An oxygen evolution reaction (OER) electrocatalyst for acidic media comprises a metal oxide structure comprising a pyrochlore phase of chemical formula A2B2On, wherein A comprises one or more A-site metals, B comprises one or more B-site metals, and 6.0≤n≤7.3. The metal oxide structure exhibits a mass current density of at least about 20 A/g at an over-potential of 0.22 V in 0.1 M HClO4. According to another embodiment, an electrocatalyst for acidic media comprises a porous metal oxide structure having particulate walls separating a plurality of pores, where each particulate wall comprises interconnected primary particles. The porous metal oxide structure comprises a pyrochlore phase of chemical formula A2B2On, wherein A comprises one or more A-site metals, B comprises one or more B-site metals, and 6.0≤n≤7.3.