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Leaching of uranium, thorium and rare earth from the monazite selective solution residue were studied by conventional leaching--two-stage countercurrent leaching was studied. The effects of various factors on the leaching was investigated. The results show that the leaching rates of uranium, thorium and rare earth are 98.66 %, 95.37 % and 64.23%, respectively under suitable conditions using conventional leaching method. Using the two-stage countercurrent leaching method, the leaching rates of uranium, thorium and rare earth can be increased by 0.5%~1.0%, the residual acid of the leaching solution can be reduced by more than 50%, and the solid-liquid separation performance of the slurry can be improved to a certain extent. [ABSTRACT FROM AUTHOR]

Regular hollow catalysts have aroused increasing attention in electrocatalysis owing to large surface area, many more active centers and fast mass transfer. Nevertheless, the structure regulation of regular hollow catalysts, especially octahedrons, is scarcely reported. Herein, by developing a facile strategy, we successfully integrate Ru clusters and Cu–MoO2 nanocrystals into a fused nearly hollow Ru–Cu–MoO2 octahedron encapsulated in carbon. Due to the synergic effect and the advantageous structure and composition, such a multiple-nanocomponent catalyst merely requires 22 and 48 mV overpotentials at a current density of 10 mA cm−2 for the hydrogen evolution reaction (HER) in 1 M KOH and 0.5 M H2SO4 solutions, respectively. More importantly, in alkaline seawater, nearly hollow Ru–Cu–MoO2 octahedrons also present remarkable HER activity (23 mV @ 10 mA cm−2), indicating potential applications in hydrogen production from seawater electrolysis. Furthermore, density functional theory (DFT) calculation results unveil that the excellent catalytic activity of Ru–Cu–MoO2 is on account of its relatively low hydrogen adsorption Gibbs free energy (ΔGH*) and water adsorption energy. The present work provides a new approach for designing advanced Ru-based catalysts for the HER and beyond. [ABSTRACT FROM AUTHOR]

Highly efficient and stable Pt-based electrocatalysts have attracted significant attention for hydrogen generation via water splitting. However, the main obstacles in their industrial application are the scarcity and high cost of Pt resources. Herein, we proposed a novel confined replacement method to synthesize PtCu nanoalloys with molybdenum dioxide supported by a porous octahedral carbon matrix (PtCu–MoO2@C) via a metal–organic framework (MOF)-assisted strategy. Cu-based MOFs and MOF-derived octahedral carbon served as substrates to co-promote the formation and high dispersion of PtCu nanoalloys by the in situ reduction of Pt ions, resulting in fast electron transfer during the hydrogen evolution reaction (HER). As expected, our electrocatalyst requires very small overpotentials (24 mV in 1.0 M KOH and 42 mV in 0.5 M H2SO4) to achieve the current density of 10 mA cm−2. Moreover, it exhibits a superior mass activity (0.30 A mgPt−1 at −0.05 V in alkaline media and 0.49 A mgPt−1 at −0.05 V in acidic media), which is about 1.6 times that of commercial Pt/C catalysts, and high durability when compared with that of Pt/C, with a nearly 100% faradaic yield of hydrogen production. This synthetic strategy can provide new approaches to the design of noble metal-based electrocatalysts for future energy systems. [ABSTRACT FROM AUTHOR]

Phosphorization engineering is an alternative method to explore highly efficient electrocatalysts for water splitting. Herein, a heterostructure consisting of Ni2P and Ni3S2 supported on commercial nickel foam (Ni3S2–Ni2P/NF) was prepared through the conversion of some Ni3S2 molecules into Ni2P by phosphorization engineering. Electrochemical tests revealed that the partial phosphorization of Ni3S2 effectively enhanced the catalytic activity of the host electrocatalyst towards the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in 1 M KOH; in particular, the Ni3S2–Ni2P/NF electrode exhibited the current density of 50 mA cm−2 at the very low OER overpotential of 287 mV and needed the low overpotential of 130 mV to afford 10 mA cm−2 for the HER. Moreover, the alkaline electrolyzer assembled by two Ni3S2–Ni2P/NF electrodes could deliver 10 mA cm−2 at the low voltage of 1.58 V and exhibited excellent durability during electrolysis for 15 h. Therefore, our study opens up an attractive fabrication strategy for highly active heterostructure electrocatalysts. [ABSTRACT FROM AUTHOR]

Phosphorization engineering is an alternative method to explore highly efficient electrocatalysts for water splitting. Herein, a heterostructure consisting of Ni 2 P and Ni 3 S 2 supported on commercial nickel foam (Ni 3 S 2 -Ni 2 P/NF) was prepared through the conversion of some Ni 3 S 2 molecules into Ni 2 P by phosphorization engineering. Electrochemical tests revealed that the partial phosphorization of Ni 3 S 2 effectively enhanced the catalytic activity of the host electrocatalyst towards the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in 1 M KOH; in particular, the Ni 3 S 2 -Ni 2 P/NF electrode exhibited the current density of 50 mA cm -2 at the very low OER overpotential of 287 mV and needed the low overpotential of 130 mV to afford 10 mA cm -2 for the HER. Moreover, the alkaline electrolyzer assembled by two Ni 3 S 2 -Ni 2 P/NF electrodes could deliver 10 mA cm -2 at the low voltage of 1.58 V and exhibited excellent durability during electrolysis for 15 h. Therefore, our study opens up an attractive fabrication strategy for highly active heterostructure electrocatalysts.

Theoretical calculations reveal that intrinsic pentagons in the basal plane can contribute to the local electronic redistribution and the contraction of band gap, making the carbon matrix possess superior binding affinity and electrochemical reactivity. To experimentally verify this, a pentagon-defect-rich carbon nanomaterial was constructed by means of in situ etching of fullerene molecules (C 60 ). The electrochemical tests show that, relative to hexagons, such a carbon-based material with abundant intrinsic pentagon defects makes much greater contribution to the electrocatalytic oxygen reduction activity and electric double layer capacitance. It shows a four-electron-reaction mechanism similar to commercial Pt/C and other transition-metal-based catalysts, and a higher specific capacitance than many reported metal-free carbon materials. These results show the influence of intrinsic pentagon defects for developing carbon-based nanomaterials toward energy conversion and storage devices., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Transition metal phosphides (TMPs) are considered to be superb catalysts for water splitting. In this work, we introduce an efficient strategy to fabricate dicobalt phosphide (Co 2 P) quantum dots embedded in N, P dual-doped carbon (Co 2 P@NPC) on carbon cloth (Co 2 P@NPC/CC) by in situ carbonization of cobalt ion induced phytic acid (PA) and polyaniline (PANI) macromolecule precursors. As a highly efficient self-supported electrode, it has a low onset overpotential (74 mV at 1 mA cm -2 ) approaching that of the commercial Pt/C catalyst for the hydrogen evolution reaction (HER) in acidic media. Meanwhile, it also shows very low overpotentials of only 116 and 129 mV at 10 mA cm -2 with robust stability in acidic and alkaline media, respectively.