Electron Diffusion Length and Charge Separation Efficiency in Nanostructured Ternary Metal Vanadate Photoelectrodes

Abstract:

Ternary metal vanadates have recently emerged as promising photoelectrode materials for sunlight-driven water splitting. Here, we show that highly active nanostructured BiVO₄ films can be deposited onto fluorine-doped tin oxide (FTO) substrates by a facile sequential dipping method known as successive ionic layer adsorption and reaction (SILAR). After annealing and deposition of a cobalt phosphate (Co-Pi) co-catalyst, the photoelectrodes produce anodic photocurrents (under 100 mW cm^-2 broadband illumination, 1.23 V vs. RHE) in pH 7 phosphate buffer that are on par with the highest reported in the literature for similar materials. To gain insight into the reason for the good performance of the deposited films, and to identify factors limiting their performance, incident photon-to-electron conversion efficiency spectra have been analyzed using a simple diffusion–reaction model to quantify the electron diffusion length (L_n; the average distance travelled before recombination) and charge separation efficiency (η_sep) in the films. The results indicate that η_sep approaches unity at sufficiently positive applied potential but the photocurrent is limited by significant charge collection losses due to a short L_n relative to the film thickness. The Co-Pi catalyst is found to improve η_sep at low potentials as well as increase L_n at all potentials studied. These findings help to clarify the role of the Co-Pi co-catalyst and show that there could be room for improvement of BiVO₄ photoanodes deposited by SILAR if L_n can be increased.

• Periodical: Materials Science Forum (Volume 941)
• Pages: 2121-2127
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.941.2121
• Online since: December 2018
• Authors: Siti Nur'ain Binti Haji Yassin, Nur Afifah Haniyyah Halidi, Soong Leong Sim, Ye Ru Liu, James Robert Jennings*
• Keywords: Charge Separation Efficiency, Electron Diffusion Length, SILAR, Ternary Metal Vanadates

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