The development of renewable energy and the related conversion and storage technologies plays a crucial role in achieving the global goal of carbon neutrality. In particular, green hydrogen produced by water electrolysis with renewable electricity is regarded as one of the most promising pathways for solving the energy crisis and environmental issues in modern society. However, the sluggish kinetics of water-splitting reactions, namely, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), remains a bottleneck to the water electrolysis technology. Although considerable ‘fancy’ electrocatalytic materials, such as nanoparticles, nanowires and nanosheets, have been developed in the lab, unfortunately, few of them can be readily utilized under industrial conditions. The main reason is that industrial sectors need catalysts to simultaneously meet the requirements of low cost, high activity, long-term durability and easy mass production. Recently, high entropy-alloys (HEAs) have been found to be of great potential as efficient catalytic materials for water electrolysis due to their compositional flexibility, structural stability, and strong alloying effects. In this talk, we will report our recent progresses in the development of HEA water-splitting catalysts based on physical metallurgy principles. Specifically, self-supported non-precious-metal-based HEA catalysts with hierarchical porous structures were mass-produced by modulating phase separation, spinodal decomposition or eutectic reaction. These HEA electrodes simultaneously exhibited superior activity and outstanding long-term durability towards alkaline HER and OER. The underlying mechanism responsible for the enhanced catalytic performance will be also discussed.