Electronic Supplementary Information

Effect of Lattice Strain in Electrocatalytic Activity of IrO2 for Water Splitting

Wei Sunadagger Zhiqiang Wangb dagger Waqas Qamar Zamana Zhenhua Zhoua Limei Caoa Xue-Qing Gongb Ji Yanga

a State Environmental Protection Key Laboratory of Environmental Risk Assessment and Control on Chemical Processes School of Resources and Environmental Engineering East China University of Science and Technology 130 Meilong Road Shanghai 200237 PR China

b Key Laboratory for Advanced Materials Center for Computational Chemistry and Research Institute of Industrial Catalysis East China University of Science and Technology 130 Meilong Road Shanghai 200237 PR China

Corresponding author yangjiecusteducn

Electronic Supplementary Material (ESI) for ChemCommThis journal is copy The Royal Society of Chemistry 2018

Experimental methods

Materials preparation

All Iridium oxides are prepared via the hydrothermal synthesis In detail 3 mL of 567

mM iridium chloride (IrCl33H2O gt98 purity) precursor was added to 10 mL of 01 M

sodium hydroxide (NaOH AR purity) and an additional 10 mL of deionized water was

mixed into the solution Then the whole solution was transferred to a 40-mL Teflon-lined

pressure vessel and loaded into an oven to heat the solution to 150 degC for 720 min The

vessels were cooled naturally at room temperature The precipitates were suction filtered

and washed with deionized water twice to remove other ions The remaining solid on the

filter was dried to dehydration in an oven at 60 degC at least 30 min The dried powders were

transferred to a crucible and annealed at different temperature for 6 h

Electrode preparation and Electrochemical Measurements

The electrodes used for the electrochemical measurements are prepared as follows 6

mg of fresh catalyst powders are dispersed in 15 mL of 21 vv isopropanolwater and 15

uL Nafion solution added into the solution Then ultrasonicating them for approximately

30 min to form a homogeneous ink Next 75 μL of ink deposited on tailored Ti plate

Here a saturated calomel electrode (SCE) is employed as a reference and a polished and

cleaned Pt foil with a 15 cm times 1 cm reaction area were used for the counter electrode The

SCE was calibrated with respect to the RHE in all three types of pH solution using a high

purity hydrogen saturated electrolyte with a Pt foil as the working electrode1 The OER

determinations under the 01 M perchloric acid (HClO4 AR purity) solution The working

electrodes were cycled a least 5 times until the curves were observed to overlap in the

curves then the data of the cyclic voltammetry (CV) and polarization curves were

recorded at the specified scan rate

Materials Characterizations

The crystal structure of the catalysts were investigated using powder X-ray diffraction

(XRD) using a Dmax2550 V apparatus with a Cu-Kα radiation source (λ=15406 Aring) A

JEM-2100 transmission electron microscope was used to obtain the TEM images Raman

spectra were determined using a iuvia refl instrument with a laser source wavelength of

514 nm The surface properties of the catalysts were determined via X-ray photoelectron

spectroscopy (XPS) using an ESCALAB 250Xi instrument with a Al-Kα radiation source

The XPS spectra were calibrated with respect to C-1s at the binding energy of 2846 eV

The X-ray absorption data (XAS) at the Ir LIII edge of the samples which were mixed with

LiF to reach 50 mg were recorded at room temperature in transmission mode using ion

chambers using the BL14W1 beam line of the Shanghai Synchrotron Radiation Facility

(SSRF) China

Benchmarking calculations

The different factors involved in Fig 2c are benchmarked using the Un-A sample In detail

for crystallinity calculations the background of the peaks in XRD patterns is considered

and deducted by Kα function Although the Un-A and A-200 are amorphous a weak (101)

peak is identified in the pattern so that the crystallinity of all samples are calculated based

on the (101) intensity For the particle size surface area ECSAs and the 5d occupation

states the index is calculated as

i

Un A

ww

Where wi is the property value of the samples wUn-A is the non-annealing case

Specific activity

The specific activity2 of catalyst can be defined by specific current density js which is

calculated by dividing the current density per geometric area (jgeo) at a given overpotential

by the roughness factor (RF) of the surface The RF is calculated by taking the estimated

ECSA and dividing by the geometric area of the electrode 025 cm2 Thus js is given by

fellow equation

025

geos

jj

ECSA

Here jgeo is the current density (mA cm-2) at the η=0350 V

Figures and Tables

Fig S1 XRD patterns of prepared IrO2 oxides under different annealing temperatures The vertical line corresponds to the standard IrO2 diffraction peaks with card number of 15-0870

Fig S2 TEM images of the prepared IrO2 clear crystal particle observed under 400 degC

Table S1 Surface area and particle size of different IrO2 samples

Samples BET surface area (m2 g-1)

TEM particle sizea (nm)

Scherrer particle sizeb

(nm)Un-A 459 172 NAA-200 282 193 NAA-400 221 322 2611A-600 137 453 3291A-800 116 521 4911

a Average particle size

b Scherrer equation K=089 λ=0154 nm B is the peak cos( )KD

B

FWHM θ is the diffraction position

Fig S3 (a)-(g) are the normalized CVs of Un-A A-200 A-400 A-500 A-600 A-700 and A-800 respectively (h) The calculated ECSAs of different IrO2 samples by using the green rejoin in normalized CV curves The current determined by CV method includes two parts capacitor current (ic) and Faradic current (iF) ic is linear based on the scan rate determined by ic=Cd∙ν The parameter Cd is crucial factor associated with electrochemical active sites Thus it can be normalized by iν= Cd (constant) +iFν both obtaining the Cd value and marked Faradic current to determine the onset potential of OER activity The region between vertical orange lines is chosen to estimate Cd value ECSAs = CdCs where Cs=00035 mF cm-2 based on the reported value2 The loading mass of iridium dioxides is 005 mg in all samples

Fig S4 Normalized Ir-LIII edge XANES spectra for the prepared materials The upper left inset corresponds to ldquowhite linerdquo region and (b) is their ldquowhite linerdquo intensity ratio relative to Un-A

FigS5 The contribution of these five factors to the OER activity (a)-crystallinity (b)-BET surface area (current density are normalized by BET) (c)-ECSAs (current density are normalized by ECSAs) (d)-particle size (e)-5d electrons occupation states Firstly it clearly shows that higher crystallinity led to the lower OER activity The smaller sizes or larger surface areas are usually to pursue to enhance catalysts OER activity BET surface area TEM particle size and ECSAs are used for such evaluations However we not find higher OER activity corresponding to large surface area or smaller particle size Comparatively the relationship between the ECSAs of catalyst and its OER activity is more closely related to BET The critical point is the electronic structure of the activated sites10 We use the 5d occupation states to describe this key point because Ir-5d electrons determine its valence states It can clearly find that the filling of the 5d occupation states also not agreement with the OER activity trend but more electrons on 5d states seems better for OER activity

FigS6 The Rietveld refinement of XRD patterns of prepared IrO2 samples The R-factors and errors are shown in each figure

FigS7 (a)-(c) are the fitting results of double Ir-Ir shell in the range of 24-41 Aring The k range is 2-14 Aring (d) The cell parameters of IrO2 prepared at different annealing temperature The variation of ca ratio is consistent with XRD refinements

Fig S8 Fitting results of Ir-O shell for different annealing temperature prepared IrO2 by using IFEFFIT IrO2 fitting parameters are a=b=45051 Aring c=31586 Aring space=P42mnm Ir-O2-c=19604 Aring Ir-O4-c=19988 Aring

Table S2 Results of fitted Ir-O shell in EXAFS by IFEFFIT Sample Scattered

pathaCoordination

numberbDistance (Aring)

Δσ2 (Aring2) R-factor

Un-A Ir-O 6 19905 000485 0000076A-200 Ir-O 6 19887 000720 0000191A-400 Ir-O2-c 2 19314

Ir-O4-c 4 19885 000592 0007975

A-600 Ir-O2-c 2 18933Ir-O4-c 4 19810 000522 0000171

A-800 Ir-O2-c 2 18900Ir-O4-c 4 19820 000518 0000167

Notes a and b indicate the scattered path and coordination number for Un-A and A-200 are amorphous so we think that their Ir-O coordination type just has only one

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

Experimental methods

Materials preparation

All Iridium oxides are prepared via the hydrothermal synthesis In detail 3 mL of 567

mM iridium chloride (IrCl33H2O gt98 purity) precursor was added to 10 mL of 01 M

sodium hydroxide (NaOH AR purity) and an additional 10 mL of deionized water was

mixed into the solution Then the whole solution was transferred to a 40-mL Teflon-lined

pressure vessel and loaded into an oven to heat the solution to 150 degC for 720 min The

vessels were cooled naturally at room temperature The precipitates were suction filtered

and washed with deionized water twice to remove other ions The remaining solid on the

filter was dried to dehydration in an oven at 60 degC at least 30 min The dried powders were

transferred to a crucible and annealed at different temperature for 6 h

Electrode preparation and Electrochemical Measurements

The electrodes used for the electrochemical measurements are prepared as follows 6

mg of fresh catalyst powders are dispersed in 15 mL of 21 vv isopropanolwater and 15

uL Nafion solution added into the solution Then ultrasonicating them for approximately

30 min to form a homogeneous ink Next 75 μL of ink deposited on tailored Ti plate

Here a saturated calomel electrode (SCE) is employed as a reference and a polished and

cleaned Pt foil with a 15 cm times 1 cm reaction area were used for the counter electrode The

SCE was calibrated with respect to the RHE in all three types of pH solution using a high

purity hydrogen saturated electrolyte with a Pt foil as the working electrode1 The OER

determinations under the 01 M perchloric acid (HClO4 AR purity) solution The working

electrodes were cycled a least 5 times until the curves were observed to overlap in the

curves then the data of the cyclic voltammetry (CV) and polarization curves were

recorded at the specified scan rate

Materials Characterizations

The crystal structure of the catalysts were investigated using powder X-ray diffraction

(XRD) using a Dmax2550 V apparatus with a Cu-Kα radiation source (λ=15406 Aring) A

JEM-2100 transmission electron microscope was used to obtain the TEM images Raman

spectra were determined using a iuvia refl instrument with a laser source wavelength of

514 nm The surface properties of the catalysts were determined via X-ray photoelectron

spectroscopy (XPS) using an ESCALAB 250Xi instrument with a Al-Kα radiation source

The XPS spectra were calibrated with respect to C-1s at the binding energy of 2846 eV

The X-ray absorption data (XAS) at the Ir LIII edge of the samples which were mixed with

LiF to reach 50 mg were recorded at room temperature in transmission mode using ion

chambers using the BL14W1 beam line of the Shanghai Synchrotron Radiation Facility

(SSRF) China

Benchmarking calculations

The different factors involved in Fig 2c are benchmarked using the Un-A sample In detail

for crystallinity calculations the background of the peaks in XRD patterns is considered

and deducted by Kα function Although the Un-A and A-200 are amorphous a weak (101)

peak is identified in the pattern so that the crystallinity of all samples are calculated based

on the (101) intensity For the particle size surface area ECSAs and the 5d occupation

states the index is calculated as

i

Un A

ww

Where wi is the property value of the samples wUn-A is the non-annealing case

Specific activity

The specific activity2 of catalyst can be defined by specific current density js which is

calculated by dividing the current density per geometric area (jgeo) at a given overpotential

by the roughness factor (RF) of the surface The RF is calculated by taking the estimated

ECSA and dividing by the geometric area of the electrode 025 cm2 Thus js is given by

fellow equation

025

geos

jj

ECSA

Here jgeo is the current density (mA cm-2) at the η=0350 V

Figures and Tables

Fig S1 XRD patterns of prepared IrO2 oxides under different annealing temperatures The vertical line corresponds to the standard IrO2 diffraction peaks with card number of 15-0870

Fig S2 TEM images of the prepared IrO2 clear crystal particle observed under 400 degC

Table S1 Surface area and particle size of different IrO2 samples

Samples BET surface area (m2 g-1)

TEM particle sizea (nm)

Scherrer particle sizeb

(nm)Un-A 459 172 NAA-200 282 193 NAA-400 221 322 2611A-600 137 453 3291A-800 116 521 4911

a Average particle size

b Scherrer equation K=089 λ=0154 nm B is the peak cos( )KD

B

FWHM θ is the diffraction position

Fig S3 (a)-(g) are the normalized CVs of Un-A A-200 A-400 A-500 A-600 A-700 and A-800 respectively (h) The calculated ECSAs of different IrO2 samples by using the green rejoin in normalized CV curves The current determined by CV method includes two parts capacitor current (ic) and Faradic current (iF) ic is linear based on the scan rate determined by ic=Cd∙ν The parameter Cd is crucial factor associated with electrochemical active sites Thus it can be normalized by iν= Cd (constant) +iFν both obtaining the Cd value and marked Faradic current to determine the onset potential of OER activity The region between vertical orange lines is chosen to estimate Cd value ECSAs = CdCs where Cs=00035 mF cm-2 based on the reported value2 The loading mass of iridium dioxides is 005 mg in all samples

Fig S4 Normalized Ir-LIII edge XANES spectra for the prepared materials The upper left inset corresponds to ldquowhite linerdquo region and (b) is their ldquowhite linerdquo intensity ratio relative to Un-A

FigS5 The contribution of these five factors to the OER activity (a)-crystallinity (b)-BET surface area (current density are normalized by BET) (c)-ECSAs (current density are normalized by ECSAs) (d)-particle size (e)-5d electrons occupation states Firstly it clearly shows that higher crystallinity led to the lower OER activity The smaller sizes or larger surface areas are usually to pursue to enhance catalysts OER activity BET surface area TEM particle size and ECSAs are used for such evaluations However we not find higher OER activity corresponding to large surface area or smaller particle size Comparatively the relationship between the ECSAs of catalyst and its OER activity is more closely related to BET The critical point is the electronic structure of the activated sites10 We use the 5d occupation states to describe this key point because Ir-5d electrons determine its valence states It can clearly find that the filling of the 5d occupation states also not agreement with the OER activity trend but more electrons on 5d states seems better for OER activity

FigS6 The Rietveld refinement of XRD patterns of prepared IrO2 samples The R-factors and errors are shown in each figure

FigS7 (a)-(c) are the fitting results of double Ir-Ir shell in the range of 24-41 Aring The k range is 2-14 Aring (d) The cell parameters of IrO2 prepared at different annealing temperature The variation of ca ratio is consistent with XRD refinements

Fig S8 Fitting results of Ir-O shell for different annealing temperature prepared IrO2 by using IFEFFIT IrO2 fitting parameters are a=b=45051 Aring c=31586 Aring space=P42mnm Ir-O2-c=19604 Aring Ir-O4-c=19988 Aring

Table S2 Results of fitted Ir-O shell in EXAFS by IFEFFIT Sample Scattered

pathaCoordination

numberbDistance (Aring)

Δσ2 (Aring2) R-factor

Un-A Ir-O 6 19905 000485 0000076A-200 Ir-O 6 19887 000720 0000191A-400 Ir-O2-c 2 19314

Ir-O4-c 4 19885 000592 0007975

A-600 Ir-O2-c 2 18933Ir-O4-c 4 19810 000522 0000171

A-800 Ir-O2-c 2 18900Ir-O4-c 4 19820 000518 0000167

Notes a and b indicate the scattered path and coordination number for Un-A and A-200 are amorphous so we think that their Ir-O coordination type just has only one

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

spectra were determined using a iuvia refl instrument with a laser source wavelength of

514 nm The surface properties of the catalysts were determined via X-ray photoelectron

spectroscopy (XPS) using an ESCALAB 250Xi instrument with a Al-Kα radiation source

The XPS spectra were calibrated with respect to C-1s at the binding energy of 2846 eV

The X-ray absorption data (XAS) at the Ir LIII edge of the samples which were mixed with

LiF to reach 50 mg were recorded at room temperature in transmission mode using ion

chambers using the BL14W1 beam line of the Shanghai Synchrotron Radiation Facility

(SSRF) China

Benchmarking calculations

The different factors involved in Fig 2c are benchmarked using the Un-A sample In detail

for crystallinity calculations the background of the peaks in XRD patterns is considered

and deducted by Kα function Although the Un-A and A-200 are amorphous a weak (101)

peak is identified in the pattern so that the crystallinity of all samples are calculated based

on the (101) intensity For the particle size surface area ECSAs and the 5d occupation

states the index is calculated as

i

Un A

ww

Where wi is the property value of the samples wUn-A is the non-annealing case

Specific activity

The specific activity2 of catalyst can be defined by specific current density js which is

calculated by dividing the current density per geometric area (jgeo) at a given overpotential

by the roughness factor (RF) of the surface The RF is calculated by taking the estimated

ECSA and dividing by the geometric area of the electrode 025 cm2 Thus js is given by

fellow equation

025

geos

jj

ECSA

Here jgeo is the current density (mA cm-2) at the η=0350 V

Figures and Tables

Fig S1 XRD patterns of prepared IrO2 oxides under different annealing temperatures The vertical line corresponds to the standard IrO2 diffraction peaks with card number of 15-0870

Fig S2 TEM images of the prepared IrO2 clear crystal particle observed under 400 degC

Table S1 Surface area and particle size of different IrO2 samples

Samples BET surface area (m2 g-1)

TEM particle sizea (nm)

Scherrer particle sizeb

(nm)Un-A 459 172 NAA-200 282 193 NAA-400 221 322 2611A-600 137 453 3291A-800 116 521 4911

a Average particle size

b Scherrer equation K=089 λ=0154 nm B is the peak cos( )KD

B

FWHM θ is the diffraction position

Fig S3 (a)-(g) are the normalized CVs of Un-A A-200 A-400 A-500 A-600 A-700 and A-800 respectively (h) The calculated ECSAs of different IrO2 samples by using the green rejoin in normalized CV curves The current determined by CV method includes two parts capacitor current (ic) and Faradic current (iF) ic is linear based on the scan rate determined by ic=Cd∙ν The parameter Cd is crucial factor associated with electrochemical active sites Thus it can be normalized by iν= Cd (constant) +iFν both obtaining the Cd value and marked Faradic current to determine the onset potential of OER activity The region between vertical orange lines is chosen to estimate Cd value ECSAs = CdCs where Cs=00035 mF cm-2 based on the reported value2 The loading mass of iridium dioxides is 005 mg in all samples

Fig S4 Normalized Ir-LIII edge XANES spectra for the prepared materials The upper left inset corresponds to ldquowhite linerdquo region and (b) is their ldquowhite linerdquo intensity ratio relative to Un-A

FigS5 The contribution of these five factors to the OER activity (a)-crystallinity (b)-BET surface area (current density are normalized by BET) (c)-ECSAs (current density are normalized by ECSAs) (d)-particle size (e)-5d electrons occupation states Firstly it clearly shows that higher crystallinity led to the lower OER activity The smaller sizes or larger surface areas are usually to pursue to enhance catalysts OER activity BET surface area TEM particle size and ECSAs are used for such evaluations However we not find higher OER activity corresponding to large surface area or smaller particle size Comparatively the relationship between the ECSAs of catalyst and its OER activity is more closely related to BET The critical point is the electronic structure of the activated sites10 We use the 5d occupation states to describe this key point because Ir-5d electrons determine its valence states It can clearly find that the filling of the 5d occupation states also not agreement with the OER activity trend but more electrons on 5d states seems better for OER activity

FigS6 The Rietveld refinement of XRD patterns of prepared IrO2 samples The R-factors and errors are shown in each figure

FigS7 (a)-(c) are the fitting results of double Ir-Ir shell in the range of 24-41 Aring The k range is 2-14 Aring (d) The cell parameters of IrO2 prepared at different annealing temperature The variation of ca ratio is consistent with XRD refinements

Fig S8 Fitting results of Ir-O shell for different annealing temperature prepared IrO2 by using IFEFFIT IrO2 fitting parameters are a=b=45051 Aring c=31586 Aring space=P42mnm Ir-O2-c=19604 Aring Ir-O4-c=19988 Aring

Table S2 Results of fitted Ir-O shell in EXAFS by IFEFFIT Sample Scattered

pathaCoordination

numberbDistance (Aring)

Δσ2 (Aring2) R-factor

Un-A Ir-O 6 19905 000485 0000076A-200 Ir-O 6 19887 000720 0000191A-400 Ir-O2-c 2 19314

Ir-O4-c 4 19885 000592 0007975

A-600 Ir-O2-c 2 18933Ir-O4-c 4 19810 000522 0000171

A-800 Ir-O2-c 2 18900Ir-O4-c 4 19820 000518 0000167

Notes a and b indicate the scattered path and coordination number for Un-A and A-200 are amorphous so we think that their Ir-O coordination type just has only one

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

Figures and Tables

Fig S1 XRD patterns of prepared IrO2 oxides under different annealing temperatures The vertical line corresponds to the standard IrO2 diffraction peaks with card number of 15-0870

Fig S2 TEM images of the prepared IrO2 clear crystal particle observed under 400 degC

Table S1 Surface area and particle size of different IrO2 samples

Samples BET surface area (m2 g-1)

TEM particle sizea (nm)

Scherrer particle sizeb

(nm)Un-A 459 172 NAA-200 282 193 NAA-400 221 322 2611A-600 137 453 3291A-800 116 521 4911

a Average particle size

b Scherrer equation K=089 λ=0154 nm B is the peak cos( )KD

B

FWHM θ is the diffraction position

Fig S3 (a)-(g) are the normalized CVs of Un-A A-200 A-400 A-500 A-600 A-700 and A-800 respectively (h) The calculated ECSAs of different IrO2 samples by using the green rejoin in normalized CV curves The current determined by CV method includes two parts capacitor current (ic) and Faradic current (iF) ic is linear based on the scan rate determined by ic=Cd∙ν The parameter Cd is crucial factor associated with electrochemical active sites Thus it can be normalized by iν= Cd (constant) +iFν both obtaining the Cd value and marked Faradic current to determine the onset potential of OER activity The region between vertical orange lines is chosen to estimate Cd value ECSAs = CdCs where Cs=00035 mF cm-2 based on the reported value2 The loading mass of iridium dioxides is 005 mg in all samples

Fig S4 Normalized Ir-LIII edge XANES spectra for the prepared materials The upper left inset corresponds to ldquowhite linerdquo region and (b) is their ldquowhite linerdquo intensity ratio relative to Un-A

FigS5 The contribution of these five factors to the OER activity (a)-crystallinity (b)-BET surface area (current density are normalized by BET) (c)-ECSAs (current density are normalized by ECSAs) (d)-particle size (e)-5d electrons occupation states Firstly it clearly shows that higher crystallinity led to the lower OER activity The smaller sizes or larger surface areas are usually to pursue to enhance catalysts OER activity BET surface area TEM particle size and ECSAs are used for such evaluations However we not find higher OER activity corresponding to large surface area or smaller particle size Comparatively the relationship between the ECSAs of catalyst and its OER activity is more closely related to BET The critical point is the electronic structure of the activated sites10 We use the 5d occupation states to describe this key point because Ir-5d electrons determine its valence states It can clearly find that the filling of the 5d occupation states also not agreement with the OER activity trend but more electrons on 5d states seems better for OER activity

FigS6 The Rietveld refinement of XRD patterns of prepared IrO2 samples The R-factors and errors are shown in each figure

FigS7 (a)-(c) are the fitting results of double Ir-Ir shell in the range of 24-41 Aring The k range is 2-14 Aring (d) The cell parameters of IrO2 prepared at different annealing temperature The variation of ca ratio is consistent with XRD refinements

Fig S8 Fitting results of Ir-O shell for different annealing temperature prepared IrO2 by using IFEFFIT IrO2 fitting parameters are a=b=45051 Aring c=31586 Aring space=P42mnm Ir-O2-c=19604 Aring Ir-O4-c=19988 Aring

Table S2 Results of fitted Ir-O shell in EXAFS by IFEFFIT Sample Scattered

pathaCoordination

numberbDistance (Aring)

Δσ2 (Aring2) R-factor

Un-A Ir-O 6 19905 000485 0000076A-200 Ir-O 6 19887 000720 0000191A-400 Ir-O2-c 2 19314

Ir-O4-c 4 19885 000592 0007975

A-600 Ir-O2-c 2 18933Ir-O4-c 4 19810 000522 0000171

A-800 Ir-O2-c 2 18900Ir-O4-c 4 19820 000518 0000167

Notes a and b indicate the scattered path and coordination number for Un-A and A-200 are amorphous so we think that their Ir-O coordination type just has only one

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

Fig S2 TEM images of the prepared IrO2 clear crystal particle observed under 400 degC

Table S1 Surface area and particle size of different IrO2 samples

Samples BET surface area (m2 g-1)

TEM particle sizea (nm)

Scherrer particle sizeb

(nm)Un-A 459 172 NAA-200 282 193 NAA-400 221 322 2611A-600 137 453 3291A-800 116 521 4911

a Average particle size

b Scherrer equation K=089 λ=0154 nm B is the peak cos( )KD

B

FWHM θ is the diffraction position

Fig S3 (a)-(g) are the normalized CVs of Un-A A-200 A-400 A-500 A-600 A-700 and A-800 respectively (h) The calculated ECSAs of different IrO2 samples by using the green rejoin in normalized CV curves The current determined by CV method includes two parts capacitor current (ic) and Faradic current (iF) ic is linear based on the scan rate determined by ic=Cd∙ν The parameter Cd is crucial factor associated with electrochemical active sites Thus it can be normalized by iν= Cd (constant) +iFν both obtaining the Cd value and marked Faradic current to determine the onset potential of OER activity The region between vertical orange lines is chosen to estimate Cd value ECSAs = CdCs where Cs=00035 mF cm-2 based on the reported value2 The loading mass of iridium dioxides is 005 mg in all samples

Fig S4 Normalized Ir-LIII edge XANES spectra for the prepared materials The upper left inset corresponds to ldquowhite linerdquo region and (b) is their ldquowhite linerdquo intensity ratio relative to Un-A

FigS5 The contribution of these five factors to the OER activity (a)-crystallinity (b)-BET surface area (current density are normalized by BET) (c)-ECSAs (current density are normalized by ECSAs) (d)-particle size (e)-5d electrons occupation states Firstly it clearly shows that higher crystallinity led to the lower OER activity The smaller sizes or larger surface areas are usually to pursue to enhance catalysts OER activity BET surface area TEM particle size and ECSAs are used for such evaluations However we not find higher OER activity corresponding to large surface area or smaller particle size Comparatively the relationship between the ECSAs of catalyst and its OER activity is more closely related to BET The critical point is the electronic structure of the activated sites10 We use the 5d occupation states to describe this key point because Ir-5d electrons determine its valence states It can clearly find that the filling of the 5d occupation states also not agreement with the OER activity trend but more electrons on 5d states seems better for OER activity

FigS6 The Rietveld refinement of XRD patterns of prepared IrO2 samples The R-factors and errors are shown in each figure

FigS7 (a)-(c) are the fitting results of double Ir-Ir shell in the range of 24-41 Aring The k range is 2-14 Aring (d) The cell parameters of IrO2 prepared at different annealing temperature The variation of ca ratio is consistent with XRD refinements

Fig S8 Fitting results of Ir-O shell for different annealing temperature prepared IrO2 by using IFEFFIT IrO2 fitting parameters are a=b=45051 Aring c=31586 Aring space=P42mnm Ir-O2-c=19604 Aring Ir-O4-c=19988 Aring

Table S2 Results of fitted Ir-O shell in EXAFS by IFEFFIT Sample Scattered

pathaCoordination

numberbDistance (Aring)

Δσ2 (Aring2) R-factor

Un-A Ir-O 6 19905 000485 0000076A-200 Ir-O 6 19887 000720 0000191A-400 Ir-O2-c 2 19314

Ir-O4-c 4 19885 000592 0007975

A-600 Ir-O2-c 2 18933Ir-O4-c 4 19810 000522 0000171

A-800 Ir-O2-c 2 18900Ir-O4-c 4 19820 000518 0000167

Notes a and b indicate the scattered path and coordination number for Un-A and A-200 are amorphous so we think that their Ir-O coordination type just has only one

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

Fig S3 (a)-(g) are the normalized CVs of Un-A A-200 A-400 A-500 A-600 A-700 and A-800 respectively (h) The calculated ECSAs of different IrO2 samples by using the green rejoin in normalized CV curves The current determined by CV method includes two parts capacitor current (ic) and Faradic current (iF) ic is linear based on the scan rate determined by ic=Cd∙ν The parameter Cd is crucial factor associated with electrochemical active sites Thus it can be normalized by iν= Cd (constant) +iFν both obtaining the Cd value and marked Faradic current to determine the onset potential of OER activity The region between vertical orange lines is chosen to estimate Cd value ECSAs = CdCs where Cs=00035 mF cm-2 based on the reported value2 The loading mass of iridium dioxides is 005 mg in all samples

Fig S4 Normalized Ir-LIII edge XANES spectra for the prepared materials The upper left inset corresponds to ldquowhite linerdquo region and (b) is their ldquowhite linerdquo intensity ratio relative to Un-A

FigS5 The contribution of these five factors to the OER activity (a)-crystallinity (b)-BET surface area (current density are normalized by BET) (c)-ECSAs (current density are normalized by ECSAs) (d)-particle size (e)-5d electrons occupation states Firstly it clearly shows that higher crystallinity led to the lower OER activity The smaller sizes or larger surface areas are usually to pursue to enhance catalysts OER activity BET surface area TEM particle size and ECSAs are used for such evaluations However we not find higher OER activity corresponding to large surface area or smaller particle size Comparatively the relationship between the ECSAs of catalyst and its OER activity is more closely related to BET The critical point is the electronic structure of the activated sites10 We use the 5d occupation states to describe this key point because Ir-5d electrons determine its valence states It can clearly find that the filling of the 5d occupation states also not agreement with the OER activity trend but more electrons on 5d states seems better for OER activity

FigS6 The Rietveld refinement of XRD patterns of prepared IrO2 samples The R-factors and errors are shown in each figure

FigS7 (a)-(c) are the fitting results of double Ir-Ir shell in the range of 24-41 Aring The k range is 2-14 Aring (d) The cell parameters of IrO2 prepared at different annealing temperature The variation of ca ratio is consistent with XRD refinements

Fig S8 Fitting results of Ir-O shell for different annealing temperature prepared IrO2 by using IFEFFIT IrO2 fitting parameters are a=b=45051 Aring c=31586 Aring space=P42mnm Ir-O2-c=19604 Aring Ir-O4-c=19988 Aring

Table S2 Results of fitted Ir-O shell in EXAFS by IFEFFIT Sample Scattered

pathaCoordination

numberbDistance (Aring)

Δσ2 (Aring2) R-factor

Un-A Ir-O 6 19905 000485 0000076A-200 Ir-O 6 19887 000720 0000191A-400 Ir-O2-c 2 19314

Ir-O4-c 4 19885 000592 0007975

A-600 Ir-O2-c 2 18933Ir-O4-c 4 19810 000522 0000171

A-800 Ir-O2-c 2 18900Ir-O4-c 4 19820 000518 0000167

Notes a and b indicate the scattered path and coordination number for Un-A and A-200 are amorphous so we think that their Ir-O coordination type just has only one

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

Fig S4 Normalized Ir-LIII edge XANES spectra for the prepared materials The upper left inset corresponds to ldquowhite linerdquo region and (b) is their ldquowhite linerdquo intensity ratio relative to Un-A

FigS5 The contribution of these five factors to the OER activity (a)-crystallinity (b)-BET surface area (current density are normalized by BET) (c)-ECSAs (current density are normalized by ECSAs) (d)-particle size (e)-5d electrons occupation states Firstly it clearly shows that higher crystallinity led to the lower OER activity The smaller sizes or larger surface areas are usually to pursue to enhance catalysts OER activity BET surface area TEM particle size and ECSAs are used for such evaluations However we not find higher OER activity corresponding to large surface area or smaller particle size Comparatively the relationship between the ECSAs of catalyst and its OER activity is more closely related to BET The critical point is the electronic structure of the activated sites10 We use the 5d occupation states to describe this key point because Ir-5d electrons determine its valence states It can clearly find that the filling of the 5d occupation states also not agreement with the OER activity trend but more electrons on 5d states seems better for OER activity

FigS6 The Rietveld refinement of XRD patterns of prepared IrO2 samples The R-factors and errors are shown in each figure

FigS7 (a)-(c) are the fitting results of double Ir-Ir shell in the range of 24-41 Aring The k range is 2-14 Aring (d) The cell parameters of IrO2 prepared at different annealing temperature The variation of ca ratio is consistent with XRD refinements

Fig S8 Fitting results of Ir-O shell for different annealing temperature prepared IrO2 by using IFEFFIT IrO2 fitting parameters are a=b=45051 Aring c=31586 Aring space=P42mnm Ir-O2-c=19604 Aring Ir-O4-c=19988 Aring

Table S2 Results of fitted Ir-O shell in EXAFS by IFEFFIT Sample Scattered

pathaCoordination

numberbDistance (Aring)

Δσ2 (Aring2) R-factor

Un-A Ir-O 6 19905 000485 0000076A-200 Ir-O 6 19887 000720 0000191A-400 Ir-O2-c 2 19314

Ir-O4-c 4 19885 000592 0007975

A-600 Ir-O2-c 2 18933Ir-O4-c 4 19810 000522 0000171

A-800 Ir-O2-c 2 18900Ir-O4-c 4 19820 000518 0000167

Notes a and b indicate the scattered path and coordination number for Un-A and A-200 are amorphous so we think that their Ir-O coordination type just has only one

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

FigS5 The contribution of these five factors to the OER activity (a)-crystallinity (b)-BET surface area (current density are normalized by BET) (c)-ECSAs (current density are normalized by ECSAs) (d)-particle size (e)-5d electrons occupation states Firstly it clearly shows that higher crystallinity led to the lower OER activity The smaller sizes or larger surface areas are usually to pursue to enhance catalysts OER activity BET surface area TEM particle size and ECSAs are used for such evaluations However we not find higher OER activity corresponding to large surface area or smaller particle size Comparatively the relationship between the ECSAs of catalyst and its OER activity is more closely related to BET The critical point is the electronic structure of the activated sites10 We use the 5d occupation states to describe this key point because Ir-5d electrons determine its valence states It can clearly find that the filling of the 5d occupation states also not agreement with the OER activity trend but more electrons on 5d states seems better for OER activity

FigS6 The Rietveld refinement of XRD patterns of prepared IrO2 samples The R-factors and errors are shown in each figure

FigS7 (a)-(c) are the fitting results of double Ir-Ir shell in the range of 24-41 Aring The k range is 2-14 Aring (d) The cell parameters of IrO2 prepared at different annealing temperature The variation of ca ratio is consistent with XRD refinements

Fig S8 Fitting results of Ir-O shell for different annealing temperature prepared IrO2 by using IFEFFIT IrO2 fitting parameters are a=b=45051 Aring c=31586 Aring space=P42mnm Ir-O2-c=19604 Aring Ir-O4-c=19988 Aring

Table S2 Results of fitted Ir-O shell in EXAFS by IFEFFIT Sample Scattered

pathaCoordination

numberbDistance (Aring)

Δσ2 (Aring2) R-factor

Un-A Ir-O 6 19905 000485 0000076A-200 Ir-O 6 19887 000720 0000191A-400 Ir-O2-c 2 19314

Ir-O4-c 4 19885 000592 0007975

A-600 Ir-O2-c 2 18933Ir-O4-c 4 19810 000522 0000171

A-800 Ir-O2-c 2 18900Ir-O4-c 4 19820 000518 0000167

Notes a and b indicate the scattered path and coordination number for Un-A and A-200 are amorphous so we think that their Ir-O coordination type just has only one

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

FigS6 The Rietveld refinement of XRD patterns of prepared IrO2 samples The R-factors and errors are shown in each figure

FigS7 (a)-(c) are the fitting results of double Ir-Ir shell in the range of 24-41 Aring The k range is 2-14 Aring (d) The cell parameters of IrO2 prepared at different annealing temperature The variation of ca ratio is consistent with XRD refinements

Fig S8 Fitting results of Ir-O shell for different annealing temperature prepared IrO2 by using IFEFFIT IrO2 fitting parameters are a=b=45051 Aring c=31586 Aring space=P42mnm Ir-O2-c=19604 Aring Ir-O4-c=19988 Aring

Table S2 Results of fitted Ir-O shell in EXAFS by IFEFFIT Sample Scattered

pathaCoordination

numberbDistance (Aring)

Δσ2 (Aring2) R-factor

Un-A Ir-O 6 19905 000485 0000076A-200 Ir-O 6 19887 000720 0000191A-400 Ir-O2-c 2 19314

Ir-O4-c 4 19885 000592 0007975

A-600 Ir-O2-c 2 18933Ir-O4-c 4 19810 000522 0000171

A-800 Ir-O2-c 2 18900Ir-O4-c 4 19820 000518 0000167

Notes a and b indicate the scattered path and coordination number for Un-A and A-200 are amorphous so we think that their Ir-O coordination type just has only one

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

FigS7 (a)-(c) are the fitting results of double Ir-Ir shell in the range of 24-41 Aring The k range is 2-14 Aring (d) The cell parameters of IrO2 prepared at different annealing temperature The variation of ca ratio is consistent with XRD refinements

Fig S8 Fitting results of Ir-O shell for different annealing temperature prepared IrO2 by using IFEFFIT IrO2 fitting parameters are a=b=45051 Aring c=31586 Aring space=P42mnm Ir-O2-c=19604 Aring Ir-O4-c=19988 Aring

Table S2 Results of fitted Ir-O shell in EXAFS by IFEFFIT Sample Scattered

pathaCoordination

numberbDistance (Aring)

Δσ2 (Aring2) R-factor

Un-A Ir-O 6 19905 000485 0000076A-200 Ir-O 6 19887 000720 0000191A-400 Ir-O2-c 2 19314

Ir-O4-c 4 19885 000592 0007975

A-600 Ir-O2-c 2 18933Ir-O4-c 4 19810 000522 0000171

A-800 Ir-O2-c 2 18900Ir-O4-c 4 19820 000518 0000167

Notes a and b indicate the scattered path and coordination number for Un-A and A-200 are amorphous so we think that their Ir-O coordination type just has only one

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

Fig S8 Fitting results of Ir-O shell for different annealing temperature prepared IrO2 by using IFEFFIT IrO2 fitting parameters are a=b=45051 Aring c=31586 Aring space=P42mnm Ir-O2-c=19604 Aring Ir-O4-c=19988 Aring

Table S2 Results of fitted Ir-O shell in EXAFS by IFEFFIT Sample Scattered

pathaCoordination

numberbDistance (Aring)

Δσ2 (Aring2) R-factor

Un-A Ir-O 6 19905 000485 0000076A-200 Ir-O 6 19887 000720 0000191A-400 Ir-O2-c 2 19314

Ir-O4-c 4 19885 000592 0007975

A-600 Ir-O2-c 2 18933Ir-O4-c 4 19810 000522 0000171

A-800 Ir-O2-c 2 18900Ir-O4-c 4 19820 000518 0000167

Notes a and b indicate the scattered path and coordination number for Un-A and A-200 are amorphous so we think that their Ir-O coordination type just has only one

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

Table S2 Results of fitted Ir-O shell in EXAFS by IFEFFIT Sample Scattered

pathaCoordination

numberbDistance (Aring)

Δσ2 (Aring2) R-factor

Un-A Ir-O 6 19905 000485 0000076A-200 Ir-O 6 19887 000720 0000191A-400 Ir-O2-c 2 19314

Ir-O4-c 4 19885 000592 0007975

A-600 Ir-O2-c 2 18933Ir-O4-c 4 19810 000522 0000171

A-800 Ir-O2-c 2 18900Ir-O4-c 4 19820 000518 0000167

Notes a and b indicate the scattered path and coordination number for Un-A and A-200 are amorphous so we think that their Ir-O coordination type just has only one

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

Fig S9 XRD patterns of transition metals doped IrO2 (a)3 The Co-doped a-pyrolyzed-IrO2 b-pyrolyzed-Ir07Co03Ox c-pyrolyzed-IrCo2Ox d-leached-Ir07Co03Ox and (e)-pyrolyzed-Co3O4 (b)4 Ni and (c)5 Cu-doped cases The characteristic diffraction peaks of IrO2 are indicated in the figures We can clearly find that the doping of Co Ni and Cu give rise to a shift to a high angle in the diffraction peak positions with a Miller index (h k l) of l ne 0 Thus the c axis is reduced according to the Bragg equation

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993

References(1) Liang Y Li Y Wang H Zhou J Wang J Regier T Dai H Nat Mater 2011 10 780(2) McCrory C C L Jung S Peters J C Jaramillo T F J Am Chem Soc 2013 135 16977(3) Hu W Zhong H Liang W Chen S ACS applied materials amp interfaces 2014 6 12729(4) Reier T Pawolek Z Cherevko S Bruns M Jones T Teschner D Selve S Bergmann

A Nong H N Schloumlgl R Mayrhofer K J J Strasser P J Am Chem Soc 2015 137 13031

(5) Sun W Song Y Gong X-Q Cao L-m Yang J Chem Sci 2015 6 4993