Highly dispersed redox-active polyoxometalates’ periodic deposition on multi-walled carbon nanotubes for boosting electrocatalytic triiodide reduction in dye-sensitized solar cells

Abstract

Polyoxometalates (POMs) have been considered as an efficient catalyst for triiodide reduction in dye-sensitized solar cells (DSSCs). However, agglomeration of POMs limits the improvement in power conversion efficiency (PCE) of DSSCs. In this paper, we improve our previous synthesis process by a simple ultrasonic driving strategy. A series of highly dispersed POM nanoparticles periodically deposited on multi-walled carbon nanotube (MWCNT) nanocomposites (abbreviated as POMs/CNTs) is synthesized, which increases the active sites by improving the dispersion degree and inhibiting the aggregation of POM molecules. Additionally, CNTs as a conductive support skeleton and physical barrier promote the rapid electron transfer and protect POM molecules from chemical degradation. The nanocomposites exhibit well-distributed morphology, and highly dispersed POM nanoparticles about tens of nanometers in diameter are in intimate contact with CNTs. Powder X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy demonstrate that POM nanoparticles have been periodically deposited on CNTs. POM/CNT counterelectrodes (CEs) exhibit a more remarkable performance towards triiodide reduction than pure CNT CEs, indicating that POMs deposited on CNTs boost electrocatalytic triiodide reduction. Among these POM/CNT CEs, the Co₄PW₉/CNT CE exhibits the best photovoltaic behavior with a high power conversion efficiency (PCE) of 7.60%, which is superior to that of the Pt CE (6.59%). The excellent activity originates from the synergistic effect between the high redox activity of POMs and the excellent conductive ability of CNTs. This work provides a foundation for preparing advanced high-efficient CE catalysts of POM materials.