Chelating Co-reduction Strategy for the Synthesis of High-Entropy Alloy Aerogels.

Aerogels, as three-dimensional porous materials, have attracted much attention in almost every field owing to their unique structural properties. Designing high-entropy alloy aerogels (HEAAs) to quinary and above remains an enormous challenge due to the different reduction potentials and nucleation/growth kinetics of different constituent metals. Herein, a novel and universal chelating co-reduction strategy to prepare HEAAs at room temperature in the water phase is proposed. The addition of chelators (ethylenediaminetetraacetic acid tetrasodium salt, sodium citrate, salicylic acid, and 4,4'-bipyridine) with a certain strong coordination capacity can adjust the reduction potential of different metal components, which is the key to synthesize single-phase solid solution alloys successfully. The optimized AgRuPdAuPt HEAA can be an excellent electrocatalyst for hydrogen evolution reaction (HER) with an ultrasmall overpotential of 22 mV at 10 mA cm-2 and excellent stability for 24 h in an alkaline solution. In situ Raman spectroscopy unveils the enhanced hydrogen evolution reaction mechanism of HEAAs. Overall, this work provides a novel chelating co-reduction strategy for the facile and versatile synthesis and design of advanced HEAAs and broadens the development and utilization of multi-elemental alloy electrocatalysts.

Noble Metal (Pt, Rh, Pd, Ir) Doped Ru/CNT Ultra-Small Alloy for Acidic Hydrogen Evolution at High Current Density.

There are still great challenges to prepare high-efficiency Ru-based catalysts that are superior to Pt/C under acidic conditions, especially under high current conditions. In this work, a series of surfactant-free noble metal doped Ru/CNT (M-Ru/CNT, M = Pt, Rh, Pd, Ir, CNT stands for carbon nanotube) are prepared by microwave reduction method in 1 minute with ≈3-3.5 nm in size for the first time. In 0.5 m H2 SO4 , the overpotential of Pt-Ru/CNT (Pt: 4.94 at %) is only 12 mV. What's more, it also has much larger electrochemical surface area and intrinsic activity than Pt/C. Pt-Ru/CNT still has an ultra-small overpotential under high current density (113 mV at 500 mA cm-2 , 155 mV at 1000 mA cm-2 ). At the same time, it possesses excellent stability regardless of high current or low current after the durability test of 100 h. Theoretical calculation also deeply reveals that Ru is the main adsorption site of H+ . The comparison of the electronic structure of a series of noble metals adjusted by Ru shows that Pt has the most excellent Gibbs free energy of the adsorbed hydrogen and promotes the desorption of the product.

Ordered Vacancies on the Body-Centered Cubic PdCu Nanocatalysts.

Defect engineering has become one of the important considerations in today's electrocatalyst design. However, the vacancies in the ordered crystal structure (especially body-centered cubic (bcc) and the effect of ordered vacancies (OVs) on the electronic fabric have not been researched yet. In this work, we report the inaugural time of the generation of OVs in the bcc architecture and discuss the insight of the modulation system of the material and its part in the electrochemical N2 reduction reaction (NRR). OV-PdCu-2 achieves the highest Faradaic efficiency value of 21.5% at 0.05 V versus RHE. When the potential increases to 0 V versus RHE, the highest ammonia yield is 55.54 µg h-1 mgcat-1, which is significantly better than the unetched PdCu nanoparticles (12.83 µg h-1 mgcat-1). It is the latest reported catalyst to date in the NRR process at 0 V versus RHE (see Supporting Information).

Superfast Synthesis of Densely Packed and Ultrafine Pt-Lanthanide@KB via Solvent-Free Microwave as Efficient Hydrogen Evolution Electrocatalysts.

At present, it is still a great challenge to synthesize refractory Pt-based electrocatalysts with excellent active specific surface area, specific activity, and stability by a simple method. Here, a superfast and solvent-free microwave strategy is reported to synthesize refractory ultrafine (≈3 nm) Pt-lanthanide@Ketjen Black (PtM@KB, M = La, Gd, Tb, Er, Tm, and Yb) alloy with densely packed as efficient hydrogen evolution electrocatalysts in a domestic microwave oven for the first time. The optimized Pt61 La39 @KB delivers excellent hydrogen evolution reaction (HER) activity with a low overpotential of 38 mV (10 mA cm-2 ) and a high TOF value of 44.13 s-1  (100 mV) in 0.5 m H2 SO4 , and performs well in 1.0 m KOH. This method can also be used to grow catalysts on carbon cloth (CC) directly. PtLa@CC shows an overpotential of 99 mV (1000 mA cm-2 ) in 0.5 m H2 SO4 and can maintain activity after 500 h. Theoretical calculations reveal the enhanced stability and activity owing to the higher vacancy formation energy of Pt atoms and the optimized value of ΔGH* . Solvent-free microwave strategy constitutes a significant insight into the development of refractory electrocatalyst with ultrafine size and highly dense, which can also work well at high current densities.

Preparation of Functionalized Mesoporous Silica as a Novel Carrier and Immobilization of Laccase.

Amino-modified mesoporous silica (SBA-15-NH2) was prepared by hydrothermal method, which is a kind of excellent carrier for enzyme immobilization. The structure of SBA-15 was characterized by SEM and FTIR, which proved that amino group was successfully attached to the surface of SBA-15. The carrier had good mesoporous structure proved by nitrogen adsorption and desorption test. Using SBA-15-NH2 as the carrier, the optimal conditions of laccase immobilization by two different cross-linking methods were explored. At the same time, the properties of the immobilized enzyme and free enzyme were compared. The results showed that the activity of immobilized laccase by two-step method (2977.5 U/g) was much higher than that by one-step method (239.5 U/g). The optimal conditions were as follows: free laccase (35°C, pH=4.5), two-step immobilized laccase (40°C, pH=4.0), one-step immobilized laccase (35°C, pH=4.0). The two-step method was more adaptable to temperature. The pH adaptation range of the immobilized enzyme is wider, and the thermal stability is greatly enhanced. After five cycles of repeated reaction, the residual enzyme activity of two-step and one-step methods was 56% and 43% of the original. The treatment of simulated wastewater containing 2,4-dichlorophenol (2,4-DCP) by immobilized laccase was also studied. Under optimum conditions (40°C, pH=5.0, 20 mg/L), the removal of 2,4-DCP reached 89.06%. The immobilized laccase is really effective for treatment of 2,4-DCP-containing wastewater.