Final Report - Strategic Environmental Research and Development ...

Log Conc.
was done to compare the effect of addition of lanthanide cations on the kinetics of the oxygen
reduction reaction. Figures 3.2a, 3.2b and 3.2c show the polarization curves of Ce 3+ Pr 3+ and
La 3+ cations respectively with concentrations ranging from 50 to 600 ppm. Ce 3+ , Pr 3+ and La 3+
inhibited ORR to varying extents. Ce 3+ shifted the cathodic arm of the curve near the corrosion
potential to the maximum extent while La 3+ barely caused a change in the cathodic arm of the
curve. An increase in cathodic kinetics was observed at potentials below -1.0 V SCE for all the
solutions with inhibitor additions compared to the chloride-only solution. The inhibitors shifted
the open circuit potential (OCP) to negative potentials away from the pitting potential thus
improving the corrosion resistance by decreasing the tendency for pit initiation. This shift in
OCP to active potentials for Ce 3+ and Pr 3+ was higher at concentrations of 50 ppm – 300 ppm
and lower at 600 ppm while the shift in OCP for La 3+ was same at all concentrations of 50 ppm –
600 ppm.
[ N a + ] T
[ C e 3 + O T = 100 . 00 m M
] T O T = 2 . 14 m M
[ C l ] T O T = 100 . 00 m M
0
-2
-4
H + Natural pH
O H
N a + C l
NaOH
C e 3 + C e ( O H ) 3 ( c )
C e C l 2 +
C e O H 2 +
C e C l + C e ( O H ) 2 + 2
C e ( O H ) 4
C e ( O H ) 3
-6
-8
-10
-12
0 2 4 6 8 10 12 14
pH
(a)
98