Topochemical Synthesis of Two-Dimensional Transition-Metal Phosphides Using Phosphorene Templates

Transition-metal phosphides (TMPs) have emerged as a fascinating class of narrow-gap semiconductors and electrocatalysts. However, they are intrinsic nonlayered materials that cannot be delaminated into two-dimensional (2D) sheets. Here, we demonstrate a general bottom-up topochemical strategy to synthesize a series of 2D TMPs (e.g. Co₂ P, Ni₁₂ P₅ , and Co_x Fe_2-x P) by using phosphorene sheets as the phosphorus precursors and 2D templates. Notably, 2D Co₂ P is a p-type semiconductor, with a hole mobility of 20.8 cm²  V^-1  s^-1 at 300 K in field-effect transistors. It also behaves as a promising electrocatalyst for the oxygen evolution reaction (OER), thanks to the charge-transport modulation and improved surface exposure. In particular, iron-doped Co₂ P (i.e. Co_1.5 Fe_0.5 P) delivers a low overpotential of only 278 mV at a current density of 10 mA cm^-2 that outperforms the commercial Ir/C benchmark (304 mV).