Ultrasmall NiFe layered double hydroxide strongly coupled on atomically dispersed FeCo-NC nanoflowers as efficient bifunctional catalyst for rechargeable Zn-air battery

An atomically dispersed FeCo-NC material with the 3D flower-like morphology was used as a unique substrate for the controllable deposition of ultrasmall NiFe layered double hydroxide nanodots (termed as NiFe-NDs) to simultaneously promote the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The size-limiting growth of NiFe-NDs (similar to 4.0 nm in diameter) was realized via the confinement of the 3D flower-like mesoporous structure and the rich N/O functionality of FeCo-NC. Benefiting from the distinctive structure with the simultaneously maximum exposure of both OER and ORR active sites, the NiFe-ND/FeCo-NC composite showed an ORR halfwave potential of 0.85 V and an OER potential of 1.66 V in 0.1 mol L-1 KOH at 10.0 mA cm(-2). In-situ Raman analysis suggested the activity of OER was derived from the Ni sites on NiFe-ND/FeCo-NC. Moreover, the NiFe-ND/FeCo-NC-assembled Zn-air battery (ZAB) exhibited a very small discharge- charge voltage gap of 0.87 V at 20 mA cm(-2) and robust cycling stability. Furthermore, the NiFe-ND/FeCo-NC composite was also applicable for fabricating all-solid-state ZAB to power wearable electronics with superior cycling stability under deformation. Our work could enlighten a new applicable branch of atomically dispersed metal-nitrogen-carbon materials as unique substrates for fabricating multifunctional electrocatalysts.