Phosphorus-Mo ₂ C@carbon nanowires toward efficient electrochemical hydrogen evolution: Composition, structural and electronic regulation

To explore high-performance electrocatalysts, electronic regulation on active sites is essentially demanded. Herein, we propose controlled phosphorus doping to effectively modify the electronic configuration of nanostructured Mo ₂ C, accomplishing a benchmark performance of noble-metal-free electrocatalysts in the hydrogen evolution reaction (HER). Employing MoO _x -phytic acid-polyaniline hybrids with tunable composition as precursors, a series of hierarchical nanowires composed of phosphorus-doped Mo ₂ C nanoparticles evenly integrated within conducting carbon (denoted as P-Mo ₂ C@C) are successfully obtained via facile pyrolysis under inert flow. Remarkably, P-doping into Mo ₂ C can increase the electron density around the Fermi level of Mo ₂ C, leading to weakened Mo-H bonding toward promoted HER kinetics. Further density functional theory calculations show that the negative hydrogen-binding free energy (ΔG _H∗ ) on pristine Mo ₂ C gradually increases with P-doping due to electron transfer and steric hindrance by P on the Mo ₂ C surface, indicating the effectively weakened strength of Mo-H. With optimal doping, a ΔG _H∗ approaching 0 eV suggests a good balance between the Volmer and Heyrovsky/Tafel steps in HER kinetics. As expected, the P-Mo ₂ C@C nanowires with controlled P-doping (P: 2.9 wt%) deliver a low overpotential of 89 mV at a current density of -10 mA cm ^-2 and striking kinetic metrics (onset overpotential: 35 mV, Tafel slope: 42 mV dec ^-1 ) in acidic electrolytes, outperforming most of the current noble-metal-free electrocatalysts. Elucidating feasible electronic regulation and the remarkably enhanced catalysis associated with controlled P-doping, our work will pave the way for developing efficient noble-metal-free catalysts via rational surface engineering.