Gas-Phase Cation Exchange toward Porous Single-Crystal CoO Nanorods for Catalytic Hydrogen Production

As a promising catalyst for hydrogen evolution, cobaltous oxide (CoO) with good crystallinity and large surface is highly anticipated to enhance the catalytic performance. Here we present a facile route for the fabrication of porous single-crystal (PS) CoO nanorods (NRs) by gas phase cation exchange of ZnO NRs. The single-crystal structure of ZnO template is well-preserved after the cation exchange, and numerous nanopores form in the PS CoO NRs because of the volume shrinkage. As-synthesized PS CoO NRs exhibit outstanding catalytic activities for NaBH₄ hydrolysis in alkaline solutions, outperforming polycrystalline CoO NRs and even noble metal catalysts

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 (CN̅sd), 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 (CN̅), and the orbitalwise coordination number (CN^α). Especially, the theoretical prediction made by the CN̅sd descriptor is very consistent with experimental results and universal for various TMOs (e.g., MnO_<i>x</i> and RuO₂), enabling the rational design of novel catalysts

Millisecond Laser Ablation of Molybdenum Target in Reactive Gas toward MoS₂ Fullerene-Like Nanoparticles with Thermally Stable Photoresponse

As a promising material for photoelectrical application, MoS₂ has attracted extensive attention on its facile synthesis and unique properties. Herein, we explored a novel strategy of laser ablation to synthesize MoS₂ fullerene-like nanoparticles (FL-NPs) with stable photoresponse under high temperature. Specifically, we employed a millisecond pulsed laser to ablate the molybdenum target in dimethyl trisulfide gas, and as a result, the molybdenum nanodroplets were ejected from the target and interacted with the highly reactive ambient gas to produce MoS₂ FL-NPs. In contrast, the laser ablation in liquid could only produce core–shell nanoparticles. The crucial factors for controlling final nanostructures were found to be laser intensity, cooling rate, and gas reactivity. Finally, the MoS₂ FL-NPs were assembled into a simple photoresponse device which exhibited excellent thermal stability, indicating their great potentialities for high-temperature photoelectrical applications

Double Open-Circuit Voltage of Three-Dimensional ZnO/CdTe Solar Cells by a Balancing Depletion Layer

Three-dimensional (3D) heterojunction solar cells (HSCs) were fabricated by thermal deposition of a compact CdTe layer onto ZnO nanorods (NRs). Although the 3D architecture obviously improves the short-circuit current of HSCs, the open-circuit voltage is rather low, and this problem can be addressed by inserting an intermediate layer between ZnO NRs and the CdTe layer. On the basis of experimental and theoretical analyses, we found that the low open-circuit voltage mainly arose from the incomplete depletion layer and serious recombination of carriers at the CdTe/ZnO interface. The CdS intermediate layer can redistribute the depletion regions and eliminate the interface defects, thus remarkably improving the open-circuit voltage

Top-Down Preparation of Active Cobalt Oxide Catalyst

Cobalt oxide is a cheap catalyst for the oxygen evolution reaction; however, the low activity limits its practical application. Herein we report the preparation of a highly active Co₃O₄ catalyst via a top-down process, namely, laser fragmentation. The fierce laser irradiation generates fine and clean nanoparticles with abundant oxygen vacancies which simultaneously improve the adsorption energy and electrical conduction. As a result, the catalytic performance of the product reaches the top level of cobalt oxide, even outperforming the noble-metal catalyst, RuO₂

Hierarchical, Ultrathin Single-Crystal Nanowires of CdS Conveniently Produced in Laser-Induced Thermal Field

Hierarchical nanowires (HNWs) exhibit unique properties and have wide applications, while often suffering from imperfect structure. Herein, we report a facile strategy toward ultrathin CdS HNWs with monocrystal structure, where a continuous-wave (CW) Nd:YAG laser is employed to irradiate an oleic acid (OA) solution containing precursors and a light absorber. The high heating rate and large temperature gradient generated by the CW laser lead to the rapid formation of tiny zinc-blende CdS nanocrystals which then line up into nanowires with the help of OA molecules. Next, the nanowires experience a phase transformation from zinc-blende to wurtzite structure, and the transformation-induced stress creates terraces on their surface, which promotes the growth of side branches and eventually results in monocrystal HNWs with an ultrathin diameter of 24 nm. The one-step synthesis of HNWs is conducted in air and completes in just 40 s, thus being very simple and rapid. The prepared CdS HNWs display photocatalytic performance superior to their nanoparticle counterparts, thus showing promise for catalytic applications in the future

Tuning Band Structure of Cadmium Chalcogenide Nanoflake Arrays via Alloying for Efficient Photoelectrochemical Hydrogen Evolution

Owing to their high extinction coefficient and moderate band gap, cadmium chalcogenides are known as common semiconductors for photoelectric conversion. Nevertheless, no ideal cadmium chalcogenide with proper band structure is available yet for photoelectrochemical hydrogen evolution. In this work, we modified the band structure of CdTe via alloying with Se to achieve a ternary compound (CdSe_0.8Te_0.2) with n-type conduction, a narrower band gap, and a more negative band position compared to those of CdSe and CdTe. This novel material exhibits strong light absorption over a wider spectrum range and generates more vigorous electrons for hydrogen reduction. As a result, a photoelectrode based on nanoflake arrays of the new material could achieve a photocurrent density 2 times that of its CdSe counterpart, outperforming similar materials previously reported in the literature. Moreover, the quick transfer of holes achieved in the novel material was found to depress photocorrosion processes, which led to improved long-term working stability

Gain High-Quality Colloidal Quantum Dots Directly from Natural Minerals

Green and simple synthesis of high-quality colloidal quantum dots (CQDs) is of great importance and highly anticipated yet not fully implemented. Herein, we achieve the direct conversion of natural minerals to highly uniform, crystalline lead sulfide CQDs based on laser irradiation in liquid. The trivial fragmentation of mineral particles by an intense nanosecond laser was found to create a localized high degree of monomer supersaturation in oleic acid, initiating the LaMer growth of uniform CQDs. The photoconductive device made of these CQDs exhibits a competitive temporal response of photocurrent with those highly sensitive photodetectors based on PbS CQDs reported in the literature. Our synthesis strategy paves the way for the most environmentally friendly and convenient mass production of high-quality uniform CQDs

Copper Nanoparticles with Abundant Defects as a pH-Universal Catalyst for Hydrogen Evolution Reaction

The development of low-cost, high-activity, and pH universal catalysts is essential in hydrogen evolution reaction (HER) via industrial electrolysis of water. Here, we report the rapid and scalable preparation of defect-rich copper catalysts as electrocatalysts for all-pH HER by electric discharge in liquid (EDL) technology. The defects upshift the d-band center of copper, improve water dissociation and hydrogen adsorption, and ultimately improve the intrinsic catalytic activity. Thus, the overpotentials of Cu catalysts reach 180 mV in 0.5 M H2SO4, 269 mV in 1 M PBS, and 152 mV at 10 m A cm–2 in 1 M KOH. In addition, the Cu catalysts also exhibit lower overpotentials at high current density (1 A cm–2), superior to commercial Pt/C in neutral and alkaline solutions. Our work demonstrates that the EDL is a powerful technique for preparing metallic catalyst, and introducing defects into copper nanoparticles provides a versatile and friendly strategy for improving intrinsic catalytic performance

Zinc-Blende CdS Nanocubes with Coordinated Facets for Photocatalytic Water Splitting

To develop catalysts that are efficient and stable under aggressive catalytic conditions, we detail a synthetic approach to producing zinc-blende cadmium sulfide (CdS) nanocubes (NCs), a metastable CdS polymorph that is terminated by coordinated facets. The hydrogen generation activity of these CdS NCs (∼11.6 mmol g^–1 h^–1) was nearly 4 times higher than that of wurtzite CdS nanoparticles (∼2.7 mmol g^–1 h^–1) and 2 times higher than that of irregularly shaped zinc-blende CdS nanoparticles (∼5.9 mmol g^–1 h^–1). Furthermore, the NCs also exhibited much improved long-term performance compared to the performance of these controlled photocatalysts. Finally, the density functional theory calculation and site-specific Au photodeposition demonstrate that the improved activity and stability can be attributed to the enhanced charge-flow steering and coordinated facet terminations