The global practical implementation of proton exchange membrane fuel cells (PEMFCs) heavily relies on the advancement of highly effective platinum (Pt)-based electrocatalysts for the oxygen reduction reaction (ORR). To achieve high ORR performance, electrocatalysts with highly accessible reactive surfaces are needed to promote the uncovering of active positions for easy mass transportation. In this critical review, we introduce different approaches for the emerging development of effective ORR electrocatalysts, which offer high activity and durability. The strategies, including morphological engineering, geometric configuration modification via supporting materials, alloys regulation, core–shell, and confinement engineering of single atom electrocatalysts (SAEs), are discussed in line with the goals and requirements of ORR performance enhancement. We review the ongoing development of Pt electrocatalysts based on the syntheses, nanoarchitecture, electrochemical performances, and stability. We eventually explore the obstacles and research directions on further developing more effective electrocatalysts.

Principles of inexpensive biotechnology are being increasingly used to address the problems posed by the use of lithium-sulfur batteries. We used chitin, a low-cost marine biowaste product, as a precursor for the in-situ preparation of chitin-derived nitrogen-doped hierarchical porous carbon fibers (CNHPCFs) containing abundant pores. These materials are characterized by varying morphologies and high specific surface areas and present a hierarchical porous structure. CNHPCFs adsorb polysulfides, exhibit good ionic conductivity, and can be potentially used to generate green energy. These properties help address the problems of volume expansion and slow transport. The CNHPCF-1@S cathode exhibits excellent cycling performance and high capacity (1368.80 mAh·g⁻¹ at 0.2 C; decay rate: 0.011% per turn at 5 C). The high electrochemical reversibility recorded for CNHPCF-1@S and the stepwise reaction mechanism followed were studied using the in-situ X-ray diffraction and in-situ Raman spectroscopy techniques. The results reported herein can potentially help develop new ideas for the recycling and treatment of marine biofertilizers. The results can also provide a platform to improve the application prospects of lithium-sulfur batteries.

Carbon nanotube (CNT) clusters grown in situ in three-dimensional (3D) porous graphene networks (3DG-CNTs), with integrated structure and remarkable electronic conductivity, are desirable S host materials for Li–S batteries. 3DG-CNT exhibits a high surface area (1, 645 m²·g^-1), superior electronic conductivity of 1, 055 S·m^-1, and a 3D porous networked structure. Large clusters of CNTs anchored on the inner walls of 3D graphene networks act as capillaries, benefitting restriction of agglomeration by high contents of immersed S. Moreover, the capillary-like CNT clusters grown in situ in the pores efficiently form restricted spaces for Li polysulfides, significantly reducing the shuttling effect and promoting S utilization throughout the charge/discharge process. With an areal S mass loading of 81.6 wt.%, the 3DG-CNT/S electrode exhibits an initial specific capacity reaching 1, 229 mA·h·g^-1 at 0.5 C and capacity decays of 0.044% and 0.059% per cycle at 0.5 and 1 C, respectively, over 500 cycles. The electrode material also reveals a remarkable rate performance and the large capacity of 812 mA·h·g^-1 at 3 C.