Temperature dependence of electrocatalytic and photocatalytic ...
Supporting information
Temperature dependence of electrocatalytic and photocatalytic oxygen evolution reaction rates using NiFe oxide Ela Nurlaela,† Tatsuya Shinagawa,† Muhammad Qureshi, Dattatray S. Dhawale, Kazuhiro Takanabe* [†] These authors contributed equally to this work
Division of Physical Sciences and Engineering KAUST Catalysis Center (KCC) King Abdullah University of Science and Technology (KAUST) 4700 KAUST, Thuwal, 23955-6900 (Saudi Arabia) E-mail: [email protected]
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Characterization This section summarizes the characterization of various materials, including Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) Scanning transmission electron microscopy (STEM) electron energy-loss spectroscopy (EELS) X-ray diffraction (XRD) X-ray photoelectron spectroscopy (XPS) Inductively coupled plasma (ICP) atomic emission spectroscopy (AES) Diffuse reflectance ultraviolet-visible (DR UV-Vis) spectroscopy
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Figure S1. (A) SEM image and (B) XRD patterns of bare Ni foam (NF).
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Figure S2. (A) TEM image, (B) corresponding electron diffraction pattern and (C) STEM image of NiFeOx/NF.
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Figure S3. (A, B) TEM images, (C) electron diffraction and (D) EELS of 2.2 wt% NiFeOx/Ta3N5 before reaction.
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Figure S4. (A) TEM image and (B) STEM image of 2.2 wt% NiFeOx/Ta3N5 after photocatalytic reaction.
Figure S5. XRD patterns of bare Ta3N5 and NiFeOx/Ta3N5.
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Figure S6. XPS spectra of NiFeOx powder and NiFeOx/Ta3N5 before/after photocatalytic reaction: (A) Ni 2p, (B) Fe 2p, (C) O 1s (D) C 1s , (E) Ta 4f and (F) N 1s, Ta 4p3/2.
np
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Figure S7. DR UV-Vis spectra of bare Ta3N5 and NiFeOx/Ta3N5.
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Electrochemistry
Figure S8. Linear sweep voltammograms (LSVs) using various catalysts in 1.0 M of (A) NaOH and (B) KOH. (C) LSVs using NiOx/NF catalysts in 0.01, 0.1 and 1.0 M of NaOH. All measurements were carried out with bubbling O2 at a scan rate of −1 mV s−1 and at 298 K.
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Figure S9. Tafel relation using NiFeOx/NF electrocatalysts in (A) NaOH and KOH at 0.1 or 1 M and in (B) 1.0 M of MOH (M: Li, Na, K and Cs).
Figure S10. Experimentally observed Tafel slope from Figure 2 in the main text against temperature.
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Detailed discussion on the OER description over NiFeOx In conjunction with micro-kinetic analyses, the theoretical aspect of the observed OER dependence on the temperature described in the main text will be addressed. The elementary steps for the oxygen evolution reaction (OER) with proton coupled electron transfer (PCET) are as follows:1,2
M OH
MOH e ,
MOH OH
MO OH
MO H 2O e ,
MOOH e ,
(1) (2) (3)
where M denotes a site on the surface. Regarding the coverage expression, θ0, θ1 and θ2 denote the surface coverage by empty sites, MOH and MO, respectively. Based on the observed Tafel slope of 40 mV dec−1 as shown in Figure 3A, Equation 3 is assumed to be the rate determining step (rds) to describe the electric currents. Under the considered condition, the forward reaction rate in Equation 1: r1 k1 0aOH k1aOH ,
(4)
and the backward reaction rate in Equation 1: r1 k 1aOH 1 ,
(5)
are in equilibrium, which gives the following coverage description:
0
1 , K exp f 1 aOH 0 1
(6)
where r is the reaction rate, k is the reaction rate constant, and ax represents the activity of ion x. The same argument is applied to Equation 2: r2 k 21aOH ,
(7)
r2 k 2aH 2O 2 ,
(8)
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a H 2O
1
aOH K 20 exp f 2
2 ,
(9)
where K0x is the ratio of k0x/k0−x and k0 is the standard rate constant of k. Additionally, the following relationship is true among the coverage terms: 2
i
1.
(10)
i 0
Combining Equations 6, 9 and 10 gives the following coverage expression:
2
2 K10 K 20 exp f 1 2 aOH
2 a H 2O K10 exp f 1 aOH a H 2O K10 K 20 exp f 1 2 aOH
,
(11)
where f is F/RT and F is Faraday’s constant. Equation 11 yields the following kinetic rate description: r3 k3 2 aOH , I nFA
(12) 3 K10 K 20 exp f 1 2 k30 exp 1 3 f 4 aOH
2 a H 2O K10 exp f 1 aOH a H 2O K10 K 20 exp f 1 2 aOH
.
(13)
When Equation 3 is the rds with MOH (θ1) being the surface predominant species, the theoretical Tafel slope is 40 mV dec−1.1,2 Under such conditions, the following assumption can be made: 1
0 and 1
2 ,
(14)
which corresponds to a H 2O
aOH K 20 exp f 2 ,
(15)
and K10 exp f 1 aOH
1,
(16)
respectively. With these inequalities, Equation 11 is simplified to:
2
K 20 exp f 2 aOH a H 2O
.
(17)
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Thus, the overall rate description can also be rewritten as the following: r3
2 k 30 K 20 aOH
a H 2O
exp f
1 3
3
2 .
(18)
Notably, for Equation 3 to be the rds, the conditions k03 > 1, i.e., the light intensity is very high and e dark and kr are small. Then, by assuming that kred. is smaller than k’e,, and kO is smaller than k’h2, the following equation is derived: vreact
K e K h 2 kO k red . I , kr
(45)
where Ke and Kh2 are the equilibrium constants between the rates of ke/k’e and kh2/k’h2, respectively. The rate of photoexcited electrons and holes is equal to a half order of the equilibrium constant of the electrons between the surface and the bulk, the equilibrium constant of the holes between the surface and the cocatalyst, the oxygen and hydrogen evolution rates, the absorption coefficient of the material, the light intensity, and the rate of the recombination reaction.
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Figure S18. Calculated carrier mobility dependence on temperature in the experimental condition.
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Figure S19. Calculated reversible voltage for water electrolysis as a function of temperature.
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Figure S20. Experimentally measured relative solution resistance (closed symbols) and relative solution viscosity taken from literature (lines) with respect to temperature. The designated numbers correspond to the applied potential on the RHE scale during resistance measurement. The solution resistance was measured by impedance at 100 kHz with 10 mV amplitude.
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Figure S21. Calculated oxygen solubility compiled against temperature. The oxygen solubility is calculated with the extended Sechenov equation.
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References (1)
Shinagawa, T.; Garcia-Esparza, A. T.; Takanabe, K. Sci. Rep. 2015, 5, 13801.
(2)
Koper, M. T. M. Chem. Sci. 2013, 4, 2710-2723.
(3)
Bard, A. J.; Faulkner, L. R. ELECTROCHEMICAL METHOD: Fundamentals and
Applications; John Wiley & Sons, Inc., New York, 2010. (4)
Parthasarathy, A.; Srinivasan, S.; Appleby, A. J. J. Electrochem. Soc. 1992, 139,
2530-2537. (5)
Hui-jun, L.; Qian, X.; Chuan-wei, Y.; Ya-zhe, C.; Yong-lian, Q. Int. J. Electrochem.
Sci. 2011, 6, 3483-3496. (6) Hisatomi, T.; Maeda, K.; Takanabe, K.; Kubota, J.; Domen, K. J. Phys. Chem. C 2009, 113, 21458-21466.
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Temperature dependence of electrocatalytic and photocatalytic oxygen evolution reaction rates using NiFe oxide Ela Nurlaela,† Tatsuya Shinagawa,† Muhammad Qureshi, Dattatray S. Dhawale, Kazuhiro Takanabe* [†] These authors contributed equally to this work
Division of Physical Sciences and Engineering KAUST Catalysis Center (KCC) King Abdullah University of Science and Technology (KAUST) 4700 KAUST, Thuwal, 23955-6900 (Saudi Arabia) E-mail: [email protected]
S1
Characterization This section summarizes the characterization of various materials, including Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) Scanning transmission electron microscopy (STEM) electron energy-loss spectroscopy (EELS) X-ray diffraction (XRD) X-ray photoelectron spectroscopy (XPS) Inductively coupled plasma (ICP) atomic emission spectroscopy (AES) Diffuse reflectance ultraviolet-visible (DR UV-Vis) spectroscopy
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Figure S1. (A) SEM image and (B) XRD patterns of bare Ni foam (NF).
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Figure S2. (A) TEM image, (B) corresponding electron diffraction pattern and (C) STEM image of NiFeOx/NF.
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Figure S3. (A, B) TEM images, (C) electron diffraction and (D) EELS of 2.2 wt% NiFeOx/Ta3N5 before reaction.
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Figure S4. (A) TEM image and (B) STEM image of 2.2 wt% NiFeOx/Ta3N5 after photocatalytic reaction.
Figure S5. XRD patterns of bare Ta3N5 and NiFeOx/Ta3N5.
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Figure S6. XPS spectra of NiFeOx powder and NiFeOx/Ta3N5 before/after photocatalytic reaction: (A) Ni 2p, (B) Fe 2p, (C) O 1s (D) C 1s , (E) Ta 4f and (F) N 1s, Ta 4p3/2.
np
S7
Figure S7. DR UV-Vis spectra of bare Ta3N5 and NiFeOx/Ta3N5.
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Electrochemistry
Figure S8. Linear sweep voltammograms (LSVs) using various catalysts in 1.0 M of (A) NaOH and (B) KOH. (C) LSVs using NiOx/NF catalysts in 0.01, 0.1 and 1.0 M of NaOH. All measurements were carried out with bubbling O2 at a scan rate of −1 mV s−1 and at 298 K.
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Figure S9. Tafel relation using NiFeOx/NF electrocatalysts in (A) NaOH and KOH at 0.1 or 1 M and in (B) 1.0 M of MOH (M: Li, Na, K and Cs).
Figure S10. Experimentally observed Tafel slope from Figure 2 in the main text against temperature.
S10
Detailed discussion on the OER description over NiFeOx In conjunction with micro-kinetic analyses, the theoretical aspect of the observed OER dependence on the temperature described in the main text will be addressed. The elementary steps for the oxygen evolution reaction (OER) with proton coupled electron transfer (PCET) are as follows:1,2
M OH
MOH e ,
MOH OH
MO OH
MO H 2O e ,
MOOH e ,
(1) (2) (3)
where M denotes a site on the surface. Regarding the coverage expression, θ0, θ1 and θ2 denote the surface coverage by empty sites, MOH and MO, respectively. Based on the observed Tafel slope of 40 mV dec−1 as shown in Figure 3A, Equation 3 is assumed to be the rate determining step (rds) to describe the electric currents. Under the considered condition, the forward reaction rate in Equation 1: r1 k1 0aOH k1aOH ,
(4)
and the backward reaction rate in Equation 1: r1 k 1aOH 1 ,
(5)
are in equilibrium, which gives the following coverage description:
0
1 , K exp f 1 aOH 0 1
(6)
where r is the reaction rate, k is the reaction rate constant, and ax represents the activity of ion x. The same argument is applied to Equation 2: r2 k 21aOH ,
(7)
r2 k 2aH 2O 2 ,
(8)
S11
a H 2O
1
aOH K 20 exp f 2
2 ,
(9)
where K0x is the ratio of k0x/k0−x and k0 is the standard rate constant of k. Additionally, the following relationship is true among the coverage terms: 2
i
1.
(10)
i 0
Combining Equations 6, 9 and 10 gives the following coverage expression:
2
2 K10 K 20 exp f 1 2 aOH
2 a H 2O K10 exp f 1 aOH a H 2O K10 K 20 exp f 1 2 aOH
,
(11)
where f is F/RT and F is Faraday’s constant. Equation 11 yields the following kinetic rate description: r3 k3 2 aOH , I nFA
(12) 3 K10 K 20 exp f 1 2 k30 exp 1 3 f 4 aOH
2 a H 2O K10 exp f 1 aOH a H 2O K10 K 20 exp f 1 2 aOH
.
(13)
When Equation 3 is the rds with MOH (θ1) being the surface predominant species, the theoretical Tafel slope is 40 mV dec−1.1,2 Under such conditions, the following assumption can be made: 1
0 and 1
2 ,
(14)
which corresponds to a H 2O
aOH K 20 exp f 2 ,
(15)
and K10 exp f 1 aOH
1,
(16)
respectively. With these inequalities, Equation 11 is simplified to:
2
K 20 exp f 2 aOH a H 2O
.
(17)
S12
Thus, the overall rate description can also be rewritten as the following: r3
2 k 30 K 20 aOH
a H 2O
exp f
1 3
3
2 .
(18)
Notably, for Equation 3 to be the rds, the conditions k03 > 1, i.e., the light intensity is very high and e dark and kr are small. Then, by assuming that kred. is smaller than k’e,, and kO is smaller than k’h2, the following equation is derived: vreact
K e K h 2 kO k red . I , kr
(45)
where Ke and Kh2 are the equilibrium constants between the rates of ke/k’e and kh2/k’h2, respectively. The rate of photoexcited electrons and holes is equal to a half order of the equilibrium constant of the electrons between the surface and the bulk, the equilibrium constant of the holes between the surface and the cocatalyst, the oxygen and hydrogen evolution rates, the absorption coefficient of the material, the light intensity, and the rate of the recombination reaction.
S22
Figure S18. Calculated carrier mobility dependence on temperature in the experimental condition.
S23
Figure S19. Calculated reversible voltage for water electrolysis as a function of temperature.
S24
Figure S20. Experimentally measured relative solution resistance (closed symbols) and relative solution viscosity taken from literature (lines) with respect to temperature. The designated numbers correspond to the applied potential on the RHE scale during resistance measurement. The solution resistance was measured by impedance at 100 kHz with 10 mV amplitude.
S25
Figure S21. Calculated oxygen solubility compiled against temperature. The oxygen solubility is calculated with the extended Sechenov equation.
S26
References (1)
Shinagawa, T.; Garcia-Esparza, A. T.; Takanabe, K. Sci. Rep. 2015, 5, 13801.
(2)
Koper, M. T. M. Chem. Sci. 2013, 4, 2710-2723.
(3)
Bard, A. J.; Faulkner, L. R. ELECTROCHEMICAL METHOD: Fundamentals and
Applications; John Wiley & Sons, Inc., New York, 2010. (4)
Parthasarathy, A.; Srinivasan, S.; Appleby, A. J. J. Electrochem. Soc. 1992, 139,
2530-2537. (5)
Hui-jun, L.; Qian, X.; Chuan-wei, Y.; Ya-zhe, C.; Yong-lian, Q. Int. J. Electrochem.
Sci. 2011, 6, 3483-3496. (6) Hisatomi, T.; Maeda, K.; Takanabe, K.; Kubota, J.; Domen, K. J. Phys. Chem. C 2009, 113, 21458-21466.
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