Integrated Three-Dimensional Carbon Nanopolyhedron/Metal Sulfides: An Efficient Electrocatalyst Toward Oxygen Reduction Reaction

Yi-Wen Yang,Bing-Ye Song

doi:10.3389/fenrg.2021.673923

Abstract

Carbon-based materials hybridized with metal sulfides have gained growing attention as catalytic materials for oxygen reduction reaction (ORR) due to their synergistic effects in terms of richer structural features and higher electrochemical activities. Here, a series of Zn/Co/Fe-based metal-organic frameworks (MOFs) as the precursors, which can be adopted as efficient ORR catalysts, were synthesized through a sulfuration–calcination treatment. The effects of precursor composition, heteroatom doping, and pyrolysis temperature on the structure and electrochemical performance of the catalysts were discussed in detail. It is found that well-grown carbon nanotubes (CNTs) on the surface of graphitic carbon matrix are formed under the synergy effect of trimetallic-based species during pyrolysis. Benefiting from the three-dimensional unique structure with appropriate dopants and high porosity, the catalyst derived from the optimized Zn/Co/Fe-MOFs achieves a half-wave potential of 0.87 V in an alkaline medium for ORR, which is comparable with commercial electrocatalysts. In addition, an outstanding ORR durability of the proposed catalyst in alkaline media was also demonstrated. This work highlights the potential to rationally design and fabricate high-performance ORR catalysts for commercialization.

Highlights

With the exhaustion of traditional fossil fuels, the demand for renewable energy and high-efficiency energy conversion technologies is increasingly becoming more urgent (Shabani et al, 2020)
First, the structures and micromorphologies of the metal-organic frameworks (MOFs)-derived precursors, intermediate products, and final Zn/Co/Fe–S–N-doped carbon (NC) catalysts are observed by SEM and TEM, the chemical components and valence state of elements of Zn/Co/Fe–S–NC and control samples are analyzed by XRD and XPS
This indicates the successful loading of metal sulfides (Zn–S, Co–S, Fe–S) on 3D carbon nanopolyhedron and the doping of S is conducive to the formation of the porous structure of the material

Summary

Introduction

With the exhaustion of traditional fossil fuels, the demand for renewable energy and high-efficiency energy conversion technologies (such as electrolytic splitting of water and fuel cells) is increasingly becoming more urgent (Shabani et al, 2020). Due to the sluggish kinetics of the ORR, commercial noble metal-based catalysts (such as Pt/C, Pd/C) are required to accelerate the processes (Katsounaros et al, 2014; Yu et al, 2017). The exploration of more efficient and cost-effective non-noble metal ORR catalysts is imperative for the development of renewable energy technologies (Chung et al, 2017). Over the past few decades, a large number of low-cost alternatives with ORR catalytic performance have been investigated as substitutes for noble metal-based catalysts (Zhang et al, 2015; Zhu et al, 2016). Numerous studies have shown that nitrogen metal embedded into carbon are the active sites with desirable binding energy for O=O dissociation and O2 adsorption/desorption for ORR (Zhao et al, 2013; Zhang et al, 2018)

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Conclusion