1 research outputs found
Revisiting the Redox Properties of Hydrous Iridium Oxide Films in the Context of Oxygen Evolution
The
electrochemistry of hydrous iridium oxide films (HIROF) is
revisited. Cyclic voltammograms of HIROFs display two reversible redox
couples commonly assigned to the IrĀ(III)/IrĀ(IV) and IrĀ(IV)/IrĀ(V) transitions,
respectively. However, compared to the first, the second redox couple
has significantly less charge associated with it. This effect is interpreted
as partial oxidation of IrĀ(IV) as limited by nearest neighbor repulsion
of resulting IrĀ(V) sites. Thus, the redox process is divided into
two steps: one preceding and one overlapping the oxygen evolution
reaction (OER). Here, the āsuper-nernstianā pH dependence
of the redox processes in the HIROF is used to expose how pH controls
the overpotential for oxygen evolution, as evidenced by the complementary
increased formation of IrĀ(V) oxide. A recently formulated binuclear
mechanism for the OER is employed to illustrate how hydrogen bonding
may suppress the OER, thus implicitly favoring IrĀ(V) oxide formation
above the thermodynamic onset potential for the OER at low pH