Cu ₂ O Nanocube Anchored Co ₃ O ₄ Nanosheet: An Interfacial Avenue for Efficient Green Hydrogen Production Through Alkaline Water Electrolysis

ABSTRACT The paper investigates a highly active and durable Cu 2 O/Co 3 O 4 heterostructure composite for electrocatalytic overall water splitting (OWS) in an alkaline electrolyte. A strongly coupled interfacial synergy between Cu 2 O and Co 3 O 4 , as shown by spectroscopy and theoretical studies, modulates the electronic structure and enhances catalytic activity that imparts the efficient bifunctional hydrogen and oxygen evolution reaction (HER and OER) activities in the composite. The heterostructure is composed of metal‐like Cu 2 O and oxygen vacancy (O V )‐confined Co 3 O 4 . Whereas Co 3 O 4 and Cu 2 O individually show considerably high overpotentials ( η 10 ) of 354 and 234 mV for HER and 450 and 860 mV for OER ( j = 10 mA cm −2 ), respectively, the Cu 2 O/Co 3 O 4 composite achieves a notably lower η 10 of 170 mV for HER, 230 mV for OER. Improved mass activity (MA), surface area, turnover frequency (TOF), and Faradaic efficiency (FE) converge together to enhance the catalytic activity. A two‐electrode Cu 2 O/Co 3 O 4 || Cu 2 O/Co 3 O 4 electrolyzer efficiently performs OWS at a cell voltage of 1.78 V for five days without a significant change in current density. Additionally, the electrolyzer successfully generates green hydrogen, powered by a 3.0 V solar panel. This work underlines the promise of strongly coupled metal oxide systems as an economical alternative to noble metal‐based electrocatalysts for water‐splitting applications.