Electrodeposition of metals, chalcogenides, and metal chalcogenides from ionic liquids
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In this work we describe the electrodeposition of metals, chalcogenides, and metal chalcogenides from ionic liquids and investigate the fundamental electrochemical processes occurring during electrodeposition. This work covers two main projects: the electrodeposition of elemental selenium and the general electrodeposition of amorphous transition metal chalcogenides. Selenium was electrodeposited from diethyl selenite in N, N – propylmethylpiperidinium bis(trifluoromethanesulfon)imide. The electrochemical processes were investigated using in-situ UV-VIS spectroscopy and diethyl selenite was found to proceed through a step-wise reduction from Se⁴⁺→Se⁰→Se²⁻. A conformal film of amorphous elemental selenium was formed upon applying a potential of E = -1.0 V vs. Pt QRE. In addition a general procedure for the electrodeposition of group 6 transition metal chalcogenides was devised using the tetrachalcogenometallate as a single precursor for electrodeposition. Molybdenum sulfide and molybdenum selenide were electrodeposited from tetraphenylphosphonium tetrathiomolybdate and tetraselenomolybdate, respectively. In-situ UV-VIS spectroelectrochemistry revealed that these both undergo an anodic deposition of the MoE₃ (E = S, Se) and a cathodic corrosion mechanism yielding MoE₃₋[subscript x] (0 < x < 1). The oxidation states of the resulting films were confirmed using XPS and found to range from 4+ to 6+. These films showed exceptional activity for the hydrogen evolution reaction. The MoS [subscript x] catalyst was coupled with an organic layer protected p-Si(111) substrate and was shown to exhibt high activity for the photoelectrocatalytic hydrogen evolution reaction. The deposition had to be altered due to the limitations of p-type silicon, this involved the addition of a proton source to induce cathodic deposition of the MoS [subscript x] catalyst. The resulting films showed onset potential of +140 mV vs. RHE, which was comparable to Pt (+200 mV vs. RHE) in the same system.