Creation of Interfacial S4-Sn-N2 Electron Pathways for Efficient Light-Driven Hydrogen Evolution.

Establishing effective charge transfer channels between two semiconductors is key to improving photocatalytic activity. However, controlling hetero-structures in situ and designing binding modes pose significant challenges. Herein, hydrolytic SnCl2·2H2O is selected as the metal source and loaded in situ onto a layered carbon nitriden supramolecular precursor. A composite photocatalyst, S4-Sn-N2, with electron pathways of SnS2 and tubular carbon nitriden (TCN) is prepared through pyrolysis and vulcanization processes. The contact interface of SnS2-TCN is increased significantly, promoting the formation of S4-Sn-N2 micro-structure in a Z-scheme charge transfer channel. This structure accelerates the separation and transport of photogenerated carriers, maintains the stronger redox ability, and improves the stability of SnS2 in this series of heterojunctions. Therefore, the catalyst demonstrated exceptional photocatalytic hydrogen production efficiency, achieving a reaction rate of 86.4 µmol h-1, which is 3.15 times greater than that of bare TCN.

A green and environmentally benign route to synthesizing Z-scheme Bi2S3-TCN photocatalyst for efficient hydrogen production.

Designing and developing photocatalysts with excellent performance in order to achieve efficient hydrogen production is an important strategy for addressing future energy and environmental challenges. Traditional single-phase photocatalytic materials either have a large bandgap and low visible light response or experience rapid recombination of the photogenerated carriers with low quantum efficiency, seriously hindering their photocatalytic applications. To solve these issues, an important solution is to construct well-matched heterojunctions with highly efficient charge separation capabilities. To this end, an in situ sulfurization reaction was adopted after the deposition of Bi3+ supramolecular complex on a layered supramolecular precursor of tubular carbon nitride (TCN). X-ray diffraction (XRD) patterns confirmed that the as-prepared sample has a good crystalline structure without any other impurities, while high-resolution transmission electron microscopy (HR-TEM) revealed that the heterojunction possesses a 2D structure with a layer of nano-array on its surface. Combined Fourier-transform infrared (FT-IR) spectra and energy-dispersive X-ray spectroscopy (EDX) revealed the interfacial interactions. Owing to the formation of the Z-scheme heterojunction, the visible light adsorption and the separation efficiency of the photo-generated carriers are both obviously enhanced, leaving the high energy electrons and high oxidative holes to participate in the photocatalytic reactions. As a result, the photocatalytic hydrogen evolution rate of Bi2S3-TCN achieves 65.2 µmol g-1·h-1. This proposed green and environmentally benign route can also be applied to construct other sulfides with 2D TCN, providing some important information for the design and optimization of novel carbon-nitride-based semiconductors.

Cu-coupled Fe/Fe3C covered with thin carbon as stable win-win catalysts to boost electro-Fenton reaction for brewing leachate treatment.

The electro-Fenton oxidation is one of the powerful approaches for achieving the complete mineralization of organic pollutants in water. The key dilemma for efficient industrial application of electro-Fenton oxidation is the complicated post-processing of iron sludge, and the cost and risk associated with H2O2 transportation and storage. Herein, Cu-coupled Fe/Fe3C covered with carbon layer on carbon felt (Cu-Fe/Fe3C@C), engineered by a hydrothermal reaction followed by the consequent thermal-treatment in N2 atmosphere, as a self-supported integrated cathode were used for an onsite oxygen reduction reaction and a Fenton oxidation reaction. Experimental evidences demonstrate that, at the operating potential of -1.1 V, Fe3C can selectively catalyze O2 into H2O2 by 2e reduction pathways with assistance of metal Cu. Meanwhile, metal Fe and Cu incorporated into Cu-Fe/Fe3C@C simultaneously motivate the onsite Fenton oxidation arose by H2O2. Such a win-win catalyst presented high activity in the electro-Fenton process. In acidic environment, the efficient mineralization rate of methylene blue, nitrobenzene, phenol, and bisphenol A can reach more than 70% in 60 min, as well as the excellent stability and durability due to the protection of graphited carbon layer. Compared with tradition electrochemical degrade system, the prepared Cu-Fe/Fe3C@C electrode as cathode for practical refractory brewing leachate treatment reveal more efficient decolorization and mineralization, saving 14.3% of electricity.

Controlled Atmosphere Corrosion Engineering toward Inhomogeneous NiFe-LDH for Energetic Oxygen Evolution.

The "Fe effect" can maximize the activity of nickel-iron layered double hydroxides (NiFe-LDH) toward oxygen evolution reaction (OER) when the iron content, the lattice distortion, the conductivity, and other related factors are well balanced. It is difficult for the homogeneous NiFe-LDH to take good care of the above requirements at the same time. Herein, we proposed an elaborate atmosphere corrosion strategy to construct porous NiFe-LDH with rich edge/surface-Fe defects on Ni foam (NF). Such edge/surface-Fe defects, mainly caused by the local unequal-stoichiometric ratio of Fe/Ni in the nanometer or subnanometer region, are determined by the unbalanced permeating of the acid vapor and the confined reaction of local Fe and Ni species ionized by the acid vapor. Benefiting from the abundant and fantastic edge/surface-Fe defects, the optimal NiFe-LDH prepared by atmosphere corrosion is more energetic for OER than that synthesized in conventional liquid phase, only a potential of 1.481 and 1.552 VRHE to respectively achieve the current density of 100 and 1000 mA cm-2 as well as a satisfactory stability and reproducibility. An overall water-splitting system assembled by inhomogeneous NiFe-LDH and commercial Pt-C can reach a current density of 100 mA cm-2 at a solar cell of 1.72 V. Additionally, the atmosphere corrosion is very suitable for the large-scale, green, and economic synthesis of metal-based catalysts with high enrichment of defects, highlighting its potential for device and industrial applications.

A Unique Fe-N4 Coordination System Enabling Transformation of Oxygen into Superoxide for Photocatalytic CH Activation with High Efficiency and Selectivity.

Selective oxidation of CH bonds is one of the most important reactions in organic synthesis. However, activation of the α-CH bond of ethylbenzene by use of photocatalysis-generated superoxide anions (O2 •- ) remains a challenge. Herein, the formation of individual Fe atoms on polymeric carbon nitride (CN), that activates O2  to create O2 •- for facilitating the reaction of ethylbenzene to form acetophenone, is demonstrated. By utilizing density functional theory and materials characterization techniques, it is shown that individual Fe atoms are coordinated to four N atoms of CN and the resultant low-spin Fe-N4  system (t2g 6 eg 0 ) is not only a great adsorption site for oxygen molecules, but also allows for fast transfer of electrons generated in the CN framework to adsorbed O2 , producing O2 •- . The oxidation reaction of ethylbenzene triggered by O2 •- ions turns out to have a high conversion rate of 99% as well as an acetophenone selectivity of 99%, which can be ascribed to a novel reaction pathway that is different from the conventional route involving hydroxyl radicals and the production of phenethyl alcohol. Furthermore, it possesses great potential for other CH activation reactions besides ethylbenzene oxidation.

Porous Palladium Nanomeshes with Enhanced Electrochemical CO2 -into-Syngas Conversion over a Wider Applied Potential.

Electrochemical conversion of CO2 into syngas, which can be used directly in the classical petroleum industrial processes, provides a powerful approach for achieving the recycling of anthropogenic carbon. Pd has previously been reported to be capable of converting CO2 into syngas with various CO/H2 ratios, but only at limited applied potential, which is mainly attributed to fewer active sites exposed toward electrocatalysis. Herein, high-performance Pd nanomeshes (NMs) assembled with branch-like Pd nanoparticles were designed and synthesized by using a simple interface-induced self-assembly strategy; these NMs could catalyze CO2 -into-syngas conversion with a high current density in a wide applied potential range from -0.5 to -1.0 V (vs. reversible hydrogen electrode). Further evidence validated that the enhanced activity of the Pd NMs was not only caused by the crosslinked network structure accelerating electron transport, but also by the greater number of edge and/or corner active sites exposed on the surface of the NMs, which facilitated CO2 adsorption, CO2 .- formation, COOH* stabilization, and CO generation. Under optimal operating conditions, Pd NMs could balance two competing reactions: CO2 reduction and hydrogen evolution. The resultant syngases with the ideal and tunable CO/H2 ratio between 0.5:1 and 1:1 could be used directly for methanol synthesis and Fischer-Tropsch reactions.

Engineering a stereo-film of FeNi3 nanosheet-covered FeOOH arrays for efficient oxygen evolution.

Electrochemical oxygen evolution reaction (OER) can be accelerated by employing transition-metal-based catalysts to obtain the desired activity and durability. Considering the promoting effect of the electrode structure on catalyzing OER, a stereo-film on carbon cloth comprising FeNi3 nanosheet-covered FeOOH (F@FeNi3-CC) was engineered by the hydrothermal reaction and subsequent synchronous electrodeposition of Fe and Ni ions. In F@FeNi3-CC, the FeOOH array not only provides the Fe source of FeNi3 nanosheets during the cathodic electrodeposition, but also functions as the support for the ultrathin FeNi3 nanosheets. Such a stereo-film with good electrolyte-permeability also offers expedited electrolyte/reactant transmission paths. The tailored FeNi3 nanosheet offers abundant exposed catalytic sites by virtue of the in situ derived hydroxide layer during anodic oxidation and also acts as the current collector to accelerate charge transport. The F@FeNi3-CC electrode yields outstanding catalytic activity towards OER in alkaline media, particularly at low potential of 1.50 V and large current density of 100 mA cm-2, accompanied with the excellent long-term stability. These results are significant for the construction of stereo-film electrodes for various engineering applications.

CoSex nanocrystalline-dotted CoCo layered double hydroxide nanosheets: a synergetic engineering process for enhanced electrocatalytic water oxidation.

Manipulating the electrical conductivity and morphology of Co-based (hydr)oxides is significant for optimizing energy conversion in the oxygen evolution reaction (OER). Herein, 2D CoSex nanocrystalline-dotted porous CoCo layered double hydroxide nanosheets (Co-Se NSs) were designed and synthesized via a modified in situ reduction and interface-directed assembly in an inert atmosphere. During the synchronous reduction/precipitation reaction between Co2+-oleylamine and NaHSe at the toluene-water interface, the hydrated Co-O and Co-Se clusters are generated and sequentially assemble under strong extrusion driven by the interfacial tension. Owing to the enriched vacancies on the lateral surfaces, the obtained loose and porous Co-Se NS presents low crystallinity. Moreover, electrons could spontaneously transfer from the CoCo LDH to the neighboring CoSex nanocrystallites due to the stronger electron-withdrawing capability of metallic CoSex, and thus more Co atoms in the CoCo layered double hydroxide (LDH) present a high oxidation state. This synergistic manipulation in the structure, component, and electron configuration of the Co-Se NS can increase the density of the OER active-sites, improve the electrical conductivity, and also offer a large accessible surface area and permeable channels for ion adsorption and transport. As a result, the resulting Co-Se NSs feature high catalytic activity towards OER, in particular a low onset potential of 1.48 V and an overpotential of only 290 mV at a current density of 10 mA cm-2 for the Co-Se-2 NS, as well as good stability in an accelerated durability test. The strategy developed here provides a reliable and valid way to synthesize multicomponent NSs, and is able to be extended to other areas of application.

In-situ structure reconstitution of NiCo2Px for enhanced electrochemical water oxidation.

Gaining insight into the structure evolution of transition-metal phosphides during anodic oxidation is significant to understand their oxygen evolution reaction (OER) mechanism, and then design high-efficiency transition metal-based catalysts. Herein, NiCo2Px nanowires (NWs) vertically grown on Ni foam were adopted as the target to explore the in-situ morphology and chemical component reconstitution during the anodic oxidation. The major factors causing the transformation from NiCo2Px into the hierarchical NiCo2Px@CoNi(OOH)x NWs are two competing reactions: the dissolution of NiCo2Px NWs and the oxidative re-deposition of dissolved Co2+ and Ni2+ ions, which is based primarily on the anodic bias applied on NiCo2Px NWs. The well balance of above competing reactions, and local pH on the surface of NiCo2Px NW modulated by the anodic oxidation can serve to control the anodic electrodeposition and rearrangement of metal ions on the surface of NiCo2Px NWs, and the immediate conversion into CoNi(OOH)x. Consequently, the regular hexagonal CoNi(OOH)x nanosheets grew around NiCo2Px NWs. Benefiting from the active catalytic sites on the surface and the sufficient conductivity, the resultant NiCo2Px@CoNi(OOH)x arrays also display good OER activity, in terms of the fast kinetics process, the high energy conversion efficiency, especially the excellent durability. The strategy of in-situ structure reconstitution by electrochemical reaction described here offers a reliable and valid way to construct the highly active systems for various electrocatalytic applications.