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  1. The development of anode materials with high-rate capability is critical to high-power lithium batteries. T-Nb 2 O 5 has been widely reported to exhibit pseudocapacitive behavior and fast lithium storage capability. However, the other polymorphs of Nb 2 O 5 prepared at higher temperatures have the potential to achieve even higher specific capacity and tap density than T-Nb 2 O 5 , offering higher volumetric power and energy density. Here, micrometer-sized H-Nb 2 O 5 with rich Wadsley planar defects (denoted as d-H-Nb 2 O 5 ) is designed for fast lithium storage. The performance of H-Nb 2 O 5more »with local rearrangements of [NbO 6 ] octahedra blocks surpasses that of T-Nb 2 O 5 in terms of specific capacity, rate capability, and stability. A wide range variation in the valence of niobium ions upon lithiation was observed for defective H-Nb 2 O 5 via operando X-ray absorption spectroscopy. Operando extended X-ray absorption fine structure and ex situ Raman spectroscopy analyses reveal a large and reversible distortion of the structure in the two-phase region. Computation and ex situ X-ray diffraction analysis reveal that the shear structure expands along major lithium diffusion pathways and contracts in the direction perpendicular to the shear plane. Planar defects relieve strain through perpendicular arrangements of blocks, minimizing volume change and enhancing structural stability. In addition, strong Li adsorption on planar defects enlarges intercalation capacity. Different from nanostructure engineering, our strategy to modify the planar defects in the bulk phase can effectively improve the intrinsic properties. The findings in this work offer new insights into the design of fast Li-ion storage materials in micrometer sizes through defect engineering, and the strategy is applicable to the material discovery for other energy-related applications.« less
    Free, publicly-accessible full text available January 19, 2023
  2. One of the key challenges that hinders broad commercialization of proton exchange membrane fuel cells is the high cost and inadequate performance of the catalysts for the oxygen reduction reaction (ORR). Here we report a composite ORR catalyst consisting of ordered intermetallic Pt-alloy nanoparticles attached to an N-doped carbon substrate with atomically dispersed Fe–N–C sites, demonstrating substantially enhanced catalytic activity and durability, achieving a half-wave potential of 0.923 V ( vs.  RHE) and negligible activity loss after 5000 cycles of an accelerated durability test. The composite catalyst is prepared by deposition of Pt nanoparticles on an N-doped carbon substrate withmore »atomically dispersed Fe–N–C sites derived from a metal–organic framework and subsequent thermal treatment. The latter results in the formation of core–shell structured Pt-alloy nanoparticles with ordered intermetallic Pt 3 M (M = Fe and Zn) as the core and Pt atoms on the shell surface, which is beneficial to both the ORR activity and stability. The presence of Fe in the porous Fe–N–C substrate not only provides more active sites for the ORR but also effectively enhances the durability of the composite catalyst. The observed enhancement in performance is attributed mainly to the unique structure of the composite catalyst, as confirmed by experimental measurements and computational analyses. Furthermore, a fuel cell constructed using the as-developed ORR catalyst demonstrates a peak power density of 1.31 W cm −2 . The strategy developed in this work is applicable to the development of composite catalysts for other electrocatalytic reactions.« less