Tetrazole-stabilized Ag nanoparticles incorporated into TiO2 nanotubes for oxygen electroreduction†

Abstract

Herein, a heterostructured design strategy involving Ag nanoparticles (Ag NPs) stabilized with 5-(2-mercaptoethyl)tetrazole and immobilized on titania nanotubes for the oxygen reduction reaction (ORR) is reported. Bare titania nanotubular layers were annealed in air (TNT) or in a hydrogen atmosphere (hTNT), and their composites with tetrazole-stabilized Ag NPs (tz-Ag NPs) were evaluated for their ORR performance in alkaline media. The activity of the tz-Ag NP/TNT composites was shown to correlate with TNT doping level, which can be controlled by varying the annealing conditions. In all cases, the tz-Ag NP/hTNT composite shows more positive ORR onset and half-wave potentials (E_1/2) than the tz-Ag NP/TNT composite. An increase in tz-Ag NP loading onto the TNT and hTNT matrix leads to a decrease in the overpotential of O₂ reduction. The hTNT electrocatalyst loaded with a high amount of tz-Ag NPs (24 μg cm⁻²) exhibits superior ORR activity over a bare Ag electrode in terms of ORR onset and half-wave potentials. Ag NPs stabilized with tetrazole demonstrate an improved ORR performance in alkaline media compared to Ag NPs capped with citrate. The TNT electrodes loaded with tz-Ag NPs have shown high electrocatalytic activity toward the ORR indicating their suitability as cathode materials in alkaline fuel cells.