Bottom‐up Generation of Miniaturized Coaxial Double Electrodes with Tunable Porosity

Abstract

effi cient electrochemical devices, particularly in the fi eld of implantable biofuel cells and biosensors. Among other parameters, the diffusion and redox reaction of molecules such as oxygen determines the operating voltage and thus the effi ciency of oxygen-dependent biofuel cells. [ 25,26 ] The present work introduces a new and straightforward strategy for the bottom-up fabrication of a miniaturized coaxial electrode architecture based on highly organized porous gold as a structural material with controllable thickness and pore diameter. Preliminary experiments were carried out with goldcoated glass slides and, subsequently, gold microwires served as substrates for the deposition of silica particles using the Langmuir-Blodgett (LB) technique to form a colloidal crystal on their surface.These silica opals were fi lled by electrodeposition with alternating metal layers in order to obtain a fi nal porous structure with two independently addressable macroporous gold electrodes. They constitute an extremely miniaturized and fully integrated electrochemical cell of either planar or cylindrical geometry with a characteristic active volume in the range of 0.1 µL, which can be further decreased if needed. Due to the controllable porosity and thickness of the electrode materials the approach that we present here opens a new path for the fabrication of electrochemical cells combining a signifi cantly decreased footprint with an increase in active surface area.The LB technique has been used for a long time for the controllable deposition of amphiphilic molecules or nanoparticles from a water-air interface onto the surface of a substrate. [27][28][29][30][31] It presents a very convenient approach to form homogeneous and well-organized colloidal crystals, which is complementary to other techniques that have been used such as controlled evaporation, electrophoretic deposition, and dip coating. [ 32 ] After dispersing the nanoparticles at the water-air interface of the LB trough, the compression of the fi lm is followed by measuring the surface tension as a function of fi lm area. The quality of the compression can be illustrated by depositing a defi ned number of silica particle layers on a solid substrate ( Figure 1 a).The so-obtained colloidal crystal is used as a template during a subsequent electrodeposition step. In order to obtain the fi nal miniaturized two electrode electrochemical cell, alternating gold-nickel-gold metal layers were generated in the colloidal crystal template, with the nickel layer playing the role of a sacrifi cial spacer between the two gold layers (Figure 1 b). In a fi rst set of experiments, a fl at gold substrate coated with multilayers of silica particles was used for the successive electrodeposition of gold, nickel, and gold under potentiostatic conditions. After dissolving the intermediate nickel layer (Figure 1 c), the structure is stabilized by incorporating a small amount of nail varnish at the extremities of the sandwich-type structure (in the The demand for miniaturized and eventually...

An enzymatic glucose/O2 biofuel cell operating in human blood

“…All experiments were performed with bare and smooth carbon fibers which can explain the leaking of the redox polymers. Therefore, the use of more sophisticated porous and cylindrical electrodes in combination with our bioelectrocatalysts would be the perfect candidates to optimize the BFC (Karajic et al, 2015). The porosity will offer high specific surface to improve the current while maintaining the geometric surface area and will also allow retaining the polymer and protecting the hydrogel within its structure.…”

Optimal Thickness of a Porous Micro‐Electrode Operating a Single Redox Reaction

“…Five porous gold‐coated electrodes made of 5, 7, 11, 15 and 19 half‐layers ( HL ) of pores were manufactured according to a three‐step procedure . An organized colloidal template of silica beads of diameter μm was first deposited on a gold wire of radius R 1 =125 μm, using the Langmuir‐Blodgett technique and controlling the number of bead layers ,.…”

“…In the recent past decades, porous electrodes, which are of major interest for the design of miniaturized electro‐devices such as bio‐batteries or bio‐sensors, have recieved considerable attention both from modeling and experimental points of view . A well‐defined pore size and pore distribution of the porous material may be achieved by using the Langmuir‐Blodgett templating technique, providing a high surface‐to‐volume ratio (specific area) ,. Such a feature allows the electrodes to produce much higher electrical current per unit volume than classical flat electrodes of the same macroscopic size .…”

Miniaturized Electrochemical Device from Assembled Cylindrical Macroporous Gold Electrodes

“…Over the past decade, different technologies have been explored to downscale the dimensions of such devices. Fabrication of electrochemical platforms has been largely supported by screen‐printing, photolithography, and electrodeposition techniques that were widely used for the design of miniature devices such as micro‐batteries, micro‐fuel cells, micro‐supercapacitors, electroanalytical systems, and nanofluidic devices (e.g. for biodetection, redox cycling for single‐molecule electrochemistry in femtoliter volumes etc.)…”

“…In previous work, we have demonstrated that a fully integrated miniaturized electrochemical cell can be elaborated based on a bottom‐up approach, leading to a coaxial arrangement of two macroporous microelectrodes. The use of the Langmuir–Blodgett (LB) technique in the elaboration process permits us to precisely tune the inter‐electrode distance.…”