Cunku Dong

Photochemical Synthesis of Ultrafine Cubic Boron Nitride Nanoparticles under Ambient Conditions

Cubic boron nitride (c-BN) is a super-hard material whose hardness increases dramatically with decreasing size. However, c-BN nanoparticles (NPs) with sizes less than 10 nm have never been obtained. Herein we report a simple strategy towards the synthesis of ultrafine c-BN NPs with an average size of 3.5 nm. The method, under ambient conditions, exploits a laser-induced photochemical effect and employs dioxane solution of ammonia borane (AB) as a liquid target. Meanwhile, total dehydrogenation of AB is realized by laser irradiation. Therefore, this approach shows great potential for the preparation of super-hard NPs as well as controllable dehydrogenation.

A stable inverse opal structure of cadmium chalcogenide for efficient water splitting

Cadmium chalcogenide nanocrystals (CCNCs) are regarded as promising materials for photoelectrochemical (PEC) water splitting. However, the relatively low PEC response and poor stability restrict their practical applications. In the present work, we demonstrate that a well-designed inverse opal structure (IOS) composed of CCNCs can achieve an unprecedentedly high photocurrent and hydrogen production rate. In particular, the IOS electrode remains stable during 3 h of continuous illumination, which is even superior to those photoanodes with surface passivation and/or co-catalysts. Quantitative investigation reveals that the IOS possesses high charge-separation efficiency and light-absorption capacity, which eventually result in excellent PEC performance.

Laser synthesis of clean mesocrystal of cupric oxide for efficient gas sensing

Mesocrystals are known to be unusual materials derived from the self-assembly of nanoparticles. However, their advantages arising from their unique structure have not been fully exploited to date owing to hindrance by a secondary phase. Herein, we employ a pulsed laser to synthesize mesocrystalline cupric oxide (CuO) with pure phase and clean surface. A gas sensor based on a CuO mesocrystal exhibits the highest sensitivity, the fastest response, and the best selectivity ever reported towards ethanol. Our study elucidates the inherent characteristics of mesocrystals and clears doubts regarding their practicability.

Tuning the selectivity and activity of Au catalysts for carbon dioxide electroreduction via grain boundary engineering: a DFT study

Au catalysts possess a high activity to yield gaseous carbon monoxide (CO) at moderate overpotentials for the carbon dioxide CO2 electrochemical reduction reaction (CO2RR). However, tuning selectivity remains a massive challenge towards the production of hydrocarbon species at relatively low potentials. In this study, by means of first principles calculations we propose a promising strategy to tune the selectivity and activity of Au catalysts via grain boundary (GB) engineering. The GB sites on the Au(110) surface are identified to strongly bind *CO so as to compensate for the unsaturated coordination of GB atoms, leading to a high selectivity toward CH3OH; its catalytic performance is comparable to Cu for generating CH4. In addition, GBs on the Au(100) surface are also investigated for comparison, which can greatly promote CO production. Our findings suggest that GB engineering is an effective means to improve the CO2RR performance of a given catalyst, which will motivate reasonable design and synthesis of novel electrocatalysts for CO2 reduction to produce hydrocarbon species.

Localized Defects on Copper Sulfide Surface for Enhanced Plasmon Resonance and Water Splitting

Surficial defects in semiconductor can induce high density of carriers and cause localized surface plasmon resonance which is prone to light harvesting and energy conversion, while internal defects may cause serious recombination of electrons and holes. Thus, it is significant to precisely control the distribution of defects, although there are few successful examples. Herein, an effective strategy to confine abundant defects within the surface layer of Cu1.94 S nanoflake arrays (NFAs) is reported, leaving a perfect internal structure. The Cu1.94 S NFAs are then applied in photoelectrochemical (PEC) water splitting. As expected, the surficial defects give rise to strong LSPR effect and quick charge separation near the surface; meanwhile, they provide active sites for catalyzing hydrogen evolution. As a result, the NFAs achieve the top PEC properties ever reported for Cux S-based photocathodes.

CdO nanoflake arrays on ZnO nanorod arrays for efficient detection of diethyl ether

We report the template synthesis and gas detection of CdO porous nanoflake arrays (P-NFAs) on ZnO nanorod arrays. The P-NFAs possesses a large surface-to-volume ratio, high-energy exposed surface, unimpeded channels for gas flow, and hierarchical holes. As a result, the device exhibits excellent sensing properties upon exposure to diethyl ether.

Cuprous ions embedded in ceria lattice for selective and stable electrochemical reduction of carbon dioxide to ethylene

Electrochemical reduction of carbon dioxide (CO2) shows high potential to remedy greenhouse gas emission and over-dependence on fossil fuels; nevertheless, it remains a big challenge to selectively reduce CO2 to a hydrocarbon fuel with high energy density. Here we report a novel electrocatalyst, ceria doped with cuprous ions, which can produce ethylene selectively and stably; specifically, the faradaic efficiency for ethylene reaches 47.6% at −1.1 V vs. RHE, and the high current density is maintained steadily for several hours. The active sites are experimentally identified as cuprous ions which are stabilized by ceria and responsible for long term durability. Furthermore, theoretical calculations indicate that cuprous ions favor C–C coupling and thus have high selectivity to ethylene. Our work demonstrates that doping an inert substrate with active ions is an effective way to improve the selectivity and stability of catalysis, which promises high yield of hydrocarbon fuels.

Laser-Prepared CuZn Alloy Catalyst for Selective Electrochemical Reduction of CO2 to Ethylene

Laser ablation in liquid was used to prepare homogeneous copper-zinc alloy catalysts that exhibited excellent selectivity for C2H4 in CO2 electroreduction, with faradaic efficiency values as high as 33.3% at a potential of -1.1 V (vs reversible hydrogen electrode). The high proximity of Cu and Zn atoms on the surface of the catalyst was found to facilitate both stabilization of the CO* intermediate and its transfer from Zn atoms to their Cu neighbors, where further dimerization and protonation occur to give rise to a large amount of ethylene product. The new homogeneous nanocatalyst, along with the mechanism proposed for its performance, may be very helpful for in-depth understanding of processes related to carbon dioxide electroreduction and conversion.

Bond-Energy-Integrated Descriptor for Oxygen Electrocatalysis of Transition Metal Oxides

Unraveling a descriptor of catalytic reactivity is essential for fast screening catalysts for a given reaction. Transition metal (TM) compounds have been widely used for oxygen electrocatalysis. Nevertheless, there is a lack of an exact descriptor to predict their catalytic behavior so far. Herein, we propose that the bond-energy-integrated orbitalwise coordination number ([Formula: see text]), which takes into account both geometrical and electronic structures around the active site, can serve as a simple and accurate descriptor for catalysts consisting of TM oxides (TMOs) as well as avoid excessive computation burden. This descriptor exhibits a strong scaling relation with the activity in oxygen electrocatalysis, with a goodness of fit higher than those of the usual coordination number (cn), the generalized coordination number ([Formula: see text]), and the orbitalwise coordination number (CNα). Especially, the theoretical prediction made by the [Formula: see text] descriptor is very consistent with experimental results and universal for various TMOs (e.g., MnO x and RuO2), enabling the rational design of novel catalysts.

ZnO nanosheets with atomically thin ZnS overlayers for photocatalytic water splitting

Zinc oxide is a cost-efficient and eco-friendly material for solar-to-chemical energy conversion. However, the relatively wide band gap and poor stability restrict its practical applications. Herein, we report on the modification of ZnO nanosheets with a porous atomically thin ZnS overlayer. The as-prepared ZnS/ZnO/ZnS sandwich nanosheets exhibit a reduced band gap (2.72 eV) and yet a slightly elevated conduction band minimum, which remarkably broadens the wavelength range for light absorption and generates electrons with enough reducing capability. At the same time, the newly-prepared sandwich nanosheets possess alternatively exposed ZnS and ZnO surface patches, which attract and accommodate photo-generated holes and electrons, respectively. In addition, the ZnS overlayer catalyzes and accelerates hole-consumption reactions, thus preserving electrons for efficient water splitting. As a result, the ZnS/ZnO/ZnS sandwich nanosheets demonstrate intensive light absorption, fast charge separation, long electron lifetime, and eventually the highest hydrogen production rate reported for oxide catalysts so far. This work proves that passivation with an ultrathin layer is a potent approach for energy-band engineering, and semiconductor sandwich nanostructures are promising for highly efficient water splitting under sunlight.