Controlling the Size of Au Nanoparticles on Reducible Oxides with the Electrochemical Potential

Abstract

Controlling the size of Au nanoparticles (NPs) and their interaction with the oxide support is important for their catalytic performance in chemical reactions, such as CO oxidation and water-gas shift. It is known that the oxygen vacancies at the surface of support oxides form strong chemical bonding with the Au NPs and inhibit their coarsening and deactivation. The resulting Au/oxygen vacancy interface also acts as an active site for oxidation reactions. Hence, small Au NPs are needed to increase the density of the Au/oxide interface. A dynamic way to control the size of the Au NPs on an oxide support is desirable but has been missing in the field. Here, we demonstrate an electrochemical method to control the size of the Au NPs by controlling the surface oxygen vacancy concentration of the support oxide. Oxides with different reducibilities, La 0.8 Ca 0.2 MnO 3±δ and Pr 0.1 Ce 0.9 O 2−δ , are used as model support oxides. By applying the electrochemical potential, we achieve a wide range of effective oxygen pressures, pO 2 (10 −37 −10 14 atm), in the support oxides. Applying the cathodic potential creates a high concentration of oxygen vacancies and forms finely distributed Au NPs with sizes of 7−13 nm at 700−770 °C in 10 min, while the anodic potential oxidizes the surface and increases the size of the Au NPs. The onset cathodic potential required to create small Au NPs depends strongly on the reducibility of the support oxide. The Au NPs did not undergo sintering even at 700−770 °C under the cathodic potential and also were stable in catalytically relevant conditions without potential.

External Voltage-Induced Restructuring of the Solid-State Electrode/Electrolyte Interface Revealed by X-ray Photoelectron Spectroscopy Depth Profiling Analysis

“…The corresponding O/Zr ratio of the reacted cathode (Figure f) is close to 0 when sputtering for 1 to 4 min, and it gradually increases to 2 (the same value as the bulk YSZ). The results are consistent with the theory that the applied voltage lowers the oxygen chemical potential at the cathode side, − which induces enough low p O 2 to decompose YSZ.…”

Quantifying Electrochemical Driving Force for Exsolution in Perovskite Oxides by Designing Graded Oxygen Chemical Potential

“…However, while these factors can affect the exsolution thermodynamically, the kinetics of exsolution can be rather slow, requiring several hours or even tens of hours of annealing at elevated temperatures . On the contrary, electrochemically driven exsolution, triggered by applying an external electrical stimulus, can induce high-density and well-dispersed nanoparticles within just several minutes, as shown in recent literature reports. − Applying a cathodic potential to the perovskite oxide can induce a decrease in the oxygen chemical potential ( μ O ) (or effective oxygen partial pressure, p O 2 eff ) of the oxide. The exsolution driven electrochemically has been shown to occur with much more accelerated kinetics compared with thermal reduction, the reason for which is still yet to be clarified .…”

The metal–support interaction effect in the carbon-free PEMFC cathode catalysts

“…3i). 68 3.1.3 Modied transition metal oxide carriers. To compensate for the shortcomings of the pristine TMOs carriers, the doping strategies and heterostructure formation are regarded as efficient methods for high-performance PEMFCs.…”

“…(i) SEM images of the thermal stability for the Au NPs on the PCO support. Reproduced with permission 68. Copyright 2022, American Chemical Society.…”