Highly active and durable La_0.6Ca_0.4(CrMnFeCo₂Ni)O₃ high entropy perovskite oxide as electrocatalyst for oxygen evolution reaction in alkaline media

•Electrocatalytic activity of La(CrMnFeCo2Ni)O3 high entropy perovskite oxide (HEPO) for OER was effectively enhanced by A-site Ca-doping.•La0.6Ca0.4B2Co exhibits low η10 (340 mV) and superior durability with < 20 mV increase in η10 in 200 h.•The excellent OER performance was a synergetic effect from the rich oxidation states of B-site metals and presence of oxygen vacancies induced by Ca-doping.•High configuration entropy may also contribute to the OER activity and durability.