NiCo(2)O(4) nanoparticles rich in oxygen vacancies: Salt-Assisted preparation and boosted water splitting

NiCo(2)O(4) is a promising catalyst toward water splitting to hydrogen. However, low conductivity and limited active sites on the surfaces hinder the practical applications of NiCo(2)O(4) in water splitting. Herein, small sized NiCo(2)O(4) nanoparticles rich in oxygen vacancies were prepared by a simple salt-assisted method. Under the assistance of KCl, the formed NiCo(2)O(4) nanoparticles have abundant oxygen vacancies, which can increase surface active sites and improve charge transfer efficiency. In addition, KCl can effectively limit the growth of NiCo(2)O(4), and thus reduces its size. In comparison with NiCo(2)O(4) without the assistance of KCl, both the richer oxygen vacancies and the reduced nanoparticle sizes are favorable for the optimal NiCo(2)O(4)-2KCl to expose more active sites and increase electrochemical active surface area. As a result, it needs only the overpotentials of 129 and 304 mV to drive hydrogen and oxygen evolution at 10 mA cm(−2) in 1 M KOH, respectively. When NiCo(2)O(4)-2KCl is applied in a symmetrical water splitting cell, a voltage of ∼1.66 V is only required to achieve the current density of 10 mA cm(−2). This work shows that the salt-assisted method is an efficient method of developing highly active catalysts toward water splitting to hydrogen.