 The FACO-NIRU-HEA catalyst was found to be highly efficient at both HER and OER, while maintaining long-term stability. This was due to the formation of a spinel oxide layer which preserved the active sites inherited from the HEA's intrinsic structure. This work provides a pathway for the design and manufacture of other metallic electro-catalysts, as well as a benchmark for assessing the efficiency-stability relationship. This article was authored by Kong Wang, Zhou Yanxia, Yulu, and others.