Highly dispersed redox-active polyoxometalates periodic deposition on multi-walled carbon nanotubes for boosting electrocatalytic triiodide reduction in dye-sensitized solar cells
Polyoxometalates (POMs) have been considered as an efficient catalyst for triiodide reduction in dye-sensitized solar cells (DSSCs). However, the agglomeration of POMs limits the improvement of 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 POMs nanoparticles periodic deposition on multi-walled carbon nanotubes (MWCNTs) nanocomposites (abbreviated as POMs/CNTs) are synthesized, which increases the active sites by improving the dispersion degree and inhibiting the aggregation of POMs molecules. Additionally, CNTs as a conductive support skeleton and physical barrier promote the rapidly electron transfer and protect POMs molecules from chemical degradation. The nanocomposites exhibit well-distributed morphology, and highly dispersed POMs nanoparticles about tens of nanometers in diameter are in intimate contact with the CNTs. Power X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy demonstrate that POMs nanoparticles have been periodically deposited on the CNTs. POMs/CNTs counter electrodes (CEs) exhibit the remarkable performance towards triiodide reduction than pure CNTs CE, indicating that POMs deposited on the CNTs boosts electrocatalytic triiodide reduction. Among these POMs/CNTs CEs, Co4PW9/CNTs exhibits the best photovoltaic behavior with high power conversion efficiency (PCE) of 7.60%, which is superior to that of Pt CE (6.59%). The excellent activity is originated from the synergistic effect between the high redox activity of POMs and excellent conductive ability of CNTs. This work provides a foundation for preparing advanced high-efficient CE catalysts of POMs materials.