Evolution of Stibine at Antimony Cathodes

The formation of stibine at antimony cathodes was studied by absorbing the cathode gas and analyzing the solution for antimony. The parameters studied were p H, salt concentration, temperature, and current density. Results indicated that stibine was formed by the electrochemical discharge of a water molecule upon an antimony atom which was in contact with either two adsorbed hydrogen atoms or an adsorbed hydrogen molecule. Rate of the reaction was found to depend upon the voltage difference between electrode and solution. The stibine formed was inert to acid, but was readily decomposed by alkali. Stibine is probably formed by discharge of a water molecule on two adsorbed hydrogen atoms or a hydrogen molecule. Decreased rates of stibine formation in highly acid solution are thought to mean that high voltages, and, therefore, high overvoltages are not associated with hydronium ion discharge, but with water discharge.