Self-Supporting FeOOH/NiFe-LDH Heterostructures with a Built-In Electric Field for Efficient and Durable Alkaline Seawater Oxidation

Efficient and durable oxygen evolution reaction (OER) catalysts are crucial for the generation of hydrogen via alkaline seawater electrolysis. Herein, an FeOOH/NiFe-LDH heterostructure with a built-in electric field (BEF) has been synthesized on Ni foam through a one-step cathodic electrodeposition. The formed BEF accelerates the OER kinetics by optimizing the interfacial electronic structure and enhancing the mass transfer and stabilizes the structure of the catalyst by Fe-O-Ni-O-Fe coupling bonds. In addition, the BEF and FeOOH mutually reduce the adsorption of Cl^- on the catalyst. Accordingly, FeOOH/NiFe-LDH demonstrates an outstanding OER catalytic performance in alkaline seawater electrolytes. In detail, FeOOH/NiFe-LDH displays small η₁₀₀ values of 265 and 278 mV in alkaline simulated and natural seawater, respectively, and achieves exceptional durability with smooth operation for ∼150 h at 250 mA cm^-2, albeit in a high-salt electrolyte (1 M KOH and 2.5 M NaCl). When FeOOH/NiFe-LDH is used as the anode of the AEM electrolyzer, the cell in alkaline simulated seawater delivers low voltages of 1.59 and 1.92 V at 100 and 500 mA cm^-2, respectively. The cell also shows excellent durability after operation over 110 h at 250 mA cm^-2 with an insignificant voltage increase of only 27 mV (∼0.25 mV h^-1). This work provides insight into the catalytic mechanism of the BEF-based heterostructure as anodic catalysts for alkaline seawater electrolysis.