Two-dimensional MOF/MOF derivative arrays on nickel foam as efficient bifunctional coupled oxygen electrodes

Oxygen electrocatalysis, exemplified by the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), is central to energy storage and conversion technologies such as fuel cells, metal-air batteries, and water electrolysis. However, highly effective and inexpensive earth-abundant materials are sought after to replace the noble metal-based electrocatalysts currently in use. Recently, metal-organic frameworks (MOFs) and carbon-based MOF derivatives have attracted considerable attention as efficient catalysts due to their exceedingly tunable morphologies, structures, compositions, and functionalization. Here, we report two-dimensional (2D) MOF/MOF derivative coupled arrays on nickel foam as binder-free bifunctional ORR/OER catalysts with enhanced electrocatalytic activity and stability. Their remarkable electrochemical properties are primarily attributed to fully exposed active sites and facilitated charge-transfer kinetics. The coupled and hierarchical nanosheet arrays produced via our growth-pyrolysis-regrowth strategy offer promise in the development of highly active electrodes for energy-related electrochemical devices.