Carbon nanotubes in situ embedded with NiS nanocrystals outperform Pt in dye-sensitized solar cells: interface improved activity

Designing a Pt-free counter electrode (CE) electrocatalyst with superior catalytic activity for triiodide (I-3(-)) reduction and electrochemical stability for dye-sensitized solar cells (DSSCs) is always challenging. An active-site-enriched NiS/multiwalled carbon nanotube (CNT) composite was synthesized using smallsized NiS nanoparticles in situ embedded in CNTs through the hot-injection method. A DSSC fabricated with the NiS/CNT CE exhibited an excellent activity to I-3(-) reduction with a surprising photoelectric conversion efficiency (PCE) of 10.82%, outperforming Pt (8.03%). The superior catalytic activity and stability of NiS/CNTs were also observed from electrochemical characterization. DFT calculations revealed that this satisfactory activity was mainly attributed to the appropriate binding energy of I-3(-) on the Ni atoms of the embedded NiS at the unique NiS-CNT interface. Moreover, the strong bonding in the NiS and CNT interface with reduced work function facilitated electron delocalization from embedded NiS nanoparticles to the C walls of CNTs, where the charge-transfer ability was improved. Thus, the as-synthesized NiS/CNT composite is a promising CE material to replace the expensive Pt electrocatalyst in DSSCs.