Electroreduction of nitrate to ammonia offers a promising pathway for nutrient recycling and recovery from wastewater with energy and environmental sustainability. There have been considerable efforts on the regulation of reaction pathways to facilitate nitrate-to-ammonia conversion over the competing hydrogen evolution reaction but only with limited success. Here, we report a Cu single-atom gel (Cu SAG) electrocatalyst that produces NH 3 from both nitrate and nitrite under neutral conditions. Given the unique mechanism of NO 2 − activation on Cu SAGs with spatial confinement and strengthened kinetics, a pulse electrolysis strategy is presented to cascade the accumulation and conversion of NO 2 − intermediates during NO 3 − reduction with the prohibited competition from the hydrogen evolution reaction, thus substantially enhancing the Faradaic efficiency and the yield rate for ammonia production compared with constant potential electrolysis. This work underlines the cooperative approach of the pulse electrolysis and SAGs with threedimensional (3D) framework structures for highly efficient nitrate-to-ammonia conversion enabled by tandem catalysis of unfavorable intermediates.

W/Cu multilayer nanofilms and pure W nanofilms were prepared in pure Ar and He/Ar mixing atmosphere by radio frequency magnetron sputtering method. The defect evolution of the samples was characterized by Doppler broadening positron annihilation spectroscopy (DB-PAS).The results show that plenty of defects can be produced by introducing helium (He) into W/Cu multilayer nanofilms. With the natural storage time increasing, the helium located in the near surface of W/Cu multilayer nanofilm would be released gradually and induce the coalescence of the helium related defects due to the diffusion of the helium and defects. In addition, the pure W nanofilms were irradiated by 30 keV helium ions and 40 keV hydrogen (H) ions in sequence at room temperature. From the DB-PAS analysis, it can be shown that a large number of vacancy-type defects are produced due to the He and/or H irradiation. H ions would be trapped by He related defects and produced He-H-V complexes.

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Intraformational water zones are widely reported in Canadian oil sands fields. In order to pressurize a thief zone, one of the initiatives is to inject gas. However, the evaluation of gas injectivity based on a pore size distribution is still a big challenge. This study provides a multi-scale approach to study the effect of a pore size distribution on gas injectivity in intraformational water zones. The results indicate the gas effective permeability increases in a less complex and more discrete pore network. The enhancement of gas effective permeability with increased gas saturation weakens with higher complexity and lower discreteness of a pore network. A less complex and more discrete pore network better benefits the gas injectivity index.

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