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 (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 μmol/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 τ values from the TRPS curves are 22.

Enhanced visible-light photoreduction of CO2 to methanol over Mo2C/TiO2 surfaces in an optofluidic microreactor

“…22,30 The photocatalytic activity of Mo2C/TiO2 has been, however, rarely reported in the literature. 25,[31][32][33] Furthermore, an efficient system for the photocatalytic transformation of CO2 to CH3OH may not only take into account the photoactive material but the photoreactor design, trying always to effectively harness light irradiation, optimising exposure of active sites and minimizing mass transfer constraints. In this regard, the use of optofluidic microreactors may bring several advantages in the photocatalytic reduction of CO2, including large surface-area-to-volume ratio, uniform light distribution, enhanced mass transfer and fine flow control, 34 in contrast to common slurry batch-type reactors that have been demonstrated to be inefficient to induce the challenging reaction to form CH3OH, 35 due to a low surface-area-to-volume ratio because of particle agglomeration, and the required separation of the photocatalyst material from obtained products.…”

M/TiO2 (M = Fe, Co, Ni, Cu, Zn) catalysts for photocatalytic hydrogen production under UV and visible light irradiation

“…This allows the injection of photogenerated electrons from the conduction band of the semiconductor into the metal. 29 Up to now few studies on the use of non-noble metals as cocatalysts have been reported [30][31][32][33] To analyse the photocatalytic behaviour of the prepared M/TiO 2 photocatalysts (M= Fe, Co, Ni, Cu, Zn) under both visible and UV light irradiation, TiO 2 was loaded with 2 wt% of selected transition metals. Hydrogen production profiles for TiO 2 impregnated catalysts are shown in Fig.…”

Influence of Carbon Content in Ni-Doped Mo2C Catalysts on CO Hydrogenation to Mixed Alcohol

“…The enlarged XRD patterns ( Figure 1B) show that with the increase of the nickel content, the diffraction peak at 2θ of 39.5 • gradually shifts to higher angles. It indicates that Ni 2+ cations with smaller ionic radius than Mo 2+ cations are doped into the molybdenum carbide lattice, which makes the crystal plane spacing smaller [51]. Compared with the MC catalyst, the diffraction peak intensity of the β-Mo 2 C phase of the MC-Ni-X catalysts increases sharply.…”