Origin of the electrocatalytic activity in carbon nanotube fiber counter-electrodes for solar-energy conversion

TL;DR

This study uncovers the origins of electrocatalytic activity in carbon nanotube fiber counter-electrodes, linking surface chemistry and metallic content to performance, leading to improved solar cell efficiency.

Contribution

It reveals the relationship between surface oxygen groups, residual metallic nanoparticles, and catalytic activity, enabling the design of more efficient CNTf-based electrodes for solar energy conversion.

Findings

Surface oxygen groups enhance catalytic stability and current

Residual metallic Fe nanoparticles inversely affect catalytic potential

CNTf electrodes outperform platinum in dye-sensitized solar cells

Abstract

However, their electrocatalytic activity is still poorly understood. This work deciphers the origin of the catalytic activity of counter-electrodes (CEs)/current collectors made of self-standing carbon nanotubes fibers (CNTfs) using Co$^(+2)$/Co$^(+3)$ redox couple electrolytes. This is based on comprehensive electrochemical and spectroscopic characterizations of fresh and used electrodes applied to symmetric electrochemical cells using platinum-based CEs as a reference. As the most relevant findings, two straight relationships were established: i) the limiting current and stability increase rapidly with surface concentration of oxygen-containing functional groups, and ii) the catalytic potential is inversily related to the amount of residual metallic Fe catalyst nanoparticles interspersed in the CNTf network. Finally, the fine tune of the metallic nanoparticle content and the degree of functionalization enabled fabrication of efficient and stable dye-sensitized solar cells with cobalt electrolytes and CNTf-CE outperforming those with reference Pt-CEs.