Electrochemical Activity of Iron Phosphide Nanoparticles in Hydrogen Evolution Reaction

Iron phosphide (FeP) has been recently demonstrated as a very attractive electrocatalyst for the hydrogen evolution reaction (HER). However, the understanding of its properties is far from satisfactory. Herein, we report the HER performance of FeP nanoparticles is enhanced after a stability test due to reduced surface-charge-transfer resistance in the HER process. The synthetic temperature and reactant ratio are important for surface-charge-transfer resistance, the electrochemically active surface area, and HER activity. Hydrogenation apparently improves the HER performance of FeP nanoparticles by reducing the surface-charge-transfer resistance, overpotential, and Tafel slope. Enhanced HER performance is observed after a stability test for both bare and hydrogenated FeP nanoparticles in the HER due to reduced surface-charge-transfer resistance. Thus, this study may enrich our knowledge and understanding to advance HER catalysis for electrochemical hydrogen generation

Three-Dimensional Crystalline/Amorphous Co/Co₃O₄ Core/Shell Nanosheets as Efficient Electrocatalysts for the Hydrogen Evolution Reaction

Earth-abundant, low-cost electrocatalysts with outstanding catalytic activity in the electrochemical hydrogen evolution reaction (HER) are critical in realizing the hydrogen economy to lift our future welfare and civilization. Here we report that excellent HER activity has been achieved with three-dimensional core/shell Co/Co₃O₄ nanosheets composed of a metallic cobalt core and an amorphous cobalt oxide shell. A benchmark HER current density of 10 mA cm^–2 has been achieved at an overpotential of ∼90 mV in 1 M KOH. The excellent activity is enabled with the unique metal/oxide core/shell structure, which allows high electrical conductivity in the core and high catalytic activity on the shell. This finding may open a door to the design and fabrication of earth-abundant, low-cost metal oxide electrocatalysts with satisfactory hydrogen evolution reaction activities

DMSO as a C₁ Source for [2 + 2 + 1] Pyrazole Ring Construction via Metal-Free Annulation with Enaminones and Hydrazines

A cascade reaction between enaminones, hydrazines, and dimethyl sulfoxide (DMSO) for the synthesis of 1,4-disubstituted pyrazoles catalyzed by molecular iodine in the presence of Selectfluor has been realized. DMSO plays a dual role as the C1 source and the reaction medium. In addition, the synthesis of 1,3,4-trisubstituted pyrazoles using aldehydes as alternative C1 building blocks has also been achieved

Converting CoMoO₄ into CoO/MoO_<i>x</i> for Overall Water Splitting by Hydrogenation

Special structures of materials often bring in unprecedented catalytic activities, which are critical in realizing large-scale hydrogen production by electrochemical water splitting. Herein, we report a CoO/MoO_<i>x</i> crystalline/amorphous structure as an effective bifunctional electrocatalyst for water splitting. Converted from CoMoO₄ by hydrogenation, the CoO/MoO_<i>x</i>, featured with crystalline CoO in amorphous MoO_<i>x</i> matrix, displays superior catalytic activities toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). It shows small onset overpotentials of 40 and 230 mV for the HER and OER in 1.0 M KOH, respectively, and overall water splitting starting at 1.53 V with a robust stability. The high catalytic activity of the CoO/MoO_<i>x</i> is benefited from the large defect-rich interface between CoO and MoO_<i>x</i>, along with the amorphous nature of MoO_<i>x</i>. Thus, this study demonstrates the effectiveness of structural manipulation in developing highly active electrocatalysts for overall electrochemical water splitting

Two Different Roles of Metallic Ag on Ag/AgX/BiOX (X = Cl, Br) Visible Light Photocatalysts: Surface Plasmon Resonance and Z-Scheme Bridge

Ag/AgX/BiOX (X = Cl, Br) three-component visible-light-driven (VLD) photocatalysts were synthesized by a low-temperature chemical bath method and characterized by X-ray diffraction patterns, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and UV–vis diffuse reflectance spectra. The Ag/AgX/BiOX composites showed enhanced VLD photocatalytic activity for the degradation of rhodamine B, which was much higher than Ag/AgX and BiOX. The photocatalytic mechanisms were analyzed by active species trapping and superoxide radical quantification experiments. It revealed that metallic Ag played a different role for Ag/AgX/BiOX VLD photocatalysts, surface plasmon resonance for Ag/AgCl/BiOCl, and the Z-scheme bridge for Ag/AgBr/BiOBr

Converting CoMoO₄ into CoO/MoO_<i>x</i> for Overall Water Splitting by Hydrogenation

Special structures of materials often bring in unprecedented catalytic activities, which are critical in realizing large-scale hydrogen production by electrochemical water splitting. Herein, we report a CoO/MoOx crystalline/amorphous structure as an effective bifunctional electrocatalyst for water splitting. Converted from CoMoO4 by hydrogenation, the CoO/MoOx, featured with crystalline CoO in amorphous MoOx matrix, displays superior catalytic activities toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). It shows small onset overpotentials of 40 and 230 mV for the HER and OER in 1.0 M KOH, respectively, and overall water splitting starting at 1.53 V with a robust stability. The high catalytic activity of the CoO/MoOx is benefited from the large defect-rich interface between CoO and MoOx, along with the amorphous nature of MoOx. Thus, this study demonstrates the effectiveness of structural manipulation in developing highly active electrocatalysts for overall electrochemical water splitting

Facile in situ fabrication of a direct Z-scheme BiOCl/bismuth niobate heterojunction and its effective photodegradation of RhB

Bismuth-based photocatalytic technology has been a promising way to degrade contaminants in the aqueous system. In this work, a direct Z-scheme BiOCl/Bi3NbO7 heterojunction with a different molar ratio of Bi and Nb elements was fabricated through a facile in situ growth method. The structural and photoelectric characteristics of these as-prepared samples were investigated by SEM, XPS, TEM, XRD, BET, UV-vis DRS, PL, EIS and TPC. The photocatalytic activity was evaluated by the degradation of RhB, and its mechanism was analyzed by the active species trapping experiments and DFT calculation. The results showed that compared with other as-prepared samples, BN-4 had the highest activity for RhB degradation with the value of the rate constant (k) being 0.01664 min−1. The reason that might be those different molar ratios of Bi and Nb elements in BiOCl/Bi3NbO7 heterojunction would impact the interface structure. And an appropriate molar ratio of that could bring a lower interface resistance that enhances the photocatalytic activity. The •OH and •O2− were the main active substances during the RhB photocatalytic process, and a reasonable degradation pathway was proposed.</p

Edge Engineering of Carbon Nitride Nanodots with Pocket-like Sites for Effective Photoreduction of Bicarbonate to CO under Visible Light

Abundant pocket-like defects are engineered on the edge of carbon nitride nanodots (CN1.9), using hydrazine groups to attack carbon atoms which results in CN heterocycle opening of porous graphitic C3N4. These edge defects on CN1.9 not only modulate the electronic structure, extend light absorption, and promote photoexcited electron transfer but also lead to c(HCO3–)/c(CO2, aq)-dependent photocatalytic CO evolution in CO2 bubbling HCO3– aqueous solution (pH ≈ 7.1∼7.5). Even in the N2/HCO3– system (pH ≈ 8.17), wherein c(HCO3–) is about 67 times higher than c(CO2, aq), the CO production also attains 48.6 μmol g–1 h–1 on CN1.9. In the same experimental condition, almost no CO produces except for H2 on graphitic carbon nitride (GCN). DFT theoretical calculation reveals that edge defects prefer to contact with HCO3– and proton to orient a special reaction pathway of HCO3* → H2CO3* → CO on CN1.9 with a relatively low-energy barrier rather than HCO3* → H2O–CO2* → CO on GCN

The autocorrelation check for residuals in ARIMA model.

<p>Note: A = modelling data from 1956 to 2008, B = modelling data from 1956 to 2012.</p

The parameter estimation of ARIMA model for two modelling data set.

<p>*: Parameter estimation was considered statistically significant (<i>P</i><0.05).</p