Porous Pd/NiFeO_x Nanosheets Enhance the pH-Universal Overall Water Splitting

Modulating the morphology and chemical composition is an efficient strategy to enhance the catalytic activity for water splitting, since it is still a great challenge to develop a bifunctional catalyst for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) over a wide pH range. Herein, Pd/NiFeO_x nanosheets are synthesized with tightly arranged petal nanosheets and uniform mesoporous structure on nickel foam (NF). The porous 2D structure yields a larger surface area and exposes more active sites, facilitating water splitting at all pH values. The overpotential of Pd/NiFeO_x nanosheets for OER is only 180, 169, and 310 mV in 1 m KOH, 0.5 m H₂SO₄, and 1 m phosphate-buffered saline (PBS) conditions at 10 mA cm⁻² current density, as well as excellent HER activity with ultralow overpotential in a wide pH range. When using porous Pd/NiFeO_x nanosheets as bifunctional catalysts for water splitting, it just required a cell voltage of 1.57 V to reach a current density of 20 mA cm⁻² with nearly 100% faradic efficiency in alkaline conditions, which is much lower than that of benchmark Pt/CǁRuO₂ (1.76 V) couples, along with the improving stability benefiting from the good corrosion resistance of the inner NiFeO_x nanosheets.