Nanoporous Au formation on Au substrates via high voltage electrolysis

Nanoporous Au (NPG) films often show distinctly different properties than bare Au electrodes, which make them suitable for various applications in (electro)catalysis or (bio)sensing. A great deal of effort has gone into finding suitable preparation techniques that can be used to target structural properties, such as the pore size or the surface-to-volume ratio. Many of the methods described for preparing these NPG films require 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 bare Au electrodes. One approach is to prepare in a first step a Au oxide film by high voltage (HV) electrolysis in a KOH solution, which in a second step is reduced either electrochemically or in the presence of H₂O₂. The resulting NPG structures as well as 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 the HV electrolysis. The NPG film can also be prepared directly by applying electrolysis voltages that result in anodic contact glow discharge electrolysis (aCGDE) over an extended period of time. 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.