Progress in Preparation and Research of Water Electrolysis Catalyst for Transition Metal Phosphide

Confronted with growing energy crisis and environmental challenges, water electrolysis for hydrogen production can provide high-density, clean and renewable energy, but limited by sluggish kinetics of two half reaction, anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction(HER). Noble-metal-based electrocatalysts can decrease overpotential and accelerate kinetics dramatically, but limited by its scarcity and high cost. Transitional metal catalysts are abundant, low cost and have potential to become excellent catalyst due to unique electronic structure. Beginning from basic principle of electrocatalysis, this paper focuses on the synthesis method of transitional metal phosphide (TMP), and further discusses modification methods of TMP, including phase tuning, element doping/alloying, interfacial/structural engineering and three-dimensional architecture. Finally, the challenges of TMP are analyzed and future research focuses are prospected.

PITTING MECHANISM OF MILD STEEL IN MARGINALLY SOUR ENVIRONMENTS: PIT PROPAGATION BASED ON ACIDIFICATION BY CATALYTIC OXIDATION OF DISSOLVED HYDROGEN SULFIDE

The present work studies pit propagation in marginally sour environments and proposes a credible mechanism. Both thermodynamic calculation and experimental measurement confirmed that H2S can be oxidized by traces of dissolved O2 into SO42- and H+ in the aqueous solutions near room temperature with the transitional metal ions serving as a catalyst. This acidification phenomenon would be more effective near the steel surface, especially inside a pit, where Fe2+ ions are most abundant. Therefore, the saturation degree of mackinawite would be lower inside the pit, which would prohibit the pitting from annihilation.

Moiré flat bands in twisted 2D hexagonal vdW materials

Moiré superlattices in twisted bilayer graphene (TBG) and its derived structures can host exotic correlated quantum phenomena because the narrow moiré flat minibands in those systems effectively enhance the electron-electron interaction. Correlated phenomena are also observed in 2H-transitional metal dichalcogenides moiré superlattices. However, the number of moiré systems that have been explored in experiments are still very limited. Here we theoretically investigate a series of two-dimensional (2D) twisted bilayer hexagonal materials (TBHMs) beyond TBG at fixed angles of 7.34◦ and 67.34◦ with 22 2D van der Waals (vdW) layered materials that are commonly studied in experiments. First-principles calculations are employed to systemically study the moiré minibands in these systems. We find that flat bands with narrow bandwidth generally exist in these systems. Some of the systems such as twisted bilayer In2Se3, InSe, GaSe, GaS and PtS2 even host ultra-flat bands with bandwidth less than 20 meV even for such large angles, which make them especially appealing for further experimental investigations. We further analysis the characters of moiré flat bands and provides guidance for further exploration of 2D moiré superlattices that could host strong electron correlations.

Degradation of organic pollutant in restaurant wastewater using the homogenous catalysis with Mn(II) and EDTA

It can be seen that the objects of wastewater that need to be treated are quite diverse in types and complex in terms of reaction mechanisms. The methods mainly focus on the treatment of toxic organic compounds, especially phenols or plant protection agents in industrial wastewater, paper industry, food production, textile industry, printing industry... The activation of H2O2 and O2 by complexes of transitional metal ions and suitable ligands creates oxidizing agents and ecologically healthy products. The intermediate substances arising in the activation process such as free radicals OH., O2., HO2., ... can oxidize many compounds, especially the ability to attack the aroma of organic pollutants. In this paper, the results of research on treating organic pollution in restaurant wastewater with H2O2 are presented as a catalyst of complexes between Mn2+ ions and EDTA. The conditions including pH, EDTA/Mn2+, the concentration of H2O2, Mn2+ were investigated to obtain the optimum conditions for improving COD treatment efficiency. This work proposes a method based on formation of the Mn(II)-EDTA complex, b=1; with the optimal conditions of other factors as following [H2O2]0 = 0,75.10-3 mol/L; [Mn(EDTA)]2- = 33,33 mol/L, pH=10.5; t = 15 minutes. The initial COD of 1025 mg/L decreased to 135 mg/L after the proposed procedure. The results provide solutions of homogeneous complex catalysts for domestic/restaurant and industrial wastewater treatment at room temperature and atmosphere.

Two-dimensional molybdenum carbide 2D-Mo2C as a superior catalyst for CO2 hydrogenation

Early transitional metal carbides are promising catalysts for hydrogenation of CO2. Here, a two-dimensional (2D) multilayered 2D-Mo2C material is prepared from Mo2CTx of the MXene family. Surface termination groups Tx (O, OH, and F) are reductively de-functionalized in Mo2CTx (500 °C, pure H2) avoiding the formation of a 3D carbide structure. CO2 hydrogenation studies show that the activity and product selectivity (CO, CH4, C2–C5 alkanes, methanol, and dimethyl ether) of Mo2CTx and 2D-Mo2C are controlled by the surface coverage of Tx groups that are tunable by the H2 pretreatment conditions. 2D-Mo2C contains no Tx groups and outperforms Mo2CTx, β-Mo2C, or the industrial Cu-ZnO-Al2O3 catalyst in CO2 hydrogenation (evaluated by CO weight time yield at 430 °C and 1 bar). We show that the lack of surface termination groups drives the selectivity and activity of Mo-terminated carbidic surfaces in CO2 hydrogenation.