Phosphorus-Mo2C@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 a controlled phosphorus doping to effective modify the electronic configuration of nanostructured Mo2C, accomplishing the benchmarking performance of noble-metal-free electrocatalysts in hydrogen evolution reaction (HER). Employing MoOx-phytic acid-polyaniline hybrids with tunable composition as precursors, a series of hierarchical nanowires composed of phosphorus-doped Mo2C nanoparticles evenly integrating within conducting carbon (denoted as P-Mo2C@C) are successfully obtained via facile pyrolysis under inert flow. Remarkably, P-doping into Mo2C can increase the electron density around Fermi level of Mo2C, leading to weakened Mo-H bonding toward promoted HER kinetics. The further density function theory calculations show that the negative hydrogen-binding free energy (ΔGH*) on pristine Mo2C gradually increases with P-doping due to electron transfer and steric hindrance by P on Mo2C surface, indicating the effectively weakened strength of Mo-H. With an optimal doping, a ΔGH* approaching to 0 eV suggests a good balance between Volmer and Heyrovsky/Tafel steps in HER kinetics. As expected, the P-Mo2C@C nanowires with a controlled P-doping (P: 2.9 wt.%) delivers a low overpotential of 89 mV at the 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 current noble-metal-free electrocatalysts. Elucidating the feasible electronic regulation and the remarkably enhanced catalysis associated with controlled P-doping, our work would pave a way for developing efficient noble-metal-free catalysts via rational surface engineering.