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Oxygen vacancy (VO) engineering has proved to be an effective approach for improving the hydrogen evolution reaction (HER) performance of low-cost metal oxide electrocatalysts. Cerium dioxide (CeO2), an abundant rare-earth metal oxide, is famous for its easy formation of VO and high oxygen mobility, which is believed to be conducive to its application in electrocatalytic HER. Herein, this study reports a facile modification strategy using rGO as a conductive support for CeO2 nanocrystals and introducing the transition metal Ni as the active dopant, resulting in the construction of the Ni–rGO/CeO2 electrocatalyst. It is found that rGO decoration prevents the aggregation of CeO2 NCs and increases the VO concentration in the CeO2 nanocrystals as well, while the introduced Ni leads to further formation of VO and serves as the active site for the HER reaction. Thus, the Ni–rGO/CeO2 electrocatalyst shows relatively low overpotential, a low Tafel slope, and great stability for HER, which is attributed to the synergistic effect of rGO decoration and Ni doping. This kind of facile strategy is promising for the design of noble-metal-free and low-cost electrocatalysts by the functional modification of CeO2-based nanocatalysts. [ABSTRACT FROM AUTHOR]

Black phosphorus (BP) is an emerging two-dimensional semiconductor material, which has interesting structural features and broad application prospects in the fields of optoelectronic devices, energy storage, and biomedicine. However, a large amount of evidence is still needed to clarify the potential mechanism for the synthesis of high-quality BP crystals in chemical vapor transport (CVT) reactions. In this work, high-purity BP crystals were synthesized by the CVT method in an amorphous red phosphorus (aRP), Sn and I2 system. We found that the synthesis of BP experienced the three stage structural transformation of aRP–P4-Hittorf's phosphorus (HP)–BP. First, the phase transition of aRP and P4 molecules was reversible in the sublimation stage; then, the P4 molecules were gradually transformed into the HP structure in the transportation and deposition stage; however, the nucleation of BP quickly inhibited the growth of HP and completed the phase transition quickly; finally, the remaining P4 molecules were transformed into the BP structure, which promoted the growth of BP crystals. Crystallization kinetics explained the nucleation mechanism during the formation of BP, and the competitive nucleation between HP and BP provided the possibility for the bottom-up preparation of BP nanobelts. [ABSTRACT FROM AUTHOR]