Abstract
Properties of Corning thin‐film 
electrodes in contact with 0.005–0.5Msolutions of sulfuric acid in aqueous solvents containing 
were characterized. Schottky‐Mott plots gave flatband potentials 
in the range 0–0.2V vs. SCE and charge carrier densities in the range 
in 0.01M sulfuric acid, independent of solvent composition. Standard reduction potentials vs. SCE in 0.01M acid at room temperature were calculated from equilibrium compositions to be −0.04V for 
, 0.33V for
and 0.14V for 
in water and −0.06V for 
, 0.28V for 
and 0.11V for 
in 50 v/v/o aq. 
. Voltammetric data show that establishment of protonic equilibrium is rapid compared with cathodic reduction of TH+ at 
in water and in 50 v/o aq. 
. In contrast, protonic equilibration between the two electron‐transfer steps is slow for thionine‐l‐sulfonic acid. Voltammetric data show that reduction of TH+ and oxidation of 
are kinetically controlled at both 
and Pt electrodes with reversibility greater at platinum than at
. Reversibility is slightly reduced by addition of 
to the solvent. Rectification (inhibition of oxidation of 
) is not severe enough to prevent the use of 
as a selective anode but may reduce efficiency of photogalvanic conversion. Weak but persistent adsorption of TH+ on 
activates photogalvanic conversion. Adsorption of 
varied considerably from sample to sample of 
and was strong in some cases. Both oxidation and reduction of the Fe+3/Fe+2 couple are much less reversible at 
than at Pt. Rectification (inhibition of oxidation of Fe2+) is pronounced. Both oxidation and reduction on 
become more reversible with increasing fraction of 
; the major effect is enhancement of oxidation of Fe2+ but even with 
the couple is much less reversible than at Pt. Implications of the data with respect to efficiency of totally illuminated thin‐layer iron‐thionine photogalvanic cells are discussed.