Cu2 P7 -CoP Heterostructure Nanosheets Enable High-Performance of 5-Hydroxymethylfurfural Electrooxidation.

Electrooxidation of 5-hydroxymethylfural (HMF) into 2,5-furandicarboxylicacid (FDCA) has been regarded as a promising sustainable approach to achieve value-added chemicals. However, it is still impeded by the unsatisfactory performance of electrocatalysts. Here, Cu2 P7 -CoP heterostructure nanosheets were reported to enable powerful HMF electrooxidation. The Cu2 P7 -CoP heterostructure nanosheets were fabricated by microwave-assisted deep eutectic solvent (DES) approach, along with subsequent phosphiding. The Cu2 P7 -CoP heterostructure nanosheets enabled a superb 100 % HMF conversion at 1.43 V (vs. RHE) with 98.8 % FDCA yield and 98 % Faradaic efficiency (FE), demonstrating its promising application in HMF electrooxidation. X-ray photoelectron spectroscopy (XPS) analysis, open-circuit potential (OCP) approach and density functional theory (DFT) calculation uncovered that the electron transfer and redistribution between Cu2 P7 and CoP improved the adsorption capacity of HMF and modulated the catalytic performance. This study not only offered a powerful electrocatalyst for HMF electrooxidation, but also provided a conceptually new strategy for the heterostructure catalyst design.

Ionic-Liquid-Assisted One-Step Synthesis of CoO Nanosheets as Electrocatalysts for Oxygen Evolution Reaction.

The sluggish oxygen evolution reaction (OER) hinders the development of electrocatalytic water splitting for energy conversion and storage. Therefore, it is imperative to explore the cost-effective and highly efficient noble-metal-free electrocatalysts for OER. Herein, we are introducing such OER electrocatalyst based on Co, fabricated through an ionic-liquid-assisted one-step synthesis, where ionic liquid played a dual role as solvent cum structure-directing agent. Besides possessing large-accessible surface area and numerous active sites, the as-prepared stable CoO nanosheets exhibited excellent electrochemical activity through establishing an extensive contact with the electrolyte. Under alkaline conditions, the overpotential to achieve a current density of 10 mA cm-2 is only 320 mV, and the Tafel slope is as small as 70 mV dec-1. Thus, our work provides a new pathway for designing and engineering the highly efficient non-noble metal OER electrocatalysts by using ionic liquids.

Vanadium-Doped WS2 Nanosheets Grown on Carbon Cloth as a Highly Efficient Electrocatalyst for the Hydrogen Evolution Reaction.

Two-dimensional transition-metal dichalcogenides have been widely studied as electrocatalysts for the hydrogen evolution reaction (HER). However, limited active sites and poor conductivity hinder their application. To solve these disadvantages, heteroatom doping has attracted wide attention because it can not only increase the active sites but also affect the intrinsic catalytic properties of the electrocatalyst. Herein, we grew vanadium-doped WS2 nanosheets on carbon cloth (V-WS2 /CC) as an electrocatalyst for HER under acidic and alkaline conditions. With a proper vanadium doping concentration, the electrochemical surface areas of V0.065 -WS2 /CC were 9.6 and 2.6 times as large as that of pure WS2 electrocatalyst under acidic and alkaline conditions, respectively. In addition, the charge-transfer resistance also decreased with moderate vanadium doping. Based on this, the synthesized vanadium-doped WS2 nanosheets exhibited good stability with high HER catalytic activity and could reach a current density of 10 mA cm-2 at overpotentials of 148 and 134 mV in 0.5 m H2 SO4 and 1 m KOH, respectively. The corresponding Tafel slopes were 71 and 85 mV dec-1 . Therefore, our synthesized vanadium-doped WS2 nanosheets can be a promising electrocatalyst for the production of hydrogen over a wide pH range.

Controllable 1D and 2D Cobalt Oxide and Cobalt Selenide Nanostructures as Highly Efficient Electrocatalysts for the Oxygen Evolution Reaction.

The relationship between controllable morphology and electrocatalytic activity of Co3 O4 and CoSe2 for the oxygen evolution reaction (OER) was explored in alkaline medium. Based on the time-dependent growth process of cobalt precursors, 1D Co3 O4 nanorods and 2D Co3 O4 nanosheets were successfully synthesized through a facile hydrothermal process at 180 °C under different reaction times, followed by calcination at 300 °C for 2 h. Subsequently, 1D and 2D CoSe2 nanostructures were derived by selenization of Co3 O4 , which achieved the controllable synthesis of CoSe2 without templating agents. By comparing the electrocatalytic behavior of these cobalt-based catalysts in 1 m KOH electrolyte toward the OER, both 2D Co3 O4 and 2D CoSe2 nanocrystals have lower overpotentials and better electrocatalytic stability than that of 1D nanostructures. The 2D CoSe2 nanosheets require overpotentials of 372 mV to reach a current density of 50 mA cm-2 with a small Tafel slope of 74 mV dec-1 . A systematic contrast of the electrocatalytic performances for the OER increase in the order: 1D Co3 O4 <2D Co3 O4 <1D CoSe2 <2D CoSe2 . This work provides fundamental insights into the morphology-performance relationships of both Co3 O4 and CoSe2 , which were synthesized through the same approach, providing a solid guide for designing OER catalysts.

Ionic Liquid as Reaction Medium for Synthesis of Hierarchically Structured One-Dimensional MoO2 for Efficient Hydrogen Evolution.

Hierarchically structured one-dimensional (1D) MoO2 is synthesized for the first time in ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][Tf2N]). The synthesis system is very simple (single [BMIM][Tf2N] solvent plus MoO2(acac)2 reactant). [BMIM][Tf2N] itself works as both the reaction medium and the template for the formation of these interesting 1D MoO2 particles with ultrathin nanosheet subunits. The as-synthesized hierarchically 1D MoO2_40 particles exhibit remarkable electrocatalytic activity with good long-term cycle stability for the hydrogen evolution reaction (HER) in acidic media. The HER activity of present synthesized MoO2 is comparable to those of the most active Mo-based electrocatalysts in acid media reported up to now. Therefore, the ionic liquid route provides us with a newly powerful tool for the synthesis of interesting alternative to noble metal catalysts for efficient electrocatalytic production of hydrogen in acidic environment.

Fabrication of cellulose self-assemblies and high-strength ordered cellulose films.

Based on the formation of cellulose hydrogels in NaOH/urea aqueous solvent media, cellulose self-assembly precursor is acquired. It is proved that the water uptake capability of the cellulose hydrogels depends highly on the cross-link degree (CLD) of cellulose. With varying CLD and concentration of cellulose, a variety of morphologies of cellulose self-assemblies, including sheets with perfect morphology, high-aspect-ratio fibers, and disorganized segments and network, are formed through evaporation. Furthermore, cellulose films are fabricated by diecasting and evaporating the cellulose hydrogels, resulting in a 3D-ordered structure of closely stacking of cellulose sheets. The mechanical test indicates both tensile strength and flexibility of the cellulose films are greatly improved, which is attributed to the formation of the orderly stacking of cellulose sheets. The study is expected to lay an important foundation on the preparation of ordered and high-strength cellulose materials.

Boosting electrocatalytic hydrogen evolution via partial oxidation of rhenium through cobalt modification in nanoalloy structure.

Although the theoretical electrocatalytic activity of rhenium (Re) for the hydrogen evolution reaction is comparable to that of platinum, the experimental performance of reported rhenium-based electrocatalysts remains unsatisfactory. Herein, we report a highly efficient and stable electrocatalyst composed of rhenium and cobalt (Co) nanoalloy embedded in nitrogen-doped carbon film (Re3Co2@NCF). The Re3Co2@NCF electrocatalyst exhibited remarkable hydrogen evolution performance, with an overpotential as low as 30 ± 3 mV to reach a current density of 10 mA cm-2. In addition, the Re3Co2@NCF demonstrated exceptional stability over several days at a current density of 150 mA cm-2. Theoretical calculations revealed that alloying cobalt with rhenium altered the electronic structure of the metals, causing partial oxidation of the superficial metal atoms. This modification provided a balance for various intermediates' adsorption and desorption, thereby boosting the intrinsic activity of rhenium for hydrogen evolution reaction. This work improves the electrocatalytic performance of rhenium to its theoretical activity, suggesting a promising future for rhenium-based electrocatalysts.