Sandwich structured Fe3O4/NiFe LDH/Fe3O4 as a bifunctional electrocatalyst with superior stability for highly sustained overall water splitting

Modifying electrocatalysts' structures and regulating their reaction kinetics is essential to improve the performance of electrocatalysts. Here, we report the Fe3O4/NiFe layered double hydroxides/Fe3O4 (Fe3O4/NiFe LDH/Fe3O4) with a sandwich structure by a one-step hydrothermal process. The interface synergistic effect between Fe3O4 and NiFe LDH together with abundant electroactive sites encapsulated inside the Fe3O4 oxide layer can stabilize important charge transfer intermediates and promote the reaction kinetics, which could result in remarkable electrochemical performance. As a result, the resulting Fe3O4/NiFe LDH/Fe3O4 exhibits the lowest overpotential requirements of η10 = 134 mV and η50 = 267 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 M KOH, respectively. A two-electrode electrolyzer assembled with Fe3O4/NiFe LDH/Fe3O4 as both cathode and anode require a low cell voltage of 1.648 V to achieve the current density response of 10 mA cm−2 toward overall water splitting. Furthermore, the Fe3O4/NiFe LDH/Fe3O4 also displays excellent industrial catalytic performance by simulating the industrial electrolysis for OER, requiring only 353 mV at the large current density of 1000 mA cm−2. This work puts a deep insight into the role of the confined space of transition metal-based catalysts in electrocatalysis.