The study explores the optimization of acidic oxygen evolution electrocatalysis by precisely modulating the Ru-O covalency in RuOx using lanthanide (Ln) elements. The introduction of Ln elements, with their 4f orbital electron configurations, minimizes external influences and enables continuous tuning of the Ru-O covalency. Theoretical calculations confirm that the durability of Ln-RuOx follows a volcanic trend as a function of Ru-O covalency, with Er-RuOx identified as the optimal catalyst, showing a stability 35.5 times higher than that of RuOx. Experimental results demonstrate that Er-RuOx requires only 1.837 V to reach 3 A cm^-2 and exhibits long-term stability at 500 mA cm^-2 for 100 h with a degradation rate of 37 μV h^-1. The enhanced performance of Er-RuOx is attributed to its optimized Ru-O covalency, which reduces the formation of oxygen vacancies and prevents overoxidation of Ru species. This work provides a novel approach for stabilizing Ru-based OER electrocatalysts, contributing to the development of more economic and efficient PEMWE systems for green hydrogen production.The study explores the optimization of acidic oxygen evolution electrocatalysis by precisely modulating the Ru-O covalency in RuOx using lanthanide (Ln) elements. The introduction of Ln elements, with their 4f orbital electron configurations, minimizes external influences and enables continuous tuning of the Ru-O covalency. Theoretical calculations confirm that the durability of Ln-RuOx follows a volcanic trend as a function of Ru-O covalency, with Er-RuOx identified as the optimal catalyst, showing a stability 35.5 times higher than that of RuOx. Experimental results demonstrate that Er-RuOx requires only 1.837 V to reach 3 A cm^-2 and exhibits long-term stability at 500 mA cm^-2 for 100 h with a degradation rate of 37 μV h^-1. The enhanced performance of Er-RuOx is attributed to its optimized Ru-O covalency, which reduces the formation of oxygen vacancies and prevents overoxidation of Ru species. This work provides a novel approach for stabilizing Ru-based OER electrocatalysts, contributing to the development of more economic and efficient PEMWE systems for green hydrogen production.