Zinc‐Mediated Template Synthesis of Fe‐N‐C Electrocatalysts with Densely Accessible Fe‐N_x Active Sites for Efficient Oxygen Reduction

Abstract

Owing to their earth abundance, high atom utilization, and excellent activity, single iron atoms dispersed on nitrogen‐doped carbons (Fe‐N‐C) have emerged as appealing alternatives to noble‐metal platinum (Pt) for catalyzing the oxygen reduction reaction (ORR). However, the ORR activity of current Fe‐N‐C is seriously limited by the low density and inferior exposure of active Fe‐Nx species. Here, a novel zinc‐mediated template synthesis strategy is demonstrated for constructing densely exposed Fe‐Nx moieties on hierarchically porous carbon (SA‐Fe‐NHPC). During the thermal treatment of 2,6‐diaminopyridine/ZnFe/SiO2 complex, the zinc prevents the formation of iron carbide nanoparticles and the SiO2 template promotes the generation of hierarchically pores for substantially improving the accessibility of Fe‐Nx moieties after subsequent leaching. As a result, the SA‐Fe‐NHPC electrocatalysts exhibit an unprecedentedly high ORR activity with a half‐wave potential (E1/2) of 0.93 V in a 0.1 m KOH aqueous solution, which outperforms those for Pt/C catalyst and state‐of‐the‐art noble metal‐free electrocatalysts. As the air electrode in zinc–air batteries, the SA‐Fe‐NHPC demonstrates a large peak power density of 266.4 mW cm−2 and superior long‐term stability. Therefore, the developed zinc‐mediated template synthesis strategy for boosting the density and accessibility of Fe‐Nx species paves a new avenue toward high‐performance ORR electrocatalysts.

Multilayer stabilization for fabricating high-loading single-atom catalysts

“…Furthermore, the Fe-SA-NSFC-based Zn-air battery delivered a specific capacity of 792.1 mAh g Zn −1 at 10 mA cm −2 , corresponding to ∼96.6% utilization of the theoretical capacity (∼820 mAh g Zn −1 ) (Fig. 5c) 18 . It worked stably in a mechanically rechargeable battery by only refuelling the consumed zinc anode and electrolytes at the end of each discharge.…”

“…The N 1s spectrum revealed the presence of four types of N species, namely, pyridinic N (398.6 eV), Fe-N (399.5 eV), graphitic N (401.2 eV), and oxidized N (402.5 eV) ( Fig. 2c) 18 . The high content of FeN 4 (15.0%) was attributed to the pronounced N-coordination sites that anchored Fe and enabled the formation of FeN 4 moieties with a high density.…”

Synthesis and Performance of MOF-Based Non-Noble Metal Catalysts for the Oxygen Reduction Reaction in Proton-Exchange Membrane Fuel Cells: A Review

“…The high performance was attributed to a well-graphitized structure that ensured good electrical conductivity for electron transfer, while the high specific surface area offered abundant space to uniformly distribute the atomically isolated Fe active sites and increase the area of contact with the electrolyte. In an alkaline electrolyte, the SA-Fe-NHPC catalyst synthesized by Chen et al presented the best performance [ 84 ]. This catalyst showed higher ORR activity than the benchmark Pt/C catalyst tested under the same conditions, presenting a half-wave potential of 0.93 V (0.85 V for Pt/C).…”

“…Chen et al used Zn-mediated template synthesis to prepare a hierarchically porous carbon with densely exposed Fe-N x moieties (SA-Fe-NHPC) [ 84 ]. More specifically, SA-Fe-NHPC was fabricated by the pyrolysis of the nitrogen-rich 2,6-diaminopyridine/Zn 2+ -Fe 3+ /SiO 2 complex followed by etching.…”

Confined Synthesis of N, P Co–Doped 3D Hierarchical Carbons as High‐Efficiency Oxygen Reduction Reaction Catalysts for Zn–Air Battery

“…[25] However, most of the reported methods nowadays including the synthesis of regular SiO 2 nanoparticles or spheres, polymerization of carbon source on SiO 2 and removing SiO 2 template under harsh HF or NaOH solutions, which brings tedious steps for the synthesis of carbon catalysts and limits the advantages of SiO 2 template. [26][27] Therefore, it is very attractive to develop more facile and convenient method to synthesis carbons based on SiO 2 template.…”