Preparation of nanohybrid electrocatalyst based on reduced graphene oxide sheets decorated with Pt nanoparticles for hydrogen evolution reaction

Enhanced electrocatalytic hydrogen evolution by molybdenum disulfide nanodots anchored on MXene under alkaline conditions

Efficient hydrogen production through electrocatalysis represents a promising path for the future clean energy. Molybdenum disulfide (MoS₂) is a good substitute for platinum-based catalysts, due to its low cost and high activity. However, the limited active sites and low electrical conductivity of MoS₂ hinder its large-scale industrial application under alkaline conditions. Herein, we constructed MoS₂ nanodots anchored on an MXene/nickel foam (MoS₂ NDs/MXene/NF) heterostructure by a cascade polymerization synthesis and in situ vulcanization. The prepared heterostructure displays an ultralow overpotential of 94 mV at a current density of 10 mA cm^-2 with a Tafel slope of only 59 mV dec^-1 in alkaline (1 M KOH) hydrogen evolution reaction (HER), and is better than conventional MoS₂ electrocatalysts reported so far. Fine structural analysis indicates that MoS₂ NDs are dispersed uniformly on the surface of the heterostructure with consistent orientation, leading to the improvement of MoS₂ conductivity with more paths for electron transfer. Moreover, the orientation of the synthesized MoS₂ NDs was verified to expose the more (002) crystal plane, which exhibits higher activity than other planes. Our results demonstrate that MoS₂ NDs with heterostructure design and preferential growth can serve as high-efficiency noble-metal free electrocatalysts for the HER in alkaline solution.

Reduced Graphene Oxide Supported Zinc Tungstate Nanoparticles as Proficient Electro-Catalysts for Hydrogen Evolution Reactions

The nanocomposites of reduced graphene oxide (rGO) supported zinc tungstate nanoparticles (ZnWO4-NPs) receive considerable attention in electro-catalytic hydrogen evolution reactions (HER) and reveal significantly higher electro-catalytic performances than pure ZnWO4-NPs in alkaline media (i.e., 0.5 M KOH electrolyte). The polarization studies show that the ZnWO4-NPs@rGO nanocomposites exhibit low energy loss and good electrode stability during electrochemical reactions for HER. Furthermore, the Tafel slope of ZnWO4-NPs@rGO nanocomposites is found to be approximately 149 mV/dec, which closely agrees with the reported Tafel values of the noble metal electrocatalyst. In contrast, the performance of the ZnWO4-NPs@rGO nanocomposite is found to be approximately 1.5 times higher than that of ZnWO4-NPs in hydrogen production efficiency. Our results emphasize the significance of the nanocomposites with enhanced electro-catalytic activities by lowering the energy loss during electro-catalysis in an alkaline medium.

Plasmon-enhanced hydrogen evolution reaction on a Ag-branched-nanowire/Pt nanoparticle/AgCl nanocomposite

A plasmon-enhanced photocatalytic system was designed with Ag-Pt-AgCl nanocomposites. Branched nanowires of Ag (AgBNWs) were first synthesized on indium-doped tin oxide-coated glass by electrodeposition. Then, the AgBNWs were dipped into an aqueous solution of Na2[PtCl6] at different concentrations from 1 to 5 mM to deposit Pt nanoparticles (PtNPs) on the AgBNWs via galvanic displacement. During the PtNP deposition, eluted Ag+ ions reacted with Cl- ions to precipitate AgCl on the AgBNWs. The obtained AgBNW/PtNP/AgCl nanocomposites exhibited plasmonic absorption at approximately 465 nm. The nanocomposites were then examined as photoelectrodes for hydrogen evolution. The hybridization of the PtNPs on the AgBNWs significantly decreased the overpotential for water splitting in the dark, and the large number of PtNPs resulted in a higher efficiency compared to a conventional catalyst. Under blue-light irradiation (479 nm, 100 mW cm-2), the overpotential decreased by -110 mV, and the current density increased by 27.8 mA cm-2. Under red-light irradiation (631 nm, 100 mW cm-2), the shift in onset potential was small, which could be attributed to the mismatching of the plasmonic absorption band with the excitation wavelength. The nanocomposite without AgCl (AgBNW/PtNP) was less effective at lowering the overpotential but more effective at improving the onset potential than AgBNW/PtNP/AgCl. These electrochemical behaviors were explained by the synergistic effect of the plasmon-induced photocurrent and charge transfer between Ag, Pt, and AgCl. The nanocomposite retained its photocatalytic activity after 400 cycles; therefore, the AgBNW/PtNP/AgCl nanocomposite could be useful for hydrogen evolution devices.