Sodium‐ion batteries (SIBs), which are an alternative to lithium‐ion batteries (LIBs), have attracted increasing attention due to their low cost of Na resources and similar Na storage mechanism to LIBs. Compared with anode materials and electrolytes, the development of cathode materials lags behind. Therefore, the key to improving the specific energy and promoting the application of SIBs is to develop high‐performance sodium intercalation cathode materials. Transition‐metal oxides are one of the most promising cathode materials for SIBs owing to their excellent energy density, high specific discharge capacity, and environmentally friendly nature. In the present work, the latest progress in the research of transition‐metal oxides is summarized. Moreover, the existing challenges are discussed, and a series of strategies are proposed to overcome these drawbacks. This review aims at providing guidance for the development of metal oxides in the next stage.

We design a carbon-free Si/polyaniline hybrid anode composed of porous Si dendrites and oxalic acid doped polyaniline coatings.

High-entropy solid-solution alloys have generated significant interest in energy conversion technologies. However, structurally ordered high-entropy intermetallic (HEI) nanoparticles (NPs) have been rarely reported in electrocatalysis applications. Here, we demonstrate structurally ordered PtIrFeCoCu HEI (PIFCC-HEI) NPs with extremely superior performance for both oxygen reduction reaction (ORR) and H2/O2 fuel cells. The PIFCC-HEI NPs show an average diameter of 6 nm. Atomic structural characterizations including atomic-resolution energy-dispersive spectroscopy (EDS) mapping technology confirm the ordered intermetallic structure of PIFCC-HEI NPs. As an electrocatalyst for ORR, the PIFCC-HEI/C achieves an ultrahigh mass activity of 7.14 A mgnoble metals –1 at 0.85 V and extraordinary durability over 60 000 potential cycles. Moreover, the fuel cell assembled with PIFCC-HEI/C as the cathode delivers an ultrahigh peak power density of 1.73 W cm–2 at a back pressure of 1.0 bar and almost no working voltage decay after 80 h operation, certifying the top-level performance among reported fuel cells. Theoretical calculations combined with experimental results reveal that the superior performance of PIFCC-HEI/C for ORR and fuel cells is attributed to its ultrahigh-activity facets. Especially, the (001) facet affords the lowest activation barriers for the rate-limiting step, the optimal downshift of the d-band center, and more efficient regulation of electron structures for ORR. This work not only opens up a new avenue for the fabrication of high-activity facets in the catalysts but also highlights structurally ordered HEI NPs as sufficiently effective catalysts in practical fuel cells and other potential energy-related applications.

No abstract

No abstract