Unraveling the Factors Affecting the Electrochemical Performance of MoS₂–Carbon Composite Catalysts for Hydrogen Evolution Reaction: Surface Defect and Electrical Resistance of Carbon Supports

Abstract

In MoS2–carbon composite catalysts for hydrogen evolution reaction (HER), the carbon materials generally act as supports to enhance the catalytic activity of MoS2 nanosheets. The carbon support provides a large surface area for increasing the MoS2 edge site density, and its physical structure can affect the electron transport rate in the composite catalysts. However, despite the importance of the carbon materials, direct observation of the effects of the physical properties of the carbon supports on the HER activity of MoS2–carbon composite catalysts has been hardly reported. In this work, we conduct an experimental model study to find the fundamental and important understanding of the correlation between the structural characteristics of carbon supports and the HER performance of MoS2–carbon composite catalysts using surface-modified graphitic carbon shell (GCS)-encapsulated SiO2 nanowires (GCS@SiO2 NWs) as support materials for MoS2 nanosheets. The surface defect density and the electrical resistance of GCS@SiO2 NWs are systematically modulated by control of H2 gas flow rates during the carbon shell growth on the SiO2 NWs. From in-depth characterization of the model catalysts, it is confirmed that the intrinsic catalytic activity of MoS2–carbon composites for the HER is improved linearly with the conductance of the carbon supports regardless of the MoS2 edge site density. However, in the HER polarization curve, the apparent current density increases in proportion to the product of the number of MoS2 edge sites and the conductance of GCS@SiO2 NWs.

Modulating Catalytic Activity and Durability of PtFe Alloy Catalysts for Oxygen Reduction Reaction Through Controlled Carbon Shell Formation

“…Nevertheless, it is expected that the pore size of the carbon shells might be reduced due to their enhanced crystallinity after increasing the annealing temperature [31,32,33,34,35,36,37]. In addition, when the samples are heated at H 2 -mixed N 2 gas atmosphere, the thickness of the carbon shells can decrease since H 2 gas etches the activated carbon sites and decreases the growth rate of carbon layers during the formation of the graphitic carbon layer [38,39]. Accordingly, for PtFe 700_Ar and PtFe 900_Ar samples, thicker carbon shell layers might be obtained compared to those of PtFe 700_H 2 and PtFe 900_H 2 , respectively.…”

“…The change in the carbon shell structure according to the annealing conditions can be understood to be for the following reasons. During the course of carbon shell formation, the strong interaction between H 2 molecules and carbon disrupts the C−C bond formation on the metal nanoparticles and carbon layers is etched under H 2 atmosphere, creating more defects and large pores [38,39]. In contrast, inert Ar gas does not affect the defect formation and carbon etching during the heat treatment, meaning dense and thick carbon shells can be formed [31,32,33,34,35,36,37].…”

Nanomaterial‐Based Electrochemical Sensors: Mechanism, Preparation, and Application in Biomedicine

“…[ 32 ] For impurities, the insertion of carbon/nitrogen atoms will cause an increase in the density of states near the Fermi level. Therefore, the lattice customization strategy provides enhanced conduction paths for carriers, effectively activating redox reactions and promoting electron transfer [32a,33] . For lattice defects, more vacancies are produced due to the missing atom from its original lattice site, which is beneficial to capture electrons and improve catalyst activity.…”

Density Functional Theory Studies of Doping and Curvature Effects on the Electrocatalytic Hydrogen Evolution Activity of Carbon Nanotubes

“…Carbon-based materials are widely used as HER catalyst because of their adjustable molecular structures, abundance, and strong tolerance to acidic/alkaline environments. − Although carbon-based materials are inert to HER, the active site of the system can be modulated by doping atoms and tuning surface curvatures. Theoretical and experimental studies have shown that carbon-based materials with nonmetal atom doping can change the local charge or spin density of carbon atoms and improve the catalytic performance of carbon atoms. − In nonmetal atoms, nitrogen (N) atom doping is used because the triple-coordination characteristic of nitrogen atoms can well match with the sp 2 -hybridized carbon bonding structure, and the geometrical structure of the sp 2 -carbon networks will not change when nitrogen atoms are doped. − …”