Fabrication of Ni/NiFe-LDH Core-Shell Schottky Heterojunction as Ultrastable Bifunctional Electrocatalyst for Ampere-Level Current Density Water Splitting

The practical application of NiFe-based materials as high-performance water splitting electrocatalysts is severity restricted by their inferior hydrogen evolution reaction (HER) activity and long-term stability under large current density. Herein, we report a three-dimensional core-shell Ni/NiFe-layered double hydroxide (LDH) Schottky heterojunction on iron foam (Ni/NiFe-LDH/ IF) electrode, in which a Ni metal nano-layer was directly deposited on the NiFe-LDH support grown in situ on commercial IF. Such an assembly enhanced the interfacial strength of the Ni/NiFe-LDH/IF electrode, promoted electron transfer and increased the adsorption energy of OH- as proved by density functional theory calculations. Consequently, the ultralow overpotentials (eta) of 56 and 277 mV for HER and 140 and 330 mV for the oxygen evolution reaction (OER) resulted in the current densities of 10 and 1000 mA cm-2, respectively. The fabricated Ni/NiFe-LDH/IF two-electrode electrolyzer exhibited excellent water splitting characteristics, which produced the current densities of 10 and 1000 mA cm-2 at cell voltage of only 1.49 and 1.87 V, versus a reversible hydrogen electrode, respectively, which exceeded that of a commercial Pt/C||RuO2 catalyst. Moreover, the Ni/NiFe-LDH/IF electrolyzer demonstrated extremely high stability at 1000 mA cm-2 without a significant decay for more than 1500 h in a 1 M KOH solution and for 250 h at 60 degrees C in a 6 M KOH solution. This study proposes a scalable and extendable strategy for designing highly efficient and ultrastable electrocatalysts for hydrogen production at an ampere-level current density.