Identification and extraction of cementation patterns in sand modified by MICP: New insights at the pore scale.

Microbially induced calcium carbonate precipitation (MICP) is an environmentally friendly technology that improves soil permeability resistance through biocementation. In this study, 2D microscopic analysis and 3D volume reconstruction were performed on river sand after 24 cycles of bio-treatment based on stacked images and computed tomography (CT) scanning data, respectively, to extract biocementation patterns between particles. Based on the mutual validation findings of the two techniques, three patterns in the biocemented sand were identified as G-C-G, G-C, and G-G. Specifically, 2D microscopic analysis showed that G-C-G featured multi-particle encapsulation and bridging, with a pore filling ratio of 81.2%; G-C was characterized by locally coated particle layers, with a pore filling ratio of 19.7%; and the G-G was marked by sporadic filling of interparticle pores, with a pore filling ratio of 11.7%. G-C-G had the best cementation effect and permeability resistance (effective sealing rate of 68.5%), whereas G-C (effective sealing rate of 2.4%) had a relatively minor contribution to pore-filling and flow sealing. 3D volume reconstruction showed that G-C-G had the highest pore filling rate, followed by G-G and G-C. The average filling ratios of area and volume for G-C-G were 83.979% and 77.257%, respectively; for G-G 20.360% and 23.600%; and for G-C 11.545% and 11.250%. The analysis of the representative element volume (REV) was conducted, and the feasibility and reliability of the micro-scale pattern extraction results were confirmed to guide the analysis of macro-scale characteristics. The exploration of the effectiveness of cementation patterns in fluid sealing provides valuable insights into effective biocementation at the pore scale of porous media, which may inspire future research.

Boosting activity and selectivity of glycerol oxidation over platinum-palladium-silver electrocatalysts via surface engineering.

A series of platinum-palladium-silver nanoparticles with tunable structures were synthesized for glycerol electro-oxidation in both alkaline and acidic solutions. Electrochemical results indicate that the catalysts show superior activity in alkaline solutions relative to acidic solutions. In alkaline solutions, the peak current densities of ammonia-etched samples are approximately twice those of saturated-NaCl-etched samples. Ammonia-etched platinum-palladium-silver (PtPd@Ag-NH3) exhibits a peak current density of 9.16 mA cm-2, which is 18.7 and 10 times those of the Pt/C and Pd/C, respectively. The product distribution was analyzed by high performance liquid chromatography. Seven products including oxalic acid, tartronic acid, glyoxylic acid, glyceric acid (GLA), glyceraldehyde (GALD), glycolic acid, and dihydroxyacetone (DHA) were detected. The NH3·H2O etched samples tend to generate more GALD, while the NaCl etched samples have a great potential to produce DHA. The addition of Pd atoms can facilitate glycerol oxidation pathway towards the direction of GALD generation. The Pt@Ag-NaCl possesses the largest DHA selectivity of 79.09% at 1.3 V, while the Pt@Ag-NH3 exhibits the largest GLA selectivity of 45.01% at 0.5 V. The PtPd@Ag-NH3 exhibits the largest C3/C2 ratio of 17.45. The selectivity and product distribution of glycerol electro-oxidation can be tuned by engineering the surface atoms of the as-synthesized catalysts.

Selective Electro-Oxidation of Glycerol to Dihydroxyacetone by PtAg Skeletons.

Developing high-performance electrocatalysts for the selective conversion of glycerol into value-added chemicals is of great significance. Herein, three-dimensional nanoporous PtAg skeletons were studied as catalysts for the electro-oxidation of glycerol. The structural features of the PtAg skeletons were revealed by electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-vis spectroscopy. The electrochemical activity of the catalysts was examined by cyclic voltammetry, linear sweeping voltammetry, and chronoamperometry. The resulting PtAg skeletons exhibit a peak current density of 7.57 mA cm-2, which is 15.4-fold higher than that of Pt/C, making the PtAg skeletons one of the best electrocatalysts for glycerol oxidation. High-performance liquid chromatography results show that the PtAg skeletons yield a remarkable dihydroxyacetone selectivity of 82.6%, which has so far been the second largest value reported in the literature. The superior activity and selectivity of the PtAg skeletons are ascribed to the large surface area and abundant Pt(111) facets. Additionally, the effects of glycerol and KOH concentrations and reaction time on product selectivity were investigated.

Exceptional Performance of Hierarchical Ni-Fe (hydr)oxide@NiCu Electrocatalysts for Water Splitting.

Developing low-cost bifunctional electrocatalysts with superior activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of great importance for the widespread application of the water splitting technique. In this work, using earth-abundant transition metals (i.e., nickel, iron, and copper), 3D hierarchical nanoarchitectures, consisting of ultrathin Ni-Fe layered-double-hydroxide (Ni-Fe LDH) nanosheets or porous Ni-Fe oxides (NiFeOx ) assembled to a metallic NiCu alloy, are delicately constructed. In alkaline solution, the as-prepared Ni-Fe LDH@NiCu possesses outstanding OER activity, achieving a current density of 10 mA cm-2 at an overpotential of 218 mV, which is smaller than that of RuO2 catalyst (249 mV). In contrast, the resulting NiFeOx @NiCu exhibits better HER activity, yielding a current density of 10 mA cm-2 at an overpotential of 66 mV, which is slightly higher than that of Pt catalyst (53 mV) but superior to all other transition metal (hydr)oxide-based electrocatalysts. The remarkable activity of the Ni-Fe LDH@NiCu and NiFeOx @NiCu is further demonstrated by a 1.5 V solar-panel-powered electrolyzer, resulting in current densities of 10 and 50 mA cm-2 at overpotentials of 293 and 506 mV, respectively. Such performance renders the as-prepared materials as the best bifunctional electrocatalysts so far.

Influences of permeation of vanadium ions through PVDF-g-PSSA membranes on performances of vanadium redox flow batteries.

The preparation and physical characterization of a poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid) (PVDF-g-PSSA) membrane prepared by a solution-grafting method were described. These membranes exhibited high conductivity with a value 3.22 x 10(-2) S/cm at 30 degrees C. ICP studies revealed that the PVDF-g-PSSA membrane showed dramatically lower vanadium ion permeability compared to Nafion 117. Trivalent vanadium ions had the highest permeability through all these membranes in contrast to pentavalent vanadium ions with the lowest. The VRB with the low-cost PVDF-g-PSSA membrane exhibited a higher performance than that with Nafion 117 under the same operating conditions, and its energy efficiency reached 75.8% at 30 mA/cm(2). The performance of VRB with the PVDF-g-PSSA membrane can be maintained after more than 200 cycles at a current density of 60 mA/cm(2).