Coupling Bimetallic Oxides/Alloys and N-Doped Carbon Nanotubes as Tri-Functional Catalysts for Overall Water Splitting and Zinc–Air Batteries

An effectively multifunctional electrocatalyst is crucial for catalyzing the reactions occurred at electrodes in zinc–air batteries and water splitting cells, such as oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR). Herein, two non-noble metal-based multifunctional electrocatalysts of N-doped carbon nanotubes NCNT/CoFe–CoFe2O4 and NCNT/MnO–(MnFe)2O3 are prepared by a simple solvothermal procedure, followed by two-step annealing under the argon and ammonia atmosphere. The resultant electrocatalysts exhibit good trifunctional performances for HER, ORR, and OER. Notably, the NCNT/CoFe–CoFe2O4 and NCNT/MnO–(MnFe)2O3 assembled zinc–air batteries exhibit high energy densities of 727 and 776 W h kgZn–1 at the current density of 20 mA cm–2, respectively. Furthermore, the NCNT/CoFe–CoFe2O4-based rechargeable zinc–air battery remains excellent durability after discharge–charge cycle testing for 22 h, comparable to the noble metal-based catalyst (Pt/C + IrO2)-assembled zinc–air battery. Furthermore, the NCNT/CoFe–CoFe2O4 and NCNT/MnO–(MnFe)2O3-assembled water splitting cells need ∼1.65 and 1.70 V, respectively, to deliver a current density of 10 mA cm–2, lower than that of IrO2–Pt/C (1.71 V) and present excellent durability under long-term electrolysis. This work provides a facile strategy to prepare highly active multiple functional electrocatalysts for energy conversion and storage.