Effect of Ni Sulfate Residue on Oxygen Evolution Reaction (OER) in Porous NiFe@NiFe Layered Double Hydroxide.

The development of cost-effective and high-performance oxygen evolution reaction (OER) catalysts is a significant challenge. This study presents the synthesis of binder-free NiFe@NiFe layered double hydroxide (NNF) via one-pot electrodeposition on carbon paper and Ni foam at high current densities. The presence of Ni sulfate residues on the prepared NNF is also investigated. The findings indicate that Ni sulfate significantly improves OER performance and durability. The sulfate content can be controlled by varying the method and duration of washing. NNF prepared through dipping (NNF-D) exhibits outstanding OER activity with a low overpotential of 241 mV, which is 25 mV lower than that of NNF washed for 60 s (NNF-W-60 s) at 10 mA cm in 1 m KOH. Furthermore, density functional theory analyses indicate that the Ni sulfate residue helps modify the electronic structure, thereby optimizing the binding strength of *OOH. This synthetic strategy is expected to inspire the development of next-generation catalysts utilizing various adsorbates.