## 1 Introduction  
Hydrogen is emerging as a versatile and sustainable energy carrier, set to play a key role in the global transition to cleaner energy systems. As a zero-emission fuel, it can be used across multiple sectors, including transportation, industry, and power generation, reducing reliance on fossil fuels. The European Union (EU) is at the forefront of hydrogen development, establishing policies and initiatives to accelerate its adoption. An important part of these efforts is the \"Hydrogen Backbone\", a pan-European network of pipelines connecting hydrogen production, storage, and consumption locations. This infrastructure is aimed at creating a robust market and ensuring cost-effective hydrogen distribution. While hydrogen combustion or utilization in fuel cells does not produce CO\({}_{2}\), it is not necessarily a clean energy carrier since its production (e.g., from methane) may be associated with notable CO\({}_{2}\) emissions. Therefore, hydrogen is assigned to \"colors\" based on its production method and associated environmental impact. Gray hydrogen is derived from natural gas through steam methane reforming, emitting significant amounts of CO\({}_{2}\). Blue hydrogen also originates from natural gas but incorporates carbon capture and storage (CCS) to reduce emissions, making it a lower-carbon alternative. Brown or black hydrogen is produced from coal, resulting in even higher CO\({}_{2}\) emissions. Other colors (turquoise, purple, etc.) are associated with specific production methods. Most notably, green hydrogen is produced via water electrolysis powered by renewable electricity, making it entirely carbon-free and thus the most desirable type of hydrogen in the long run. Green hydrogen is produced through water electrolysis, using renewable electricity to split water (H\({}_{2}\)O) into hydrogen (H\({}_{2}\)) and oxygen (O\({}_{2}\)). The process involves applying electrical potential across electrodes submerged in water, causing oxidation at the anode (producing O\({}_{2}\)) and reduction at the cathode (producing H\({}_{2}\)). Three main electrolysis technologies include _(i)_ alkaline electrolysis, _(ii)_ proton exchange membrane (PEM), and _(iii)_ solid oxide electrolysis (SOEC) [1; 2]. Alkaline electrolysis is the most mature technology and uses liquid electrolytes such as potassium hydroxide solution. It is also less expensive but slower to respond to dynamic loads [3]. PEM electrolysis relies on a proton-conducting membrane, offering high efficiency, reliability, and flexibility, but at a higher cost [4]. Finally, SOEC is an emerging technology, which operates at high temperatures, improving efficiency but requiring durable materials [5]. To optimize hydrogen production via electrolysis, intensive research efforts are ongoing. The main focus is on the behavior of hydrogen bubbles on the cathode, as their formation and detachment significantly influence the efficiency of the electrolysis process. Although previous studies examined the impact of bubble dynamics on electrical current density, several research gaps remain. Specifically, the transitional behavior between different bubble coalescence regimes under varying applied potentials has not been comprehensively characterized. Moreover, the direct correlation between applied potential, bubble departure size, frequency, and current density fluctuations requires further quantification. Our study addresses these gaps by combining high-speed imaging with potentiostat measurements to systematically analyze bubble departure behavior and its impact on the electrochemical hydrogen production. The main reason for this is the fact that the volume ratio between H\({}_{2}\) and O\({}_{2}\) emerging from electrodes is 2:1, meaning that what is happening on the cathode side is the limiting factor from the hydrodynamic point of view.