## 1 Introduction  
Electrode technology is a key component in electrochemical reactions and is widely utilized across various industrial sectors. The study of electrodes began in the early 19 th century with the invention of batteries [1], and over time, electrodes have become an essential component in energy storage and conversion devices. In particular, with the rapid development of green energy transition technologies in the 21 st century, the importance of electrodes has become even more pronounced. Today, electrodes play a critical role not only in energy storage systems such as batteries [2; 3; 4; 5; 6; 7; 8; 9; 10], fuel cells [11; 12; 13], and supercapacitors [14; 15; 16], but also in hydrogen production through water electrolysis [17; 18; 19; 20; 21]. Both battery-based energy storage systems and water electrolysis technology are crucial in driving the transition to sustainable energy, highlighting the increasing importance of electrode technology in these fields. Electrode technology is being researched with a focus on maximizing reaction efficiency and stability to improve performance in various applications. To optimize the reaction efficiency of electrodes, various factors must be considered, including the reaction environment [22; 23; 24], electrode materials [25; 26; 27; 28], electrolytes [29; 30; 31], power supply conditions [32; 33; 34], and electrode modification [5; 6; 7; 8; 9; 10; 35; 36]. Among these, electrode modification is currently dependent on techniques such as additive manufacturing [5; 6; 7] and electrodeposition [8; 9; 10], which face limitations in terms of practicality. While these methods have shown meaningful results in research settings, they may encounter challenges when scaled for industrial applications due to issues such as reduced adhesion between the electrode substrate and additives, leading to delamination during use. This is particu-larly true when the substrate material or electrolyte composition is not adequately considered, which can exacerbate detachment under operational conditions. Additionally, these techniques often fail to adequately control surface morphology and material uniformity, potentially compromising long-term durability. In contrast, micro- and nano-structured modifications applied directly to the electrode surface, as proposed in this study, avoid these adhesion issues by structuring the original substrate material itself [37; 38; 39; 40; 41]. This eliminates concerns about delamination, resulting in enhanced durability and stability over extended use. Optimizing the material structure in this way allows for simultaneous improvement in electrochemical performance and industrial practicality. In this study, we aim to develop electrodes by applying micro- and nano-structured modifications to various metal electrodes using chemical processes. These methods have demonstrated high productivity and durability in previous research [37; 38; 39; 40; 41], and we plan to evaluate their electrochemical performance using the electroflotation (EF) process. EF, as illustrated in Figure 1, is an emerging wastewater treatment technology that has garnered attention in recent years for its numerous advantages over traditional methods, such as dissolved air flotation (DAF) [42; 43; 44]. EF effectively separates solids from liquids by utilizing gases produced during water electrolysis, offering significant benefits in terms of cost efficiency, stability, and environmental protection. The fundamental efficiency of EF depends on the amount and size of gas bubbles generated per unit electrode area. Smaller and more abundant bubbles improve separation efficiency by continuously facilitating efficient contact between the electrode and the liquid, which is closely related to reactivity [35; 36; 45; 46]. In this study, we will select industrial-grade metals suitable for bubble generation, apply micro- and nano-structures to these metals, and meticulously examine bubble size and quantity during the EF process to develop electrodes with enhanced reactivity.