Surface Modification of Multi-Walled Carbon Nanotubes via Hemoglobin-Derived Iron and Nitrogen-Rich Carbon Nanolayers for the Electrocatalysis of Oxygen Reduction.

Wensheng Li,Lingtao Sun,Rong Hu,Wenli Liao,Yanrong Li,Chaozhong Guo,Zhongbin Li

doi:10.3390/ma10050564

Abstract

The great challenge of boosting the oxygen reduction reaction (ORR) activity of non-noble-metal electrocatalysts is how to achieve effective exposure and full utilization of nitrogen-rich active sites. To realize the goals of high utilization of active sites and fast electron transport, here we report a new strategy for synthesis of an iron and nitrogen co-doped carbon nanolayers-wrapped multi-walled carbon nanotubes as ORR electrocatalyst (N-C@CNT-Fe) via using partially carbonized hemoglobin as a single-source precursor. The onset and half-wave potentials for ORR of N-C@CNT-Fe are only 45 and 54 mV lower than those on a commercial Pt/C (20 wt.% Pt) catalyst, respectively. Besides, this catalyst prepared in this work has been confirmed to follow a four-electron reaction mechanism in ORR process, and also displays ultra-high electrochemical cycling stability in both acidic and alkaline electrolytes. The enhancement of ORR activity can be not only attributed to full exposure and utilization of active site structures, but also can be resulted from the improvement of electrical conductivity owing to the introduction of CNT support. The analysis of X-ray photoelectric spectroscopy shows that both Fe–N and graphitic-N species may be the ORR active site structures of the prepared catalyst. Our study can provide a valuable idea for effective improvement of the electrocatalytic activity of non-noble-metal ORR catalysts.

Highlights

The development of low-cost and high-performance oxygen reduction electrocatalysts is a key solution for rapid commercialization of various metal-air batteries (MABs) and fuel cells (FCs) [1]
A finding is that the width of two diffraction peaks increases largely, compared with the X-ray diffraction (XRD) pattern of Carbon nanotubes (CNT), which may be explained by the influence of lower graphitization degree [17,18]
The XRD pattern of N-C@CNT-Fe exhibits more complex phase composition, and a series of sharp peaks are displayed at 30.2◦, 35.6◦, 43.2◦, 53.6◦, 57.1◦ and 62.7◦, which can be ascribed to crystalline

Summary

Introduction

The development of low-cost and high-performance oxygen reduction electrocatalysts is a key solution for rapid commercialization of various metal-air batteries (MABs) and fuel cells (FCs) [1]. It is found that the packing and agglomeration of NC-based catalysts decreases the surface density of N-doped active sites and further limits their effective utilization, significantly impeding the enhancement of the ORR electrocatalytic activity [9,10,11] To solve these problems, we previously proposed an interesting method to prepare iron and nitrogen co-doped carbons-modified carbon nanospheres via utilization of a blood protein pyropolymer derived from pig blood as a simple Fe–N-enriched precursor [12,13]. We previously proposed an interesting method to prepare iron and nitrogen co-doped carbons-modified carbon nanospheres via utilization of a blood protein pyropolymer derived from pig blood as a simple Fe–N-enriched precursor [12,13] This method can avoid the agglomeration of blood protein during pyrolysis process, and enhance the electronic conductivity of the catalyst and expose more N-rich active sites on its surface, largely facilitating the fast electron-transport of the ORR. The prepared catalyst (N-C@CNT-Fe) shows outstanding ORR electrocatalytic activity as well as better stability compared with a commercial Pt-based catalyst in both alkaline and acidic solutions

Materials and Chemicals

Synthesis of CNT-Based Catalysts

Characterizations and Electrochemical Tests of CNT-Based Catalysts

Results and Discussion

In Figure

Conclusions