Cadmium underpotential deposition on CdSe and CdS quantum dot films: size dependent underpotential shift

•Potentiodynamic ac-dc monitoring of Cd upd and opd on CdSe and CdS QD films.•Dc and ac responses show similar dependences of the upd on the QD size.•The upd starting potential increases with the QD size.•High overpotential of 3D growth favors adlayer deposition on semiconductor substrates.

Underpotential deposition of cadmium from aqueous solution of cadmium salt (0.1 M Na2SO4 + 10 mM CdSO4, pH 4) was examined by cyclic voltammetry and potentiodynamic electrochemical impedance spectroscopy on сhemical bath deposited CdSe and CdS quantum dot (QD) film electrodes. QD size was thermally controlled during CdSe film deposition and the post-synthesis thermal treatment of CdS QDs in Ar gas medium. The increase of the substrate particle diameter from few nm to almost bulk dimensions resulted in a positive shift of the upd starting potential by approx. 0.2 V. The discovered size effect showed some similarity with the size effects reported in literature for metal upd on metal, thus indicating the general nature of the upd control by substrate particle size on different types of substrates. However, the size effects in cadmium upd on cadmium chalcogenides were observed at smaller particles than those in metal upd on metal particles.