensional nanostructure materials utilizing a variety of nanofabrication techniques and crystal growth methods. [1,5,6,13±20] However, it is still a challenge to synthesize an aligned and well-distributed single-crystal nanowire array. Electrochemical synthesis using a template is one of the most efficient methods for the growth of nanowires because the growth occurs almost exclusively in the direction normal to the substrate surface. [20] In addition, anodic aluminum oxide possesses uniform and nearly parallel porous structures; hence they have been used as an ideal template to produce cylindrical nanowires with a narrow diameter distribution. As CdS is one of the most important II±VI group semiconductors, having vital applications in solar cells and optoelectronic and electronic devices, the AC electrodeposition of CdS nanowires in porous anodic aluminum oxide (AAO) templates has been investigated.[21±23]However, structural studies have demonstrated that large numbers of stacking faults and twinned segments are present in these nanowires. [23] Recently, an aligned CdS singlecrystal nanowire array has been produced using DC electrolysis in AAO templates from a dimethylsulfoxide (DMSO) solution containing cadmium chloride and elemental sulfur.[24] Here we report a new electrochemical process to prepare CdS single-crystal nanowires using electrochemically induced deposition [25] in the pores of an AAO template from an acidic chemical bath containing cadmium chloride and thioacetamide (TAA). The details of the growth of the AAO templates, the deposition of the CdS, and the characterization of the nanowires can be found in the Experimental section. Figure 1a shows a typical transmission electron microscopy (TEM) image of CdS nanowires prepared by electrochemically induced deposition in the AAO template with pore diameters of about 90 nm. It can be seen that the diameter of the nanowires is about 90 nm, which corresponds to the diameter of the pores of the template used. The lengths of the nanowires range from 3 to 5 mm after deposition for 8 h. Figure 1b shows a TEM image of the nanowires deposited in the template with pore diameters of about 20 nm; the uniform diameters of about 20 nm and smooth surfaces are clearly visible. After deposition for 8 h, the length of the nanowire is up to 10 mm, which is 2±3 times as long as the nanowires deposited in a template with pore diameters of 90 nm under the same deposition conditions. This experimental result indicates that the growth rate of the nanowire increases with decreasing pore size of the AAO template.The chemical composition of the nanowires was determined using X-ray energy dispersion analysis (EDAX) and Raman spectroscopy. The EDAX spectrum shown in Figure 2a reveals that the nano...

Transition‐metal phosphides have flourished as promising candidates for oxygen evolution reaction (OER) electrocatalysts. Herein, it is demonstrated that the electrocatalytic OER performance of CoP can be greatly improved by constructing a hybrid CoP/TiOx heterostructure. The CoP/TiOx heterostructure is fabricated using metal–organic framework nanocrystals as templates, which leads to unique hollow structures and uniformly distributed CoP nanoparticles on TiOx. The strong interactions between CoP and TiOx in the CoP/TiOx heterostructure and the conductive nature of TiOx with Ti3+ sites endow the CoP–TiOx hybrid material with high OER activity comparable to the state‐of‐the‐art IrO2 or RuO2 OER electrocatalysts. In combination with theoretical calculations, this work reveals that the formation of CoP/TiOx heterostructure can generate a pathway for facile electron transport and optimize the water adsorption energy, thus promoting the OER electrocatalysis.

Co-assembly of chromophore guests with host matrices can afford materials which have photofunctionalities different from those of individual components. Compared with clay and zeolite materials, the use of metal–organic frameworks (MOFs) as a host structure for fabricating luminescent host–guest materials is still at an early stage. Herein, we report the incorporation of a laser dye, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), into stilbene-based and naphthalene-based MOF systems. The resulting materials exhibit blue/red two-color emission, and the intensity ratio of blue to red fluorescence varies in different planes within the MOF crystal as detected by 3D confocal fluorescence microscopy. The observed changes in ratiometric fluorescence suggest the occurrence of energy transfer from MOF host to DCM molecules, which can be further confirmed by periodic density functional theoretical (DFT) calculations. Moreover, selective changes in luminescence behavior are observed on treating the guest@MOF samples with volatile organic compounds (methanol, acetone and toluene), indicating that these host–guest systems have potential applications as fluorescence sensors. It can be expected that by rational selection of MOF hosts and guest chromophores with suitable emissive colors and energy levels, a wide variety of multi-color luminescent and energy-transfer systems can readily be prepared in a similar manner.

Hydrogen generation from water splitting could be an alternative way to meet increasing energy demands while also balancing the impact of energy being supplied by fossil-based fuels. The efficacy of water splitting strongly depends on the performance of electrocatalysts. Herein, we report a unique space-confined earth-abundant electrocatalyst having the bifunctionality of simultaneous hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), leading to high-efficiency water splitting. Outperforming Pt/C or RuO catalysts, this mesoscopic, space-confined, bifunctional configuration is constructed from a monolithic zeolitic imidazolate framework@layered double hydroxide (ZIF@LDH) precursor on Ni foam. Such a confinement leads to a high dispersion of ultrafine CoO nanoparticles within the N-doped carbon matrix by temperature-dependent calcination of the ZIF@LDH. We demonstrate that the OER has an overpotential of 318 mV at a current density of 10 mA cm, while that of HER is -106 mV @ -10 mA cm. The voltage applied to a two-electrode cell for overall water splitting is 1.59 V to achieve a stable current density of 10 mA cm while using the monolithic catalyst as both the anode and the cathode. It is anticipated that our space-confined method, which focuses on earth-abundant elements with structural integrity, may provide a novel and economically sound strategy for practical energy conversion applications.

No abstract

Semiconductor photocatalysts have recently received growing attention, but still meet the challenges of a weak separation ability of photogenerated electrons and holes, which leads to energy loss. In this work, we utilize ultralonglived triplet excitons to promote the separation of electronhole pairs and to realize the efficient transformation from excitons to carriers. Room temperature phosphorescent (RTP) carbon dots (CDs) were selected as a model system, which were highly dispersed onto g-C 3 N 4 and exhibited largely enhanced photocatalytic and electrochemical activities compared with those of typical fluorescent CD systems. Both experimental and density functional theory calculations show that the ultralong-lived triplet excitons from RTP CD@g-C 3 N 4 serve as an "energy sustained-release capsule" and thus effectively regulate the recombination of excitons and boost the intrinsic photocatalytic performances (including water splitting and dye degradation). Therefore, this work provides a new design strategy to use ultralong-lived triplet excitons as high-efficiency photocatalysts.