In-liquid plasma for surface engineering of Cu electrodes with incorporated SiO2 nanoparticles: From micro to nano

A robust and efficient route to modify the chemical and physical properties of polycrystalline Cu wires via versatile plasma electrolysis is presented. Silica nanoparticles (11 nm) have been introduced during the electrolysis to tailor the surface structure of the Cu electrode. The influence of these silica nanoparticles on the structure of the Cu electrodes during plasma electrolysis over a wide array of applied voltages and processing time is investigated systematically. Homogeneously distributed 3D coral-like microstructures are observed by scanning electron microscopy on the Cu surface after the in-liquid plasma treatment. These 3D microstructures grow with increasing plasma processing time. Interestingly, the microstructured copper electrode is composed of Cu(II) oxide as a thin outer shell and a significant amount of inner Cu(I) oxide. Furthermore, the oxide film thickness (between 1 and 70 μm), the surface morphology, and the chemical composition can be tuned by controlling the plasma parameters. Remarkably, the fabricated microstructures can be transformed to nanospheres assembled in coral-like microstructures by a simple electrochemical treatment.