Radiation Electrochemistry of the Colloidal Cadmium Microelectrode. Catalysis of Hydrogen Formation by Organic Free Radicals

Article abstract of DOI:10.1021/j150609a031

Cadmium sols with a mean particle size of 11 nm or less were obtained in the radiolytic reduction of Cd²⁺ ions in the presence of 1E-4 - 1E-3 base-M sodium polyvinyl sulfate.These sols which contained small concentrations of residual Cd²⁺ were found to catalyze the formation of hydrogen by 1-hydroxy-1-methylethyl radicals, (CH3)2COH, as efficiently as the sols of the previously studied noble metals.The organic radicals transfer electrons to the colloidal particles at a practically diffusion-controlled rate.The cathodically charged colloidal particles first reduce and deposit residual cadmium ions and then store excess electrons.Both the stored electrons and the deposited cadmium atoms are able to produce H2 from water.The reduction of water by deposited cadmium atoms is explained by a two-step mechanism: (1) dissolution of an atom as Cd²⁺ to leave negative charges on the colloidal particle and (2) transfer of these charges to water.The mechanism of catalysis is also described in terms of an equivalent electrical circuit, in which the colloidal microelectrode appears as a capacitance for the storage of reduction equivalents.A 3E-4 M cadmium solution (containing ca. 3E-5 M residual Cd²⁺ ions) was found to have a capacity of 0.98 F/L for the storage of excess electrons.