# Remodelling hierarchical NiCo2O4@ZnS nanorods with multi-walled carbon nanotubes as a counter electrode for dye-sensitized solar cell applications

## TL;DR

This paper introduces a new platinum-free counter electrode for dye-sensitized solar cells using a nanocomposite of NiCo2O4, ZnS, and carbon nanotubes, achieving high efficiency.

## Contribution

The novel contribution is the synthesis of a hierarchical NiCo2O4@ZnS/MWCNT nanocomposite that enhances solar cell performance without using platinum.

## Key findings

- The NCO@Z-MWCNT nanocomposite achieved a power conversion efficiency of 10.03%, surpassing the platinum reference.
- ZnS and MWCNTs together improved charge transport and electrocatalytic activity.
- The composite showed enhanced thermal stability and reduced charge-transfer resistance.

## Abstract

A hierarchical NiCo2O4@ZnS/MWCNT (NCO@Z-MWCNTs) nanocomposite was synthesized to serve as a platinum-free counter electrode for dye-sensitized solar cells (DSSCs). The nanocomposite comprised spinel NiCo2O4 nanorods, ZnS associated with the surface of the nanorods, and an interconnected multi-walled carbon nanotube (MWCNT) network, and it was synthesized via a low-temperature solution-based hydrothermal method. XRD confirmed the presence of cubic NiCo2O4 and zinc blende ZnS phases, while FESEM–EDS and XPS analyses verified the incorporation of ZnS and the formation of a conductive carbon framework interconnecting adjacent nanorods. ZnS, rather than acting as an isolated catalytic component, was considered to contribute additional sulfide-related surface sites and to modulate the interfacial electronic environment of the NiCo2O4 nanorods, which likely facilitated redox reactions involving the I−/I3− couple. Meanwhile, the MWCNT network established continuous electron transport pathways, effectively reducing interfacial resistance and enhancing charge-transfer efficiency. Thermogravimetric and electrochemical analyses revealed enhanced thermal stability, improved redox kinetics, and a significant reduction in charge-transfer resistance compared with pristine NiCo2O4.The optimized NCO@Z–MWCNT 9wt% counter electrode achieved a power conversion efficiency of 10.03% under AM 1.5 G illumination, exceeding that of the Pt reference device (9.6%). Overall, the improved performance was attributed to the combined contributions of ZnS surface modification and the conductive MWCNT network, which together enhanced charge transport and electrocatalytic activity. This work demonstrates a scalable strategy for developing cost-effective, durable, and high-performance counter electrodes for dye-sensitized solar cells.

The online version contains supplementary material available at 10.1038/s41598-026-38255-7.