The Importance of Ligand Selection on the Formation of Metal Phosphonate-Derived CoMoP and CoMoP2 Nanoparticles for Catalytic Hydrogen Evolution

Coordination polymers (CPs) and metal-organic frameworks (MOFs) have emerged as versatile precursors for transition-metal phosphides catalysts. However, the controlled synthesis of CPs-derived bimetallic phosphides remains a challenge, as mixtures of various phosphide phases are often formed. Here, it is shown that controlling the formation of pure CoMoP and CoMoP2 nanoparticles requires a careful choice of the ligands used to construct the precursors based on the chemical properties of the metals. In particular, the nature and number of the coordination moieties of the ligand play key roles. CoMoP and CoMoP2 particles coated with N-doped carbon were derived from phosphonate-based CPs and compared as hydrogen evolution reaction (HER) electrocatalysts in acidic medium. CoMoP2 is more active and shows a turnover frequency (TOF) of 0.9 s(-1) compared to 0.4 s(-1) for CoMoP. The higher intrinsic activity of the CoMoP2 catalytic sites correlates with the differences in the electronic structure of the materials, with a larger charge transfer from the molybdenum to the phosphorus found for CoMoP2.