NiCo2O4 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.

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