Hierarchical Spear‐Like CuMn ₂ O ₄ Spinel Architectures as High‐Performance Bifunctional Electrocatalysts for Alkaline HER and OER

CuMn 2 O 4 and Cu 1 . 5 Mn 1 . 5 O 4 mixed‐metal copper‐manganese oxide spinels were synthesized via a hydrothermal route to investigate the influence of composition and morphology on bifunctional electrocatalysis for alkaline water splitting. Structural and microscopic analyses revealed that CuMn 2 O 4 forms a hierarchical spear‐like architecture, whereas Cu 1 . 5 Mn 1 . 5 O 4 develops plate‐like assemblies. Owing to its open, porous nanosheet network and abundant surface‐exposed Mn active sites, CuMn 2 O 4 delivers markedly enhanced catalytic performance, requiring overpotentials of only 290 mV for the oxygen evolution reaction (OER) and 17 mV for the hydrogen evolution reaction (HER) at 10 mA·cm −2 . It also exhibits small Tafel slopes of 98.2 mV·dec −1 (OER) and 59.1 mV·dec −1 (HER), along with excellent durability over extended chronoamperometric operation (10 h for OER and 16 h for HER). The superior activity is further supported by a large electrochemically active surface area (27.31 mF·cm −2 ), attributed to the hierarchical porous structure that facilitates charge transfer and mass transport. These results highlight CuMn 2 O 4 as a promising, earth‐abundant bifunctional catalyst for efficient alkaline water splitting.