Improved electrocatalysis and electrophoretic deposition due to the strong synergy between Au and Ag nanoparticles

Abstract

Here we demonstrate that every time Au and Ag NPs are physically mixed together they outperform their monometallic counterparts upon electrocatalysis of hydroquinone (HQ) and electrophoretic deposition (EPD) coverage.We chemically synthesize citrated-coated Au and Ag nanoparticles (NPs), mix them at the following percent ratios: Au100-xAgx (Au90Ag10, Au75Ag25, Au50Ag50, Au25Ag75, Au10Ag90), and form films via EPD using HQ as mediate molecule. We encountered good agreement between Optical Extinction Spectroscopy (OES) calculations and Linear Scan Voltammetry (LSV) oxidation peaks which indicated two size populations around ∼2 and 4 nm for Au and 8 nm diameters for Ag NPs. During EPD, HQ electrocatalysis follows the order: Au75Ag25 >Au50Ag50 >Au25Ag75 >Au90Ag10 > Au NPs > Au10Ag90 > Ag NPs. This is remarkable because Au25Ag75 outperforms the Au90Ag10 mixture indicating that “less is more” in the sense that ∼ 70% less Au content in the mixture is more electroactive upon HQ. This suggests that Ag NPs are also playing an important role in the mixture. Also, Au NPs play a role as for example the addition of 10% Au to pure Ag NPs increases more than 3 orders of magnitude the coverage (1.3 x 1012 NPs) with respect to monometallic Ag (7.5 x 108 NPs). XPS exhibits electron transfer from Ag to Au NPs which confirms the electronic mechanism in the mixture.Kinetic studies show that the smallest 2 nm diam. Au NPs are responsible for the fastest kinetic due to lower overpotentials. These experiments reveal that small Au NPs (2 nm diam.) and Ag NPs in the mixture team up toward electrocatalysis of HQ which then favors the deposition of NPs by EPD. Fine control on the composition, size, and coverage of deposited metal Au and Ag NPs within the same film are crucial in the design of advanced optoelectronic devices.