A Perovskite Electronic Structure Descriptor for Electrochemical CO2

Subscriber access provided by University of Glasgow Library

C: Surfaces, Interfaces, Porous Materials, and Catalysis

A Perovskite Electronic Structure Descriptor for Electrochemical CO Reduction and the Competing H Evolution Reaction 2

2

Jonathan Hwang, Karthik Akkiraju, Juan Corchado-García, and Yang Shao-Horn J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b04120 • Publication Date (Web): 03 Sep 2019 Downloaded from pubs.acs.org on September 3, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

A Perovskite Electronic Structure Descriptor for Electrochemical CO2 Reduction and the Competing H2 Evolution Reaction Authors: Jonathan Hwang1, Karthik Akkiraju1, Juan Corchado-García2, Yang Shao-Horn1,2,3,* 1 Department

of Materials Science and Engineering, 2Research Laboratory of Electronics, 3Department

of Mechanical Engineering,

Massachusetts Institute of Technology, Cambridge, MA, USA

Corresponding Authors Email: [email protected]

1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract The electrochemical reduction of CO2 (CO2RR) to high-value products is an attractive means to simultaneously address the negative effects of increasing CO2 emissions and the ever-present societal demand for chemicals and fuels. However, the rational development of novel catalyst chemistries for this reaction is needed to tune the activity and selectivity of the CO2RR, especially for increasingly complex chemistries such as oxides, sulfides, and phosphides. In this work, we explore a diverse chemical range of transition metal perovskite oxides (ABO3) by determining their surface binding energies towards COads and Hads using density functional theory (DFT) and by evaluating their CO2RR activity and selectivity. We find that tuning perovskite chemistry results in the ability to electrochemically reduce CO2 to CH4. We propose the O 2p-band center as a rational design parameter that faithfully captures the energetics of Hads and COads binding that influence hydrogen evolution reaction (HER) and CO2RR activity. A higher O 2p-band center results in higher HER activity while an intermediate O 2p-band center improves favorability for CH4 evolution. In the process, we identify a group of perovskites (i.e. LaCoO3, GdCoO3, NdCoO3) as chemistries that have not, to date, been reported previously for CH4 evolution activity at relatively low overpotentials (-0.6 to -0.8 VRHE). Introduction The mitigation of CO2 emissions in the 21st century remains one of the current grand scientific challenges, requiring innovative novel technologies that convert CO2 into chemical and fuels for energy storage.1 Electrochemical CO2 reduction (CO2RR) has emerged as a promising technology to address this challenge;2-3 yet despite its promise, its widespread employment has been hampered by the lack of available active and selective catalysts for electrocatalytic

2


Page 2 of 28

Page 3 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


conversion of CO2 to the targeted product of interest.4-5 As a result, designing and engineering CO2 reduction catalysts remains paramount to advancing such technologies. Thus far, researchers have significantly focused on metal CO2RR catalysts, beginning with the work of Hori and co-workers,6-7 which have experimentally shown that metals could be grouped into distinct families based on their selectivity toward reaction products during CO2RR: H2 (Ni, Fe, Pt, Ti); HCOOH (Pb, Hg, In, Sn, Cd, Tl); CO (Au, Ag, Zn, Pd, Ga); CH4 and higher order products (Cu). Recently, Rossmeisl et. al. have employed a statistical classification approach to identify COads and Hads surface binding energy, or free energy change of adsorption, as key descriptors to distinguish the selectivity of metals towards H2 (HER), CO, HCOOH, and CH4 (i.e. greater than 2 e- products).8 Both Hads and COads are strong descriptors to distinguish between H2 evolution (strong Hads and strong COads binding), CO evolution (intermediate Hads binding, weak COads binding) and HCOOH formation (weak Hads binding, weak COads binding).8 Further, a combination of intermediate Hads binding energy and intermediate COads binding energy, such that the catalyst favors COads coverage over Hads coverage, promotes the formation of higher order products such as methane or methanol.8 The fact that Hads and COads binding could explain trends in CO2RR selectivity aligns with the mechanistic rationale developed by Nørskov and coworkers.9-10 The strength of COads binding dictates how poisoned the surface is with COads to inhibit further reduction of CO2RR reaction intermediates under strong COads binding (H2-forming group) or how easily COads/HCOOHads desorbs from the surface upon their formation under weak COads binding (CO and HCOOH forming group).8

These insights have been probed

experimentally with surface-enhanced infrared absorption spectroscopy (SEIRAS) that show COads poisoning and easy desorption of COads on Pt and Au surfaces, respectively, under CO2RR conditions.11 Increasing Hads binding enhances the favorability of greater Hads coverage and HER

3



evolution, which also influences the degree to which direct protonation of adsorbed CO2 to form HCOOH is favored.8 The described rationale illuminates why Cu with a relatively intermediate COads and Hads binding energy currently stands alone among monometallic metals as having high product selectivity towards methane and higher order products7, 12 through oxygenated reaction intermediates such as C-bound (HCOads) and O-bound (OCH3,ads, OC2H5,ads) species.11 Such insights have paved the way for researchers to design and discover novel chemistries with tunable activity and selectivity for the CO2RR. In the class of monometallic catalysts, a roughly positive correlation between Hads and COads binding energies is observed, which can be attributed to adsorbate scaling relations on monometallic chemistries.13-15 To overcome these constraints and engineer higher activity catalysts with selectivity towards higher order products (> 2e- transferred), researchers have sought to explore previously uninvestigated CO2RR catalysts with the possibility of inducing distinctive adsorbate binding configurations not possible on monometallic surfaces.16 For instance, the influence of surface geometry and electronic structure of MxLy (M = metal, L = ligand) compounds leads to metal carbides exhibiting weaker carbon binding relative to their parent metal17 while metal sulfides can stabilize CHOads on sulfur sites and adsorb COads on metal sites.18 These effects on surface energetics explain the ability of Mo2C catalysts to produce CH4 (~0.1% FE)19 or MoS2 to form n-propanol (~3.5% FE).20 Similarly, investigation of Fe(Mn)-N-C and Ni2P chemistries found that these chemistries could catalyze the formation of methane (~0.2-0.4% FE)21 or methylglyoxal and 2,3-furandiol (~70% FE).22 Based on the ongoing success with MxLy materials systems for electrocatalyzing CO2RR, we leverage the perovskite structural family (ABO3), previously explored extensively for oxygen reduction reaction, oxygen evolution reaction and CO oxidation, to guide the materials search for active CO2 reduction catalysts selective towards high-energy density chemicals in oxide materials.

4


Page 4 of 28

Page 5 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Perovskites can accommodate nearly all possible cations from the periodic table onto the A and B sites while maintaining the same structural motif,23 allowing for systematic studies of chemical and electronic effects on catalytic properties, while minimizing surface structural effects.24-25 This potential for chemical flexibility has motivated investigations into perovskite-type metal oxide chemistries, primarily strontium-substituted cuprates, as catalysts for CO2RR in alkaline electrolyte, where methanol, ethanol, and n-propanol were reported as the dominant products26 followed by reports of methane, ethylene, and carbon monoxide as primary products upon a revisitation of the work.27 Some aspects of the differing results were attributed to the presence of differing La1.8Sr0.2CuO4/La0.9Sr0.1CuO3 mixed phases between the two studies as a result of synthetic challenges, hindering a physical understanding into the origin of catalytic favorability for formation of higher order hydrocarbons such as methane and ethylene.27 In this work, we combine experiment and theory to systematically investigate a diverse range of ABO3 perovskite metal oxide chemistries in order to understand the key physical factors dictating CO2RR performance. We first conducted density functional theory (DFT) calculations on transition metal oxide perovskite surfaces to determine their surface binding energies towards COads and Hads for assessment of their feasibility towards CO2RR activity. We find that unlike pure transition metals, the binding energies of COads and Hads adsorbate scale inversely, where chemistries with stronger COads binding correlate with weaker Hads bonding. Based on these results, we identify a series of promising perovskite chemistries for electrochemical CO2RR and evaluate their selectivity to HER and CO2RR. We note that despite the predominance of HER activity on these catalysts, CH4 evolution is also observed in meaningful quantities that motivate the understanding of activity descriptors, or predictive materials parameters that correlate with catalytic activity, for this class of perovskite oxide CO2RR catalysts. We find that the O 2p-band center, which has been correlated

5



to surface reactivity trends towards a diverse range of small molecules,28-29 is a useful descriptor for CO2 reduction and the competing HER activity and can rationalize these activity trends specifically due to its correlation to adsorbate binding energy (COads and Hads). Through the theoretical and experimental evaluation of CO2RR catalysts undertaken in this work, we identify LaCoO3 with electrochemical CO2 reduction formation of methane at modestly low onset overpotentials, and that fine tuning of the O 2p-band center can lead to the discovery of new oxide catalysts with selectivity towards higher order chemical products (i.e. CH4, C2H4, C2H5OH, etc..). This study points to the high chemical flexibility of the perovskite metal oxide system and its utility towards the addressing catalyst materials design for the complex CO2 reduction reaction. Experimental Methods Materials Synthesis and Characterization LaMnO3, LaFeO3, and ACoO3 samples (A = La, Gd, Nd) were synthesized by solid-state reactions. La2O3, Nd2O3, Gd2O3, Mn2O3, Fe2O3, and Co3O4 precursors were heat-dried for 8 hours at 800 °C, and then stoichiometric amounts of the precursors were mixed, ground, pressed, and sintered at 1100 °C for 12 hours under air atmosphere. LaCrO3 and LaNiO3 were synthesized by a glycine-nitrate combustion synthesis, in which stoichiometric amounts of the La(NO3)36H2O, Cr(NO3)39H2O and Ni(NO3)36H2O precursors were dissolved in DI water (Milli-Q, 18 M Ohm cm). Glycine was added and the solution was gradually heated to remove the water, followed by calcination for 10 hours at 400 °C. The resulting powder was ground, pressed, and sintered at 1100 °C (LaCrO3) or 800 °C (LaNiO3) for 12 hours. The phase purity of the synthesized metal oxide powders was assessed by x-ray diffraction (Panalytical X’Pert Pro), indicating phase purity (Fig. S1). X-ray photoelectron spectroscopy (XPS) were conducted using an Al Kα radiation (1486.7 eV) and a pass energy of 50 eV (Thermo

6


Page 6 of 28

Page 7 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scientific) to determine that evaluation of CO2RR activity is not affected by possible impurities introduced during the synthesis procedure (Fig. S2). Additionally, the oxide specific surface areas were quantified by Brunauer-Emmett-Teller (Table S1). Electrochemical CO2 Reduction Measurements Perovskite oxide inks were prepared with a 5:1 mass ratio of the synthesized metal oxide to acid-treated acetylene black (Chevron). The mixture was suspended in tetrahydrofuran (99.9%, Sigma-Aldrich) and a 5% weight of ion-exchanged Nafion solution, an ink mixture found to provide accurate and reliable measures of electrochemical activity.30-32 The prepared ink was drop cast on Toray carbon paper (Fuel Cell Store, TGP-H-060) so that a total of 600 µg catalyst per electrode was deposited and then dried overnight prior to electrochemical evaluation. Electroreduction of CO2 was performed in a 2-compartment H-cell, with the Pt mesh counter electrode separated from the catholyte by a Nafion 117 (Fuel Cell Store) membrane to prevent re-oxidation of CO2 reduction products by the counter electrode. Care was also taken to avoid the introduction of any metal impurities, as trace amounts of metal contaminants can deposit on the catalyst surface under CO2 reduction conditions and consequently influence CO2 reduction activity and selectivity,33-34 and so all glassware were cleaned sequentially by 1 M KOH (Alfa Aesar, 99.99%), Aqua Regia (3:1 HCl:HNO3), and boiling DI water (Millipore, 18.2 M Ω cm) for 1 hour each. The Nafion 117 membrane was conditioned prior to electrochemical measurements sequentially by 0.5 M H2SO4, 0.5 M H2O2, and 0.5 M KClO4 for ~1 hour each, and then rinsed with DI water prior to electrochemical measurements. 0.1 M KHCO3 electrolyte was prepared by vigorously bubbling a solution of 0.1 M KOH (Millipore Suprapur, > 99.995%) in DI water (Millipore, 18.2 M Ω cm) with CO2 gas (Airgas, 99.999% purity) for at least 30 min. The pH of the prepared electrolyte was confirmed to be 6.8 prior to use in CO2 electroreduction

7



measurements. An Ag/AgCl leak-free reference electrode (Pine Research) calibrated to the reference hydrogen electrode (RHE) was used for all measurements, and iR correction was applied post-electrolysis. CVs were capacitance-corrected in post-processing by averaging the forward and backward scan for each cycle. Product detection of gas-phase products were made by gas chromatography (SRI Instruments, 6’’ Hayesep-D and 6’’ Molsieve-13x columns), where the headspace of the cathodic chamber was continuously flushed with CO2 into the GC sample loop. H2 was detected by the thermal conductivity detector (TCD) while organic compounds (CH4, CO, C2H4, and C2H6) were detected by flame ionization detector (FID) (Fig. S3). Chronoamperometry (CA) measurements were conducted for each potential (-0.48 VRHE to -1.08VRHE). The first gas sampling was taken 10 minutes into the CA measurement, and multiple gas samplings were taken at intervals of 20 minutes over the course of the 2-hour CA measurement. Liquid-phase products were analyzed after electrolysis using 1H-NMR (Bruker 500 MHz); 35 µL of a 100 mM phenol and 100 mM dimethyl sulfoxide (DMSO) reference solution in D2O standard was added to 700 µL of collected electrolyte, and a water-suppression protocol was followed to minimize the water peak intensity. Potentials were measured against an Ag/AgCl reference electrode and converted to reversible hydrogen electrode (RHE). Electrochemical impedance spectra (EIS) was conducted prior to electrochemical measurements for correction of solution resistance by iR. Cyclic voltammetry measurements were conducted with a scan rate of 20 mV s-1 between 0 VRHE and ~ -0.9 VRHE. A reference sample of just the Toray carbon paper substrate of the same geometric surface area (~1.5 mA cm-2) was also measured to characterize contribution of activity originating from the substrate, which was minimal relative to the perovskite oxide ink activities. At high overpotentials and high current densities, mass diffusion limitations35 on the CO2RR activity and stability of perovskites

8


Page 8 of 28

Page 9 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


examined in this study were negligible as the partial activity for H2 and CH4 were fairly constant throughout the 2-hour CA (Fig. S4). The current was normalized by both geometric surface area of the electrode and oxide surface area as determined by BET. A Biologic SP-200 potentiostat was used for all experiments. Density Functional Theory Density Functional Theory (DFT) calculations were performed with the Vienna Ab-initio Simulation Package (VASP) using the Projector-Augmented plane-wave method with the Perdew– Wang-91 Generalized Gradient Approximation (GGA) plus Hubbard U (Ueff = 3.5, 4, 4, 3.3, and 6.4 eV for Cr, Mn, Fe, Co, and Ni, respectively) method to treat the exchange–correlation interactions, and a solvent stabilization of 0.1 eV was applied for COads.9 All adsorbate energies were calculated on the thermodynamically stable (100) AO-terminated perovskite surface.36-37 Such surface structures were chosen based on experimental evidence of AO termination first-row transition metal perovskite thin films with chemistries ranging from titanites,38 ferrites,39 and nickelates40 in the as-grown state, and AO termination stability in the presence of gaseous H2O and CO2 species.29,

41

Further support comes from theoretical studies finding thermodynamic

favorability for AO-terminated (001) surfaces on bare cobaltite surfaces36-37 as well as under electrocatalytic hydrogenation reactions conditions for first row transition metal lanthanide catalysts.28 Further details for the DFT calculation parameters have been described previously (Table S2).42-43 Results and Discussion

9



Figure 1: Stable configuration for A) COads and B) Hads adsorption on (100) perovskite surfaces as determined from DFT calculations. C) Map of COads and Hads binding energies for LaBO3 (red diamond, B = transition metal) and ACoO3 (teal diamond, A = rare earth lanthanide) perovskites studied in this work. Data points of monometallic transition metals that preferentially produce H2 (black circle), C1+ products (orange circle), CO (green circle), and HCOOH (blue circle). Data adapted with permission from Ref.8 We find that perovskite chemistries can access a new regime of surface properties not accessible by monometallic catalysts. We calculated the binding energy of favorable CO (Fig. 1A) and H adsorption (Fig 1B) configurations on (100) perovskite surfaces using DFT, where bonding of Hads to the oxygen site was thermodynamically favorable. The Hads adsorption energy on LaFeO3 and the cobaltites (ACoO3) was found to be similar in magnitude to the H2-forming group of monometallic chemistries, while the early transition metal LaCrO3 exhibits HCOOH-forming group-like H adsorption energetics (Fig. 1C).8 Late transition metal chemistry LaNiO3 exhibited the strongest H adsorption energetics, ~0.8 eV stronger binding for Had than Pt-like catalysts (Fig. 1C).8 The trend of stronger Hads adsorption on perovskites with more electronegative B-site transition metal ions is consistent with previous theoretical studies of Hads adsorption on surface

10


Page 10 of 28

Page 11 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


oxygen sites,44-45 which has been attributed to higher availability of free valence of more covalent oxides to react with hydrogen, leading to stronger hydrogen adsorption.46 The adsorption of CO on perovskites binds coordinatively through its oxygen to the perovskite surface (Fig. 2A), where the surface binding to COads decreases with increasingly electronegative cations in the B-site of the LaBO3 series, similar to weakened oxygen binding28, 47 with increased metal-oxygen covalency. LaNiO3 was found as an exception in the trend, which is hypothesized to results from a metal-oxygen strength that is too weak to stabilize COads via oxygen coordination to the B sites of the perovskite surface (Fig. S5). The weak oxygen adsorption energy on LaNiO3 has been previously reported in theoretical studies.28,

48

Overall, Hads and COads

adsorption strength to the LaMO3 (001) surface was inversely correlated instead of positively correlated as established for monometallic surfaces.13-15 Therefore, it is possible to tune the surface energetics of the perovskite by choice of cations in the A and/or B site to break the linear scaling in the binding energetics of CO2RR intermediates that limit CO2RR activity and selectivity on transition metal surfaces,13-15 approaches applied to previous work on transition metal sulfides, phosphides, and carbides.17, 49 Of particular interest is to examine CO2RR activity and selectivity on perovskites like LaFeO3 and ACoO3 that have similar energetics to Cu, which could potentially reduce CO2 to higher order products.

11



Figure 2: A) CVs of lanthanide perovskites under CO2-saturated 0.1 M KHCO3 electrolyte with 20 mv s-1 scan rate. B) Partial current density of H2. C) Partial current density of CH4. All current densities were normalized by oxide surface area as determined by BET.

We experimentally evaluated the CO2RR activity of select perovskite chemistries shown in Fig. 1C. First, cyclic voltammetry (CV) measurements under CO2-saturated 0.1 M KHCO3 electrolyte were conducted to quantify the total CO2RR current/activity, where distinct total mass activities (Fig. S6) and specific area activities determined from BET oxide surface area (Fig. 2A) were obtained. Partial current densities at each potential were determined over the course of chronoamperometry (CA) currents (in the range from -0.48 VRHE to -1.23 VRHE) with Faradaic efficiency of CO2RR products determined from gas chromatography or NMR. The main gas products observed were H2 (Fig. 2B), trace CO (Fig. S7), and CH4 (Fig. 2C). Additionally, trace HCOOH was the only liquid product of CO2RR observed in trace amounts as detected by NMR (Fig. S8). The total Faradaic efficiency primarily add up to ~100%, and CH4 or CO evolution contributes to < 1% of the total charge passed at each potential (Table S3). The high selectivity towards HER instead of CO2RR has also been observed in other nonmetallic catalysts such as

12


Page 12 of 28

Page 13 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


transition metal carbides,19 sulfides,20, 49 and phosphides.22, 49 Further, the predominance of H2 in addition to more minor observations of CH4 and CO in the product distribution compares more similarly to the gas products observed in the more recent work of Mignard et. al. on strontiumdoped cuprates,27 although differences in the employment of a gas diffusion electrode cell configuration, catalyst electrode formulation, temperature and pressure conditions, and catalyst phase purity (mixed layered/perovskite phase) hinder direct comparisons. Of great interest to note in this work is that the Co, Mn0.5Cu0.5, and Fe of the lanthanide perovskites can catalyze CH4 formation on CO2RR, which is expected by having similar surface binding energies of COads and Hads to Cu (Fig. 1C). In contrast, Mn and Cr of the lanthanides exhibit negligible CH4 evolution, due to the similarity of their strong COads binding energies to Pt-like species while having relatively weaker Hads binding energies.

13



Figure 3: A) Correlation of partial current density of H2 and CH4 normalized by specific surface area with computed bulk O 2p-band center of perovskites (with respect to the Fermi level). B) Correlation of partial current density of H2 vs. computed Hads adsorption energy. C) Correlation of the partial current density of CH4 vs. computed COads adsorption energy. The metal-oxygen covalency of perovskites, as quantified by the bulk O 2p-band center relative to the Fermi level43, 50-53 computed from DFT (Fig. S9) was found to correlate with the partial activity towards HER and CH4 evolution (Fig. 3A). Higher metal-oxygen covalency resulted in higher HER current (Fig. 3A, top) while a volcano-like dependency on metal-oxygen covalency was observed for CH4 partial current density (Fig. 3A, bottom). The bulk O 2p-band center relative to the Fermi level43, 50-53 computed from DFT correlates negatively and positively with computed binding energy of Hads (Fig. S10) and COads (Fig. S11), respectively. The correlation with the surface electronic structure (surface O 2p-band center) relative to the Fermi level shows comparable or slightly better trends than that of bulk O 2p-band center (Fig. S12). We further use the Sabatier principle, where the surface binding energy to relevant reaction intermediates like Hads, Oads/OHads/OOHads, and Nads governs the activity for HER/HOR,54 ORR,5556

and NRR,57 respectively, to examine the correlation between binding energy of Hads or COads

with CO2RR activity and selectivity trends. Stronger H adsorption was found to exhibit a linear correlation with increasing HER activity (Fig. 3B), which indicates that these perovskites lie on the weak-binding leg of the volcano for HER activity, limited by weak Hads adsorption,58-59 and the most covalent oxides measured in this study possess the strongest Hads binding and highest HER activity. This finding is in agreement with previous work that have shown that two highly covalent oxides, Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) and Pr0.5(Ba0.5Sr0.5)0.5Co0.8Fe0.2O3-δ have high

14


Page 14 of 28

Page 15 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


HER in alkaline solution, and that further increasing of covalency by generating Co4+ species can further increase the HER activity.60 The CH4 activity trend follows a volcano-like shape as a function of COads binding (Fig. 3C), where LaCoO3 exhibits the maximum CH4 activity out of oxides studied here. If the COads binding is too strong, like for LaCrO3 and LaMnO3 chemistries, the surface is poisoned by COads or any downstream reaction intermediate species like H2COads or OCH3,ads prior to desorption of CH4 species.9 For Pt surfaces, which exhibits comparable COads binding energies (-1.43 eV) as the strong COads binding chemistries in this study (LaCrO3, LaMnO3), poisoning of with COads species during CO2RR has been previously directly observed experimentally.11 If the binding of COads is too weak, CO2RR is limited by adsorption of reactant species like CO2.10 Observation of CH4 activity thus requires an optimal CO binding energy found for LaCoO3 in this study.

Figure 4: CH4 evolution activity comparison among catalysts in this work (LaCoO3 and GdCoO3) and previously published data on CH4-evolving catalysts (Mo2C, Cu) on a normalized catalyst surface area basis.19

15



The most active catalyst for CH4 evolution in this study, LaCoO3, was found to have an onset potential for CH4 evolution at ~ -0.6 VRHE, which rivals, or even exceed the state-of-the-art methane evolving catalysts like Cu (~ -0.8 VRHE)19 and non-Cu CH4 evolving catalysts like Mo2C.19 Mechanistically, the Tafel slope of LaCoO3 (-362 mV dec-1) was found to differ significantly from Cu (-54 mV dec-1) and the high Tafel slope gave rise to much lower CH4 partial current densities for LaCoO3 at high overpotentials relative to Cu (Fig. 4). The similarity between Tafel slopes for LaCoO3 and Mo2C19 indicate that unlike Cu, for which the COads → CHOads step is the rate-limiting step,9-10 an alternative (electro)chemical step is likely responsible for the higher onset for CH4 evolution and higher Tafel slope. On Mo2C catalysts, the triggering of a C-O bond scission pathway (CO2,ads → COads + Oads) was found to be more energetically favorable for the initial formation of CH4,19 hence the higher CH4 evolution onset potential for Mo2C compared to Cu (~-0.6VRHE vs. -0.8 VRHE). Further, the higher Tafel slope for CH4 evolution in Mo2C was rationalized by a microkinetic analysis of the C-O bond scission pathway, where the majority of surface sites was occupied by Hads and OHads (~0.9 ML) and the rate-limiting C-O bond scission chemical step was highly insensitive to applied electrochemical potential.19 Alternatively, DFT calculations on rutile oxides suggest that a pathway through the formation of adsorbed formate (HCOOHads), where protonation of HCOOHads is potential-determining can also result in higher onset potential of methane or methanol.61 Therefore, it could be possible that the optimal metaloxygen covalency of LaCoO3 triggers one of the described alternative reaction pathways for CH4 evolution, or another previously unexplored mechanism, that results in the low overpotentials for the onset of CH4 formation. While the role of binding of COads and Hads on the CO2RR activity and selectivity were considered, it is also possible that the role of OHads plays a significant role in total activity and the

16


Page 16 of 28

Page 17 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


competition between HER and CO2RR for non-monometallic catalysts as the metal oxides; on metal oxides, hydroxyl adsorption is typically quite facile,62-63 leading to a large population of spectator OHads species occupying surface sites on oxides under CO2RR conditions.64 These effects may play a role in this study; the OHads binding energy for LaCoO3 calculated in this study is -0.58 eV compared to a relatively weaker binding of -0.07 eV for Cu.9 Thus, understanding the role oxygenated species (OHads/Oads) as spectators species or reaction intermediates, and then developing strategies to tune oxygenated species on oxides independently of COads and Hads through experimental design parameters like strain48, 65 may play a role in the design of practical oxide catalysts for CO2RR. Lastly, the stability of perovskite metal oxide chemistries remains an important consideration for evaluation of this materials family as CO2RR catalysts. Although LaCoO3, the chemistry with the highest CH4 evolution favorability among the chemistries investigated in this study, was found to exhibit bulk structural stability under CO2RR conditions (Fig. S13), continued evaluation of long-term stability will be greatly aided by a dynamic picture of the active surface state under in-situ conditions. This may involve monitoring of structural, chemical, and electronic evolution of the active surface state to further understand the possible effects of factors not limited to surface reconstruction,66 surface segregation,67-70 amorphization,71-72 on catalytic activity and stability. Understanding these phenomena opens up additional avenues to building upon the bulksurface model described in this work. Nevertheless, the utility of metal-oxygen covalency as a facile descriptor for both CO2RR selectivity to CH4 and the competing HER offers a potentially useful parameter to search the wide oxide materials space for useful CO2RR electrocatalysts.

Conclusions

17



We examine a class of perovskite oxide CO2RR catalysts and systematically report on their favorability for producing CH4 and H2, in turn developing materials design principles for tuning CH4 and H2 formation for this materials class. The most active catalyst for CH4 evolution among the catalysts identified in this study, LaCoO3, exhibits an onset potential that is among the statethe-art to date. By systematically evaluating a diverse range of perovskite oxides for CO2RR, we identify metal-oxygen covalency, quantified as the bulk O 2p-band center relative to the Fermi level, as an activity descriptor that can rationalize activity and selectivity trends for both CO2RR conversion to CH4 and the competing HER. We find that increased covalency correlates with increasing HER activity as hydrogen adsorption increases. However, CH4 partial activity follows a volcano relationship with covalency, which translates to ideally having an intermediate COads binding energy to enhance CH4 activity. As a result, we highlight the O 2p-band center as a promising descriptor for perovskite metal oxides that can enable efficient computational searches of novel CO2RR catalysts and the rationalization of their activity trends.

Supporting Information Further details on the materials characterization, electrochemical CO2RR activity measurements, and computational analysis. Acknowledgements J.H and J.C-G was supported by Eni S.p.A. K.A was supported by BASF Corporation. This research used resources of the National Energy Research Scientific Computing Center, a DOE office of Science User Facility Supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-5CH11231, and the Extreme Science and Engineering

18


Page 18 of 28

Page 19 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562 References 1. Lewis, N. S.; Nocera, D. G., Powering the planet: chemical challenges in solar energy utilization. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 15729-35. 2. Whipple, D. T.; Kenis, P. J. A., Prospects of CO2 utilization via direct heterogeneous electrochemical reduction. J. Phys. Chem. Lett. 2010, 1, 3451-3458. 3. Jouny, M.; Luc, W.; Jiao, F., General techno-economic analysis of CO2 electrolysis systems. Ind. Eng. Chem. Res. 2018, 57, 2165-2177. 4. Benson, E. E.; Kubiak, C. P.; Sathrum, A. J.; Smieja, J. M., Electrocatalytic and homogeneous approaches to conversion of CO2 to liquid fuels. Chem. Soc. Rev. 2009, 38, 89-99. 5. Qiao, J.; Liu, Y.; Hong, F.; Zhang, J., A review of catalysts for the electroreduction of carbon dioxide to produce low-carbon fuels. Chem. Soc. Rev. 2014, 43, 631-75. 6. Hori, Y., Electrochemical CO2 reduction on metal electrodes. 2008, 42, 89-189. 7. Hori, Y.; Wakebe, H.; Tsukamoto, T.; Koga, O., Electrocatalytic process of CO selectivity in electrochemical reduction of CO2 at metal electrodes in aqueous media. Electrochimica Acta 1994, 39, 1833-1839. 8. Bagger, A.; Ju, W.; Varela, A. S.; Strasser, P.; Rossmeisl, J., Electrochemical CO2 reduction: a classification problem. Chemphyschem 2017, 18, 3266-3273. 9. Peterson, A. A.; Abild-Pedersen, F.; Studt, F.; Rossmeisl, J.; Norskov, J. K., How copper catalyzes the electroreduction of carbon dioxide into hydrocarbon fuels. Energy. Environ. Sci. 2010, 3, 1311-1315. 10. Peterson, A. A.; Nørskov, J. K., Activity descriptors for CO2 electroreduction to methane on transition-metal catalysts. J. Phys. Chem. Lett. 2012, 3, 251-258. 11. Katayama, Y.; Nattino, F.; Giordano, L.; Hwang, J.; Rao, R. R.; Andreussi, O.; Marzari, N.; Shao-Horn, Y., An in situ surface-enhanced infrared absorption spectroscopy study of electrochemical CO2 reduction: selectivity dependence on surface C-bound and O-bound reaction intermediates. J. Phys. Chem. C 2019, 123, 5951-5963. 12. Kuhl, K. P.; Cave, E. R.; Abram, D. N.; Jaramillo, T. F., New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces. Energy. Environ. Sci. 2012, 5, 7050-7059. 13. Calle-Vallejo, F.; Martinez, J. I.; Garcia-Lastra, J. M.; Rossmeisl, J.; Koper, M. T., Physical and chemical nature of the scaling relations between adsorption energies of atoms on metal surfaces. Phys. Rev. Lett. 2012, 108, 116103. 14. Abild-Pedersen, F.; Greeley, J.; Studt, F.; Rossmeisl, J.; Munter, T. R.; Moses, P. G.; Skulason, E.; Bligaard, T.; Norskov, J. K., Scaling properties of adsorption energies for hydrogen-containing molecules on transition-metal surfaces. Phys. Rev. Lett. 2007, 99, 016105. 15. Montemore, M. M.; Medlin, J. W., Scaling relations between adsorption energies for computational screening and design of catalysts. Catal. Sci. Technol. 2014, 4, 3748-3761. 16. Li, Y.; Sun, Q., Recent advances in breaking scaling relations for effective electrochemical conversion of CO2. Adv. Energy Mater. 2016, 6.

19



17. Michalsky, R.; Zhang, Y.-J.; Medford, A. J.; Peterson, A. A., Departures from the adsorption energy scaling relations for metal carbide catalysts. J. Phys. Chem. C 2014, 118, 13026-13034. 18. Chan, K.; Tsai, C.; Hansen, H. A.; Nørskov, J. K., Molybdenum sulfides and selenides as possible electrocatalysts for CO2 reduction. ChemCatChem 2014, 6, 1899-1905. 19. Kim, S. K.; Zhang, Y.-J.; Bergstrom, H.; Michalsky, R.; Peterson, A., Understanding the Low-Overpotential Production of CH4 from CO2 on Mo2C Catalysts. ACS Catal. 2016, 6, 20032013. 20. Francis, S. A.; Velazquez, J. M.; Ferrer, I. M.; Torelli, D. A.; Guevarra, D.; McDowell, M. T.; Sun, K.; Zhou, X.; Saadi, F. H.; John, J., et al., Reduction of aqueous CO2 to 1-propanol at MoS2 electrodes. Chem. Mater. 2018, 30, 4902-4908. 21. Varela, A. S.; Ranjbar Sahraie, N.; Steinberg, J.; Ju, W.; Oh, H. S.; Strasser, P., Metaldoped nitrogenated carbon as an efficient catalyst for direct CO2 electroreduction to CO and hydrocarbons. Angew. Chem. Int. Ed. Engl. 2015, 54, 10758-62. 22. Calvinho, K. U. D.; Laursen, A. B.; Yap, K. M. K.; Goetjen, T. A.; Hwang, S.; Murali, N.; Mejia-Sosa, B.; Lubarski, A.; Teeluck, K. M.; Hall, E. S., et al., Selective CO2 reduction to C3 and C4 oxyhydrocarbons on nickel phosphides at overpotentials as low as 10 mV. Energy. Environ. Sci. 2018, 11, 2550-2559. 23. Smit, J. P.; Stair, P. C.; Poeppelmeier, K. R., The adaptable lyonsite structure. Chemistry 2006, 12, 5944-53. 24. Voorhoeve, R. J.; Johnson, D. W., Jr.; Remeika, J. P.; Gallagher, P. K., Perovskite oxides: materials science in catalysis. Science 1977, 195, 827-33. 25. Hwang, J.; Rao, R. R.; Giordano, L.; Katayama, Y.; Yu, Y.; Shao-Horn, Y., Perovskites in catalysis and electrocatalysis. Science 2017, 358, 751-756. 26. Schwartz, M.; Cook, R. L.; Kehoe, V. M.; MacDuff, R. C.; Patel, J.; Sammells, A. F., Carbon dioxide reduction to alcohols using perovskite-type electrocatalysts. J. Electrochem. Soc. 1993, 140. 27. Mignard, D.; Barik, R. C.; Bharadwaj, A. S.; Pritchard, C. L.; Ragnoli, M.; Cecconi, F.; Miller, H.; Yellowlees, L. J., Revisiting strontium-doped lanthanum cuprate perovskite for the electrochemical reduction of CO2. J. CO2 Util. 2014, 5, 53-59. 28. Lee, Y. L.; Gadre, M. J.; Shao-Horn, Y.; Morgan, D., Ab initio GGA+U study of oxygen evolution and oxygen reduction electrocatalysis on the (001) surfaces of lanthanum transition metal perovskites LaBO(3) (B = Cr, Mn, Fe, Co and Ni). Phys. Chem. Chem. Phys. 2015, 17, 21643-63. 29. Hwang, J.; Rao, R. R.; Katayama, Y.; Lee, D.; Wang, X. R.; Crumlin, E.; Venkatesan, T.; Lee, H. N.; Shao-Horn, Y., CO2 reactivity on cobalt-based perovskites. J. Phys. Chem. C 2018, 122, 20391-20401. 30. Suntivich, J.; Gasteiger, H. A.; Yabuuchi, N.; Shao-Horn, Y., Electrocatalytic measurement methodology of oxide catalysts using a thin-film rotating disk electrode. J. Electrochem. Soc. 2010, 157, B1263. 31. Suntivich, J.; May, K. J.; Gasteiger, H. A.; Goodenough, J. B.; Shao-Horn, Y., A perovskite oxide optimized for oxygen evolution catalysis from molecular orbital principles. Science 2011, 334, 1383-5. 32. Wei, C.; Rao, R. R.; Peng, J.; Huang, B.; Stephens, I. E. L.; Risch, M.; Xu, Z. J.; ShaoHorn, Y., Recommended practices and benchmark activity for hydrogen and oxygen electrocatalysis in water splitting and fuel cells. Adv. Mater. 2019, 31, e1806296.

20


Page 20 of 28

Page 21 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


33. Hori, Y.; Konishi, H.; Futamura, T.; Murata, A.; Koga, O.; Sakurai, H.; Oguma, K., “Deactivation of copper electrode” in electrochemical reduction of CO2. Electrochimica Acta 2005, 50, 5354-5369. 34. Clark, E. L.; Resasco, J.; Landers, A.; Lin, J.; Chung, L.-T.; Walton, A.; Hahn, C.; Jaramillo, T. F.; Bell, A. T., Standards and protocols for data acquisition and reporting for studies of the electrochemical reduction of carbon dioxide. ACS Catal. 2018, 8, 6560-6570. 35. Lobaccaro, P.; Singh, M. R.; Clark, E. L.; Kwon, Y.; Bell, A. T.; Ager, J. W., Effects of temperature and gas-liquid mass transfer on the operation of small electrochemical cells for the quantitative evaluation of CO2 reduction electrocatalysts. Phys. Chem. Chem. Phys. 2016, 18, 26777-26785. 36. Chen, Z.; Kim, C. H.; Thompson, L. T.; Schneider, W. F., LDA+U evaluation of the stability of low-index facets of LaCoO3 perovskite. Surf. Sci. 2014, 619, 71-76. 37. Zhang, S.; Han, N.; Tan, X., Density functional theory calculations of atomic, electronic and thermodynamic properties of cubic LaCoO3 and La1−xSrxCoO3 surfaces. RSC Adv. 2015, 5, 760-769. 38. Kawasaki, M.; Takahashi, K.; Maeda, T.; Tsuchiya, R.; Shinohara, M.; Ishiyama, O.; Yonezawa, T.; Yoshimoto, M.; Koinuma, H., Atomic Control of the SrTiO3 Crystal Surface. Science 1994, 266, 1540-2. 39. Druce, J.; Téllez, H.; Burriel, M.; Sharp, M. D.; Fawcett, L. J.; Cook, S. N.; McPhail, D. S.; Ishihara, T.; Brongersma, H. H.; Kilner, J. A., Surface termination and subsurface restructuring of perovskite-based solid oxide electrode materials. Energy Environ. Sci. 2014, 7, 3593-3599. 40. Burriel, M.; Wilkins, S.; Hill, J. P.; Muñoz-Márquez, M. A.; Brongersma, H. H.; Kilner, J. A.; Ryan, M. P.; Skinner, S. J., Absence of Ni on the outer surface of Sr doped La2NiO4 single crystals. Energy Environ. Sci. 2014, 7, 311-316. 41. Stoerzinger, K. A.; Hong, W. T.; Azimi, G.; Giordano, L.; Lee, Y.-L.; Crumlin, E. J.; Biegalski, M. D.; Bluhm, H.; Varanasi, K. K.; Shao-Horn, Y., Reactivity of perovskites with water: Role of hydroxylation in wetting and implications for oxygen electrocatalysis. J. Phys. Chem. C 2015, 119, 18504-18512. 42. 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. 43. Hong, W. T.; Stoerzinger, K. A.; Lee, Y.-L.; Giordano, L.; Grimaud, A.; Johnson, A. M.; Hwang, J.; Crumlin, E. J.; Yang, W.; Shao-Horn, Y., Charge-transfer-energy-dependent oxygen evolution reaction mechanisms for perovskite oxides. Energy. Environ. Sci. 2017, 10, 21902200. 44. Giordano, L.; Karayaylali, P.; Yu, Y.; Katayama, Y.; Maglia, F.; Lux, S.; Shao-Horn, Y., Chemical reactivity descriptor for the oxide-electrolyte interface in Li-ion batteries. J. Phys. Chem. Lett. 2017, 8, 3881-3887. 45. Østergaard, T. M.; Giordano, L.; Castelli, I. E.; Maglia, F.; Antonopoulos, B. K.; ShaoHorn, Y.; Rossmeisl, J., Oxidation of ethylene carbonate on Li metal oxide surfaces. J. Phys. Chem. C 2018, 122, 10442-10449. 46. Fung, V.; Wu, Z.; Jiang, D. E., New bonding model of radical adsorbate on lattice oxygen of perovskites. J. Phys. Chem. Lett. 2018, 9, 6321-6325.

21



47. Montoya, J. H.; Doyle, A. D.; Nørskov, J. K.; Vojvodic, A., Trends in adsorption of electrocatalytic water splitting intermediates on cubic ABO3 oxides. Phys. Chem. Chem. Phys. 2018, 20, 3813-3818. 48. Akhade, S. A.; Kitchin, J. R., Effects of strain, d-band filling, and oxidation state on the surface electronic structure and reactivity of 3d perovskite surfaces. J. Chem. Phys. 2012, 137, 084703. 49. Landers, A. T.; Fields, M.; Torelli, D. A.; Xiao, J.; Hellstern, T. R.; Francis, S. A.; Tsai, C.; Kibsgaard, J.; Lewis, N. S.; Chan, K., et al., The predominance of hydrogen evolution on transition metal sulfides and phosphides under CO2 reduction conditions: an experimental and theoretical study. ACS Energy Letters 2018, 3, 1450-1457. 50. Suntivich, J.; Hong, W. T.; Lee, Y.-L.; Rondinelli, J. M.; Yang, W.; Goodenough, J. B.; Dabrowski, B.; Freeland, J. W.; Shao-Horn, Y., Estimating hybridization of transition metal and oxygen states in perovskites from O K-edge X-Ray absorption spectroscopy. J. Phys. Chem. C 2014, 118, 1856-1863. 51. Jacobs, R.; Hwang, J.; Shao-Horn, Y.; Morgan, D., Assessing correlations of perovskite catalytic performance with electronic structure descriptors. Chem. Mater. 2019, 31, 785-797. 52. Lee, Y. L.; Kleis, J.; Rossmeisl, J.; Shao-Horn, Y.; Morgan, D., Prediction of solid oxide fuel cell cathode activity with first-principles descriptors. Energy. Environ. Sci. 2011, 4, 39663970. 53. Grimaud, A.; May, K. J.; Carlton, C. E.; Lee, Y. L.; Risch, M.; Hong, W. T.; Zhou, J.; Shao-Horn, Y., Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solution. Nat. Commun. 2013, 4, 2439. 54. Skúlason, E.; Tripkovic, V.; Björketun, M. E.; Gudmundsdóttir, S.; Karlberg, G.; Rossmeisl, J.; Bligaard, T.; Jónsson, H.; Nørskov, J. K., Modeling the electrochemical hydrogen oxidation and evolution reactions on the basis of density functional theory calculations. J. Phys. Chem. C 2010, 114, 18182-18197. 55. Vojvodic, A.; Nørskov, J. K., New design paradigm for heterogeneous catalysts. Natl. Sci. Rev. 2015, 2, 140-149. 56. Nørskov, J. K.; Rossmeisl, J.; Logadottir, A.; Lindqvist, L.; Kitchin, J. R.; Bligaard, T.; Jónsson, H., Origin of the overpotential for oxygen reduction at a fuel-cell cathode. J. Phys. Chem. B 2004, 108, 17886-17892. 57. Montoya, J. H.; Tsai, C.; Vojvodic, A.; Norskov, J. K., The challenge of electrochemical ammonia synthesis: A new perspective on the role of nitrogen scaling relations. ChemSusChem 2015, 8, 2180-6. 58. Trasatti, S., Work function, electronegativity, and electrochemical behaviour of metals. J. Electroanal. Chem. Interfacial Electrochem. 1972, 39, 163-184. 59. Nørskov, J. K.; Bligaard, T.; Logadottir, A.; Kitchin, J. R.; Chen, J. G.; Pandelov, S.; Stimming, U., Trends in the exchange current for hydrogen evolution. J. Electrochem. Soc. 2005, 152. 60. Xu, X.; Chen, Y.; Zhou, W.; Zhu, Z.; Su, C.; Liu, M.; Shao, Z., A perovskite electrocatalyst for efficient hydrogen evolution reaction. Adv. Mater. 2016, 28, 6442-8. 61. Karamad, M.; Hansen, H. A.; Rossmeisl, J.; Nørskov, J. K., Mechanistic pathway in the electrochemical reduction of CO2 on RuO2. ACS Catal. 2015, 5, 4075-4081. 62. Boehm, H. P., Acidic and basic properties of hydroxylated metal oxide surfaces. Discuss. Faraday Soc. 1971, 52.

22


Page 22 of 28

Page 23 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


63. Salmeron, M.; Bluhm, H.; Tatarkhanov, M.; Ketteler, G.; Shimizu, T. K.; Mugarza, A.; Deng, X.; Herranz, T.; Yamamoto, S.; Nilsson, A., Water growth on metals and oxides: binding, dissociation and role of hydroxyl groups. Faraday Discuss. 2009, 141, 221-229. 64. Deng, W.; Zhang, L.; Li, L.; Chen, S.; Hu, C.; Zhao, Z. J.; Wang, T.; Gong, J., Crucial role of surface hydroxyls on the activity and stability in electrochemical CO2 reduction. J. Am. Chem. Soc. 2019, 141, 2911-2915. 65. Yildiz, B., “Stretching” the energy landscape of oxides—Effects on electrocatalysis and diffusion. MRS Bulletin 2014, 39, 147-156. 66. Kim, Y.-G.; Javier, A.; Baricuatro, J. H.; Torelli, D.; Cummins, K. D.; Tsang, C. F.; Hemminger, J. C.; Soriaga, M. P., Surface reconstruction of pure-Cu single-crystal electrodes under CO-reduction potentials in alkaline solutions: A study by seriatim ECSTM-DEMS. J. Electroanal. Chem. 2016, 780, 290-295. 67. Hahn, C.; Abram, D. N.; Hansen, H. A.; Hatsukade, T.; Jackson, A.; Johnson, N. C.; Hellstern, T. R.; Kuhl, K. P.; Cave, E. R.; Feaster, J. T., et al., Synthesis of thin film AuPd alloys and their investigation for electrocatalytic CO2 reduction. J. Mater. Chem. A 2015, 3, 2018520194. 68. Mutoro, E.; Crumlin, E. J.; Pöpke, H.; Luerssen, B.; Amati, M.; Abyaneh, M. K.; Biegalski, M. D.; Christen, H. M.; Gregoratti, L.; Janek, J., et al., Reversible compositional control of oxide surfaces by electrochemical potentials. J. Phys. Chem. Lett. 2011, 3, 40-44. 69. 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. 70. Feng, Z.; Yacoby, Y.; Hong, W. T.; Zhou, H.; Biegalski, M. D.; Christen, H. M.; ShaoHorn, Y., Revealing the atomic structure and strontium distribution in nanometer-thick La0.8Sr0.2CoO3−δ grown on (001)-oriented SrTiO3. Energy. Environ. Sci. 2014, 7, 1166-1174. 71. Chang, S. H.; Danilovic, N.; Chang, K. C.; Subbaraman, R.; Paulikas, A. P.; Fong, D. D.; Highland, M. J.; Baldo, P. M.; Stamenkovic, V. R.; Freeland, J. W., et al., Functional links between stability and reactivity of strontium ruthenate single crystals during oxygen evolution. Nat. Commun. 2014, 5, 4191. 72. May, K. J.; Carlton, C. E.; Stoerzinger, K. A.; Risch, M.; Suntivich, J.; Lee, Y.-L.; Grimaud, A.; Shao-Horn, Y., Influence of oxygen evolution during water oxidation on the surface of perovskite oxide catalysts. J. Phys. Chem. Lett. 2012, 3, 3264-3270.

23



TOC

24


Page 24 of 28

Page 25 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47



The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47


Page 26 of 28

Page 27 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47



The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47


Page 28 of 28

A Perovskite Electronic Structure Descriptor for Electrochemical CO2

Recommend Documents