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

Abstract

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.