R. Mardosaitė “Synthesis, structure and electrochemical properties of S-containing Co-Mo oxide films” doctoral thesis defence

Author, Institution: Rasa Mardosaitė, Kaunas University of Technology

Science area, field of science: Physical Sciences, Chemistry, 03P

Scientific Supervisor: Prof. Dr. Eugenijus Valatka (Kaunas University of Technology, Physical Sciences, Chemistry, 03P)

Dissertation Defence Board of Chemistry Science Field:
Prof. Dr. Habil. Algirdas Šačkus (Kaunas University of Technology, Physical Sciences, Chemistry, 03P), chairman,
Assoc. Prof. Dr. Kristina Kantminienė (Kaunas University of Technology, Physical Sciences, Chemistry, 03P),
Prof. Dr. Vytas Martynaitis (Kaunas University of Technology, Physical Sciences, Chemistry, 03P),
Prof. Dr. Habil. Rimantas Ramanauskas (Centre for Physical Sciences and Technology, Physical Sciences, Chemistry, 03P),
Assoc. Prof. Dr. Jolanta Rousseau (Artois University, France, Technological Sciences, Chemical Engineering, 05T).

The doctoral dissertation is available at the library of Kaunas University of Technology (K. Donelaičio St. 20, Kaunas).

Annotation:

Water electrolysis would be one of the most economically and environmentally friendly, renewable method to produce hydrogen. However, one of the greatest challenges is to find the path toward an effective and noble-metal-free electrocatalyst formation. Recently, amorphous cobalt and molybdenum sulfide systems showed an increased interest in individual catalytic features. Particularly, the distinctive activity characteristics were prescribed for Co sulfides while the stability features were mostly expressed for Mo compounds. Substantial benefits could probably be provided if synergy would affect the mixed composition of Co and Mo sulfide compounds.
In this work, one-step potentiodynamic electrodeposition was applied for the synthesis of various S-containing cobalt and molybdenum oxide films on conductive glass substrates. Amorphous S-containing cobalt oxide and molybdenum oxide (Co–O–S and Mo–O–S) films were successfully electrodeposited using thiourea–cobalt chloride and thiourea–ammonium molybdate baths. The codeposition of Co–O–S and Mo–O–S significantly improved the stability and activity properties of the prepared Co–Mo–O–S films for hydrogen evolution reaction in an aqueous phosphate solution (pH 7). It was determined that the activity of Co–Mo–O–S films was extremely dependent on the pH of the electrolysis bath, the precursors concentration and the number of electrodeposition cycles. The optimization of Co–Mo–O–S synthesis conditions enabled  the synergy effect of components in terms of film activity-stability characteristics for prolonged electrolysis at a constant current density of 5 mA/cm². The electrocatalytic behavior of the best-performing Co–Mo–O–S films was found to be very close to the polycrystalline Pt electrode.