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

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 m² g⁻¹, positively shifted ORR onset potential of 67 mV and higher open circuit potential of 268 mV versus Ag/AgCl compared to N-graphene (11 m² g⁻¹, −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. (paper)