2.5 Oxygen Evolution 25
reported by Trasatti who constructed a volcano shaped activity plot based on
the heat of transition from lower to higher oxide 82. The impact of this report
lies in the fact that oxide and not metallic properties are related to activity,
which better reect the electrode interface at the reaction conditions. At the
same time the volcano plot suggests that an optimum at a specic formation
energy exists so that experimentalists are provided with a design principle. In
gure 2.5a reproduction of the analysis by Trasatti is shown, where the OER
overpotential is plotted as a function of heat of transition from lower oxide to
higher, H0
t .
RuO2
0-50-100-150-200-250-300-350
0,1
0,2
0,3
0,4
0,5
0,6
Fe3O4
Co3O4IrO2
PtO2
MnO2
Ni2O3
/V
H0
t/kJ.mol-1
PbO2
Figure 2.5: Volcano plot showing the overpotential for reaching approximately 1
mA/cm2 for OER as a function of the heat of oxide transition H0
t . The data is
digitized from 82 and only acidic measurements are included. Note that the for
RuO2, PtO2, IrO2, PbO2 and MnO2 the transition from III to IV oxidation state
is considered, while for Ni2O3, Co3O4 and Fe3O4 the II to III. Furthermore, in the
original volcano plot 1-3 values of overpotential are shown for each compound. For
simplicity, only the overpotentials which ts the trend are shown here.
Later in the 1980's Bockris and Otagawa extended the understanding of oxides
for OER by systematically investigating a series of perovskite materials based
on Co, Fe, Ni and Mn 83. A number of descriptors were investigated such
as number of d-band electrons, heat of formation for the corresponding metal
hydroxide, magnetic moment and stability limits.
In parallel with the scientic communities' eorts to understand the concepts
behind OER activity, an important discovery had been made in one of the
industrial research laboratories. Henry Beer had invented the so called Dimensionally
Stable Anodes, DSAr, 45, 84, which were used with great success in
the industrially important chlorine evolution process. The DSAsr were made