Highly\nEfficient and Robust Nickel Phosphides as Bifunctional Electrocatalysts\nfor Overall Water-Splitting

Abstract

To search for the efficient non-noble\nmetal based and/or earth-abundant electrocatalysts for overall water-splitting\nis critical to promote the clean-energy technologies for hydrogen\neconomy. Herein, we report nickel phosphide (Ni_<i>x</i>P_<i>y</i>) catalysts with the controllable\nphases as the efficient bifunctional catalysts for water electrolysis.\nThe phases of Ni_<i>x</i>P_<i>y</i> were determined by the temperatures of the solid-phase reaction\nbetween the ultrathin Ni­(OH)₂ plates and NaH₂PO₂·H₂O. The Ni_<i>x</i>P_<i>y</i> with the richest Ni₅P₄ phase synthesized at 325 °C (Ni_<i>x</i>P_<i>y</i>-325) delivered efficient and\nrobust catalytic performance for hydrogen evolution reaction (HER)\nin the electrolytes with a wide pH range. The Ni_<i>x</i>P_<i>y</i>-325 catalysts also exhibited\na remarkable performance for oxygen evolution reaction (OER) in a\nstrong alkaline electrolyte (1.0 M KOH) due to the formation of surface\nNiOOH species. Furthermore, the bifunctional Ni_<i>x</i>P_<i>y</i>-325 catalysts enabled a highly\nperformed overall water-splitting with ∼100% Faradaic efficiency\nin 1.0 M KOH electrolyte, in which a low applied external potential\nof 1.57 V led to a stabilized catalytic current density of 10 mA/cm² over 60 h.