Hexagonal Nickel/Nickel Hydroxide Nanoplates As Efficient Bifunctional Electrocatalysts for Overall Water Splitting

Abstract

Electrochemical water splitting has been considered as a promising strategy for next-generation energy storage and conversion applications by converting abundant water into extremely pure hydrogen and oxygen. However, the water splitting is limited by the high overpotentials for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Thus, numerous efforts have been dedicated to developing efficient and low-cost bifunctional catalysts. Among the various candidates, nickel-based compounds have attracted increasing interest for HER and OER due to their low cost, abundance, and high electrocatalytic activities. Herein, we report hexagonal Ni/Ni(OH)2 nanoplates via one-pot hydrothermal method with varying the ratio between metal precursor and hydrazine which is a strong chemical reductant. The bifunctional catalyst exhibited low overpotential of 171 mV and 310 mV to achieve the current density of 10 mA cm−2 for HER and OER, respectively. Also, the Ni/Ni(OH)2 nanoplates show the outstanding long-term stability for both HER and OER in 1 M KOH alkaline media. In overall water splitting system, the hybrid catalyst exhibits a current density of 10 mA cm−2 at a cell voltage 1.78 V. The high electrochemical activity and durability are mainly originated from the synergistic effect of Ni and Ni(OH)2. This work demonstrates that our simple synthetic approach can be applied to synthesize various metal/metal hydroxide composites and improve their electrochemical property for renewable energy storage application.