N8− Polynitrogen Stabilized on Nitrogen-Doped Carbon Nanotubes as an Efficient Electrocatalyst for Oxygen Reduction Reaction

Zhenhua Yao,Wangyang Ji,Tingxuan Yan,Ruiyang Fan,Maocong Hu

doi:10.3390/catal10080864

Abstract

In this work, non-traditional metal-free polynitrogen chain N8− deposited on a nitrogen-doped carbon nanotubes (PN-NCNT) catalyst was successfully synthesized by a facile cyclic voltammetry (CV) approach, which was further tested in an oxygen reduction reaction (ORR). The formation of PN on NCNT was confirmed by attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) and Raman spectroscopy. Partial positive charge of carbon within NCNT facilitated electron transfer and accordingly induced the formation of more PN species compared to CNT substrate as determined by temperature-programmed decomposition (TPD). Rotating disk electrode (RDE) measurements suggested that a higher current density was achieved over PN-NCNT than that on PN-CNT catalyst, which can be attributed to formation of the larger amount of N8− on NCNT. Kinetic study suggested a four-electron pathway mechanism over PN-NCNT. Moreover, it showed long stability and good methanol tolerance, which indicates its great potential application. This work provides insights on designing and synthesizing non-traditional metal-free catalysts for ORR in fuel cells.

Highlights

As an important electrochemical process, the oxygen reduction reaction (ORR) under alkaline conditions has been widely investigated in many applications such as alkaline fuel cells, metal–air batteries, and brine electrolysis [1,2,3,4]
Following our previous observations on PN synthesis and its application in oxygen reduction reactions, in this work, nitrogen-doped carbon nanotubes (NCNTs) were selected as substrates to synthesize a polynitrogen chain N8 − (PN) catalyst with a cyclic voltammetry (CV) method while the synthesized PN was further tested for ORR
The quantitative analysis based on temperature-programmed decomposition (TPD) determined that a larger amount of PN deposited on NCNT compared to that over CNT

Summary

Introduction

As an important electrochemical process, the oxygen reduction reaction (ORR) under alkaline conditions has been widely investigated in many applications such as alkaline fuel cells, metal–air batteries, and brine electrolysis [1,2,3,4]. The relatively sluggish kinetics of the reaction is regarded as one of the key factors that limits its performance in related applications such as proton exchange membrane fuel cells (PEMFCs) [5,6,7]. Among the factors hampering the widespread application of PEMFCs, are the high-cost and low-performance electrocatalysts, which are responsible for accelerating the sluggish oxygen reduction reaction (ORR) at the cathode, and still need to be improved [10,11]. Nonprecious metal catalysts, such as Fe-, Co-, Cu-, and Ni-based materials, can lower the cost, activity and metal leaching are the two major issues to be solved [14,15,16]

Methods

Results

Conclusion