Strongly Coupled Ni/Ni(OH)₂ Hybrid Nanocomposites as Highly Active Bifunctional Electrocatalysts for Overall Water Splitting

Abstract

Herein, interfacially coupled Ni/Ni(OH)2 nanocomposites are successfully prepared using a facile one-step hydrothermal route with addition of various amounts of hydrazine and then applied as bifunctional catalysts for overall water splitting. The reconfiguration of electrons at the metal and semiconductor interface and well-tuned compositions between Ni and Ni(OH)2 significantly promote activities for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Owing to the synergistic effect of Ni and Ni(OH)2, the optimal hybrid electrode delivers low overpotentials of 310 and 168 mV to achieve a current density of 10 mA cm–2 for OER and HER in 1 M KOH, respectively. Assembled as an alkaline electrolyzer for overall water splitting, this bifunctional catalyst for both anode and cathode exhibits an excellent low onset potential of only 1.43 V and provides a current density of 10 mA cm–2 at a very low cell voltage of 1.68 V. Furthermore, the symmetric cell shows a prominent long-term durability with negligible degradation even after 16 h continuous operation. The proposed synthesis process can be applied to other transition metals to prepare their metal/metal hydroxide hybrid composites with improved electrochemical performances for energy storage and conversion applications.