Revealing the highly effective electrocatalyst carbon nanotube-coupled Cu–Mn mixed oxide toward robust bifunctional electrochemical water splitting in alkaline medium

Abstract

The establishment of highly efficient and stable bifunctional electrocatalysts is very important for the promotion of alkaline water electrolysis. In addition, a novel hybrid electrocatalyst, which consists of Cu–Mn–O (CMO) mixed metal oxides supported on CNTs, is presented. The CNTs allow for highly conductive pathways for effective charge transfer, which in turn improves structural integrity and better access to catalytically active sites. Structural and surface characterization techniques, including XRD, HR-SEM, HR-TEM, and XPS, confirm the successful synthesis of the CNT–CMO hybrid electrocatalyst with a strong interface between the mixed metal oxide and CNTs. The CNT–CMO hybrid electrocatalyst demonstrates excellent electrocatalytic activity in 1.0 M KOH with low overpotentials of 280 mV for the HER and 251 mV for the OER at 10 mA cm⁻², along with Tafel slopes of 93 mV dec⁻¹, respectively. Additionally, the CNT–CMO hybrid electrocatalyst exhibits a greatly increased surface area when compared to the pristine CMO electrocatalyst, thereby allowing for enhanced utilization of active sites. Above all else, the CNT–CMO hybrid electrocatalyst maintains a constant current density for more than 30 hours of nearly continuous electrolysis, suggesting that high stability of this catalyst exists. The enhanced performance of the electrocatalysts is the result of a synergistic relationship between the mixed valence Cu and Mn redox sites and the high conductivity of the CNT, which together create a compatible environment for the catalytic reaction kinetics. The results further support the use of CNT-supported CMO as an earth-abundant, bifunctional electrocatalyst material for overall water splitting in alkaline solutions.