Fe-N-C catalysts, as promising non-precious metal alternatives for the oxygen reduction reaction (ORR), still suffer from severe mass transport limitations in proton exchange membrane fuel cells (PEMFCs) due to water flooding of active sites embedded in micropores. Although pore engineering through a selected template is a general strategy, the structural features of an ideal template, particularly those governing the exposure of active sites and thus affecting mass transport, remain elusive. Here, we demonstrate that low-porosity carbon templates maximize the ratio of active sites distributed at or near the surface, thereby enhancing their exposure and accessibility while reducing mass transport resistance during the ORR process. The C_lp-1@PPy and C_lp-2@PPy (PPy = polypyrrole) catalysts, derived from low-porosity carbon templates, achieve peak power densities of 0.96 and 1.03 W·cm⁻² under H₂/O₂ and 0.50 and 0.52 W·cm⁻² under H₂/air, demonstrating excellent performance in PEMFC tests. Structural and electrochemical characterizations reveal that the enhanced surface exposure of active sites effectively mitigates mass transport resistance during the ORR, thereby offering a general design principle for overcoming mass transport limitations in Fe-N-C catalysts for PEMFC applications.

Sodium ion batteries (SIBs) are a promising alternative to lithium-ion batteries for large-scale energy storage due to their cost-effectiveness and enhanced safety. Layered transition metal oxides (LTMOs) represent one of the most fascinating electrode materials owing to their superior specific capacity, environmental benignity, and facile synthesis. However, they are confronted with challenges, such as irreversible phase transition, structural instability, and insufficient battery performance. Notably, entropy engineering emerges as an effective strategy to mitigate the above issues in energy storage research. This strategy aims to achieve precise composition control and optimized structure–property relationships, thereby enabling LTMOs to overcome the aforementioned limitations. This review focuses on medium- and high-entropy oxides (MEOs and HEOs), highlighting their design principles, growth mechanisms, and applications in layered oxide cathodes for SIBs. Through an in-depth analysis of electrochemical performance, phase transition behavior, and disorder structure regulation, we provide comprehensive insights into the application prospects and optimization pathways of MEO/HEO materials in advanced SIBs. Current challenges are also discussed, offering valuable insights and perspectives to overcome the performance bottlenecks of SIBs and facilitate their large-scale deployment.