Engineering Different Reaction Centers on Hierarchical Ni/NiFe Layered Double Hydroxide Accelerating Overall Water Splitting

The insufficient and inert active sites limited the layered double hydroxides' (LDHs) hydrogen evolution reaction (HER) performance. Rationally integrating different active centers can promote bifunctional performance and synergistically enhance HER and OER performance. But it is still rarely reported to reasonably integrate different half-reaction centers and boost each other. Besides, the mechanism of different reaction centers that optimized each other is unclear. In this work, a 3D hierarchical heterostructure Ni/NiFe LDH, constructed by electrodeposition, provides abundant reaction centers that activate HER performance. Simultaneously, NiFe LDHs served as OER active centers, and metallic Ni improves its electric conductivity. Theoretical calculations also were used to confirm these further. Additionally, the unique hierarchical geometric structure increases the electrolyte contact area. The merits, as mentioned above, synergistically accelerate overall water splitting (OWS) and exhibit outstanding electrocatalysis performance. HER current density of the Ni/NiFe LDH heterostructure (312 mA cm–2) is 104 times as large as that of NiFe LDH (3.0 mA cm–2) with 150 mV overpotential. At 1.46 V, the OWS cell, constructed of both anode and cathode by as-synthesized Ni/NiFe LDH, can drive water splitting (10 mA cm–2), below noble metal Pt/C||RuO2 (1.53 V). This finding provides guidance for rationally integrating different reaction centers in bi- or multi-functional electrocatalytic processes.