CoNiFe LDH/RuO2.1 Nanosheets Superlattice as Carbon-Free Electrocatalysts for Water Splitting and Li-O2 Batteries.

Efficient electrocatalysts are highly demanded for oxygen evolution reaction (OER) in water splitting and metal-air batteries. Here, superlattice structured materials composed of CoNiFe layered double hydroxide (LDH)/ruthenium oxide nanosheets are synthesized as carbon-free electrocatalysts for OER. The positively charged CoNiFe LDH and negatively charged RuO2.1 are alternately stacked at the molecular level into superlattice-like hybrids by electrostatic interaction upon mixing their dispersions under suitable conditions. Such heterostructured composites are found to act as effective catalysts towards OER of water splitting with a small overpotential of 281 mV and Tafel plot of 48.9 mV/decade. Such composites also serve as efficient carbon-free cathode catalysts for aprotic Li-O2 batteries with remarkable higher specific capacities and lower overvoltages than RuO2 nanoparticles. The superior performance may be attributed to the peculiar superlattice structure, resulting in strong interfacial electronic coupling, better electrical conductivity and the suppression of side reactions caused by traditional carbon-based materials. Furthermore, potential difference between RuO2.1 and CoNiFe LDH nanosheets is observed directly by Scanning Kelvin Probe Microscopy, indicating that electrostatic fields might be induced in the superlattice structures, to benefit the transport of electrons and charged ions as well as the catalytic process.