SPECIATION ANALYSIS OF AQUEOUS POLYSELENIDE SOLUTIONS

Selenide and polyselenide UV-vis absorption spectroscopic characterist ics were investigated for aqueous polyselenide solutions. From these o bservations equilibria interrelationships between OH-, H+, H2Se, H2Se- , Se-=, Se-2(=), Se-3(=), and Se-4(=) were probed. The standard cell p otential for the reduction of 1/2 Se-2(=) to Se-= was determined to be -0.716 V. The equilibrium reactions of Se-3(=) with Se-= to 2 Se-2(=) and 2 Se-4(=) with Se-= to 3 Se-3(=), respectively, have pK(23) = -0. 7 (+/-0.1) and pK(34) -4.0 (+/-0.1) in 0.5 to 3M aqueous electrolytes. Consistent with these equilibria, the free energy of formation for Se -2(=), Se-3(=), and Se-4(=), have been determined as 121, 115, and 121 kJ/mol, respectively Polarization studies of these polyselenide solut ions demonstrated Pt and CoSe as efficient catalytic surfaces for the oxidation and reduction of selenide species.