No abstract

Tuning the atomic interface configuration of noble metals (NMs) and transition-metal oxides is an effective straightforward yet challenging strategy to modulate the activity and stability of heterogeneous catalysts. Herein, Pd supported on mesoporous Fe2O3 with a high specific surface area was rationally designed and chosen to construct the Pd/iron oxide interface. As a versatile model, the physicochemical environments of Pd nanoparticles (NPs) could be precisely controlled by taming the reduction temperature. The experimental and density functional theory calculation results unveiled that the catalyst in the support–metal interface confinement (SMIC) state showed significantly enhanced catalytic activity and sintering resistance for CO oxidation. The constructed Fe sites at the interfaces between FeO x overlayers and Pd NPs not only provided additional coordinative unsaturated ferrous sites for the adsorption and activation of O2, thereby facilitating the activation efficiency of O2, but also impressively changed the reaction pathway of CO oxidation. As a result, the catalyst followed the Pd/Fe dual-site mechanism instead of the classical Mars–van Krevelen mechanism. For the catalyst in the strong metal–support interaction (SMSI) state, its catalytic activity was seriously suppressed because of the excessive encapsulation of the active Pd sites by FeO x overlayers. The present study therefore provides detailed insights into the SMIC and SMSI in ferric oxide-supported Pd catalysts, which could guide the preparation of highly efficient supported catalysts for practical applications.

Mesoporous metal oxides with wide pore size, high surface area, and uniform porous structures have demonstrated excellent advantages in various fields. However, the state-of-art synthesis approaches are dominated by wet chemistry, accompanied by use of excessive solvent, and the requirement of time-consuming drying process. Herein, we report a mechanochemical solid-state route to synthesize mesoporous Al 2 O 3 (meso-Al 2 O 3 ) via aluminum isopropoxide-copolymers assembly. The obtained meso-Al 2 O 3 shows a record high surface area (∼644 m 2 g −1 ) and narrow pore size distribution (centered at ∼5 nm). Moreover, a mechanochemical nonhydrolytic sol−gel strategy is introduced to fabricate mesoporous metal (Cu, Co, Mn, Fe, Mg, Ni)-aluminum binary oxide by using anhydrous metal chlorides and aluminum isopropoxide interplay. More importantly, four or five metals-aluminum oxide complexes with abundant mesopores and single cubic crystalline phase known as high-entropy ceramics are produced. To the best of our knowledge, mesoporous high-entropy metal oxides have not been prepared before, because the high crystallization temperature would make mesopores collapse. Additionally, this high-entropy property endows (CuNiFeCoMg)O x −Al 2 O 3 with superior SO 2 -resisting performance (1000 ppm of SO 2 in N 2 at 280 °C) in the catalytic oxidation of CO compared to single CuO− Al 2 O 3 .

Developing hard carbon with a high initial Coulombic efficiency (ICE) and very good cycling stability is of great importance for practical sodium-ion batteries (SIBs). Defects and oxygen-containing groups grown along either the carbon edges or the layers, however, are inevitable in hard carbon and can cause a tremendous density of irreversible Na + sites, decreasing the efficiency and therefore causing failure of the battery. Thus, eliminating these unexpected defect structures is significant for enhancing the battery performance. Herein, we develop a strategy of applying a soft-carbon coating onto free-standing hard-carbon electrodes, which greatly hinders the formation of defects and oxygencontaining groups on hard carbon. The electrochemical results show that the soft-carbon-coated, free-standing hard-carbon electrodes can achieve an ultrahigh ICE of 94.1% and long cycling performance (99% capacity retention after 100 cycles at a current density of 20 mA g −1 ), demonstrating their great potential in practical sodium storage systems. The sodium storage mechanism was also investigated by operando Raman spectroscopy. Our sodium storage mechanism extends the "adsorption−intercalation−pore filling−deposition" model. We propose that the pore filling in the plateau area might be divided into two parts: (1) sodium could fill in the pores near the inner wall of the carbon layer; (2) when the sodium in the inner wall pores is close to saturation, the sodium could be further deposited onto the existing sodium.

Hard carbon (HC) anodes have shown extraordinary promise for sodium‐ion batteries, but are limited to their poor initial coulombic efficiency (ICE) and low practical specific capacity due to the large amount of defects. These defects with oxygen containing groups cause irreversible sites for Na+ ions. Highly graphited carbon decreases defects, while potentially blocking diffusion paths of Na+ ions. Therefore, molecular‐level control of graphitization of hard carbon with open accessible channels for Na+ ions is key to achieve high‐performance hard carbon. Moreover, it is challenging to design a conventional method to obtain HCs with both high ICE and capacity. Herein, a universal strategy is developed as manganese ions‐assisted catalytic carbonization to precisely tune graphitization degree, eliminate defects, and maintain effective Na+ ions paths. The as‐prepared hard carbon has a high ICE of 92.05% and excellent cycling performance. Simultaneously, a sodium storage mechanism of “adsorption‐intercalation‐pore filling‐sodium cluster formation” is proposed, and a clear description given of the boundaries of the pore structure and the specific dynamic process of pore filling.