Obtenção de sulfetos metálicos (M= Ni, Mo) pelo método solvotermal assistido por micro-ondas aplicados na reação de desprendimento de hidrogênio

Abstract

In general, transition metal sulfides show good activity in the Hydrogen Evolution Reaction (HER). Some of these metals, such as Mo and Ni, arouse interest in the area of electrocatalysis, since they are more abundant and very cheap than Platinum (Pt). For this hydrogen production route to be viable, we need to develop new materials that are active and stable and capable of replacing Pt. This thesis addresses the obtaining of Ni and Mo sulfides with different sulfur precursors or combined nanostructures of these two sulfides obtained by the microwave-assisted solvothermal method for application in the HER in alkaline and acid medium. The electrochemical activity was evaluated by linear sweep voltammetry curves in the cathodic direction, Tafel plots and electrochemical impedance spectroscopy (EIS). Stability was assessed by chronoamperometry or cyclic voltammetry. The nickel sulfide phases (h-NiS and o-Ni9S8) obtained from Tioureia and 1-dodecanoltiol at 200 ° C showed respectively overpotential (η) of -230 and -260 mV to deliver a current density of 10 mA cm-2 in 1M NaOH. The molybdenum sulfides (MoS2) obtained from 1-dodecanethiol and ammonium tetratiomolybdate at 260 °C showed η = -282 and η = -215 mV respectively to deliver 10 mA cm-2 in 0.5 M H2SO4. For the h-NiS/MoS2 composites, the best performances were observed for the largest coverage of the MoS2 sheets with h-NiS nanoparticles (h NiS/MoS2 5:1 and h NiS/MoS2-TTMA 5:1 composites), showing η = -193 mV and η = -150 mV respectively to deliver 10 mA cm-2. The MoS2/RGO 175/20 m/m composite showed η = -181 mV to deliver 10 mA cm-2 to the HER in 0.5 M H2SO4. Tafel slopes between 40 and 120 mV/dec indicate the Volmer-Heyrovsky mechanism for all materials. The results obtained demonstrate that the microwave method was efficient to obtain the phases of nickel sulfide and molybdenum sulfide from different sulfur precursors, and the activities displayed by the materials are of values close to the best ones already reported.