Control over fuel cell performance through modulation of pore accessibility: investigation and modeling of carbon nanotubes effects on oxygen reduction at N-graphene-based nanocomposite

Abstract

The lack of performance of graphene-based electrocatalysts for oxygen reduction (ORR) is a major concern for fuel cells which can be mastered using nanocomposites. This work is highlighted by the optimization of nitrogen(N)-doped graphene/carbon nanotubes (CNTs) nanocomposite's ORR performance examined by galvanostatic measurements in realistically approached glucose half-cells. Obtained results mark an essential step for the development of nanocarbon-based cathodes, as we specifically evaluate the electrode performance under real fuel cell conditions. The 2D simulations exclusively represent an important approach for understanding the catalytic efficiency of the nanocomposite with unique structure. The kinetics features extracted from simulations are consistent with the experimentally determined kinetics. The morphology analysis reveals a 3D porous structure. The results demonstrate that the incorporation of CNTs implements mesoscale channels for improved mass transport and leads to efficient 4-electron transfer and enhanced overall catalytic activity in pH-neutral media. The nanocomposite shows increased specific surface area of 142 m g, positively shifted ORR onset potential of 67 mV and higher open circuit potential of 268 mV versus Ag/AgCl compared to N-graphene (11 m g, -17, 220 mV). The findings are supported by 2D simulations giving qualitative evidence to the significant role of CNTs for achieving better accessibility of pores, i.e. enabling improved transfer of oxygen and OH, and providing more reaction sites in the nanocomposite. The nanocomposite demonstrates better ORR performance than constituent components regarding potential application in miniaturized single-compartment glucose-based fuel cells.

Nonprecious Metal Catalysts for Oxygen Reduction in Heterogeneous Aqueous Systems

“…277,278 The importance of pore accessibility within the surface of the catalyst was suggested by researchers using a composite of N-doped graphene and CNTs. 279 Other recent papers also report the synthesis of other metal-free catalysts for the ORR. 280−304…”

“…Zheng et al used partially oxidized graphene to incorporate pyridinic N species via the substitution of O with N during NH 3 treatments and saw that pure pyridinic N species catalyzed the two-electron reduction of O 2 to H 2 O 2 . Another group investigated the influence of different N sources on the types of N species formed in the catalyst and showed that N incorporation from glycine contributed to higher catalyst activity while NH 3 treatment etched the catalyst surface, giving higher surface area and improved access of O 2 to protected active sites. , The importance of pore accessibility within the surface of the catalyst was suggested by researchers using a composite of N-doped graphene and CNTs . Other recent papers also report the synthesis of other metal-free catalysts for the ORR. − …”