Michaela Stevens

All Publications

• Insights into Active Sites and Mechanisms of Benzyl Alcohol Oxidation on Nickel-Iron Oxyhydroxide Electrodes ACS CATALYSIS Wei, L., Hossain, M., Boyd, M. J., Aviles-Acosta, J., Kreider, M. E., Nielander, A. C., Stevens, M., Jaramillo, T. F., Bajdich, M., Hahn, C. 2023: 4272-4282

  View details for DOI 10.1021/acscatal.2c05656

  View details for Web of Science ID 000953973700001

• Material Changes in Electrocatalysis: An In Situ/Operando Focus on the Dynamics of Cobalt-Based Oxygen Reduction and Evolution Catalysts CHEMELECTROCHEM Kreider, M. E., Stevens, M. 2022

  View details for DOI 10.1002/celc.202200958

  View details for Web of Science ID 000903768500001

• Understanding the Stability of Manganese Chromium Antimonate Electrocatalysts through Multimodal In Situ and Operando Measurements. Journal of the American Chemical Society Kreider, M. E., Kamat, G. A., Zamora Zeledón, J. A., Wei, L., Sokaras, D., Gallo, A., Stevens, M. B., Jaramillo, T. F. 2022

  Abstract

  Improving electrocatalyst stability is critical for the development of electrocatalytic devices. Herein, we utilize an on-line electrochemical flow cell coupled with an inductively coupled plasma-mass spectrometer (ICP-MS) to characterize the impact of composition and reactant gas on the multielement dissolution of Mn(-Cr)-Sb-O electrocatalysts. Compared to Mn2O3 and Cr2O3 oxides, the antimonate framework stabilizes Mn at OER potentials and Cr at both ORR and OER potentials. Furthermore, dissolution of Mn and Cr from Mn(-Cr) -Sb-O is driven by the ORR reaction rate, with minimal dissolution under N2. We observe preferential dissolution of Cr totaling 13% over 10 min at 0.3, 0.6, and 0.9 V vs RHE, with only 1.5% loss of Mn, indicating an enrichment of Mn at the surface of the particles. Despite this asymmetric dissolution, operando X-ray absorption spectroscopy (XAS) showed no measurable changes in the Mn K-edge at comparable potentials. This could suggest that modification to the Mn oxidation state and/or phase in the surface layer is too small or that the layer is too thin to be measured with the bulk XAS measurement. Lastly, on-line ICP-MS was used to assess the effects of applied potential, scan rate, and current on Mn-Cr-Sb-O during cyclic voltammetry and accelerated stress tests. With this deeper understanding of the interplay between oxygen reduction and dissolution, testing procedures were identified to maximize both activity and stability. This work highlights the use of multimodal in situ characterization techniques in tandem to build a more complete model of stability and develop protocols for optimizing catalyst performance.

  View details for DOI 10.1021/jacs.2c08600

  View details for PubMedID 36453840

• Origins of wear-induced tungsten corrosion defects in semiconductor manufacturing during tungsten chemical mechanical polishing APPLIED SURFACE SCIENCE Choi, S., Kreider, M. E., Nielander, A. C., Stevens, M., Kamat, G., Koo, J., Bae, K., Kim, H., Yoon, I., Yoon, B., Hwang, K., Lee, D., Jaramillo, T. F. 2022; 598

  View details for DOI 10.1016/j.apsusc.2022.153767

  View details for Web of Science ID 000818529100002

• Strategies for Modulating the Catalytic Activity and Selectivity of Manganese Antimonates for the Oxygen Reduction Reaction ACS CATALYSIS Kreider, M. E., Gunasooriya, G., Liu, Y., Zeledon, J., Valle, E., Zhou, C., Montoya, J. H., Gallo, A., Sinclair, R., Norskov, J. K., Stevens, M., Jaramillo, T. F. 2022

  View details for DOI 10.1021/acscatal.2c01764

  View details for Web of Science ID 000844309700001

• New challenges in oxygen reduction catalysis: a consortium retrospective to inform future research ENERGY & ENVIRONMENTAL SCIENCE Stevens, M., Anand, M., Kreider, M. E., Price, E. K., Zeledon, J., Wang, L., Peng, J., Li, H., Gregoire, J. M., Hummelshoj, J., Jaramillo, T. F., Jia, H., Norskov, J. K., Roman-Leshkov, Y., Shao-Horn, Y., Storey, B. D., Suram, S. K., Torrisi, S. B., Montoya, J. H. 2022

  View details for DOI 10.1039/d2ee01333a

  View details for Web of Science ID 000834905400001

• Methods-A Practical Approach to the Reversible Hydrogen Electrode Scale JOURNAL OF THE ELECTROCHEMICAL SOCIETY Zeledon, J., Jackson, A., Stevens, M., Kamat, G. A., Jaramillo, T. F. 2022; 169 (6)

  View details for DOI 10.1149/1945-7111/ac71d1

  View details for Web of Science ID 000806520100001

• First-Row Transition Metal Antimonates for the Oxygen Reduction Reaction. ACS nano Gunasooriya, G. T., Kreider, M. E., Liu, Y., Zamora Zeledon, J. A., Wang, Z., Valle, E., Yang, A., Gallo, A., Sinclair, R., Stevens, M. B., Jaramillo, T. F., Norskov, J. K. 2022

  Abstract

  The development of inexpensive and abundant catalysts with high activity, selectivity, and stability for the oxygen reduction reaction (ORR) is imperative for the widespread implementation of fuel cell devices. Herein, we present a combined theoretical-experimental approach to discover and design first-row transition metal antimonates as excellent electrocatalytic materials for the ORR. Theoretically, we identify first-row transition metal antimonates─MSb2O6, where M = Mn, Fe, Co, and Ni─as nonprecious metal catalysts with good oxygen binding energetics, conductivity, thermodynamic phase stability, and aqueous stability. Among the considered antimonates, MnSb2O6 shows the highest theoretical ORR activity based on the 4e- ORR kinetic volcano. Experimentally, nanoparticulate transition metal antimonate catalysts are found to have a minimum of a 2.5-fold enhancement in intrinsic mass activity (on transition metal mass basis) relative to the corresponding transition metal oxide at 0.7 V vs RHE in 0.1 M KOH. MnSb2O6 is the most active catalyst under these conditions, with a 3.5-fold enhancement on a per Mn mass activity basis and 25-fold enhancement on a surface area basis over its antimony-free counterpart. Electrocatalytic and material stability are demonstrated over a 5 h chronopotentiometry experiment in the stability window identified by theoretical Pourbaix analysis. This study further highlights the stable and electrically conductive antimonate structure as a framework to tune the activity and selectivity of nonprecious metal oxide active sites for ORR catalysis.

  View details for DOI 10.1021/acsnano.2c00420

  View details for PubMedID 35377139

• Engineering metal-metal oxide surfaces for high-performance oxygen reduction on Ag-Mn electrocatalysts ENERGY & ENVIRONMENTAL SCIENCE Zeledon, J., Gunasooriya, G., Kamat, G. A., Kreider, M. E., Ben-Naim, M., Hubert, M. A., Acosta, J., Norskov, J. K., Stevens, M., Jaramillo, T. F. 2022

  View details for DOI 10.1039/d2ee00047d

  View details for Web of Science ID 000766715400001

• Acid anion electrolyte effects on platinum for oxygen and hydrogen electrocatalysis COMMUNICATIONS CHEMISTRY Kamat, G., Zeledon, J., Gunasooriya, G., Dull, S. M., Perryman, J. T., Norskov, J. K., Stevens, M., Jaramillo, T. F. 2022; 5 (1)

  View details for DOI 10.1038/s42004-022-00635-1

  View details for Web of Science ID 000757832500001

• Acid anion electrolyte effects on platinum for oxygen and hydrogen electrocatalysis. Communications chemistry Kamat, G. A., Zamora Zeledón, J. A., Gunasooriya, G. T., Dull, S. M., Perryman, J. T., Nørskov, J. K., Stevens, M. B., Jaramillo, T. F. 2022; 5 (1): 20

  Abstract

  Platinum is an important material with applications in oxygen and hydrogen electrocatalysis. To better understand how its activity can be modulated through electrolyte effects in the double layer microenvironment, herein we investigate the effects of different acid anions on platinum for the oxygen reduction/evolution reaction (ORR/OER) and hydrogen evolution/oxidation reaction (HER/HOR) in pH 1 electrolytes. Experimentally, we see the ORR activity trend of HClO4 > HNO3 > H2SO4, and the OER activity trend of HClO4 [Formula: see text] HNO3 ∼ H2SO4. HER/HOR performance is similar across all three electrolytes. Notably, we demonstrate that ORR performance can be improved 4-fold in nitric acid compared to in sulfuric acid. Assessing the potential-dependent role of relative anion competitive adsorption with density functional theory, we calculate unfavorable adsorption on Pt(111) for all the anions at HER/HOR conditions while under ORR/OER conditions [Formula: see text] binds the weakest followed by [Formula: see text] and [Formula: see text]. Our combined experimental-theoretical work highlights the importance of understanding the role of anions across a large potential range and reveals nitrate-like electrolyte microenvironments as interesting possible sulfonate alternatives to mitigate the catalyst poisoning effects of polymer membranes/ionomers in electrochemical systems. These findings help inform rational design approaches to further enhance catalyst activity via microenvironment engineering.

  View details for DOI 10.1038/s42004-022-00635-1

  View details for PubMedID 36697647

  View details for PubMedCentralID PMC9814610

• Probing the Effects of Acid Electrolyte Anions on Electrocatalyst Activity and Selectivity for the Oxygen Reduction Reaction CHEMELECTROCHEM Zamora Zeledon, J. A., Kamat, G., Gunasooriya, G., Norskov, J. K., Stevens, M., Jaramillo, T. F. 2021; 8 (13): 2467-2478

  View details for DOI 10.1002/celc.202100500

  View details for Web of Science ID 000674273100011

• Understanding Degradation Mechanisms in SrIrO3 Oxygen Evolution Electrocatalysts: Chemical and Structural Microscopy at the Nanoscale ADVANCED FUNCTIONAL MATERIALS Ben-Naim, M., Liu, Y., Stevens, M., Lee, K., Wette, M. R., Boubnov, A., Trofimov, A. A., Ievlev, A. V., Belianinov, A., Davis, R. C., Clemens, B. M., Bare, S. R., Hikita, Y., Hwang, H. Y., Higgins, D. C., Sinclair, R., Jaramillo, T. F. 2021

  View details for DOI 10.1002/adfm.202101542

  View details for Web of Science ID 000662722100001

• Isolating the Electrocatalytic Activity of a Confined NiFe Motif within Zirconium Phosphate ADVANCED ENERGY MATERIALS Sanchez, J., Stevens, M., Young, A. R., Gallo, A., Zhao, M., Liu, Y., Ramos-Garces, M. V., Ben-Naim, M., Colon, J. L., Sinclair, R., King, L. A., Bajdich, M., Jaramillo, T. F. 2021

  View details for DOI 10.1002/aenm.202003545

  View details for Web of Science ID 000639983100001

• Tuning the electronic structure of Ag-Pd alloys to enhance performance for alkaline oxygen reduction. Nature communications Zamora Zeledón, J. A., Stevens, M. B., Gunasooriya, G. T., Gallo, A. n., Landers, A. T., Kreider, M. E., Hahn, C. n., Nørskov, J. K., Jaramillo, T. F. 2021; 12 (1): 620

  Abstract

  Alloying is a powerful tool that can improve the electrocatalytic performance and viability of diverse electrochemical renewable energy technologies. Herein, we enhance the activity of Pd-based electrocatalysts via Ag-Pd alloying while simultaneously lowering precious metal content in a broad-range compositional study focusing on highly comparable Ag-Pd thin films synthesized systematically via electron-beam physical vapor co-deposition. Cyclic voltammetry in 0.1 M KOH shows enhancements across a wide range of alloys; even slight alloying with Ag (e.g. Ag0.1Pd0.9) leads to intrinsic activity enhancements up to 5-fold at 0.9 V vs. RHE compared to pure Pd. Based on density functional theory and x-ray absorption, we hypothesize that these enhancements arise mainly from ligand effects that optimize adsorbate-metal binding energies with enhanced Ag-Pd hybridization. This work shows the versatility of coupled experimental-theoretical methods in designing materials with specific and tunable properties and aids the development of highly active electrocatalysts with decreased precious-metal content.

  View details for DOI 10.1038/s41467-021-20923-z

  View details for PubMedID 33504815

• Identifying and Tuning the In Situ Oxygen-Rich Surface of Molybdenum Nitride Electrocatalysts for Oxygen Reduction ACS APPLIED ENERGY MATERIALS Stevens, M., Kreider, M. E., Patel, A. M., Wang, Z., Liu, Y., Gibbons, B. M., Statt, M. J., Ievlev, A., Sinclair, R., Mehta, A., Davis, R. C., Norskov, J. K., Gallo, A., King, L. A., Jaramillo, T. F. 2020; 3 (12): 12433–46

  View details for DOI 10.1021/acsaem.0c02423

  View details for Web of Science ID 000618839200099

• Nanosized Zirconium Porphyrinic Metal-Organic Frameworks that Catalyze the Oxygen Reduction Reaction in Acid SMALL METHODS Chen, G., Stevens, M., Liu, Y., King, L. A., Park, J., Kim, T., Sinclair, R., Jaramillo, T. F., Bao, Z. 2020

  View details for DOI 10.1002/smtd.202000085

  View details for Web of Science ID 000557369400001

• Nitride or Oxynitride? Elucidating the Composition-Activity Relationships in Molybdenum Nitride Electrocatalysts for the Oxygen Reduction Reaction CHEMISTRY OF MATERIALS Kreider, M. E., Stevens, M., Liu, Y., Patel, A. M., Statt, M. J., Gibbons, B. M., Gallo, A., Ben-Naim, M., Mehta, A., Davis, R. C., Ievlev, A., Norskov, J. K., Sinclair, R., King, L. A., Jaramillo, T. F. 2020; 32 (7): 2946–60

  View details for DOI 10.1021/acs.chemmater.9b05212

  View details for Web of Science ID 000526394000025

• In Situ X-Ray Absorption Spectroscopy Disentangles the Roles of Copper and Silver in a Bimetallic Catalyst for the Oxygen Reduction Reaction CHEMISTRY OF MATERIALS Gibbons, B. M., Wette, M., Stevens, M., Davis, R. C., Siahrostami, S., Kreider, M., Mehta, A., Higgins, D. C., Clemens, B. M., Jaramillo, T. F. 2020; 32 (5): 1819–27

  View details for DOI 10.1021/acs.chemmater.9b03963

  View details for Web of Science ID 000519337600008

• Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni, N-doped Carbon Catalysts. Angewandte Chemie (International ed. in English) Koshy, D. n., Chen, S. n., Lee, D. U., Burke Stevens, M. n., Abdellah, A. n., Dull, S. n., Chen, G. n., Nordlund, D. n., Gallo, A. n., Hahn, C. n., Higgins, D. C., Bao, Z. n., Jaramillo, T. n. 2020

  Abstract

  Ni,N-doped carbon catalysts have shown promising catalytic performance for CO 2 electroreduction (CO 2 R) to CO; this activity has been attributed to the presence of nitrogen-coordinated, single metal atom active sites. However, experimentally confirming Ni-N bonding and correlating CO 2 reduction (CO 2 R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile-derived Ni, N-doped carbon electrocatalysts (Ni-PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO- 2 R to CO partial current density increased with increased Ni content before plateauing at 2 wt% which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft x-ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square-planar geometry that strongly resembles the active sites of molecular metal-porphyrin catalysts.

  View details for DOI 10.1002/anie.201912857

  View details for PubMedID 31919948

• Ternary Ni-Co-Fe oxyhydroxide oxygen evolution catalysts: Intrinsic activity trends, electrical conductivity, and electronic band structure NANO RESEARCH Stevens, M., Enman, L. J., Korkus, E., Zaffran, J., Trang, C. M., Asbury, J., Kast, M. G., Toroker, M., Boettcher, S. W. 2019; 12 (9): 2288–95

  View details for DOI 10.1007/s12274-019-2391-y

  View details for Web of Science ID 000485041800028

• Earth-Abundant Oxygen Electrocatalysts for Alkaline Anion-Exchange-Membrane Water Electrolysis: Effects of Catalyst Conductivity and Comparison with Performance in Three-Electrode Cells ACS CATALYSIS Xu, D., Stevens, M., Cosby, M. R., Oener, S. Z., Smith, A. M., Enman, L. J., Ayers, K. E., Capuano, C. B., Renner, J. N., Danilovic, N., Li, Y., Wang, H., Zhang, Q., Boettcher, S. W. 2019; 9 (1): 7–15

  View details for DOI 10.1021/acscatal.8b04001

  View details for Web of Science ID 000455286600002

• Operando X-Ray Absorption Spectroscopy Shows Iron Oxidation Is Concurrent with Oxygen Evolution in Cobalt-Iron (Oxy)hydroxide Electrocatalysts ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Enman, L. J., Stevens, M., Dahan, M., Nellist, M. R., Toroker, M., Boettcher, S. W. 2018; 57 (39): 12840–44

  Abstract

  Iron cations are essential for the high activity of nickel and cobalt-based (oxy)hydroxides for the oxygen evolution reaction, but the role of iron in the catalytic mechanism remains under active investigation. Operando X-ray absorption spectroscopy and density functional theory calculations are used to demonstrate partial Fe oxidation and a shortening of the Fe-O bond length during oxygen evolution on Co(Fe)Ox Hy . Cobalt oxidation during oxygen evolution is only observed in the absence of iron. These results demonstrate a different mechanism for water oxidation in the presence and absence of iron and support the hypothesis that oxidized iron species are involved in water-oxidation catalysis on Co(Fe)Ox Hy .

  View details for DOI 10.1002/anie.201808818

  View details for Web of Science ID 000444941600041

  View details for PubMedID 30112793

• Transition-Metal-Incorporated Aluminum Oxide Thin Films: Toward Electronic Structure Design in Amorphous Mixed-Metal Oxides JOURNAL OF PHYSICAL CHEMISTRY C Enman, L. J., Kast, M. G., Cochran, E. A., Pledger, E., Stevens, M., Boettcher, S. W. 2018; 122 (25): 13691–704

  View details for DOI 10.1021/acs.jpcc.8b00239

  View details for Web of Science ID 000437811500054

• The role of Cr doping in Ni-Fe oxide/(oxy)hydroxide electrocatalysts for oxygen evolution ELECTROCHIMICA ACTA Xu, D., Stevens, M., Rui, Y., DeLuca, G., Boettcher, S. W., Reichmanis, E., Li, Y., Zhang, Q., Wang, H. 2018; 265: 10–18

  View details for DOI 10.1016/j.electacta.2018.01.143

  View details for Web of Science ID 000425751600002

• Morphology Dynamics of Single-Layered Ni(OH)(2)/NiOOH Nanosheets and Subsequent Fe Incorporation Studied by &ITin Situ&IT Electrochemical Atomic Force Microscopy NANO LETTERS Deng, J., Nellist, M. R., Stevens, M., Dette, C., Wang, Y., Boettcher, S. W. 2017; 17 (11): 6922–26

  Abstract

  Nickel (oxy)hydroxide-based (NiOxHy) materials are widely used for energy storage and conversion devices. Understanding dynamic processes at the solid-liquid interface of nickel (oxy)hydroxide is important to improve reaction kinetics and efficiencies. In this study, in situ electrochemical atomic force microscopy (EC-AFM) was used to directly investigate dynamic changes of single-layered Ni(OH)2 nanosheets during electrochemistry measurements. Reconstruction of Ni(OH)2 nanosheets, along with insertion of ions from the electrolyte, results in an increase of the volume by 56% and redox capacity by 300%. We also directly observe Fe cations adsorb and integrate heterogeneously into or onto the nanosheets as a function of applied potential, further increasing apparent volume. Our findings are important for the fundamental understanding of NiOxHy-based supercapacitors and oxygen-evolution catalysts, illustrating the dynamic nature of Ni-based nanostructures under electrochemical conditions.

  View details for DOI 10.1021/acs.nanolett.7b03313

  View details for Web of Science ID 000415029000062

  View details for PubMedID 28991484

• Reactive Fe-Sites in Ni/Fe (Oxy)hydroxide Are Responsible for Exceptional Oxygen Electrocatalysis Activity JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Stevens, M., Trang, C. M., Enman, L. J., Deng, J., Boettcher, S. W. 2017; 139 (33): 11361–64

  Abstract

  Fe is a critical component of record-activity Ni/Fe (oxy)hydroxide (Ni(Fe)OxHy) oxygen evolution reaction (OER) catalysts, yet its precise role remains unclear. We report evidence for different types of Fe species within Ni(Fe)OxHy- those that are rapidly incorporated into the Ni oxyhydroxide from Fe cations in solution (and that are likely at edges or defects) and are responsible for the enhanced OER activity, and those substituting for bulk Ni that modulate the observed Ni voltammetry. These results suggest that the exceptional OER activity of Ni(Fe)OxHy does not depend on Fe in the bulk or on average electrochemical properties of the Ni cations measured by voltammetry, and instead emphasize the role of the local structure.

  View details for DOI 10.1021/jacs.7b07117

  View details for Web of Science ID 000408519600014

  View details for PubMedID 28789520

• Influence of Electrolyte Cations on Ni(Fe)OOH Catalyzed Oxygen Evolution Reaction CHEMISTRY OF MATERIALS Zaffran, J., Stevens, M., Trang, C. M., Nagli, M., Shehadeh, M., Boettcher, S. W., Toroker, M. 2017; 29 (11): 4761–67

  View details for DOI 10.1021/acs.chemmater.7b00517

  View details for Web of Science ID 000403530600019

• Measurement Techniques for the Study of Thin Film Heterogeneous Water Oxidation Electrocatalysts CHEMISTRY OF MATERIALS Stevens, M., Enman, L. J., Batchellor, A. S., Cosby, M. R., Vise, A. E., Trang, C. M., Boettcher, S. W. 2017; 29 (1): 120–40

  View details for DOI 10.1021/acs.chemmater.6b02796

  View details for Web of Science ID 000391898300012

• Fe (Oxy)hydroxide Oxygen Evolution Reaction Electrocatalysis: Intrinsic Activity and the Roles of Electrical Conductivity, Substrate, and Dissolution CHEMISTRY OF MATERIALS Zou, S., Burke, M. S., Kast, M. G., Fan, J., Danilovic, N., Boettcher, S. W. 2015; 27 (23): 8011–20

  View details for DOI 10.1021/acs.chemmater.5b03404

  View details for Web of Science ID 000366223200021

• Oxygen Evolution Reaction Electrocatalysis on Transition Metal Oxides and (Oxy)hydroxides: Activity Trends and Design Principles CHEMISTRY OF MATERIALS Burke, M. S., Enman, L. J., Batchellor, A. S., Zou, S., Boettcher, S. W. 2015; 27 (22): 7549–58

  View details for DOI 10.1021/acs.chemmater.5b03148

  View details for Web of Science ID 000365465600002

• Revised Oxygen Evolution Reaction Activity Trends for First-Row Transition-Metal (Oxy)hydroxides in Alkaline Media JOURNAL OF PHYSICAL CHEMISTRY LETTERS Burke, M. S., Zou, S., Enman, L. J., Kellon, J. E., Gabor, C. A., Pledger, E., Boettcher, S. W. 2015; 6 (18): 3737–42

  Abstract

  First-row transition-metal oxides and (oxy)hydroxides catalyze the oxygen evolution reaction (OER) in alkaline media. Understanding the intrinsic catalytic activity provides insight into improved catalyst design. Experimental and computationally predicted activity trends, however, have varied substantially. Here we describe a new OER activity trend for nominally oxyhydroxide thin films of Ni(Fe)O(x)H(y) > Co(Fe)O(x)H(y) > FeO(x)H(y)-AuO(x) > FeO(x)H(y) > CoO(x)H(y) > NiO(x)H(y) > MnO(x)H(y). This intrinsic trend has been previously obscured by electrolyte impurities, potential-dependent electrical conductivity, and difficulty in correcting for surface-area or mass-loading differences. A quartz-crystal microbalance was used to monitor mass in situ and X-ray photoelectron spectroscopy to measure composition and impurity levels. These new results provide a basis for comparison to theory and help guide the design of improved catalyst systems.

  View details for DOI 10.1021/acs.jpclett.5b01650

  View details for Web of Science ID 000361858800036

  View details for PubMedID 26722749

• Cobalt-Iron (Oxy)hydroxide Oxygen Evolution Electrocatalysts: The Role of Structure and Composition on Activity, Stability, and Mechanism JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Burke, M. S., Kast, M. G., Trotochaud, L., Smith, A. M., Boettcher, S. W. 2015; 137 (10): 3638–48

  Abstract

  Cobalt oxides and (oxy)hydroxides have been widely studied as electrocatalysts for the oxygen evolution reaction (OER). For related Ni-based materials, the addition of Fe dramatically enhances OER activity. The role of Fe in Co-based materials is not well-documented. We show that the intrinsic OER activity of Co(1-x)Fe(x)(OOH) is ∼100-fold higher for x ≈ 0.6-0.7 than for x = 0 on a per-metal turnover frequency basis. Fe-free CoOOH absorbs Fe from electrolyte impurities if the electrolyte is not rigorously purified. Fe incorporation and increased activity correlate with an anodic shift in the nominally Co(2+/3+) redox wave, indicating strong electronic interactions between the two elements and likely substitutional doping of Fe for Co. In situ electrical measurements show that Co(1-x)Fe(x)(OOH) is conductive under OER conditions (∼0.7-4 mS cm(-1) at ∼300 mV overpotential), but that FeOOH is an insulator with measurable conductivity (2.2 × 10(-2) mS cm(-1)) only at high overpotentials >400 mV. The apparent OER activity of FeOOH is thus limited by low conductivity. Microbalance measurements show that films with x ≥ 0.54 (i.e., Fe-rich) dissolve in 1 M KOH electrolyte under OER conditions. For x < 0.54, the films appear chemically stable, but the OER activity decreases by 16-62% over 2 h, likely due to conversion into denser, oxide-like phases. We thus hypothesize that Fe is the most-active site in the catalyst, while CoOOH primarily provides a conductive, high-surface area, chemically stabilizing host. These results are important as Fe-containing Co- and Ni-(oxy)hydroxides are the fastest OER catalysts known.

  View details for DOI 10.1021/jacs.5b00281

  View details for Web of Science ID 000351420800034

  View details for PubMedID 25700234

• Contributions to activity enhancement via Fe incorporation in Ni-(oxy) hydroxide/borate catalysts for near-neutral pH oxygen evolution CHEMICAL COMMUNICATIONS Smith, A. M., Trotochaud, L., Burke, M. S., Boettcher, S. W. 2015; 51 (25): 5261–63

  Abstract

  Ni-borate materials are oxygen evolution catalysts that operate at near-neutral pH and have been found previously to improve due to structural changes induced via anodic conditioning. We find that this increased activity after conditioning at 0.856 V vs. SCE, as measured on a turn-over frequency basis (TOF) at 400 mV overpotential (TOF = 0.38 s(-1)), accompanies significant Fe incorporation (14%). Films conditioned in Fe-free electrolyte exhibit ∼10 times lower activity (TOF = 0.03 s(-1)). By co-depositing Fe-Ni we demonstrate high activity without conditioning (TOF = 0.24 s(-1)) which improves further with shortened (∼30 min) conditioning (TOF = 1.4 s(-1)).

  View details for DOI 10.1039/c4cc08670h

  View details for Web of Science ID 000351393600012

  View details for PubMedID 25579228