Tuesday, 3 October 2017
Prince George's Exhibit Hall D/E (Gaylord National Resort and Convention Center)
Hydrogen is a very versatile element which can be used for many applications such as metallic ore reduction, hydrogen fuel cells, fertilizer and etc. In common, hydrogen can be obtained from fossil fuels with plasma and steam reforming. However, a problem arises in that both methods require high operating temperatures, which leads to use of fossil fuels and ultimately, emission of pollutants. Electrolysis of water is comparatively superior in the aspect that it could be operated at lower temperature range. Thus, the water electrolysis is introduced as a promising method for producing hydrogen. Currently, the most excellent catalyst for water electrolysis is known as platinum. However, the use of this noble metal is still limited, because of its scarcity and excessive cost. Therefore, the pressing issue to resolve this problem is synthesizing an alternative catalyst. Among them, transition metal chalcogenides are typical candidates for replacing noble metals. This work is focused on molybdenum sulfides because it has been reported that the Gibbs free energy of adsorbed atomic hydrogen on molybdenum sulfides is favorable for hydrogen evolution reaction (HER). Recently various groups have revealed that the basal planes of molybdenum sulfide films were inactive to HER, whereas the edges were highly active. In this work molybdenum sulfide precursor in electrolyte was electrochemically reduced to fabricate continuous films on annealed carbon paper via cathodic electrodeposition. The catalyst was synthesized by varying potential, concentration and deposition time. The field emission scanning electron microscope analysis confirmed the formation of molybdenum sulfide thin films on the surface of carbon paper. Through X-ray diffraction and X-ray photoelectron spectroscopy, it was confirmed that the nature of the as deposited catalyst was amorphous. The HER activity was tested by using linear sweep voltammetry in 0.5 M sulfuric acid. Electrochemical surface area was measured by conducting a cyclic voltammetry at different scan rates. The performance of this catalyst was remarkable at highly negative potentials and showed excellent stability after extensive experimentation in a proton exchange membrane water electrolyzer.