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. Co 2 P, Ni 12 P 5 , and Co x Fe 2−x P) by using phosphorene sheets as the phosphorus precursors and 2D templates. Notably, 2D Co 2 P is a p‐type semiconductor, with a hole mobility of 20.8 cm 2  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 Co 2 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).