Nanoporous Au Formation on Au Substrates via High Voltage Electrolysis**

Abstract

Nanoporous Au (NPG) films have promising properties, making them suitable for various applications in (electro)catalysis or (bio)sensing. Tuning the structural properties, such as the pore size or the surface‐to‐volume ratio, often requires complex starting materials such as alloys, multiple synthesis steps, lengthy preparation procedures or a combination of these factors. Here we present an approach that circumvents these difficulties, enabling for a rapid and controlled preparation of NPG films starting from a bare Au electrode. In a first approach a Au oxide film is prepared by high voltage (HV) electrolysis in a KOH solution, which is then reduced either electrochemically or in the presence of H2O2. The resulting NPG structures and their electrochemically active surface areas strongly depend on the reduction procedure, the concentration and temperature of the H2O2‐containing KOH solution, as well as the applied voltage and temperature during HV electrolysis. Secondly, the NPG film can be prepared directly by applying voltages that result in anodic contact glow discharge electrolysis (aCGDE). By carefully adjusting the corresponding parameters, the surface area of the final NPG film can be specifically controlled. The structural properties of the electrodes are investigated by means of XPS, SEM and electrochemical methods.

Electric Potential Distribution Inside the Electrolyte during High Voltage Electrolysis

“…The corresponding charges are depicted in Figure b). Previous XPS measurements show that primarily Au 2 O 3 is formed under these conditions . Hence, the evaluated charge is directly proportional to the amount of Au 2 O 3 formed during HV electrolysis.…”

“…Since Pt does not restructure during high voltage electrolysis, we use Au electrodes instead, which were shown to exhibit a voltage dependent Au oxide formation. 29,30 From our experiments, we will demonstrate that the current density is a better descriptor for the amount of Au oxide formed than the applied voltage.…”

“…Using the knowledge from this complementary experimental and theoretical approach, we will show how electrode materials can be selectively modified. Since Pt does not restructure during high voltage electrolysis, we use Au electrodes instead, which were shown to exhibit a voltage dependent Au oxide formation. , From our experiments, we will demonstrate that the current density is a better descriptor for the amount of Au oxide formed than the applied voltage.…”

Facet‐Dependent Formation and Adhesion of Au Oxide and Nanoporous Au on Poly‐Oriented Au Single Crystals**

“…Furthermore, we demonstrated that the final structure of the NPG film depends on the method used to reduce the Au oxide, i. e., electrochemically or in the presence of H 2 O 2 [27] . For long electrolysis times, it is even possible to form a NPG film in situ in a single step [27] …”

“…The latter phenomenon refers to a plasma that forms in a gas sheath around the working electrode at high voltages [23–25] . In both cases, the voltages can reach several hundreds of volts and the current densities are in the range of 1 to 10 A cm −2 [26–28] . Advantages of this high voltage (current density) approach are that the preparation times are significantly shorter and only an (alkaline) electrolyte is required [27] .…”