Nanoporous Au (NPG) has a porous, spongelike structure whose pores are connected by Au ligaments. The sponge-like structure often shows different properties compared to the bulk material. Possible applications for NPG films are in the fields of (bio)sensing, (electro)catalysis, or in heterogeneous catalysis. Typically, NPG films are prepared by chemical dealloying, mostly of a Ag-Au alloy. In this process, the less noble metal is dissolved, e.g., Ag, by using a HNO 3 solution. Alternatively, the dealloying process can also be induced electrochemically. A disadvantage of these dealloying processes is that Ag residues can remain in the resulting NPG film. Such trace impurities can play a significant role for example in catalytic processes. Recently it has been shown that NPG films can also be prepared by anodization (Au oxide formation at a Au anode set to a potential of a few volts versus a fixed reference with current densities of approximately 0.035 A•cm -2 ) and subsequent electrochemical reduction. Similarly, recently we have shown that NPG films can be produced by (electro)chemically reducing Au oxide films formed during high voltage (HV) electrolysis and anodic contact glow discharge electrolysis (aCGDE). The latter phenomenon refers to a plasma that forms in a gas sheath around the working electrode at high voltages. 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 . Advantages of this high voltage (current density) approach are that the preparation times are significantly shorter and only an (alkaline) electrolyte is required. 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. To further tune the formation of the NPG film, it is beneficial to understand both the growth and the interaction of the Au oxide films as well as the NPG films with the Au substrate. Within that context, Henkelmann et al. studied, for example, the densification/detachment of NPG films from Au substrates and found that the substrate's curvature and, thus, the surface morphology of the Au substrate plays an important role. Khristosov et al. demonstrated that NPG single crystals can be grown on a SiO 2 substrate up to a size of several hundred micrometers. For this purpose, a eutectic melt of Au and Ge is first prepared, which is then solidified. The Ge is subsequently removed by wet etching, NPG single crystals remain. In this work, we study the influence of the crystallographic orientation of the substrate on the formation of the Au oxide during HV electrolysis and the structure of the NPG film formed by electrochemical reduction. Such aspects can be investigated by using oriented single-crystal electrodes, an approach widely used in surface science and electrochemistry. For example, the facet-dependent oxide formation has been studied on noble metals such as Pt, Au, and on non-noble metals such as Al, Ni, Fe, or Cu. Conway and Jerkiewicz, for example, found that oxide formation occurs at different rates on the Pt(111) and the Pt(100) facets. Vvedenskii et al. studied the influence of different Cu low-indexed crystallographic orientations regarding the Cu(I) and Cu(II) oxide formation. Scholten et al. were able to show that O 2 plasma pre-treatment leads to the formation of CuO on the Cu(111) surface, while on Cu(100) primarily Cu 2 O is formed after the same experimental procedure. Also, the surface morphology in both cases differed significantly. The different structures obtained on the different facets during the pre-treatment can have a significant impact on the catalytic activity. A caveat of using such oriented single crystals is that several differently oriented single crystals are required, to study the facetdependent properties, which is a rather timeconsuming task. In recent years, poly-oriented single crystals (POSCs) have been exploited to screen processes occurring at facets with different crystallographic orientations in a single experiment. Such POSCs are created by melt-ing the end of a metal wire, which leads to the formation of a liquid bead. This bead is then slowly cooled in a controlled atmosphere, resulting in a single crystal with facets exhibiting different crystallographic orientations. Note that the distribution and size of these facets can vary depending on the metal used in the process and the size of the POSC. These electrodes were used to determine the facet-dependent restructuring of Pt electrodes during oxidation and reduction cylces or cathodic corrosion of Au and Pt. In this work, we study the growth of Au oxide on Au POSCs, prepared by HV electrolysis at a voltage close to the breakdown voltage (300 V / current density between 2.70 and 3.76 A•cm -2 ) and in the region of aCGDE (540 V / current density between 0.24 and 6.39 A•cm -2 ) for different electrolysis times (a few 100 ms up to 30 s) in 0.01 M KOH. The amount of Au oxide is inferred from the electrochemical reduction of the Au oxide film. In the second step, the Au oxide film is reduced electrochemically to form a NPG film on the Au POSC. The structural properties of the resulting Au oxides and the NPG films are investigated by optical microscopy and scanning electron microscopy (SEM). Aside from the overall structure of the entire POSC, we focus on the low-index regions, i.e., Au(111) and Au(100), and the regions vicinal to those surfaces, which consist of extended Au(111) and Au(100) terraces.