Supporting Information
Mechanistic Studies of the Oxygen Evolution Reaction Mediated
by a Nickel–Borate Thin-Film Electrocatalyst
D. Kwabena Bediako,a,b Yogesh Surendranath,a Daniel G. Noceraa,b *
a
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue,
Cambridge, MA 02139–4307. b Department of Chemistry and Chemical Biology, Harvard
University, 12 Oxford Street, Cambridge, MA 02138–2902.
Email: [email protected]
Index
Page
Figure S1. Tafel plots collected on a RDE with varying extents of mass
transport
S2
Figure S2. Tafel plots comparing sequential runs as well as incremented and
decremented potential sweeps
S3
Figure S3. Tafel plots collected in electrolytes of varying buffer strength in
the absence of supporting electrolyte
S4
Figure S4. Excess electrolyte (KNO3) effect on steady state electrode
overpotential
S5
Figure S5. Koutecký-Levich plots of catalyst activity in KBi/KNO3 electrolytes
at constant overpotential
S6
Figure S6. Koutecký-Levich plots of catalyst activity in 1 M NaClO4
electrolyte, pH 8.5
S7
Figure S7. Activity of catalyst film in KBi/KNO3 electrolyte, pH 9.2 after
operation in 1 M NaClO4 electrolyte, pH 8.5, compared that of a
freshly prepared film.
S8
Figure S8. Tafel plots collected in 0.1 and 1.0 M KOH electrolytes
S9
S1
Figure S1. Tafel plots, E = (Eapplied – iR), η = (E – E°), for a 1.0 mC cm–2 anodized
catalyst film deposited onto a Pt RDE and operated in 0.5 M KBi 1.75 M KNO3, pH 9.2
electrolyte at 2000 (▲), 600 (●), and 0 rpm with a magnetic stirrer as the sole
source of solution convection (×). The Tafel slope of each plot is 28 mV/decade.
S2
Figure S2. Tafel plots, E = (Eapplied – iR), η = (E – E°), for a 1.0 mC cm–2 anodized
catalyst film deposited onto FTO and operated in 0.5 M KBi 1.75 M KNO3, pH 9.2
electrolyte in decreasing (▲), followed immediately by increasing (●) order of
changing potentials. Tafel slopes are 30 and 31 mV/decade respectively.
S3
Figure S3. Tafel plots, E = (Eapplied – iR), η = (E – E°), for a 1.0 mC cm–2 anodized
catalyst film deposited onto FTO and operated in 1.0 (●), 0.5 (■), 0.2 (▲), and 0.1
(◆) M KBi without any added supporting electrolyte. Tafel Slopes are 34, 35, 38, and
41 mV/decade, respectively.
S4
Figure S4. Dependence of steady state electrode potential, E = (Eapplied – iR) and
overpotential, η = (E – E°) for a 1.0 mC cm–2 catalyst film operated at 0.4 mA cm–2 in
0.1 M KBi electrolyte with varying concentrations of KNO3 as supporting electrolyte.
S5
Figure S5. Steady state Koutecký-Levich plots of a 1.0 mC cm–2 catalyst film
prepared onto a Pt RDE and operated at E = 1.04 V at 2500, 1600, 900, and 625 rpm
in 40 (●), 25 (■), 16 (▲), 10 (▼), and 6.3 (◆) mM KBi electrolyte, with added KNO3 to
preserve an ionic strength of 2 M.
S6
Figure S6. Steady state Koutecký-Levich plots of a 1.0 mC cm–2 catalyst film
prepared onto a Pt RDE and operated at 2500, 1600, 1225, 900, and 625 rpm in 1 M
NaClO4 pH 8.5 electrolyte at E = 1.07 (●), 1.09 (■), 1.11 (▲), 1.13 (▼), 1.15 (◯), 1.17
(△), 1.19 (×), and 1.21 (+) V. Extrapolation to ω–1/2 = 0 yields the activationcontrolled current.
S7
Figure S7. Activity profile of a 1.0 mC cm–2 catalyst film deposited onto a Pt RDE and
operated in 0.5 M KBi 1.75 M KNO3 pH 9.2 electrolyte after operation in 1.0 M
NaClO4, pH 8.5 electrolyte (▲), compared to the activity profile of a freshly prepared
catalyst film (■).
S8
Figure S8. Tafel plots, η = (E – iR – E°), for anodized catalyst films deposited onto a
Pt RDE by passage of 1.0 mC cm–2 and operated at 2000 rpm in 0.1 M KOH 1.9 M
KNO3 pH 12.9 (●) and 1.0 M KOH 1.0 M KNO3 pH 13.8 (▲) electrolyte. Tafel slopes
are 28 and 30 mV/decade, respectively.
S9