Scale-up synthesis of high-quality solid-state-processed CsCuX (X = Cl, Br, I) perovskite nanocrystal materials toward near-ultraviolet flexible electronic properties.

High-quality CsCu2X3 and Cs3Cu2X5 (X = Cl, Br, I) nanocrystals (NCs) exhibit excellent optoelectronic, physical, and chemical properties for detection of UV radiation due to large carrier mobility and lifetime, and heavy atoms. The nanocrystal materials can be prepared via a low-cost and simple solid-state synthesis. However, poor reproducibility and complex synthesis methods of obtaining perovskite NC thin films represent a drawback for the fabrication of the commercial photoelectric device. To address these issues, we develop highly stable CsCu2X3 and Cs3Cu2X5 NC materials using a facile solid-state reaction method for the scale-up production of halogen lead-free perovskites. We suggest a distinctive way to design a series of nanocrystalline perovskites using short-term synthesis and study the mechanism of perovskite formation using thermal solid-state synthesis. These all-inorganic and lead-free CsCu2X3 and Cs3Cu2X5 exhibit large photoluminescence quantum yields (PLQYs) up to 95.2%. Moreover, flexible paper photodetectors based on this series of lead-free perovskites show strong photoselectivity and bending stability at 254 nm, 365 nm, and 405 nm wavelengths. High-quality responses with a responsivity of 1.1 × 10-3 A W-1 and detectivity of 2.71 × 109 jones under UV illumination (10 µW cm-2) at a bias voltage of 5 mV are demonstrated. These results open prospects for designing photodetectors, LEDs, and other photosensitive devices.

Ultrathin single-crystal PtSe2 nanosheets for high-efficiency O2 electroreduction to H2O2.

Electrochemical synthesis of H2O2via a two-electron oxygen reduction reaction (2e- ORR) has emerged as a promising alternative to the anthraquinone process. However, the strong competition from the 4e- pathway severely limits its activity and selectivity, especially for Pt-based catalysts. Herein, ultrathin single-crystal PtSe2 nanosheets were successfully prepared via an in situ selenization process using commercial Pt/C as a precursor, demonstrating an exclusive 2e- ORR pathway compared to the 4e- pathway of commercial Pt/C, delivering a high H2O2 selectivity over a wide pH range (>80%, up to 94.1%). Furthermore, in situ infrared spectroscopy results revealed Pt as an active center, accompanied by the key intermediate OOH* adsorption and HOOH formation.

Near-UV Phototransistors Based on an All-Inorganic Lead-Free Cs3Cu2I5/CuTCNQ Hierarchical Heterostructure.

With the rapid advances in metal halide perovskite optoelectronics, eliminating toxic lead from perovskites has been an urgent demand. However, state-of-the-art lead-free perovskite photodetectors are still challenged with issues of low photoresponse, poor stability, etc. Here, all-inorganic lead-free perovskite (Cs3Cu2I5) single crystals that possess good stability under air exposure are synthesized via a facile solid reaction method. Meanwhile, a higher photoluminescence quantum yield of 95.2% and a prolonged carrier lifetime of 1.127 µs are obtained by further optimizing the synthesis. Benefiting from the polyporous surface and hollow structure of Cu-7,7,8,8-tetracyanoquinodimethane (CuTCNQ) microtubes, more Cs3Cu2I5 nanocrystals can adhere on the innershell and outershell of CuTCNQ-15 microtubes. This unique structure contributes to the improved efficiency of utilizing incident light and promotes charge carrier generation and transportation. As a result, the hierarchical CuTCNQ/Cs3Cu2I5 (hollow microtube/nanocrystal) heterostructure phototransistor exhibits a high responsivity of 88.36 A W-1 and a large detectivity of 1.66 × 1012 Jones. The proposed lead-free perovskites and mixed-dimensional heterojunctions are promising for sensitive light detection.

Electrocatalytic two-electron oxygen reduction over nitrogen doped hollow carbon nanospheres.

The two-electron oxygen reduction reaction (2e- ORR) has become a hopeful alternative for production of hydrogen peroxide (H2O2), but its practical feasibility is hindered by the lack of efficient electrocatalysts to achieve high activity and selectivity. Herein, we successfully synthesized outstanding nitrogen doped hollow carbon nanospheres (NHCSs) for electrochemical production of H2O2. In 0.1 M KOH, NHCSs exhibit superior and sustained catalytic activity for the 2e- ORR with an unordinary selectivity of 96.6%. Impressively, such NHCSs manifest an ultrahigh H2O2 yield rate of 7.32 mol gcat.-1 h-1 and a high faradaic efficiency of 96.7% at 0.5 V in an H-cell system. Density functional theory calculations were performed to further reveal the catalytic mechanism involved.

Enhanced electrocatalytic performance of TiO2 nanoparticles by Pd doping toward ammonia synthesis under ambient conditions.

The traditional Haber-Bosch process in industry to produce NH3 leads to excessive CO2 emissions and a large amount of energy consumption. Ambient electrochemical N2 reduction is emerging as a green and sustainable alternative method to convert N2 to NH3, but is in sore need of efficient and stable electrocatalysts. Herein, we propose using Pd-doped TiO2 nanoparticles as a high-efficiency electrocatalyst to synthesize NH3 under ambient conditions. The Pd-TiO2 catalyst delivers a large NH3 yield (17.4 µg h-1 mgcat.-1) and a high faradaic efficiency (12.7%) at -0.50 V versus reversible hydrogen electrode in a neutral electrolyte, outperforming most Pd- and Ti-based electrocatalysts recently reported for N2 reduction. Most importantly, it also demonstrates extraordinary long-term electrochemical stability.

N-doped carbon nanotubes supported CoSe2 nanoparticles: A highly efficient and stable catalyst for H2O2 electrosynthesis in acidic media.

Electrocatalytic oxygen reduction reaction (ORR) provides an attractive alternative to anthraquinone process for H2O2 synthesis. Rational design of earth-abundant electrocatalysts for H2O2 synthesis via a two-electron ORR process in acids is attractive but still very challenging. In this work, we report that nitrogen-doped carbon nanotubes as a multi-functional support for CoSe2 nanoparticles not only keep CoSe2 nanoparticles well dispersed but alter the crystal structure, which in turn improves the overall catalytic behaviors and thereby renders high O2-to-H2O2 conversion efficiency. In 0.1 M HClO4, such CoSe2@NCNTs hybrid delivers a high H2O2 selectivity of 93.2% and a large H2O2 yield rate of 172 ppm·h-1 with excellent durability up to 24 h. Moreover, CoSe2@NCNTs performs effectively for organic dye degradation via electro-Fenton process. Electronic Supplementary Material: Supplementary material (SEM images, EDX mapping images, XPS spectrum, XRD patterns, RRDE voltammogram, Tafel plots, cyclic voltammograms, UV-Vis spectra, and Tables S1) is available in the online version of this article at 10.1007/s12274-021-3474-0.

Ti2O3 Nanoparticles with Ti3+ Sites toward Efficient NH3 Electrosynthesis under Ambient Conditions.

Electrocatalytic nitrogen reduction reaction (NRR) enabled by introducing Ti3+ defect sites into TiO2 through a doping strategy has recently attracted widespread attention. However, the amount of Ti3+ ions is limited due to the low concentration of dopants. Herein, we propose Ti2O3 nanoparticles as a pure Ti3+ system that performs efficiently toward NH3 electrosynthesis under ambient conditions. This work has suggested that Ti3+ ions, as the main catalytically active sites, significantly increase the NRR activity. In an acidic electrolyte, Ti2O3 achieves extraordinary performance with a high NH3 yield and a Faradaic efficiency of 26.01 µg h-1 mg-1 cat. and 9.16%, respectively, which are superior to most titanium-based NRR catalysts recently reported. Significantly, it also demonstrates a stable NH3 yield in five consecutive cycles. Theoretical calculations uncovered that the enhanced electrocatalytic activity of Ti2O3 originated from Ti3+ active sites and significantly lowered the overpotential of the potential-determining step.

Enhanced Electrochemical H2O2 Production via Two-Electron Oxygen Reduction Enabled by Surface-Derived Amorphous Oxygen-Deficient TiO2-x.

The electrochemical oxygen reduction reaction (ORR) is regarded as an attractive alternative to the anthraquinone process for sustainable and on-site hydrogen peroxide (H2O2) production. It is however hindered by low selectivity due to strong competition from the four-electron ORR and needs efficient catalysts to drive the 2e- ORR. Here, an acid oxidation strategy is proposed as an effective strategy to boost the 2e- ORR activity of metallic TiC via in-site generation of a surface amorphous oxygen-deficient TiO2-x layer. The resulting a-TiO2-x/TiC exhibits a low overpotential and high H2O2 selectivity (94.1% at 0.5 V vs reversible hydrogen electrode (RHE)), and it also demonstrates robust stability with a remarkable productivity of 7.19 mol gcat.-1 h-1 at 0.30 V vs RHE. The electrocatalytic mechanism of a-TiO2-x/TiC is further revealed by density functional theory calculations.

Honeycomb Carbon Nanofibers: A Superhydrophilic O2 -Entrapping Electrocatalyst Enables Ultrahigh Mass Activity for the Two-Electron Oxygen Reduction Reaction.

Electrocatalytic two-electron oxygen reduction has emerged as a promising alternative to the energy- and waste-intensive anthraquinone process for distributed H2 O2 production. This process, however, suffers from strong competition from the four-electron pathway leading to low H2 O2 selectivity. Herein, we report using a superhydrophilic O2 -entrapping electrocatalyst to enable superb two-electron oxygen reduction electrocatalysis. The honeycomb carbon nanofibers (HCNFs) are robust and capable of achieving a high H2 O2 selectivity of 97.3 %, much higher than that of its solid carbon nanofiber counterpart. Impressively, this catalyst achieves an ultrahigh mass activity of up to 220 A g-1 , surpassing all other catalysts for two-electron oxygen reduction reaction. The superhydrophilic porous carbon skeleton with rich oxygenated functional groups facilitates efficient electron transfer and better wetting of the catalyst by the electrolyte, and the interconnected cavities allow for more effective entrapping of the gas bubbles. The catalytic mechanism is further revealed by in situ Raman analysis and density functional theory calculations.

Biomass based iron and nitrogen co-doped 3D porous carbon as an efficient oxygen reduction catalyst.

An iron and nitrogen co-doped 3D porous carbon catalyst with high performance for oxygen reduction reaction (ORR) is produced by pyrolysis. The precursor is a mixture of red date, ferrous (Ⅱ) acetate, and graphitic carbon nitride (g-C3N4). g-C3N4 is the nitrogen source and also the sacrificial template, which plays a key role in the formation of a porous nitrogen rich carbon structure with high surface area. It is found that active sites and catalytic performance of synthetic materials are significantly influenced by the Fe content. In comparison with commercial Pt/C catalyst, the synthetic Fe-N-C with optimized composition exhibits comparable ORR activity and superior methanol tolerance. This work provides a feasible approach to develop cost-effective and highly efficient non-precious metal electrochemical catalysts for oxygen reduction.