Metal-doped Mo2C (metal = Fe, Co, Ni, Cu) as catalysts on TiO2 for photocatalytic hydrogen evolution in neutral solution

The neutral hydrogen evolution reaction (HER) is vital in the chemical industry, and its efficiency depends on the interior character of the catalyst. Herein, work function (WF) engineering is introduced via 3d metal (Fe, Co, Ni, and Cu) doping for modulating the Fermi energy level of Mo2C. The defective energy level facilitates the free water molecule adsorption and, subsequently, promotes the neutral HER efficiency. Specifically, at a current density of 10 mA/cm(2), Cu-Mo2C exhibits the best HER performance with an overpotential of 78 mV, followed by Ni-Mo2C, Co-Mo2C, Fe-Mo2C, and bare Mo2C with 90, 95, 100, and 173 mV, respectively, and the corresponding Tafel slope values are 40, 43, 42, 56, and 102 mV/dec. The modified WF can also lead to an enhanced photocatalytic efficiency owing to the lowered Schottky barrier and excellent carrier transition across the electrocatalyst-solution interface. When coupling the metal-doped Mo2C samples with TiO2, enhanced photocatalytic neutral HER rates are obtained in comparison to the case with bare TiO2. Typically, the HER rates are 521, 404, 275, 224, 147, and 112 mu mol/h for Cu, Ni, Co, Fe, bare Mo2C, and bare TiO2, respectively. Time-resolved photoluminescence spectroscopy (TRPS) and ultrafast transient absorption (TA) measurements are carried out to confirm the recombination and migration of the photogenerated carriers. The fitted t values from the TRPS curves are 22.6, 20.5, 10.1, 4.7, 4.0, 2.5, and 1.9 ns for TiO2, TiO2-Mo2C, TiO2-Fe-Mo2C, TiO2-Fe-Mo2C, TiO2-Fe-Mo2C, TiO2-Fe-Mo2C, and TiO2-Pt, respectively. Additionally, the fitted t values from the TA results are 31, 73, and 105 ps for the TiO2-Mo2C, TiO2-Cu-Mo2C, and TiO2-Pt samples, respectively. This work provides in-depth insights into the WF modulation of an electrocatalyst for improving the HER performance. (C) 2020, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Automated summary

The study introduced work function engineering by doping 3d metals into Mo2C to modulate the Fermi energy level, which enhanced the efficiency of the neutral hydrogen evolution reaction and improved photocatalytic efficiency. The modified work function also led to enhanced carrier transition and lowered Schottky barrier, ultimately improving the electrocatalytic performance.