This review addresses the recent developments and progress in the synthesis, structure and properties of MXenes, as well as their energy conversion and storage and related applications.
Atomically dispersed precious metal catalysts have emerged as a frontier in catalysis. However, a robust, generic synthetic strategy toward atomically dispersed catalysts is still lacking, which has limited systematic studies revealing their general catalytic trends distinct from those of conventional nanoparticle (NP)-based catalysts. Herein, we report a general synthetic strategy toward atomically dispersed precious metal catalysts, which consists of "trapping" precious metal precursors on a heteroatom-doped carbonaceous layer coated on a carbon support and "immobilizing" them with a SiO 2 layer during thermal activation. Through the "trapping-and-immobilizing" method, five atomically dispersed precious metal catalysts (Os, Ru, Rh, Ir, and Pt) could be obtained and served as model catalysts for unravelling catalytic trends for the oxygen reduction reaction (ORR). Owing to their isolated geometry, the atomically dispersed precious metal catalysts generally showed higher selectivity for H 2 O 2 production than their NP counterparts for the ORR. Among the atomically dispersed catalysts, the H 2 O 2 selectivity was changed by the types of metals, with atomically dispersed Pt catalyst showing the highest selectivity. A combination of experimental results and density functional theory calculations revealed that the selectivity trend of atomically dispersed catalysts could be correlated to the binding energy difference between *OOH and *O species. In terms of 2 e − ORR activity, the atomically dispersed Rh catalyst showed the best activity. Our general approach to atomically dispersed precious metal catalysts may help in understanding their unique catalytic behaviors for the ORR.
The preparation of size-and shape-controlled nanoparticles has enabled the understanding of important nanoscale catalytic phenomena, resulting in the design of advanced catalysts with enhanced activities and selectivities. Metal phosphides have recently emerged as a promising class of non-precious metal catalysts for hydrogen evolution reaction (HER), which is a cornerstone in clean and environmentally benign hydrogen production. Although significant progress has been made in metal phosphide catalysts, the impact of the metal phosphide shape has not yet been explored. Herein, we investigated the shape-dependent electrocatalytic activity of nickel phosphide nanoparticles (Ni 2 P NPs) for the HER. Spherical Ni 2 P NPs mainly composed of the Ni 2 P(001) surface showed higher HER activity than rod-shaped Ni 2 P NPs with the Ni 2 P(210) surface in terms of overpotential, Tafel slope, and turnover frequency. The results imply that the Ni 2 P(001) surface would have preferential interactions with the adsorbent and a lower activation barrier for hydrogen adsorption, promoting the overall rate of HER. This study highlights the importance of morphology control in electrocatalysts to boost catalytic performances.
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