Self-Supported 3 D Ultrathin Cobalt-Nickel-Boron Nanoflakes as an Efficient Electrocatalyst for the Oxygen Evolution Reaction.

The development of highly active and efficient nonprecious-metal electrocatalysts for the oxygen evolution reaction is important for the design of renewable energy production and storage devices. In this work, highly dense, ultrathin Co-Ni boride nanoflakes supported on a 3 D CoNi skeleton are fabricated in situ by a simple one-step, high-temperature, solid-state boronation process. As a result of the induced high electroactive surface area and low charge transfer resistance, CoNiB-700 exhibits high catalytic activity at an overpotential of 262 (η10 ) and 284 mV (η20 ) to deliver current densities of 10 and 20 mA cm-2 , respectively, with a Tafel slope of 58 mV dec-1 in an alkaline medium towards the oxygen evolution reaction. DFT calculations show that the Ni-regulated Co-B compound has a lower rate-determining energy barrier for the *OOH intermediate than the mono-Co-B compound, which facilitates the production of more active catalytic sites for an accelerated surface charge-transfer process for the oxygen evolution reaction.