Plasma Hydrogenated TiO2/Nickel Foam as an Efficient Bifunctional Electrocatalyst for Overall Water Splitting

Electrochemical water splitting is one of the most efficient technologies for hydrogen production and fabrication of low-cost, robust, and highly active electrocatalysts. It is attractive because replacing noble metal-based materials is a key issue in current catalysis research. By using H2 plasma treatment, the TiO2/nickel foam composite is converted to be an efficient bifunctional electrocatalyst toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the alkaline electrolyte. The investigation reveals the existence of abundant oxygen vacancies of TiO2, which might lead to the dramatic improvement of electrical conductivity and faster charge transfer rate; also, density functional theory (DFT) calculations suggest that the oxygen vacancies activate surrounding surface lattice oxygen to induce favorable reactive-intermediate adsorption energy of TiO2 for hydrogen evolution and adjust the strength of the chemical bonds between the TiO2 surface and reactive intermediates to more favorable values, inducing a lower energy barrier for oxygen evolution. The finding confers a unique function to TiO2 that is different from its widely accepted role as an electrocatalytically inert semiconductor material, suggesting the H2 plasma treated TiO2/nickel foam could be a bifunctional electrocatalyst for overall water splitting.