Development of nanoporous gold electrodes for electrochemical applications (original) (raw)
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Nanomaterials
Nanoporous gold (np-Au), because of its high surface area-to-volume ratio, excellent conductivity, chemical inertness, physical stability, biocompatibility, easily tunable pores, and plasmonic properties, has attracted much interested in the field of nanotechnology. It has promising applications in the fields of catalysis, bio/chemical sensing, drug delivery, biomolecules separation and purification, fuel cell development, surface-chemistry-driven actuation, and supercapacitor design. Many chemical and electrochemical procedures are known for the preparation of np-Au. Recently, researchers are focusing on easier and controlled ways to tune the pores and ligaments size of np-Au for its use in different applications. Electrochemical methods have good control over fine-tuning pore and ligament sizes. The np-Au electrodes that are prepared using electrochemical techniques are robust and are easier to handle for their use in electrochemical biosensing. Here, we review different electrochemical strategies for the preparation, post-modification, and characterization of np-Au along with the synergistic use of both electrochemistry and np-Au for applications in biosensing.
Engineering of Au/Ag Nanostructures for Enhanced Electrochemical Performance
Journal of The Electrochemical Society, 2018
The effect of nanostructuring on the electrochemical activity of a series of Au/Ag electrocatalysts, with and without graphene nanoplatelets (G) as carbon matrix support and β-cyclodextrin as capping agent, was systematically investigated using the ferri/ferrocyanide redox probe. A series of Au/Ag nanostructures with different morphologies were synthesized and characterized using a combination of spectroscopy, electron microscopy, and electroanalytical methods. Evaluation of the cyclic voltammograms obtained from the ferri/ferrocyanide redox probe using electrodes modified with the different Au/Ag nanostructures revealed significant enhancement in peak currents upon using hollow Au/Ag nanobox and porous-hollow Au/Ag nanocage analogs in comparison to conventional solid spherical Au nanoparticles. The observed improvements in electrochemical activities can be attributed to the nanoreactor cage and edge effects in the hollow cubic nanostructures. Moreover, the dispersion of the nanostructures in G and their surface modification with β-cyclodextrin further enhanced their electrochemical performance. The best performing Au/Ag nanostructure that was modified with β-cyclodextrin and G was used to fabricate an electrochemical sensor for the stress biomarker cortisol. The resulting electrochemical sensor exhibited good linear response to cortisol in the concentration range of 1 pM to 100 nM, making it a promising platform technology for monitoring the physiological stress indicator.
Review Nanoporous Gold: Fabrication, Characterization, and Applications
2009
Nanoporous gold (np-Au) has intriguing material properties that offer potential benefits for many applications due to its high specific surface area, well-characterized thiol-gold surface chemistry, high electrical conductivity, and reduced stiffness. The research on np-Au has taken place on various fronts, including advanced microfabrication and characterization techniques to probe unusual nanoscale properties and applications spanning from fuel cells to electrochemical sensors. Here, we provide a review of the recent advances in np-Au research, with special emphasis on microfabrication and characterization techniques. We conclude the paper with a brief outline of challenges to overcome in the study of nanoporous metals.
Applications of Nano- and Mesoporous Gold in Electrodes and Electrochemical Sensors
2006 International Conference on Nanoscience and Nanotechnology, 2006
A nano-or mesoporous sponge of Au is formed when the intermetallic compound AuAl 2 is de-alloyed with NaOH. The large specific surface area of the sponge, and the unique surface chemical properties of Au indicate that this porous material might usefully serve as an electrode in capacitive sensors or other specialized electrochemical cells. Results for some prototype sensor and energy storage systems are presented, and methods of controlling the nature of the porosity presented.
High surface area electrodes by template-free self-assembled hierarchical porous gold architecture
Journal of colloid and interface science, 2016
The electrode active surface area is a crucial determinant in many electrochemical applications and devices. Porous metal substrates have been employed in electrode design, however construction of such materials generally involves multistep processes, generating in many instances electrodes exhibiting incomplete access to internal pore surfaces. Here we describe fabrication of electrodes comprising hierarchical, nano-to-microscale porous gold matrix, synthesized through spontaneous crystallization of gold thiocyanate in water. Cyclic voltammetry analysis revealed that the specific surface area of the conductive nanoporous Au microwires was very high and depended only upon the amount of gold used, not electrode areas or geometries. Application of the electrode in a pseudo-capacitor device is presented.
Structure and Applications of Gold in Nanoporous Form
2017
Nanoporous gold (np-Au) has many interesting and useful properties that make it a material of interest for use in many technological applications. Its biocompatible nature and ability to serve as a support for self-assembled monolayers of alkanethiols and their derivative make it a suitable support for the immobilization of carbohydrates, enzymes, proteins, and DNA. Its chemically inert, physically robust and conductive high-surface area makes it useful for the design of electrochemistry-based chemical/bio-sensors and reactors. Furthermore, it is also used as solid support for organic molecular synthesis and biomolecules separation. Its enhanced optical property has application in design of plasmonics-based sensitive biosensors. In fact, np-Au is one of the few materials that can be used as a transducer for both optical and electrochemical biosensing. Due to the presence of low-coordination surface sites, np-Au shows remarkable catalytic activity for oxidation of molecules like carb...
Characterization of Nanoporous Gold Electrodes for Bioelectrochemical Applications
Langmuir, 2012
The high surface areas of nanostructured electrodes can provide for significantly enhanced surface loadings of electroactive materials. The fabrication and characterization of nanoporous gold (np-Au) substrates as electrodes for bioelectrochemical applications is described. Robust np-Au electrodes were prepared by sputtering a goldÀsilver alloy onto a glass support and subsequent dealloying of the silver component. Alloy layers were prepared with either a uniform or nonuniform distribution of silver and, post dealloying, showed clear differences in morphology on characterization with scanning electron microscopy. Redox reactions under kinetic control, in particular measurement of the charge required to strip a gold oxide layer, provided the most accurate measurements of the total electrochemically addressable electrode surface area, A real . Values of A real up to 28 times that of the geometric electrode surface area, A geo , were obtained. For diffusion-controlled reactions, overlapping diffusion zones between adjacent nanopores established limiting semi-infinite linear diffusion fields where the maximum current density was dependent on A geo . The importance of measuring the surface area available for the immobilization was determined using the redox protein, cyt c. The area accessible to modification by a biological macromolecule, A macro , such as cyt c was reduced by up to 40% compared to A real , demonstrating that the confines of some nanopores were inaccessible to large macromolecules due to steric hindrances. Preliminary studies on the preparation of np-Au electrodes modified with osmium redox polymer hydrogels and Myrothecium verrucaria bilirubin oxidase (MvBOD) as a biocathode were performed; current densities of 500 μA cm À2 were obtained in unstirred solutions.
Hierarchical porous gold electrodes: Preparation, characterization, and electrochemical behavior
Journal of Electroanalytical Chemistry, 2012
Hierarchical porous gold films with a well-defined bimodal architecture have been made by electrodepositing gold at a constant current around a close-packed assembly of raspberry-like latex spheres (1200/60 nm) followed by template removal. Electrodeposition was stopped when the gold was either ½ layer or 1½ layer thick as evident from oscillations in the potential vs time traces. Scanning electron microscopy (SEM) images show the hierarchical pore structure with an ensemble of small 20nmopeningslocatedinalarge20 nm openings located in a large 20nmopeningslocatedinalarge1200 nm diameter macropore. Prior to electrochemical characterization, the electrodes were cleaned either chemically and/or via UV radiation and X-ray photoelectron spectroscopy (XPS) was used to evaluate the presence of residual polystyrene. Of the three cleaning methods investigated, sonication in chloroform-acetone followed by UV radiation proved best. The surface area of the hierarchical porous gold electrodes, determined by integrating the area under the gold oxide peak, was 4Â larger than a bare gold electrode and 2Â larger than a macroporous gold electrode prepared using unimodal, 1200 nm diameter latex spheres as the template. The electrochemical performance of the electrodes relative to the macroporous gold and flat gold was undertaken using cyclic voltammetry. The results show that the non-Faradaic current scales linearly with electrode area while the Faradaic current of a diffusing electrochemically reversible redox probe (ferrocene methanol) does not. For an adsorbed redox couple (ferrocene hexanethiol), the voltammetric wave shapes and surface coverage were different for the different electrodes.
Electrochemically Triggered Pore Expansion in Nanoporous Gold Thin Films
The Journal of Physical Chemistry C, 2016
Nanoporous electrode coatings have played a significant role in enhancing the performance of catalysts and sensors. For optimal performance in these applications, the fundamental requirement is a large effective surface area (site at which catalysis and sensing events occur) with unhindered transport of reactants and products to/from the active surface. This necessitates low-density porous electrodes with an interconnected 3D network of thin conductive ligaments to maintain high effective surface area. While the logical approach to create such electrodes is to etch the ligaments uniformly through the entire porous network, accomplishing this has not been trivial. Here, we use nanoporous gold (np-Au) as a model material system to demonstrate an electrochemically-triggered etching method for restructuring sputter-deposited sub-micron np-Au thin films for enlarging the pores with minimal decrease in the effective surface area. We systematically employ time-varying potential waveforms to electrochemically modify morphologies and reveal underlying mechanisms of the etching process. The results suggest that the etch cycle at positive potentials plays a dual role of electrophoretic attraction of chloride ions and initiating the electrochemical etch. The final nanoporous morphology is dictated by a competition between ligament coarsening and ligament thinning, which provide a means to generate a wide range of electrode morphologies.