Nanoporous Ru as a Carbon- and Binder-Free Cathode for Li-O₂ Batteries

Porous carbon-free cathodes are critical to achieve a high discharge capacity and efficient cycling for rechargeable Li-O₂ battery. Herein, we present a very simple method to directly grow nanoporous Ru (composed of polycrystalline particles of ∼5 nm) on one side of a current collector of Ni foam via a galvanic replacement reaction. The resulting Ru@Ni can be employed as a carbon- and binder-free cathode for Li-O₂ batteries and delivers a specific capacity of 3720 mAhg_Ru^-1 at a current density of 200 mAg_Ru^-1. 100 cycles of continuous discharge and charge are obtained at a very narrow terminal voltage window of 2.75∼3.75 V with a limited capacity of 1000 mAhg_Ru^-1. The good performance of the nanoporous Ru@Ni cathode can be mainly attributed to the effective suppression of the by-products related to carbon or binder, the good adhesion of the catalyst to the current collector, and the good permeation of O₂ and electrolyte into the active sites of the nanoporous Ru with the open pore system. This new type electrode provides a snapshot toward developing high-performance carbon- and binder-free Li-O₂ batteries.