Enhanced Adhesion of Ultrathin Nanoporous Au Deposits by Electrochemical Oxidation of Glassy Carbon

Abstract

Electrochemical (EO) and Thermochemical (TO) oxidation have been considered as means for improved adhesion of metals to glassy carbon (GC) substrates. This paper is aimed at studying the effect of EO on the all-electrochemical processing of nanoporous gold (NPG) catalysts with emphasis on their adhesion to a GC substrate. It has been shown by two independent assessment approaches that EO improves twice the amount of retained NPG on GC helping to keep about 90% originally existing material after a two-hour rotation disk electrode test at 1600 rpm. This work also demonstrates that EO modifies the GC in a way making it more passive in the alloy deposition and subsequent dealloying processes. This effect results in a progressive nucleation density decrease with the depth of oxidation which in turn leads to a lack of continuity of the NPG layer. This trend is also accompanied by a decrease in deposition efficiency as a substantial part of the cathodic current is spent on the reduction of the pre-oxidized GC surface. Our study identifies the best outcome of the trade-off scenario between nucleation density, deposition efficiency and adhesion strength to be associated with depth of oxidation in the range 0.10 to 0.25 μm. NPG based catalyst on glassy carbon (GC).-Nanoporous Au (NPG) is a nano-material with three dimensional (3D) continuous structure featuring Au with interconnected nano-sized pores and ligaments.1 NPG and other nanoporous metals have been intensively investigated in recent years. This conductive material has an open, 3D porous framework with surface areas that even in an ultrathin NPG layer configuration could be an order of magnitude larger than the area of planar Au. Besides its continuous crystal lattice throughout the porous network, it has a pore size that is adjustable via simple thermal post-processing, which makes it potentially applicable in various fields such as electro-and gas-phase catalysis, optics, sensors and actuators. [2][3][4][5] It is known that nanoparticulate gold possesses remarkable catalytic activity toward oxidation reactions, should the particles be well supported and smaller than 5 nmin size. 6 Recently, ultrathin films of NPG have been shown to serve as catalysts for fuel cell applications as an alternative to their nanoparticle (NP) counterparts.7-9 These films are generated electrochemically under precise potential/current control, which minimizes material loss and surface contamination over the multi-step NP synthetic routines. 7,10 Compared to nanoparticle synthesis which often lacks control due to the large number of the processing steps, ultra thin films of NPG are cost effective, simple to fabricate, and show better reproducibility in terms of quality and reactivity. Another advantage of NPG films is that the edge effect that lowers the catalytic activity characteristic for NP based catalysts does not exist in NPG films due to its continuous nature. 11In our previous work, we established an all-electrochemical synthetic method for a NPG-based catalyst that maximized t...

Synthesis, characterization, and testing of Pt-NPG catalysts developed by de-alloying of electrodeposited CuxAu(1−x) thin films

“…[5] Some other techniques have also been introduced in order to address issues revealed during the course of NPG fabrication on GC substrates. More specifically, electrochemical oxidation [6] and thermochemical oxidation pre-treatments [7] of GC substrates were used to improve the adhesion between NPG and GC substrates, and seeding approaches [8,9] were implemented to enhance the nucleation density and facilitate the lateral cluster coalescence in the course of alloy electrodeposition. Overall, a continuous thin film of NPG with good catalyst activities has been successfully fabricated on both Au and GC substrates [5][6][7][8].…”

Impact of Structure and Composition on the Dealloying of CuxAu(1–x) Bulk and Nanoscale Alloys

“…However, the morphology of the NPG thin film deposited on GC exhibited isolated clusters with low nucleation density and a considerable loss was observed following testing. In order to solve these problems, a seeding method has been introduced in order to plant different metal sites on the GC surface to enhance nucleation density and fabricate eventually a continuous layer. , Also, electrochemical oxidation and thermochemical oxidation pretreatment of GC have been studied, compared and found as feasible approaches for enhancing the adhesion between NPG and GC substrate.…”