77
OH
e H O
ads
a ds
→ +
+
−
+
(6.25)
O
H O e H OOH
ads
a ds
+
→ +
+
−
+
2
(6.26)
OOH
e H O
ads → +
+
−
+
2
(6.27)
Most commonly utilized catalysts initially were the Pt group of metals until it
was discovered that these metals form oxides. Research was focused on various
conductive oxides as well as a number of various structures of noble metal oxides,
rutiles, perovskites, and other layered structures. So far, RuO 2 and IrO 2 were found
to be most active, but for practical applications, focus has been shifted to more
Earth-abundant materials.
Although the OER has been known from the late nineteenth century, only in the
recent 50 years there was significant progress in predicting the activity of the catalyst based on its property. Trasatti demonstrated that the EOR can be tied to the
enthalpy of the redox metal site and one of the earliest examples of the “volcano”type curves produced, where the catalysts’ “descriptor” (material property that best
describes its activity in the OER) would have neither too strong nor too weak
enthalpy [96]. Norskov et al. performed numerous calculations of d-band centers
and proposed that the steps (6.25) or (6.26) are rate-limiting when the surface interacts too weakly or too strongly with oxygenated species, respectively [97].
d- electron occupancy of the anti-bonding orbitals of the metal hydroxide on the
surface was also shown as a descriptor, and recently, attempts were taken to ascribe
covalency of the metal–oxygen bond as a second descriptor.
Fig. 6.5 Formic acid electrooxidation on Pt(hkl) in 1 M HClO 4 without (broken lines) and with
(full lines) Pb adatoms. Reproduced from [91] with permission of Elsevier
6.7 Oxygen Evolution Reaction
OH
e H O
ads
a ds
→ +
+
−
+
(6.25)
O
H O e H OOH
ads
a ds
+
→ +
+
−
+
2
(6.26)
OOH
e H O
ads → +
+
−
+
2
(6.27)
Most commonly utilized catalysts initially were the Pt group of metals until it
was discovered that these metals form oxides. Research was focused on various
conductive oxides as well as a number of various structures of noble metal oxides,
rutiles, perovskites, and other layered structures. So far, RuO 2 and IrO 2 were found
to be most active, but for practical applications, focus has been shifted to more
Earth-abundant materials.
Although the OER has been known from the late nineteenth century, only in the
recent 50 years there was significant progress in predicting the activity of the catalyst based on its property. Trasatti demonstrated that the EOR can be tied to the
enthalpy of the redox metal site and one of the earliest examples of the “volcano”type curves produced, where the catalysts’ “descriptor” (material property that best
describes its activity in the OER) would have neither too strong nor too weak
enthalpy [96]. Norskov et al. performed numerous calculations of d-band centers
and proposed that the steps (6.25) or (6.26) are rate-limiting when the surface interacts too weakly or too strongly with oxygenated species, respectively [97].
d- electron occupancy of the anti-bonding orbitals of the metal hydroxide on the
surface was also shown as a descriptor, and recently, attempts were taken to ascribe
covalency of the metal–oxygen bond as a second descriptor.
Fig. 6.5 Formic acid electrooxidation on Pt(hkl) in 1 M HClO 4 without (broken lines) and with
(full lines) Pb adatoms. Reproduced from [91] with permission of Elsevier
6.7 Oxygen Evolution Reaction