Noble-Metal Nanorod Cryoaerogels with Electrocatalytically Active Surface Sites

Abstract

Noble-metal-based electrocatalysts usually contain small nanoparticle building blocks to ensure a high specific surface area as the scene for the surface processes. Here, we show that relatively large noble-metal nanorods are also promising candidates to build up functional macrostructures with prominent electrocatalytic activity. After optimizing and upscaling the syntheses of gold nanorods and gold bipyramid-templated silver nanorods, cryoaerogels are fabricated on a conductive substrate via flash freezing and subsequent freeze drying. The versatile cryoaerogelation technique allows the formation of macrostructures with dendritic, open-pore structure facilitating the increase of the accessible nanorod surfaces. It is demonstrated via electrochemical oxidation and stripping test experiments that noble-metal surface sites are electrochemically active in redox reactions. Furthermore, gold nanorod cryoaerogels offer a platform for redox sensing, ethanol oxidation reaction, as well as glucose sensing. Compared to their simply drop-cast and dried counterparts, the noble-metal nanorod cryoaerogels offer enhanced activity due to the open porosity of the fabricated nanostructure while maintaining structural stability.

Interparticle Interaction Matters: Charge Carrier Dynamics in Hybrid Semiconductor–Metal Cryoaerogels

“…The highly porous nature of the coatings endows the systems with high accessible surface areas for interfacial reactions, which is a significant advantage over their simply drop‐cast nanoparticle film counterparts. [ 43,46,47 ]…”

“…The latter also showed enhanced stability in electrochemical processes, [ 45 ] which is of great importance in the practical use of cryoaerogel coatings. [ 47 ]…”

“…Afterward, the electrodes were stored in liquid nitrogen overnight before drying the electrodes in the freeze dryer or in a freezer (at −20 °C), respectively. [43,[45][46][47] Photoelectrochemical Measurements: Photoelectrochemical measurements were carried out in a lab-designed Teflon cell, in which the prepared cryoaerogel coatings were carefully rehydrated by the supporting electrolyte (discussed below). For intensity modulated photocurrent spectroscopy, the current response of the electrochemical cell was measured while irradiating the cryoaerogel sample with an LED light source operating at frequencies between 10 kHz and 1 Hz.…”

“…Afterward, the electrodes were stored in liquid nitrogen overnight before drying the electrodes in the freeze dryer or in a freezer (at −20 °C), respectively. [ 43,45–47 ]…”

“…Beside the widely used chemical gelation methods, cryogelation is a novel physical gelation technique, which includes the flash-freezing and the subsequent freeze drying of the aqueous NC solutions. [18] Its versatility and ease (no oxidative ligand removal is required in the process) allowed us to fabricate various, highly porous nanoparticle gel structures from noble metal NPs, [20,[45][46][47] semiconductor NPLs, [43] metal oxide NPs [18] as well as mixed systems. [19] These structures proved their potential in applications such as electrocatalysis and electrochemical sensing.…”