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

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.