Electrochemical and SECM Investigation of MoS₂/GO and MoS₂/rGO Nanocomposite Materials for HER Electrocatalysis

Development of advanced materials for electrocatalytic and photocatalytic water splitting is the key in utilization of renewable energy. In the present work, we have synthesized MoS₂ nanoparticles embedded over the graphene oxide (GO) and reduced graphene oxide (rGO) layer for superior catalytic activity in the hydrogen evolution process (HER). The nanocomposite materials are characterized using different spectroscopic and microscopic measurements. A Tafel slope of ∼40 mV/decade suggested the Volmer–Heyrovsky mechanism for the HER process with MoS₂/GO composite as the catalyst, which indicated that electrochemical desorption of hydrogen is the rate-limiting step. The small Tafel slope indicates a promising electrocatalyst for HER in practical application. MoS₂/GO composite material has shown superior catalytic behavior compared to that of MoS₂/rGO composite material. The HER catalytic activity of the catalysts is explored using scanning electrochemical microscopy (SECM) using the feedback and redox competition mode in SECM. The activation energy for HER activity was calculated, and the values are in the range of 17–6 kJ/mol. The lower value of activation energy suggested faster HER kinetics

Freeze-Casting of Multifunctional Cellular 3D-Graphene/Ag Nanocomposites: Synergistically Affect Supercapacitor, Catalytic, and Antibacterial Properties

Developments of new and highly effective multifunctional materials have been shown great interest in recent years. Herein, we report a simple, cost efficient, one-step, surfactant-free cellular 3D-graphene/Ag nanocomposite using the freeze-casting method and explore it further for supercapacitor, catalytic, and antibacterial applications. FE-SEM and HRTEM analyses of nanocomposites revealed a 3D-cellular network structure having continuous micrometer size open pores with uniformly decorated Ag nanoparticles of an average size of 25 nm. An electrochemical study exhibited the highest specific capacitance at 845 Fg^–1 at 5 mV s^–1 and excellent cyclic retention ∼97% even after 1000 cycles. Further, 3D-graphene/Ag nanocomposites are applied as catalyst to reduce methylene blue using NaBH₄. A rate of reduction above 99% was attained for 3D-graphene/Ag (40%) nanocomposites, which is significantly higher than that of pristine 3D-graphene. The network like structure of the 3D-graphene/Ag nanocomposite filtered out 37% of the population from total bacterial strains. Also, the 3D-graphene/Ag nanocomposite killed almost 100% of the bacterial strains after 3 h of incubation due to a merging effect of Ag ions and 3D-graphene