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

Abstract

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 ( W F ) engineering is introduced via 3 d metal (Fe, Co, Ni, and Cu) doping for modulating the Fermi energy level of Mo 2 C. 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-Mo 2 C exhibits the best HER performance with an overpotential of 78 mV, followed by Ni-Mo 2 C, Co-Mo 2 C, Fe-Mo 2 C, and bare Mo 2 C 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 W F> 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 Mo 2 C samples with TiO 2 , enhanced photocatalytic neutral HER rates are obtained in comparison to the case with bare TiO 2 . Typically, the HER rates are 521, 404, 275, 224, 147, and 112 μmol/h for Cu, Ni, Co, Fe, bare Mo 2 C, and bare TiO 2 , 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 τ values from the TRPS curves are 22.6, 20.5, 10.1, 4.7, 4.0, 2.5, and 1.9 ns for TiO 2 , TiO 2 -Mo 2 C, TiO 2 -Fe-Mo 2 C, TiO 2 -Fe-Mo 2 C, TiO 2 -Fe-Mo 2 C, TiO 2 -Fe-Mo 2 C, and TiO 2 -Pt, respectively. Additionally, the fitted τ values from the TA results are 31, 73, and 105 ps for the TiO 2 -Mo 2 C, TiO 2 -Cu-Mo 2 C, and TiO 2 -Pt samples, respectively. This work provides in-depth insights into the W F modulation of an electrocatalyst for improving the HER performance. Metals (Fe, Co, Ni and Cu) doped Mo 2 C samples are reported to promote the water adsorption performance, and then boost the neutral HER activity for working as the co-catalysts of TiO 2 .