Influence of Strain on the Surface–Oxygen Interaction and the Oxygen

Article Cite This: J. Phys. Chem. C XXXX, XXX, XXX−XXX

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Influence of Strain on the Surface−Oxygen Interaction and the Oxygen Evolution Reaction of SrIrO3 Ding-Yuan Kuo,† C. John Eom,† Jason K. Kawasaki,‡,§,# Guido Petretto,∥ Jocienne N. Nelson,‡ Geoffroy Hautier,∥ Ethan J. Crumlin,⊥ Kyle M. Shen,‡,§ Darrell G. Schlom,†,§ and Jin Suntivich†,§,* †

Department of Materials Science and Engineering, ‡Laboratory of Atomic and Solid State Physics, and §Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York 14853, United States ∥ Institute of Condensed Matter and Nanosciences (IMCN), Université catholique de Louvain, Louvain-la-Neuve 1348, Belgium ⊥ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States S Supporting Information *

ABSTRACT: Understanding how physicochemical properties of materials affect the oxygen evolution reaction (OER) has enormous scientific and technological implications for the OER electrocatalyst design. We present our investigation on the role of strain on the surface−oxygen interaction and the OER on well-defined single-termination SrIrO3 films. Our approach employs a combination of molecular-beam epitaxy, electrochemical characterizations, ambient-pressure X-ray photoelectron spectroscopy, and density functional theory (DFT). We find that inplane compressive strain weakens the surface oxygen binding strength on SrIrO3; however, it has a negligible effect on the surface oxygen electroadsorption and the OER. We explain this observation, which goes against a commonly held intuition that a change in the surface oxygen binding strength should influence surface oxygen electroadsorption and OER by recognizing that the trend in surface oxygen adsorption measured in the gas phase does not account for the presence of water in the surface oxygen electroadsorption. Inclusions of surface water molecules allow DFT to qualitatively reproduce the electroadsorption trend, highlighting the importance of surface water in the surface−oxygen interaction. Our finding suggests that a commonly held assumption between surface oxygen binding strength (in vacuum, no water) and electroadsorption (requiring water) is not always a simple one-to-one description and calls for a more in-depth investigation on the structure of water at electrochemical interfaces.

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INTRODUCTION

While the surface−oxygen interaction has been recognized to be critical, two critical questions are still open. The first is whether the binding strength between the catalyst’s surface and surface oxygen molecule measured through gas-phase adsorption is sufficient to describe the OER activity trend. The second question is to decipher how the catalysts’ structural parameters affect the surface−oxygen interaction and the OER activity. In this latter question, although a number of structural variables such as surface atomic arrangement13,14 and strain15,16 have been explored, understanding how these parameters affect the surface−oxygen interaction is complicated by the possibility that oxides can respond to structural perturbations in multiple ways. For example, in the oxide perovskite crystal structure (with general formula ABO3), the BO6 octahedra can also tilt and rotate in response to the application of strain or chemical substitutions beyond simple stretching or compressing of the B−O bond.17−20 This study is driven by our interest in establishing the fundamental relationship of strain to the surface−oxygen

Hydrogen generation from water splitting (2H2O → 2H2 + O2) can fulfill a growing need for energy-dense fuels for electric transportation and sustainable feedstock for chemical production.1−3 The water-splitting efficiency is, however, limited by the slow kinetics of the anodic half-cell reaction of the water splitting, viz., the oxygen evolution reaction (OER, alkaline: 4OH− → 2H2O + 4e− + O2).4−6 To overcome this limitation, researchers have examined a number of strategies to develop more active OER catalysts.7−10 Examples include controlling the catalyst’s electronic structure to facilitate the OER intermediate formation by either activating the lattice oxygen11 or creating a surface that is conducive to surface oxygen adsorption.9,12 In all these strategies, the common hypothesis is that the surface oxygen species (e.g., OHad, Oad, and OOHad) are the OER intermediates and that their formation energetics determine the pathway and the efficacy of the OER.4,9 In this picture, a parameter describing the binding strength between the catalyst’s surface and surface oxygen species can describe the OER activity trend because all the oxygen intermediates have the same primary metal−oxygen bonding, a principle known as the “scaling relation”.5 © XXXX American Chemical Society

Received: December 7, 2017 Revised: February 7, 2018 Published: February 7, 2018 A

DOI: 10.1021/acs.jpcc.7b12081 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry C interaction and to the OER catalysis. While Stoerzinger et al.15 and Petrie et al.16 have shown the influence of strain on the OER of perovskites (e.g., LaCoO3 and LaNiO 3), the connection between the strain and the surface−oxygen interaction is still elusive. Our approaches address this knowledge gap by (1) measuring the surface oxygen binding strength via ambient-pressure X-ray photoelectron spectroscopy (APXPS) in gas phase and (2) examining the electroadsorption of oxygen species via electrochemical characterization in the aqueous phase. The surface redox corresponding to the oxidation process of adsorbed water (e.g., H2O → OHad + H+ + e−) can provide information on the strength of the surface−oxygen interaction. We evaluate how strain impacts this surface redox to understand the impact of strain on the surface oxygen binding strength and electroadsorption of oxygen species and consequently the OER on SrIrO3. The influences of strain on the surface−oxygen interaction are crossexamined between the APXPS, the density functional theory (DFT), and the electrochemical measurement results. The introduction of the biaxial strain on SrIrO3, our model catalyst, is achieved by using molecular-beam epitaxy (MBE),21 to grow thin, commensurately strained SrIrO3 films on substrates selected to impose specific biaxial strain values. This approach allows us to evaluate the effect of strain without changing chemical compositions.22 SrIrO3 is one of the most active OER catalysts in acid and alkaline.14,21 We focus on alkaline environments for the present study to avoid the loss of Sr2+ to maintain a fair comparison to DFT.21

and edges of samples were covered with a nonconductive epoxy (OMEGABOND 101) except for the SrIrO3 films. A threeelectrode glass cell (Pine) with a potentiostat (Bio-Logic) was used for all electrochemical characterizations. The reference electrode was an Ag/AgCl electrode (Pine), calibrated to the H2 redox. A Pt wire was used as a counter electrode. All the potentials in this study were resistance-corrected potentials. The electrolyte/cell resistance was obtained from an impedance measurement by using the high-frequency intercept of the real resistance. All electrochemical characterizations were tested in 0.1 M potassium hydroxide (KOH) solution prepared by dissolving KOH pellets (99.99% purity, Sigma-Aldrich) in deionized water (18.2 MΩ cm). We first conducted cyclic voltammetry (CV) in Ar-saturated electrolytes with a 200 mV/s scan rate to investigate surface adsorption. The OER activity was measured in O2-saturated electrolytes with a 10 mV/s scan rate to reduce the capacitance current. Capacitance-free CV curves were obtained by averaging the forward and backward scans. Ambient-Pressure X-ray Photoelectron Spectroscopy. APXPS24 measurements were collected at Beamline 9.3.2 at the Advanced Light Source of the Lawrence Berkeley National Laboratory. All samples were initially brought up and held at 200 °C at 100 mTorr pO2 for 30 min to remove organics adsorbed to the sample surface. This cleaning process was monitored via the C 1s spectra. The excitation energy was tuned to 650 eV for both the O 1s spectra and its respective valence band spectra. O 1s XPS peaks were calibrated to the lower-energy edge of their respective valence band, which was assigned to be at 0 eV for samples and pO2. Calibrations have an error of ±0.1 eV, and a Shirley background correction was used for all spectra. Computation. All of the simulations were performed in the framework of DFT, using the VASP code within the projectoraugmented wave methodology.25−27 The Perdew−Burke− Ernzerhof28 was used as semilocal exchange−correlation functional. The adsorption energies were obtained considering the different adsorbates on the top of a SrIrO3 slab, whereas the overpotential was calculated according to the model proposed by Nørskov and co-workers.9 The surfaces have been modeled considering a stoichiometric slab of SrIrO3 as shown in Figure 2C, considering a 2 × 1 supercell in the x−y plane, leaving 2 equiv adsorption sites on the top of the surface. A vacuum of approximately 12 Å and a dipolar correction along the z direction have been introduced to reduce the interaction between periodic replica of the slab. The Brillouin zone has been sampled using a 6 × 6 × 1 k-point grid. For the unstrained system, the lattice parameters parallel to the surface have been kept fixed to the relaxed bulk values, and the position of the atoms has been relaxed until all of the forces were lower than 0.02 eV/Å. The strained surfaces have been obtained by scaling the lattice parameters of the initial supercell and keeping the size of the supercell fixed during the relaxation (see the Supporting Information for details).

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EXPERIMENTAL AND THEORETICAL METHODS MBE Synthesis. SrIrO3(001)p films (40 formula-units thick) (where the subscript p denotes the pseudocubic orientation) were grown by MBE on single-crystal DyScO3(110) (DSO) and (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7(001) (LSAT) at the distilled ozone oxidant pressure of 10−6 Torr and a substrate temperature of 650 °C as measured by a thermocouple. The flux of iridium was initially calibrated using a quartz crystal microbalance. By using X-ray diffraction (XRD, Rigaku SmartLab) (Figure 1) and in situ reflection high-energy electron diffraction (RHEED),23 the as-grown films were confirmed to be epitaxial. Electrochemical Characterization. Electrical contacts were made by following the same protocol as reported previously.21 Titanium wires were attached to SrIrO3 films using silver paint (Ted Pella, Leitsilber 200), and the backside

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RESULTS AND DISCUSSION Figure 1 shows the θ−2θ XRD scans for SrIrO3/DSO (∼0% inplane strain) and SrIrO3/LSAT (−1.9% biaxial strain). The clear thickness fringes indicate a smooth surface for SrIrO3 grown on either substrate, which were also monitored using RHEED patterns during MBE deposition. The structural quality of the SrIrO3 films was additionally verified using other characterization techniques (e.g., synchrotron X-ray, low-

Figure 1. θ−2θ XRD scans of SrIrO3 films grown on DSO (blue) and LSAT (red) substrates. The labeled (*) sharp peaks indicate diffraction from the substrates. B

DOI: 10.1021/acs.jpcc.7b12081 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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Figure 2. (A) APXPS for O 1s of the SrIrO3 film on DSO (top) and on LSAT (bottom) under oxygen pressures of 1 μTorr (left) and 100 mTorr (right) at room temperature. Black circles: experimental data; navy line: lattice O 1s; orange line: surface O 1s; green line: sum of the fits; y-axis: normalized intensity; x-axis: binding energy. (B) Strain-dependent Oad adsorption energies of SrIrO3 from our DFT calculations. (C) Oad adsorption models for our DFT calculations. Yellow, red, and green spheres represent Ir, O, and Sr atoms, respectively.

Figure 3. (A) CV of SrIrO3(001) on DSO (blue) and on LSAT (red) in Ar-saturated 0.1 M KOH at 200 mV/s. (B) CV of SrIrO3(001) in O2saturated 0.1 M KOH at 10 mV/s. (C) Tafel plot for the OER kinetics of SrIrO3(001) on different substrates.

strained SrIrO3/LSAT (from ∼49 to ∼48%). This observation implies a weakened surface oxygen binding strength on the strained SrIrO3/LSAT in comparison to SrIrO3/DSO. To verify the oxygen adsorption trend, we used APXPS to measure the O 1s spectra of the SrIrO3 films at 250 °C. In comparison to room-temperature measurements, we find that the relative intensity of the surface O decreases by ∼24.3% on SrIrO3/ LSAT and ∼18.4% on SrIrO3/DSO at 250 °C, providing further support for the weakened surface oxygen affinity of SrIrO3/LSAT (Figure S1). We apply DFT to examine the effect of strain (see the Supporting Information for calculation details). DFT calculations indicate that SrIrO3 initially responds to a compressive biaxial strain by tilting the IrO6 octahedra. This tilting response has no effect on the oxygen adsorption until higher compressive strain (over −1%), where tilting stops (Figure 2B) and further compression instead results in the elongation of the top-layer out-of-plane Ir−O bond. This out-of-plane Ir−O bond elongation leads to the weakening of the surface oxygen adsorption (Figure 2C). Our DFT calculation shows that the difference of O adsorption energy between strained (−2%) and unstrained SrIrO3 is about 0.5 eV. This trend is in qualitative agreement with APXPS, which shows weakened oxygen adsorption for SrIrO3/LSAT (−1.9%) in comparison to SrIrO3/DSO (∼0%).

energy electron diffraction, angle-resolved photoelectron spectroscopy, and transport measurements).23 To probe the surface oxygen binding strength of SrIrO3, we use APXPS24 to measure the oxygen partial pressure dependence of the O 1s spectra on the SrIrO3 films. Our experiment uses a 650 eV incident beam energy, at which the inelastic mean free path of photoelectrons is ∼6 Å, to obtain the surface information. Figure 2A shows the O 1s spectra of SrIrO3/DSO and SrIrO3/LSAT at pO2 of 10−6 and 10−1 Torr at room temperature, respectively. We analyzed both spectra as doublets: the lower binding energy is assigned to the bulk (lattice) oxygen and the higher binding energy to the surface oxygen,29,30 where the lattice oxygen is O2− in the SrIrO3 perovskite and the surface oxygen is the oxygen species in the top most layer including the adsorbed O. Our APXPS results reveal two major observations. First, the surface O peak of SrIrO3/LSAT shifts 0.4 eV lower in binding energy in comparison to SrIrO3/DSO with respect to the bulk lattice oxygen peak. We attribute this shift to the surface Ir−O bond length change in the compressively strained SrIrO3/ LSAT,31 which reduces the exchange interaction, consequently increasing the local charge on the surface oxygen. Second, we observe that the surface oxygen component increases with higher pO2 only for the near-zero-strained SrIrO3/DSO (from ∼48 to ∼52%) but does not change for the compressively C

DOI: 10.1021/acs.jpcc.7b12081 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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Figure 4. (A) Calculated free energies of the OER intermediates on SrIrO3/DSO (blue) and SrIrO3/LSAT (red): solid line at 1.23 V vs RHE, dashed line at 0 V vs RHE, dotted line for the minimum potential, where the thermodynamic overpotentials are downhill. Calculations assume 100% adsorbate coverage using a surface with adsorbed water as the initial state. (B) Surface adsorption phase diagram from our DFT calculation (see Figures S4 and S5).

(defined as the minimum overpotential required to bring all of the elementary steps downhill, Figure 4A) of SrIrO3/LSAT and SrIrO3/DSO are similar. Notably, the minimum overpotentials are 0.68 and 0.66 V for unstrained and strained SrIrO3, respectively. With the electroadsorption and the OER trend reproduced, we now use DFT calculations to model the oxygen electroadsorption features on SrIrO3 from CV experiments. We consider the possibility of a half-covered surface. This model reveals a wide potential window of the surface half covered by the water and the other half covered by the OHad, implying two steps of OH electroadsorption (Figure 4B). We calculate the average number of transferred electrons per Ir on the surface by integrating the area underneath the CVs to be 2.68 and 2.64 for SrIrO3/DSO and SrIrO3/LSAT, respectively (Figure S2). Given the approximate value of 2e− per Ir from the electroadsorption and our DFT calculation, we assign the first two adsorption peaks to the OHad electroadsorption (H2Oad + OH− → OHad + H2O + e−, ∼0.6 V vs RHE) and the third to Oad electroadsorption (OHad + OH− → Oad + H2O + e−, ∼1.4 V vs RHE) on SrIrO3 (see the Supporting Information for details). Our integrated CVs show a similar adsorption isotherm on strained and unstrained SrIrO3(001) (Figure S3). The number of electron transferred per Ir on the surface is close to 1 in the potential window from 0.3 to 1.25 V, which supports our assignment that the first two peaks are OH electroadsorption. Our adsorption energy measurement on SrIrO3 affords a comparison between the OHad and Oad adsorption energy on SrIrO3(001) and IrO2(110), respectively, the latter of which was extracted from our previous work.12 As shown in Figure 5, the scaling relation, which predicts a linear

With both APXPS and DFT results indicating the weakened oxygen adsorption on SrIrO3/LSAT over SrIrO3/DSO, we next examine whether the oxygen electroadsorption follows the same trend. Our CV of the single-crystal SrIrO3(001) in 0.1 M KOH shows the influence of strain on electroadsorption of oxygen species (i.e., pseudocapacitance)32 and the OER of SrIrO3 in Figure 3. The correlation between pseudocapacitance and the OER catalysis has been observed mostly on polycrystalline and amorphous OER catalysts.33−37 However, the connection between pseudocapacitance and the molecular mechanism of OER remains to be elucidated for two main reasons. (1) The electroadsorption of intermediates in pseudocapacitance of those materials cannot be assigned to a specific facet. (2) In most cases, they are also irreversible causing difficulty in distinguishing between thermodynamics and kinetics of the electroadsorption processes. Instead, we observe three quasireversible electroadsorption peaks on both SrIrO3/LSAT and SrIrO3/DSO. The first adsorption peaks occur around the same potential (0.6 V vs reversible hydrogen electrode (RHE)) on both films, whereas the second peak potential is ∼0.08 V lower for SrIrO3/LSAT than for SrIrO3/DSO (1.0 V vs RHE, Figure 3A). The third adsorption peak (1.4 V vs RHE, Figure 3B) only shows a minor difference. Our CVs of the single-crystal SrIrO3 reveal that strain does not have a significant effect on those electroadsorption peaks. Additionally, we find that strain does not significantly alter the OER kinetics on SrIrO3 (Figure 3C). This observation is in contrast with LaNiO3, where lattice compression has been shown to benefit its activity.16 We find that the compressive strain weakens the surface oxygen binding strength, but it has negligible effects on the OER and the electroadsorption of oxygen species. We hypothesize that the difference in the strain influence between the adsorption and electroadsorption is due to the difference in the starting surface, pristine surface for adsorption, and watercovered surface for electroadsorption. Because of the polar surface, many oxide surfaces are covered with water.38 We build on this hypothesis and adjust the DFT model to include adsorbed water as the initial state (Figure 4A). Note that we are not modeling the effect of the full water solvent on top of the surface. Instead, we only saturate the transition metal sites with H2O molecules and show that this simple model already captures an essential part of the physics and chemistry at play. The model shows that the presence of surface water neutralizes the influence of strain on the O adsorption energy, reducing the effect of strain on the elongation of the top-layer Ir−O bond (Figure 2C). We further extend this assumption to calculate the OER intermediate energetics (OHad, Oad, and OOHad). Our DFT calculation suggests that the theoretical OER activities

Figure 5. Experimentally measured adsorption energies of Oad and OHad on SrIrO3(001)p and IrO2(110), respectively. The adsorption energies on IrO2(110) extracted at different pHs are reproduced from ref 12. D

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The Journal of Physical Chemistry C relationship between OHad and Oad, is satisfied even when both IrO2(110) and SrIrO3(001) results are included on the same plot, suggesting that both rutile and perovskite iridates fall in the same scaling relation line. The remarkable agreement between the surface electroadsorption trend, potential, and activity implies that surface water plays an important role in the surface−oxygen interaction.39,40 An attempt to use the surface−oxygen interaction values from gas-phase measurements and DFT calculations without considering the presence of water molecule will cause an error in the electroadsorption and consequently the OER analysis. We point out that there could be a secondary effect stemming from the adsorbate’s interaction with nearsurface water molecules41 as well, for example, by the electric field at the interface and solvent effect, neither of which are included in our model. Previous computational study has shown that the adsorption energy of oxygen species varies in different solvents by considering solvation in the DFT calculation.42 We note that the actual surface structure of SrIrO3 under the electrochemical conditions may contain a range of water structures, including dissociated OHad and Had.43 The complexity of the interfacial structure is evident in the activity analysis: while we can accurately capture the surface energetics and the OER trend between SrIrO3/DSO and SrIrO3/LSAT, why SrIrO3 is significantly more active than IrO2 is still an open question. Finally, we note that we cannot eliminate the possibility that the SrIrO3 surface reconstructs when it is immersed in liquid water. In situ surface X-ray scattering previously revealed that SrTiO3(001) reconstructs in aqueous electrolytes.44 Future studies using in situ structural probes to identify the interfacial water structure in electrochemical interfaces are essential to gain more in-depth insights into the OER reactivity of SrIrO3.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Geoffroy Hautier: 0000-0003-1754-2220 Ethan J. Crumlin: 0000-0003-3132-190X Jin Suntivich: 0000-0002-3427-4363 Present Address #

Department of Materials Science and Engineering, University of Wisconsin−Madison, Madison, WI 53706, USA (J.K.K.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Amit Bhatia and Runbang Tang for their help with the X-ray measurements at the Advanced Light Source. This material is based upon the work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DE-SC-SC0018029. This work made use of the Cornell Center for Materials Research (CCMR) Shared Facilities, which are supported through the NSF MRSEC program (DMR-1120296). The Advanced Light Source is supported by the Director, Office of Basic Energy Sciences, of the U.S. Department of Energy under contract no. DE-AC02-05CH11231. D.-Y.K. is grateful for the support from the Taiwan Government Scholarship to Study Abroad. J.K.K. acknowledges the support from the Kavli Institute at Cornell for Nanoscience Science. J.N.N. acknowledges the support from the NSF Graduate Research Fellowship under grant no. DGE-1650441. This work was performed in part at the Cornell NanoScale Facility (CNF), a member of the National Nanotechnology Infrastructure Network, which is supported by the NSF (grant ECCS-0335765). Computational resources were provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifique de Belgique (F.R.S.-FNRS) under grant 2.5020.11. This work was supported by the Fonds de la Recherche Scientifique-FNRS under grant(s) no. 29120589.

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CONCLUSIONS In summary, we demonstrate that the compressive strain can weaken the surface oxygen binding strength on SrIrO3 but only after SrIrO3 can no longer respond to the compressive strain beyond octahedra tilting. However, despite affecting the surface oxygen binding strength, compressive strain does not influence the oxygen electroadsorption nor positively affect the OER activity. We attribute this observation to the presence of the surface adsorbed water, which neutralizes the impact of strain, a conclusion we reach by benchmarking the DFT model to the surface electroadsorption measurements. Our work points to the need to account for the surface-adsorbed water in the design of future catalysts, which can be examined on by combining well-defined surfaces and in situ studies. Understanding of the interfacial structure including water on electrified surfaces will be essential for the fundamental understanding of how an oxide electrocatalyst functions. Without detailed, careful experiments to assess the structure of the oxide−water interface to understand the interplay between the surface adsorption, coverage, and OER, a measurement or calculation of the surface oxygen adsorption without considering water may not correctly reflect the catalyst’s surface during electrochemistry.

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DFT computational details, adsorption energy analysis, high-temperature APXPS results, charge-transfer density, integrated CVs, DFT calculations of surface phase diagram, free energy of surface adsorbate states, energy relation of OHad and Oad, and fit parameters for the O 1s peak analysis (PDF)

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REFERENCES

(1) Cook, T. R.; Dogutan, D. K.; Reece, S. Y.; Surendranath, Y.; Teets, T. S.; Nocera, D. G. Solar Energy Supply and Storage for the Legacy and Nonlegacy Worlds. Chem. Rev. 2010, 110, 6474−6502. (2) Wagner, F. T.; Lakshmanan, B.; Mathias, M. F. Electrochemistry and the Future of the Automobile. J. Phys. Chem. Lett. 2010, 1, 2204− 2219. (3) Walter, M. G.; Warren, E. L.; McKone, J. R.; Boettcher, S. W.; Mi, Q.; Santori, E. A.; Lewis, N. S. Solar Water Splitting Cells. Chem. Rev. 2010, 110, 6446−6473. (4) Koper, M. T. M. Thermodynamic Theory of Multi-Electron Transfer Reactions: Implications for Electrocatalysis. J. Electroanal. Chem. 2011, 660, 254−260. (5) Rossmeisl, J.; Qu, Z.-W.; Zhu, H.; Kroes, G.-J.; Nørskov, J. K. Electrolysis of Water on Oxide Surfaces. J. Electroanal. Chem. 2007, 607, 83−89.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.7b12081. E

DOI: 10.1021/acs.jpcc.7b12081 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry C (6) Bernt, M.; Gasteiger, H. A. Influence of Ionomer Content in IrO2/TiO2 Electrodes on PEM Water Electrolyzer Performance. J. Electrochem. Soc. 2016, 163, F3179−F3189. (7) Trasatti, S. Electrocatalysis by oxidesattempt at a unifying approach. J. Electroanal. Chem. 1980, 111, 125−131. (8) Bockris, J. O.; Otagawa, T. The Electrocatalysis of Oxygen Evolution on Perovskites. J. Electrochem. Soc. 1984, 131, 290−302. (9) Man, I. C.; Su, H.-Y.; Calle-Vallejo, F.; Hansen, H. A.; Martínez, J. I.; Inoglu, N. G.; Kitchin, J.; Jaramillo, T. F.; Nørskov, J. K.; Rossmeisl, J. Universality in Oxygen Evolution Electrocatalysis on Oxide Surfaces. ChemCatChem 2011, 3, 1159−1165. (10) Fabbri, E.; Habereder, A.; Waltar, K.; Kötz, R.; Schmidt, T. J. Developments and Perspectives of Oxide-Based Catalysts for the Oxygen Evolution Reaction. Catal. Sci. Technol. 2014, 4, 3800−3821. (11) Grimaud, A.; Diaz-Morales, O.; Han, B.; Hong, W. T.; Lee, Y.L.; Giordano, L.; Stoerzinger, K. A.; Koper, M. T. M.; Shao-Horn, Y. Activating Lattice Oxygen Redox Reactions in Metal Oxides to Catalyse Oxygen Evolution. Nat. Chem. 2017, 9, 457−465. (12) Kuo, D.-Y.; Kawasaki, J. K.; Nelson, J. N.; Kloppenburg, J.; Hautier, G.; Shen, K. M.; Schlom, D. G.; Suntivich, J. Influence of Surface Adsorption on the Oxygen Evolution Reaction on IrO2(110). J. Am. Chem. Soc. 2017, 139, 3473−3479. (13) Mefford, J. T.; Rong, X.; Abakumov, A. M.; Hardin, W. G.; Dai, S.; Kolpak, A. M.; Johnston, K. P.; Stevenson, K. J. Water Electrolysis on La1−xSrxCoO3−δ Perovskite Electrocatalysts. Nat. Commun. 2016, 7, 11053. (14) Seitz, L. C.; Dickens, C. F.; Nishio, K.; Hikita, Y.; Montoya, J.; Doyle, A.; Kirk, C.; Vojvodic, A.; Hwang, H. Y.; Norskov, J. K.; et al. A Highly Active and Stable IrOx/SrIrO3 Catalyst for the Oxygen Evolution Reaction. Science 2016, 353, 1011−1014. (15) Stoerzinger, K. A.; Seok Choi, W.; Jeen, H.; Lee, H. N.; ShaoHorn, Y. Role of Strain and Conductivity in Oxygen Electrocatalysis on LaCoO3 Thin Films. J. Phys. Chem. Lett. 2015, 6, 487−492. (16) Petrie, J. R.; Cooper, V. R.; Freeland, J. W.; Meyer, T. L.; Zhang, Z.; Lutterman, D. A.; Lee, H. N. Enhanced Bifunctional Oxygen Catalysis in Strained LaNiO3 Perovskites. J. Am. Chem. Soc. 2016, 138, 2488−2491. (17) Vailionis, A.; Boschker, H.; Siemons, W.; Houwman, E. P.; Blank, D. H. A.; Rijnders, G.; Koster, G. Misfit Strain Accommodation in Epitaxial ABO3 Perovskites: Lattice Rotations and Lattice Modulations. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 064101. (18) May, S. J.; Kim, J.-W.; Rondinelli, J. M.; Karapetrova, E.; Spaldin, N. A.; Bhattacharya, A.; Ryan, P. J. Quantifying Octahedral Rotations in Strained Perovskite Oxide Films. Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 82, 014110. (19) Gruenewald, J. H.; Nichols, J.; Terzic, J.; Cao, G.; Brill, J. W.; Seo, S. S. A. Compressive strain-induced metal−insulator transition in orthorhombic SrIrO3 thin films. J. Mater. Res. 2014, 29, 2491−2496. (20) García-Muñ oz, J. L.; Rodríguez-Carvajal, J.; Lacorre, P.; Torrance, J. B. Neutron-diffraction study of RNiO 3 (R = La,Pr,Nd,Sm): Electronically induced structural changes across the metal-insulator transition. Phys. Rev. B: Condens. Matter Mater. Phys. 1992, 46, 4414−4425. (21) Tang, R.; Nie, Y.; Kawasaki, J. K.; Kuo, D.-Y.; Petretto, G.; Hautier, G.; Rignanese, G.-M.; Shen, K. M.; Schlom, D. G.; Suntivich, J. Oxygen Evolution Reaction Electrocatalysis on SrIrO3 Grown Using Molecular Beam Epitaxy. J. Mater. Chem. A 2016, 4, 6831−6836. (22) Schlom, D. G.; Chen, L.-Q.; Pan, X.; Schmehl, A.; Zurbuchen, M. A. A Thin Film Approach to Engineering Functionality into Oxides. J. Am. Ceram. Soc. 2008, 91, 2429−2454. (23) Nie, Y. F.; King, P. D. C.; Kim, C. H.; Uchida, M.; Wei, H. I.; Faeth, B. D.; Ruf, J. P.; Ruff, J. P. C.; Xie, L.; Pan, X.; et al. Interplay of Spin-Orbit Interactions, Dimensionality, and Octahedral Rotations in Semimetallic SrIrO3. Phys. Rev. Lett. 2015, 114, 016401. (24) Grass, M. E.; Karlsson, P. G.; Aksoy, F.; Lundqvist, M.; Wannberg, B.; Mun, B. S.; Hussain, Z.; Liu, Z. New Ambient Pressure Photoemission Endstation at Advanced Light Source Beamline 9.3.2. Rev. Sci. Instrum. 2010, 81, 053106.

(25) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169−11186. (26) Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method. Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 59, 1758−1775. (27) Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 50, 17953−17979. (28) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865−3868. (29) Crumlin, E. J.; Mutoro, E.; Liu, Z.; Grass, M. E.; Biegalski, M. D.; Lee, Y.-L.; Morgan, D.; Christen, H. M.; Bluhm, H.; Shao-Horn, Y. Surface Strontium Enrichment on Highly Active Perovskites for Oxygen Electrocatalysis in Solid Oxide Fuel Cells. Energy Environ. Sci. 2012, 5, 6081−6088. (30) Mutoro, E.; Crumlin, E. J.; Biegalski, M. D.; Christen, H. M.; Shao-Horn, Y. Enhanced Oxygen Reduction Activity on SurfaceDecorated Perovskite Thin Films for Solid Oxide Fuel Cells. Energy Environ. Sci. 2011, 4, 3689−3696. (31) Biswas, A.; Kim, K.-S.; Jeong, Y. H. Metal Insulator Transitions in Perovskite SrIrO3 Thin Films. J. Appl. Phys. 2014, 116, 213704. (32) Conway, B. E.; Gileadi, E. Kinetic Theory of PseudoCapacitance and Electrode Reactions at Appreciable Surface Coverage. Trans. Faraday Soc. 1962, 58, 2493−2509. (33) Hu, H.; Guan, B.; Xia, B.; Lou, X. W. Designed Formation of Co3O4/NiCo2O4 Double-Shelled Nanocages with Enhanced Pseudocapacitive and Electrocatalytic Properties. J. Am. Chem. Soc. 2015, 137, 5590−5595. (34) Conway, B. E.; Liu, T. Experimental Evaluation of Adsorption Behaviour of Intermediates in Anodic Oxygen Evolution at Oxidized Nickel Surfaces. J. Chem. Soc., Faraday Trans. 1 1987, 83, 1063−1079. (35) Liu, T.-C.; Conway, B. E. Evaluation of Electroactive Intermediate States in Anodic O2 Evolution at Chemically Formed Nickel Oxide: Comparison with Behaviour at Nickel Metal Anodes. J. Appl. Electrochem. 1987, 17, 983−996. (36) Bernicke, M.; Ortel, E.; Reier, T.; Bergmann, A.; de Araujo, J. F.; Strasser, P.; Kraehnert, R. Iridium Oxide Coatings with Templated Porosity as Highly Active Oxygen Evolution Catalysts: StructureActivity Relationships. ChemSusChem 2015, 8, 1908−1915. (37) Ortel, E.; Reier, T.; Strasser, P.; Kraehnert, R. Mesoporous IrO2 Films Templated by PEO-PB-PEO Block-Copolymers: Self-Assembly, Crystallization Behavior, and Electrocatalytic Performance. Chem. Mater. 2011, 23, 3201−3209. (38) Mu, R.; Zhao, Z.-j.; Dohnálek, Z.; Gong, J. Structural Motifs of Water on Metal Oxide Surfaces. Chem. Soc. Rev. 2017, 46, 1785−1806. (39) Su, H.-Y.; Gorlin, Y.; Man, I. C.; Calle-Vallejo, F.; Nørskov, J. K.; Jaramillo, T. F.; Rossmeisl, J. Identifying Active Surface Phases for Metal Oxide Electrocatalysts: A Study of Manganese Oxide BiFunctional Catalysts for Oxygen Reduction and Water Oxidation Catalysis. Phys. Chem. Chem. Phys. 2012, 14, 14010−14022. (40) Diaz-Morales, O.; Ledezma-Yanez, I.; Koper, M. T. M.; CalleVallejo, F. Guidelines for the Rational Design of Ni-Based Double Hydroxide Electrocatalysts for the Oxygen Evolution Reaction. ACS Catal. 2015, 5, 5380−5387. (41) Henderson, M. A. The Interaction of Water with Solid Surfaces: Fundamental Aspects Revisited. Surf. Sci. Rep. 2002, 46, 1−308. (42) Calle-Vallejo, F.; Krabbe, A.; García-Lastra, J. M. How Covalence Breaks Adsorption-Energy Scaling Relations and Solvation Restores Them. Chem. Sci. 2017, 8, 124−130. (43) Halwidl, D.; Stöger, B.; Mayr-Schmölzer, W.; Pavelec, J.; Fobes, D.; Peng, J.; Mao, Z.; Parkinson, G. S.; Schmid, M.; Mittendorfer, F.; et al. Adsorption of Water at the SrO Surface of Ruthenates. Nat. Mater. 2015, 15, 450−455. (44) Plaza, M.; Huang, X.; Ko, J. Y. P.; Shen, M.; Simpson, B. H.; Rodríguez-López, J.; Ritzert, N. L.; Letchworth-Weaver, K.; Gunceler, D.; Schlom, D. G.; et al. Structure of the Photo-Catalytically Active Surface of SrTiO3. J. Am. Chem. Soc. 2016, 138, 7816−7819.

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DOI: 10.1021/acs.jpcc.7b12081 J. Phys. Chem. C XXXX, XXX, XXX−XXX