cobalt phosphate is a solid chemical compound with the formula CoPO4. It is a member of the family of transition metal phosphides and is an attractive material for oxygen evolution reaction (OER) electrocatalysis due to its excellent intrinsic stability. [1] In recent years, various Co-based phosphides have been developed as efficient precatalysts for the OER in alkaline medium. [2] These materials exhibit superior stability and performance compared to conventional IrO2-based catalysts. [3] However, the structural features and mechanisms governing their activity remain unclear.
To enhance the understanding of their mechanism and provide a basis for future design, we report an investigation on the structure and properties of a novel 2D nanosheet-like ammonium cobalt phosphate hydrate (NH4CoPO4*H2O) catalyst for OER in alkaline saline solution. Our results demonstrate that NH4CoPO4*H2O achieves current density of 10 mA cm-2 at record low overpotentials of only 265 and 252 mV in 1.0 m KOH and simulated seawater electrolytes, respectively. Furthermore, the optimal thin NH4CoPO4*H2O nanosheets exhibit remarkable stability during continuous 20 h OER in the challenging alkaline saline solution environment.
The synthesis and characterization of the catalyst were performed in one step at room temperature using different raw materials. Structural characterization was performed by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The structural analysis revealed that NH4CoPO4*H2O consists of Co (II) ions encapsulated in a distorted tetrahedral structure with edge-sharing CoO6 octahedra similar to those found in cobaltates. This octahedral structure contributes to the excellent intrinsic stability of the NH4CoPO4*H2O in alkaline saline solution.