Electrocatalysts thermal decomposition

For a long time, conventional alkaline electrolyzers used Ni as an anode. This metal is relatively inexpensive and a satisfactory electrocatalyst for O2 evolution. With the advent of DSA (a Trade Name for dimensionally stable anodes) in the chlor-alkali industry [41, 42[, it became clear that thermal oxides deposited on Ni were much better electrocatalysts than Ni itself with reduction in overpotential and increased stability. This led to the development of activated anodes. In general, Ni is a support for alkaline solutions and Ti for acidic solutions. The latter, however, poses problems of passivation at the Ti/overlayer interface that can reduce the stability of these anodes [43[. On the other hand, in acid electrolysis, the catalyst is directly pressed against the membrane, which eliminates the problem of support passivation. In addition to improving stability and activity, the way in which dry oxides are prepared (particularly thermal decomposition) develops especially large surface areas that contribute to the optimization of their performance. 

Since Ru02 and Ir02 are usually prepared by thermal decomposition of suitable precursors on an inert support, the morphology of the active layer is very like that of a compressed powder [486]. The surface area plays an important role since the roughness factor can be between 102 and 103. However, the low Tafel slope observed is a clear indication of electrocatalytic effects and the high surface area is the factor which extends the low Tafel slope to much higher current densities. Thus, the combination of these two factors renders these oxides very efficient electrocatalysts for H2 evolution. 

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