Isolated active metal atoms anchored on nitrogen-doped carbon matrix have been developed as the efficient catalyst for accelerating sluggish reaction kinetics of oxygen reduction reaction (ORR). The facile rational structure engineering with abundant isolated active metal atoms is highly desirable but challenging. Herein, we demonstrate that atomically dispersed Fe sites (Fe-N₄ moieties) on the hierarchical porous nitrogen-doped carbon matrix (Fe-SA-PNC) for high ORR activity can be achieved by a dual-template assisted strategy. By thermal decomposition of NH₄Cl template, the nitrogen-doped carbon matrix is generated based on the interaction with carbon precursor of citric acid. Meanwhile, the introduction of NaCl template facilitates the formation of hierarchical porous structures, which enable more active sites exposed and improve the mass transfer. Interestingly, the dual-template strategy can inhibit the formation of iron carbide nanoparticles (NPs) by generating porous structures and avoiding of the rapid loss of nitrogen during pyrolysis. The as-made Fe-SA-PNC catalysts with well-defined Fe-N₄ active sites exhibit highly efficient ORR activity with a half-wave potential of 0.838 V versus the reversible hydrogen electrode, as well as good stability and methanol tolerance, outperforming the commercial Pt/C. The zinc-air battery (ZAB) constructed by Fe-SA-PNC also shows a higher peak power density and specific discharging capacity than that of Pt-based ZAB. The present work provides the facile strategy for tailoring nitrogen doping and porous structures simultaneously to prevent the formation NPs for achieving the well-dispersed and accessible single-atom active sites, paving a new way to design efficient electrocatalysts for ORR in fuel cells.

Transition-metal phosphides, as the promising alternatives to noble metal catalysts, have been widely used as efficient electrocatalysts for hydrogen evolution reaction (HER). In this work, three kinds of cobalt-8-hydroxyquinoline (Coq_x) with different size and nanostructures are synthesized by varying the hydrothermal conditions, which was named as Coq_x-L, Coq_x-M and Coq_x-S according to the decreased size. Accordingly, the Co_xP/NC with three different size nanostructures (Co_xP/NC-L, Co_xP/NC-M and Co_xP/NC-S) are obtained by the sequential carbonization and phosphidation of Coq_x. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results imply the identical chemical composition in these catalysts with different morphologies. Thus, systematic study is carried out to reveal the relationship between catalytic performance and morphologies of materials with the same chemical composition. The experimental result indicates that the morphology of Co_xP/NC plays a crucial role on the surface area and electron transfer. Finally, the catalyst of Co_xP/NC-S with the smallest size nanostructrue exhibits the best HER performance with a low overpotential at current density of 10 mA/cm² (η = 56.9 and 115.6 mV) and a small Tafel slope (52.3 and 69.3 mV/dec) in both 0.1 M HClO₄ and 1.0 M KOH as well as long-term stability.