TENG-driven single-droplet green electrochemical etching and deposition for chemical sensing applications

Selected area electrochemical etching (EE) and electrochemical deposition (ED) are widely used for fabricating microstructures and devices, but they require complex processes and expensive equipment and generate significant electrolyte waste. This study demonstrates a novel single-droplet electrochemical system using a triboelectric nanogenerator (TENG) for self-powered selected area EE and ED reactions. Utilizing TENG's pulsed power, Al nanostructures were created by EE, while nano-Ag and Cu2O nanocubes were synthesized by ED. The generated nanomaterials were applied to detect trace chemicals through the Surface-Enhanced Raman Scattering effect. The electrochemical reaction area can be controlled by droplet size, and patterns can be created using a needle movement platform. The size and density of nanostructures can be adjusted by the TENG's current, collision frequency, and electrolyte concentration. The deposition gradient from the center to the edge of the droplet is controlled by the distance between the needle and the substrate. COMSOL Multiphysics calculations show that a smaller D creates a larger electric field gradient. However, the varied deposition gradients were attributed to competition of electric field, diffusion effects, and capillary flow. This proposed green technology offers low cost, simplicity, no waste electrolyte, and self-powering capabilities, pioneering new research directions in EE and ED.