Influence of the Morphology of Electrodeposited Nanoparticles on the Activity of Organic Halide Reduction

Abstract

Silver nanoparticles (NP) were deposited on glassy carbon substrates using a potentiostatic dual pulse method in acetonitrile containing 1 mM AgNO₃ + 0.1 M LiClO₄. The high amount of control on the NP synthesis was utilized to investigate the influence of the NP morphology on the catalytic activity of an organic electrosynthesis reaction. Nucleation pulses at -0.4, -0.6 and -0.8 V vs. Ag/AgCl were applied in chronoamperometry measurements. Scanning electron microscopy (SEM) indicated a significant dependency of NP morphology on nucleation potential. Nucleation pulses at lower overpotential resulted in an average particle size of 116 nm, while higher overpotentials produced NP’s with sizes as low as 76 nm. For the organic electrosynthetic halide reduction, benzyl bromide was used as a model molecule. The benzyl bromide reduction activity was determined using cyclic voltammetry (CV). A proportional correlation between the nucleation peak potential and benzyl bromide reduction activity was observed. Peak potentials of the prepared NP’s with nucleation pulses of high overpotential (-0.8 V) revealed even a positive shift of 83 mV compared to a bulk Ag disk electrode. There was no indication of an altered reaction mechanism since the benzyl bromide reduction wave was characterized as a process of diffusive nature and calculated apparent transfer coefficients (a’) of the NP electrodes varied around 0.3. This is an indication of a concerted reaction mechanism in compliance with the mechanism reported on bulk Ag.