Extension of Lifetime of IrO2/Ti Electrode through the Addition of Silica Sol to the Coating Solution of the Catalyst

Iridium oxide/titanium electrodes were prepared by thermal decomposition techniques from H2IrCl6 solutions containing silica sols and tantalum buthoxide, and subjected to an oxygen evolution reaction in acidic sulfate solutions containing an organic additive (ethylene chlorohydrine, ECH). The lifetime, T, of the electrodes was determined as a function of the number of coatings, n, current density, i, and the concentration of ECH, C. The variation of T with n is shown to be linear as a function of n2.3 for electrodes from silica sol solutions and of n for electrodes from the buthoxide solution. The lifetime also varied linearly with the reciprocal of the product i·C0.7 in the range C=10-2-3×10-1mol/L. It is thus possible to estimate the value of n for achieving T=8760h (a year) at C=10-3 mol/L by a combination of the linear relations between log T and log C, and log T and log n. The values of n thus obtained were 30 and 700 for solutions of silica sols and of tantalum buthoxide, respectively. Such an extension of the lifetime by the addition of silica sols far exceeds the expectations suggested by catalyst loading.