Improved OH adsorption and effective oxygen evolution reaction on carbon-capsulated Co0.1Ni0.9O@C/CP electrode

Abstract

Hydroxide ion (OH−) adsorption is an important step in promoting the oxygen evolution reaction (OER) in alkaline media. This study aims to design a rational catalyst to obtain several OH− adsorption sites to achieve excellent OER performance: NiO was selected as the main catalyst, and a Co0.1Ni0.9O catalyst was prepared with 10 % lattice substitution of Co2+ ions. The Co0.1Ni0.9O surface was capsulated with amorphous carbon to prevent corrosion by strong alkaline media. XPS analysis revealed that Ni2+ ion defects occurred in the Co0.1Ni0.9O crystal, and highly oxidized Ni3+ ions were mixed to attain the desired stoichiometric ratio. Electrophilic Ni2O3 in a highly oxidized state promotes attack from OH− ions, which is a nucleophile, and easily transforms into a NiOOH intermediate, which ultimately leads to the rapid progress of OER. That is, the strong covalent nature between Ni3+−O2− in the Co0.1Ni0.9O/CP electrode promotes charge transfer between the cationic metal surface and the OH− adsorbate, thereby accelerating OER. Moreover, C-capsulation in the Co0.1Ni0.9O particles reduces the band gap owing to the filling of the electrons from C between the Ni 3d and O 2p orbitals. Consequently, this improved the conductivity of the electrode, effectively reducing the ohmic potential drop and energy loss between the catalyst and the current collector. Therefore, the overpotential reached by this electrode at 10 mA cm−2 was greatly reduced to 332 mV, the Tafel slope was low at 91.98 mV dec−1, and during OER with a Faraday efficiency of 94.7 %. Moreover, this excellent performance remained stable even after 10 d.