RESUMO
Controlling the concentrations of H2O and CO2 at the reaction interface is crucial for achieving efficient electrochemical CO2 reduction. However, precise control of these variables during catalysis remains challenging, and the underlying mechanisms are not fully understood. Herein, guided by a multi-physics model, we demonstrate that tuning the local H2O/CO2 concentrations is achievable by thin polymer coatings on the catalyst surface. Beyond the often-explored hydrophobicity, polymer properties of gas permeability and water-uptake ability are even more critical for this purpose. With these insights, we achieve CO2 reduction on copper with Faradaic efficiency exceeding 87% towards multi-carbon products at a high current density of -2 A cm-2. Encouraging cathodic energy efficiency (>50%) is also observed at this high current density due to the substantially reduced cathodic potential. Additionally, we demonstrate stable CO2 reduction for over 150 h at practically relevant current densities owning to the robust reaction interface. Moreover, this strategy has been extended to membrane electrode assemblies and other catalysts for CO2 reduction. Our findings underscore the significance of fine-tuning the local H2O/CO2 balance for future CO2 reduction applications.
RESUMO
Ultrafiltration (UF) is widely used in wastewater reclamation treatments. Conventional backwashing is usually performed at regular time intervals (10-120 min) with permeate and without the addition of chemicals. Chemical enhanced backwashing (CEB) is usually applied after 70-90 filtration cycles with added chemicals. These cleaning methods cause membrane fouling and require costly chemicals. Instead of conventional backwashing, we propose herein a new backwashing method involving backwashing the effluent with low doses of sodium hypochlorite (NaClO) named as BELN. The performance and cost of UF backwashing were investigated with Beijing wastewater reclamation treatment. The results showed that the transmembrane pressure (TMP) increased from 33.2 to 48.2 kPa during hydraulic backwashing after 80 filtration cycles but increased from 33.3 to 39.3 kPa during backwashing with a low NaClO content of 20 mg/L. It was also noticed that the hydraulic-irreversible fouling index decreased from 5.58 × 10-3 m2/L to 3.58 × 10-3 m2/L with the new method. According to the three-dimensional fluorescence excitation-emission (3D-EEM), the response increased from 11.9 to 15.2% with BELN. Protein-like material was identified as the main component causing membrane fouling by blocking the membrane pores. The results indicated that the low dosage of NaClO effectively stripped the fouling layer. Finally, based on an economic evaluation, the capacity of the UF process was increased from 76,959 to 109,133 m3/d with the new method. The amount of NaClO consumed for Beijing wastewater reclamation treatment was similarly compared with the conventional backwashing in per year under BELN. The new method has good potential for application.
Assuntos
Ultrafiltração , Purificação da Água , Ultrafiltração/métodos , Águas Residuárias , Membranas Artificiais , Filtração , Purificação da Água/métodosRESUMO
If combined with renewably generated electricity, electrochemical CO2 reduction (E-CO2R) could be used as a sustainable source of chemicals and fuels. Tandem catalysis approaches are attractive for providing the product selectivity, which would be required for commercial applications. Here, we demonstrate a two-step tandem electrocatalytic E-CO2R with efficient conversion of the intermediate species. The catalyst scaffold is Si(100), which is etched to form a textured surface consisting of micron-sized pyramid structures with the {111} facets. Two metals are used in the electrocatalytic cascade: Ag is employed to perform a two-electron reduction of CO2 to the intermediate CO, and Cu performs conversion to more reduced products. Using high-angle physical vapor deposition, we form separated, micron-scale areas of the two electrocatalysts on opposite sides of the pyramids, with their relative surface coverages being tunable with the deposition angle. Compared to the textured scaffolds with blanket Ag and Cu used as controls, bimetallic pyramid tandem catalysts have higher current densities and much lower faradic efficiencies (FE) for CO. These effects are due to efficient conversion of the CO formed on Ag to more reduced products on Cu. Methane is the main product to be enhanced by the cascade pathway: a bimetallic catalyst with approximately equal coverages of Ag and Cu produces methane with a FE of 62% at -1.1 VRHE, corresponding to a partial current density of 12.7 mA cm-2. We estimate an intermediate conversion yield for the CO intermediate of 80-90%, which is close to the mass-transport limited value predicted by reaction-diffusion simulations.
RESUMO
The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) in water, suspended particulate matters (SPMs), and sediments in the Lanzhou reach of the Yellow River were investigated in this study. The total PAH concentrations ranged from 548 to 2598 ng/L in water, 1502 to 11,562 ng/g in SPMs, and 181 to 1583 ng/g in sediments. The compositions of PAHs showed that 2- to 3-ring PAHs were abundant in water, 2- to 4-ring PAHs were predominant in SPMs, and 2- to 5-ring PAHs were abundant in sediments. The spatial distribution of PAHs was site-specific and PAHs varied at different sampling locations. The diagnostic ratio analysis indicated that the PAHs mainly had a pyrolytic source. The ecological risk assessment showed that the ecosystem risk of PAHs was low in the Lanzhou reach of the Yellow River.