W-based carbide derived from PW12@ZIF-8 as Pt-free catalyst on counter electrode of dye-sensitized solar cells for triiodide reduction

Abstract

The preparation of counter electrodes (CEs) catalysts at different pyrolysis temperatures will directly affect the composition, morphology, and performance of the catalysts in dye-sensitized solar cells (DSSCs) applications. Herein, four W-based carbides catalysts were derived from H3PW12O40-based ZIF-8 metal–organic frameworks (PW12@ZIF-8) by in-situ pyrolysis at 600, 700, 800, and 900 ℃ under N2 atmosphere. The pyrolysis mechanism and structure characteristics of the prepared W-based carbides with temperature variation were confirmed by TG-DTG-DSC simultaneous, XRD, XPS, TEM, SEM and N2 adsorption/desorption, which exhibits the gradual transformation of PW12@ZIF–8 → WC-C→WC→W1-xC→W2C. Furthermore, the photovoltaic performance of four different W-based carbides as CEs catalysts for regenerating I3−/I− shuttles in DSSCs were identified by photocurrent-voltage (J-V) measurement, which achieved PCEs of 4.63, 4.91, 5.05 and 5.78 %, respectively. As a result, W2C (900 ℃) provide more vacancies and defects on the catalyst surface as abundant catalytic active sites, as well as promote the appearance of more pores and voids in the morphology to diffuse and permeate electrolyte due to the highest specific surface area, and the PCE value of 5.78 % was also superior to 5.51 % of Pt CE.