The rising energy demand, coupled with the geopolitical instability in Europe, has intensified the need to reduce our reliance on fossil fuels and to develop new renewable energy technologies. Electrochemical energy conversion and storage systems, including fuel cells, water splitting, and batteries, are emerging as key solutions. Among these, hydrogen stands out as a promising energy vector for transitioning to a sustainable energy system and carbon-neutral economy. Feasible technology for green hydrogen production is water electrolysis (WE), which is based on two electrochemical reactions, namely hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). State-of-the-art catalysts for HER and OER are based on Pt and Ir, respectively. Since both Pt and Ir are expensive and scarce, reducing their usage while keeping the performance in the catalysts is paramount for economic feasibility of the WE technologies. To tackle this problem, the proposed research focuses on developing high entropy alloys (HEAs) as advanced electrocatalysts for WE using a novel radiolytic method. Leverages of radiolytic synthesis over conventional physical or chemical methods involve operation at room temperature and atmospheric pressure and environmentally friendly synthesis. The main feature of HEAs is the creation of completely new catalytic sites ideal for a specific reaction, with potentially unprecedented catalytic performance. We aim to rationally design and synthesize HEAs using a mixed experimental and theoretical approach specifically tailored for the HER and OER, with a focus on minimizing the use of precious metals (Pt, Ir and Ru) by mixing them with the more abundant transition metals (Fe, Co, Ni, Cu, Cr, Mn, Mo, V, Zn). Furthermore, these HEAs will be supported on high-surface-area carbon and titanium oxynitride supports, to maximize the number of exposed active sites and to additionally enhance their activity and stability.