Electrodeposition of Cobalt from LiCl-Based Highly Concentrated Aqueous Solution: Crystal Phase and Hydrogen Content

Abstract

The relationship between the crystal phase and absorbed hydrogen in cobalt electrodeposited from a LiCl-based highly concentrated (HC) aqueous solution was investigated using X-ray diffraction and thermal desorption spectroscopy. We expected that the use of an HC solution would enable the electrodeposition of cobalt without hydrogen evolution and the concomitant hydrogen absorption. The current efficiency of cobalt deposition was more than 99% at potentials above −0.8 V vs. Ag/AgCl, indicating that hydrogen evolution is really suppressed, but the electrodeposited cobalt accompanied the fcc phase irrespective of the deposition temperature. Moreover, electrodeposited cobalt contained a large amount of hydrogen despite the high current efficiency. The hydrogen content of cobalt obtained at 100°C was approximately 10% of that obtained at room temperature; however, the fcc phase was still co-deposited, suggesting that factors other than hydrogen could be responsible for fcc-Co formation. The reason for hydrogen inclusion from the HC solution is discussed in terms of the hydrogen reduction mechanism.