Chunming Niu

Highly Efficient Flexible Perovskite Solar Cells Using Solution-Derived NiOx Hole Contacts

A solution-derived NiOx film was employed as the hole contact of a flexible organic-inorganic hybrid perovskite solar cell. The NiOx film, which was spin coated from presynthesized NiOx nanoparticles solution, can extract holes and block electrons efficiently, without any other post-treatments. An optimal power conversion efficiency (PCE) of 16.47% was demonstrated in the NiOx-based perovskite solar cell on an ITO-glass substrate, which is much higher than that of the perovskite solar cells using high temperature-derived NiOx film contacts. The low-temperature deposition process made the NiOx films suitable for flexible devices. NiOx-based flexible perovskite solar cells were fabricated on ITO-PEN substrates, and a preliminary PCE of 13.43% was achieved.

In Situ Synthesis of Carbon Nanotube Hybrids with Alternate MoC and MoS2 to Enhance the Electrochemical Activities of MoS2

Molybdenum disulfides and carbides are effective catalysts for hydrogenation and hydridesulfurization, where MoS2 nanostructures are also highly promising materials for lithium ion batteries. High surface-to-volume ratio and strong interactions with conducting networks are crucial factors for their activities. A new hybrid structure of multiwalled carbon nanotube (MWCNT) with alternate MoC nanoparticles and MoS2 nanosheets (MoS2 + MoC-MWCNT) has been synthesized by controlled carburization of core-shell MoS2-MWCNT hybrid nanotubes and demonstrated by HRTEM, FFT, XRD, and Raman scattering. The MoS2 nanosheets (∼10 nm) remain tightly connected to MWCNT surfaces with {001} planes in parallel to MWCNT walls and the highly crystallized α-MoC particles (∼10 nm) are adhered to MWCNTs at angles of 60-80° between {111} planes and MWCNT walls. The electrochemical performances of the hybrid structures have been demonstrated as anodes for lithium ion batteries to be significantly increased by breaking MoS2 nanotubes into nanosheets (patches) on MWCNT surfaces, especially at high current rates. The specific capacities of MoS2 + MoC-MWCNT sample with ∼23% MoS2 have been demonstrated to be higher than those of MoS2-MWCNTs containing ∼70% MoS2.

Highly Efficient Photocatalyst Based on a CdS Quantum Dots/ZnO Nanosheets 0D/2D Heterojunction for Hydrogen Evolution from Water Splitting

A novel CdS/ZnO heterojunction constructed of zero-dimensional (0D) CdS quantum dots (QDs) and two-dimensional (2D) ZnO nanosheets (NSs) was rationally designed for the first time. The 2D ZnO NSs were assembled into ZnO microflowers (MFs) via an ultrasonic-assisted hydrothermal procedure (100 °C, 12 h) in the presence of a NaOH solution (0.06 M), and CdS QDs were deposited on both sides of every ZnO NS in situ by using the successive ionic-layer absorption and reaction method. It was found that the ultrasonic treatment played an important role in the generation of ZnO NSs, while NaOH was responsible to the assembly of a flower-like structure. The obtained CdS/ZnO 0D/2D heterostructures exhibited remarkably enhanced photocatalytic activity for hydrogen evolution from water splitting in comparison with other CdS/ZnO heterostructures with different dimensional combinations such as 2D/2D, 0D/three-dimensional (3D), and 3D/0D. Among them, CdS/ZnO-12 (12 deposition cycles of CdS QDs) exhibited the highest hydrogen evolution rate of 22.12 mmol/g/h, which was 13 and 138 times higher than those of single CdS (1.68 mmol/g/h) and ZnO (0.16 mmol/g/h), respectively. The enhanced photocatalytic activity can be attributed to several positive factors, such as the formation of a Z-scheme photocatalytic system, the tiny size effect of 0D CdS QDs and 2D ZnO NSs, and the intimate contact between CdS QDs and ZnO NSs. The formation of a Z-scheme photocatalytic system remarkably promoted the separation and migration of photogenerated electron-hole pairs. The tiny size effect effectively decreased the recombination probability of electrons and holes. The intimate contact between the two semiconductors efficiently reduced the migration resistance of photogenerated carriers. Furthermore, CdS/ZnO-12 also presented excellent stability for photocatalytic hydrogen evolution without any decay within five cycles in 25 h.

Ternary Sn–Ti–O Based Nanostructures as Anodes for Lithium Ion Batteries

SnO(x) (x = 0, 1, 2) and TiO(2) are widely considered to be potential anode candidates for next generation lithium ion batteries. In terms of the lithium storage mechanisms, TiO(2) anodes operate on the base of the Li ion intercalation-deintercalation, and they typically display long cycling life and high rate capability, arising from the negligible cell volume change during the discharge-charge process, while their performance is limited by low specific capacity and low electronic conductivity. SnO(x) anodes rely on the alloying-dealloying reaction with Li ions, and typically exhibit large specific capacity but poor cycling performance, originating from the extremely large volume change and thus the resultant pulverization problems. Making use of their advantages and minimizing the disadvantages, numerous strategies have been developed in the recent years to design composite nanostructured Sn-Ti-O ternary systems. This Review aims to provide rational understanding on their design and the improvement of electrochemical properties of such systems, including SnO(x) -TiO(2) nanocomposites mixing at nanoscale and nanostructured Sn(x) Ti(1-x) O(2) solid solutions doped at the atomic level, as well as their combinations with carbon-based nanomaterials.

Honeycomb-like carbon nanoflakes as a host for SnO2 nanoparticles allowing enhanced lithium storage performance

While possessing potential advantages as electrodes for lithium-ion batteries, SnO2@carbon composites have been suffering from one common drawback – aggregation of Sn particles during the repeated alloying–dealloying cycles and the resulting pulverization issue. We combat this issue through the fabrication of honeycomb-like SnO2@carbon nanoflakes (SnO2@CNFs) that are able to confine SnO2 nanoparticles within well-separated carbon cavities, so that the Li–Sn alloying–dealloying reaction occurs in the independent microreactors thus avoiding aggregation of Sn metal particles formed. The SnO2 particle size, loading amount and the coverage density are controlled by adjusting the weight ratio between the tin precursor and the CNF. Transmission electron microscopy confirms that the highly graphitic honeycomb-like CNF matrix efficiently buffers and accommodates volume changes of the Li–Sn alloy. Used as anode materials for lithium-ion batteries, the SnO2@CNFs with 66.0 wt% SnO2 display the highest lithium storage capacity, delivering a discharge capacity of 940 mA h g−1 after 150 cycles at 200 mA g−1. For the long-term and high-rate applications, the SnO2@CNFs with 41.5 wt% SnO2 show the best electrochemical performance, delivering a discharge capacity of 400 mA h g−1 at 1 A g−1 after 500 cycles.

A Hierarchical Phosphorus Nanobarbed Nanowire Hybrid: Its Structure and Electrochemical Properties

Nanostructured phosphorus-carbon composites are promising materials for Li-ion and Na-ion battery anodes. A hierarchical phosphorus hybrid, SiC@graphene@P, has been synthesized by the chemical vapor deposition of phosphorus on the surfaces of barbed nanowires, where the barbs are vertically grown graphene nanosheets and the cores are SiC nanowires. A temperature-gradient vaporization-condensation method has been used to remove the unhybridized phosphorus particles formed by homogeneous nucleation. The vertically grown barb shaped graphene nanosheets and a high concentration of edge carbon atoms induced a fibrous red phosphorus (f-RP) growth with its {001} planes in parallel to {002} planes of nanographene sheets and led to a strong interpenetrated interface interaction between phosphorus and the surfaces of graphene nanosheets. This hybridization has been demonstrated to significantly enhance the electrochemical performances of phosphorus.

Rationally Designed Porous MnOx–FeOx Nanoneedles for Low-Temperature Selective Catalytic Reduction of NOx by NH3

In this work, a novel porous nanoneedlelike MnOx-FeOx catalyst (MnOx-FeOx nanoneedles) was developed for the first time by rationally heat-treating metal-organic frameworks including MnFe precursor synthesized by hydrothermal method. A counterpart catalyst (MnOx-FeOx nanoparticles) without porous nanoneedle structure was also prepared by a similar procedure for comparison. The two catalysts were systematically characterized by scanning and transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, ammonia temperature-programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFT), and their catalytic activities were evaluated by selective catalytic reduction (SCR) of NOx by NH3. The results showed that the rationally designed MnOx-FeOx nanoneedles presented outstanding low-temperature NH3-SCR activity (100% NOx conversion in a wide temperature window from 120 to 240 °C), high selectivity for N2 (nearly 100% N2 selectivity from 60 to 240 °C), and excellent water resistance and stability in comparison with the counterpart MnOx-FeOx nanoparticles. The reasons can be attributed not only to the unique porous nanoneedle structure but also to the uniform distribution of MnOx and FeOx. More importantly, the desired Mn4+/Mnn+ and Oα/(Oα + Oβ) ratios, as well as rich redox sites and abundant strong acid sites on the surface of the porous MnOx-FeOx nanoneedles, also contribute to these excellent performances. In situ DRIFT suggested that the NH3-SCR of NO over MnOx-FeOx nanoneedles follows both Eley-Rideal and Langmuir-Hinshelwood mechanisms.

Adsorption and Deposition of Li2O2 on TiC{111} Surface.

A recent experimental study from Bruces group demonstrated the feasibility of TiC as a cathode material for Li air battery. We investigate Li2O2 adsorption and deposition on TiC{111} surface by periodic density functional theory calculation. The results showed that, upon interaction with Ti-terminated TiC{111} surface, Li2O2 clusters reassembled into a saturated periodic two atomic layer coating in which each O atom was bonded to three Ti atoms to form a O layer equivalent to the layer formed by O2 surface oxidation, and the Li atoms sat on the top. The atomic arrangement of O and Li layers is the same as that of O2Li1 layers normal to ⟨0001⟩ direction in Li2O2 crystal structure. Interface models constructed based on this lead showed that the growth of Li2O2 can be continued through a surface conduction mechanism to form Li2O2 coating with lattice parameters almost identical to those of the standard Li2O2 unit cell. The results support the experimental discovery from Bruces group.

Nanocarved MoS2-MoO2 Hybrids Fabricated Using in Situ Grown MoS2 as Nanomasks

The morphology and hybridization of nanostructures are crucial to achieve properties for various applications. An in situ grown three-dimensional (3D) MoS2 nanomask has been adopted to control the morphology and hybridization of molybdenum compounds. The in situ generated MoS2 mask on MoO3 nanobelt surfaces allowed us to fabricate a 3D c-MoO2@MoS2 hybrid nanostructure, in which c-MoO2 is a carved MoO2 nanobelt with a well-distributed hole pattern. The nanomasks have been controlled by adjusting the alignments of MoS2. The exposed MoO2 surfaces of c-MoO2@MoS2 were further sulfurated to give cw-MoO2@MoS2, in which all surfaces of MoO2 are wrapped by a few layers of MoS2. The structure synergistically enhanced the electrochemical performances of MoO2 and MoS2, especially at high current rates. Reversible capacities of 1418 and 295 mAh/g after 115 and 300 cycles still remained for the cw-MoO2@MoS2 anodes at current rates of 1 and 10 A/g, respectively.

Fabrication of g-C3N4/Au/C-TiO2 hollow structures as visible-light-driven Z-scheme photocatalysts with enhanced photocatalytic H2 evolution

The Z‐scheme photocatalytic system for water splitting based on semiconductors has exhibited great potential for H2 fuel production from renewable resources. In this work, we constructed g‐C3N4/Au/C‐TiO2 hollow spheres as an all‐solid‐state Z‐scheme photocatalytic system with Au nanoparticles as the electron mediator. The as‐synthesized g‐C3N4/Au/C‐TiO2 photocatalyst showed a remarkably enhanced photocatalytic H2 evolution rate under visible‐light irradiation (λ>420 nm), which was 86 and 42 times higher than those of pure C‐TiO2 and g‐C3N4, respectively. The enhancement of photocatalytic performance can be mainly attributed to the intentionally designed Z‐scheme system, which not only promoted the efficient transfer and separation of photogenerated electron–hole pairs, but also retained the strong redox ability of the charge carriers. In addition, the Z‐scheme system also achieved high visible‐light absorption and utilization owing to the surface plasmon resonance (SPR) effect of Au nanoparticles and hollow structures of C‐TiO2. All the factors synergistically promote the photocatalytic activity of the g‐C3N4/Au/C‐TiO2 hollow nanospheres, providing a promising method for the rational design of highly efficient visible‐light‐driven photocatalysts.