4
E. K. Hamal and M. C. Toroker
Fig. 2 Catalytic cycle of water oxidation for the Ni 1−x Fe x OOH alloy at x = 8% and 5% expansion.
Red, gray, and gold spheres represent O, Ni, and Fe atoms, respectively. Created with VESTA
visualization package [43]
We considered the following four-step mechanism that has been studied in Ref.
[17], for comparison, at alkaline conditions (see Fig. 2) [18]:
A + h
+
+ OH
−
→ B + H 2 O
( 1 )
B + h
+
+ OH
−
→ C
(2)
C + h
+
+ OH
−
→ D + H 2 O
( 3 )
D + h
+
+ OH
−
→ A + O 2
(4)
where intermediate “A” is a slab with adsorbed water molecules, intermediate “B”
has one hydroxyl group termination, intermediate “C” is the same as intermediate
“A” but has an additional oxygen atom penetrating the surface, and intermediate