Au-Seeded Ag-Nanorod Networks for Electrocatalytic Sensing

Abstract

Spherical gold nanoseed (∼5–6 nm)-induced (but not seed-mediated) silver nanorods (Hy-Au@AgNRs) of variable lengths have been synthesized by a new methodology that shows enhancement in catalytic activity as a function of nanorod length. Detailed characterization by atomic-scale resolution spectroscopy, precision scattering measurements, high-resolution microscopy, and theoretical modeling through the density functional theory (DFT) quantifies the presence of an enhanced number of multiple coaxial twin boundaries for longer Hy-Au@AgNRs, which ultimately results in an increased mechanical strain. By considering greater mechanical strain within Hy-Au@AgNRs, the density of states (DOS) calculation shows a prominent shift in electron density toward the Fermi level to assist in the tremendous catalytic activity of the longest nanorod (NR) (Hy-Au@AgNR840). Further assembling of these inherently active Hy-Au@AgNR840s by thiol click chemistry not only efficiently creates multiple low-coordinated crystal sites to improve their catalytic activity but also the resultant uniform two-dimensional (2D) platform shows better adsorptivity and easy moldability on the electrode surface for increased shelf life, a uniform porous structure to trap a large extent of redox systems, enhanced stability in a broad pH and solvent range to increase the applicability, and long-term stability under ambient conditions for safe storing, making this material a unique nonenzymatic scalable universal electrocatalytic platform. The ability of this material to act as a nonenzymatic universal catalytic platform has been verified by applying it for highly specific and ultrasensitive detection of a series of human metabolites, which include different important vitamins, potent endogenous antioxidants, essential amino acids for the biosynthesis of proteins, simple monosaccharides, and essential trace-metal ions. Our study for the first time mechanistically explores the combined role of anisometric seeding to create an intermetallic twin boundary along with its size to control the strain-induced catalytic activity to offer us a universal 2D electrocatalytic sensing platform by a combined approach of experiment and theory.

(Ag@AuAg)@Ag Nanocatalyst for the Electrocatalytic Oxygen Reduction Reaction

“…One more interesting observation is that the extent of shifting in binding energy for Ag and Au is highest for NP Au−Ag ) have also been explained based on the same mechanism by several other researchers. 28−34 As shown in Figure S8, in all nanoalloy structures, Ag remains mostly as Ag I from AgCl, 35−37 as confirmed from the peak position and intensity at around 367.2 eV (3d 5/2 ) and 373.4 eV (3d 3/2 ), 38 . The relative partial positive charge due to the presence of Ag I in the structure can easily be calculated from the ratio of the relative heights of the XPS peaks for Ag I and Ag 0 at two different spin−orbit states (3d 5/2 and 3d 3/2 ), as discussed in a later section in detail.…”

Void-Enriched and Highly Strained Porous Au–Ag Nanoalloy as a Bifunctional Electro-Catalyst in Alkaline Direct Alcohol Fuel Cell

“…The difference in diffusion rate between Au 3+ and Ag causes these void formations, named Kirkendall voids (KVs) . The KVs are the root cause for high catalytic performances as it contains multiple active catalytic sites including curved surfaces, where low coordinated steps and kinks reside. , We have provided the corresponding HRTEM images of NP alloy in Figure H where the existence of low coordinated voids can clearly be seen. Thus, possessing more number of low coordinated voids within NP alloy is expected to show greater catalytic efficacy and is evident both from Figure and Table .…”