Enhanced electrocatalytic activity of the Au-electrodeposited Pt nanoparticles-coated conducting oxide for the quantum dot-sensitized solar cells

Au was electrodeposited potentiostatically at 0.3V for 5min on nanoporous Pt nanoparticle-coated F-doped SnO₂ (FTO/Pt) substrates. For comparison, Au-electrodeposited FTO (FTO/Au) and Au-uncoated FTO/Pt were prepared. FTO/Au showed large-sized Au clusters dispersed sparsely over FTO, which resulted in lower electrocatalytic activity than FTO/Pt. In contrast, FTO/Pt exhibited poor stability unlike FTO/Au due to poisoning by the adsorption of sulfur species. The Au-electrodeposited FTO/Pt (FTO/Pt/Au) consisted of small Au clusters deposited over the entire area of Pt due to the effective Au nucleation provided by nanoporous metallic Pt. FTO/Pt/Au exhibited enhanced electrocatalytic activity and excellent stability because the small Au particles well-dispersed over the nanoporous metallic Pt network provided numerous electrochemical reaction sites, and the Pt surface was not exposed to the electrolyte. When FTO/Pt/Au was used as the counter electrode (CE) of a quantum dot-sensitized solar cell, the significantly enhanced electrocatalytic activity of the FTO/Pt/Au CE facilitated the reduction reaction of S_n ^2-+2e^- (CE) → S_n-1^2- +S ^2- at the CE/electrolyte interface, resulting in a significantly hindered recombination reaction, S_n^2-+2e^- (TiO₂ in the photoanode) → S_n-1^2- +S ^2-, and significantly improved overall energy conversion efficiency.