Thomas Hersbach

All Publications

• A multimodal flow reactor for photocatalysis under atmospheric conditions JOURNAL OF CHEMICAL PHYSICS Garcia-Esparza, A. T., Qureshi, M., Skoien, D., Hersbach, T. P., Sokaras, D. 2023; 159 (24)

  Abstract

  Photocatalysis is a promising concept for the direct conversion of solar energy into fuels and chemicals. The design, experimental protocol, and performance of a multimodal and versatile flow reactor for the characterization of powdered and immobilized photocatalysts are herein presented. Ultimately, this instrument enables rigorous evaluation of photocatalysis performance metrics. The apparatus quantifies transient gas-phase reaction products via online real-time gas analyzer mass spectrometry (RTGA-MS). For H2, the most challenging gas, the photocatalytic system's RTGA-MS gas detection sensitivity spans over three orders of magnitude and can detect down to tens of parts per million under atmospheric conditions. Using Pt nanoparticles supported on anatase TiO2 photocatalyst via wet impregnation, the instrument's capability for the characterization of photocatalytic H2 evolution is demonstrated, resulting in an apparent quantum yield (AQY) of 48.1% ± 0.9% at 320 nm, 45.7% ± 0.3% at 340 nm and 31% ± 1% at 360 nm. The photodeposition of Pt on anatase TiO2 was employed to demonstrate the instrument's capability to track the transient behavior of photocatalysts, resulting in an improved 55% ± 2% AQY for H2 evolution at 340 nm from aqueous methanol. This photocatalytic instrument enables systematic study of a wide variety of photocatalytic reactions such as water splitting and CO2 reduction to valuable C2+ fuels and chemicals.

  View details for DOI 10.1063/5.0179259

  View details for Web of Science ID 001133660000005

  View details for PubMedID 38153150

  View details for PubMedCentralID PMC10756709

• Improved electrocatalytic activity of Pt on carbon nanofibers for glucose oxidation mediated by support oxygen groups in Pt perimeter APPLIED CATALYSIS B-ENVIRONMENTAL Van der Ham, M. M., Hersbach, T. P., Delgado, J. J., Matson, B. D., Lim, J., Fuhrer, M., Van Haasterecht, T., Verhoeven, M. M., Hensen, E. M., Sokaras, D., Koper, M. M., Bitter, J. H. 2023; 338

  View details for DOI 10.1016/j.apcatb.2023.123046

  View details for Web of Science ID 001060211500001

• Universities: cut research links with fossil-fuel companies. Nature Kashtan, Y., Toweh, J., Hersbach, T. J. 2022; 612 (7940): 404

  View details for DOI 10.1038/d41586-022-04404-x

  View details for PubMedID 36513836

• pH- and Functionalization-Dependent Host-Guest Interactions Between Fluorescein and Various Poly(amidoamine) Dendrimers JOURNAL OF PHYSICAL CHEMISTRY B Hersbach, T. P., Rabin, C. 2022: 9632-9642

  Abstract

  Dendrimers are branched macromolecules that can be functionalized with a large variety of chemical moieties. Dendrimers can therefore be specifically designed to interact with target molecules. Although tailored dendrimers hold promise for targeted drug delivery and wastewater cleanup, these applications require more detailed and systematic studies on how dendrimer-guest interactions depend on environmental conditions. In light of this need, we studied pH-dependent interactions between fluorescein and poly(amidoamine) dendrimers with three different terminal groups. Crucially, both fluorescein and dendrimers have multiple protonation equilibria, which can enable interactions in different pH windows through various possible mechanisms. Such interactions are studied through UV-vis and fluorescence spectroscopies, which reveal a redshift that occurs upon fluorescein-dendrimer binding. The resulting pH-dependent spectra are complex but can be analyzed quantitatively with an open-source mathematical protocol. Consequently, we show that fluorescein binds across four pH units with amine-terminated dendrimers, across two units with hydroxyl-terminated dendrimers and does not interact attractively with carboxyl-terminated dendrimers. These functionalization-dependent host-guest interactions stabilize fluorescein's dianionic form and are predominantly electrostatically driven, with likely auxiliary hydrogen and CH-π bonding. Notably, these auxiliary mechanisms appear too weak to drive dendrimer-fluorescein interactions on their own. Overall, this work yields valuable insights into dendrimer-fluorescein association and provides a readily reproducible framework for studying host-guest interactions.

  View details for DOI 10.1021/acs.jpcb.2c06288

  View details for Web of Science ID 000888520600001

  View details for PubMedID 36378255

• Efficient and Stable Acidic Water Oxidation Enabled by Low-Concentration, High-Valence Iridium Sites ACS ENERGY LETTERS Shi, X., Peng, H., Hersbach, T. P., Jiang, Y., Zeng, Y., Baek, J., Winther, K. T., Sokaras, D., Zheng, X., Bajdich, M. 2022

  View details for DOI 10.1021/acsenergylett.2c00578

  View details for Web of Science ID 000821179900001

• Base-Accelerated Degradation of Nanosized Platinum Electrocatalysts ACS CATALYSIS Hersbach, T. P., Garcia, A. C., Kroll, T., Sokaras, D., Koper, M. M., Garcia-Esparza, A. T. 2021; 11 (15): 9904-9915

  View details for DOI 10.1021/acscatal.1c02468

  View details for Web of Science ID 000684035000092

• Electrochemical Cleaning Stability and Oxygen Reduction Reaction Activity of 1-2 nm Dendrimer-Encapsulated Au Nanoparticles CHEMELECTROCHEM Strasser, J. W., Hersbach, T. P., Liu, J., Lapp, A. S., Frenkel, A. I., Crooks, R. M. 2021; 8 (13): 2545-2555

  View details for DOI 10.1002/celc.202100549

  View details for Web of Science ID 000674273100020

• Cathodic corrosion: 21st century insights into a 19th century phenomenon CURRENT OPINION IN ELECTROCHEMISTRY Hersbach, T. P., Koper, M. M. 2021; 26

  View details for DOI 10.1016/j.coelec.2020.100653

  View details for Web of Science ID 000632822300015

• Nanoscale morphological evolution of monocrystalline Pt surfaces during cathodic corrosion PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Arulmozhi, N., Hersbach, T. P., Koper, M. M. 2020; 117 (51): 32267–77

  Abstract

  This paper studies the cathodic corrosion of a spherical single crystal of platinum in an aqueous alkaline electrolyte, to map out the detailed facet dependence of the corrosion structures forming during this still largely unexplored electrochemical phenomenon. We find that anisotropic corrosion of the platinum electrode takes place in different stages. Initially, corrosion etch pits are formed, which reflect the local symmetry of the surface: square pits on (100) facets, triangular pits on (111) facets, and rectangular pits on (110) facets. We hypothesize that these etch pits are formed through a ternary metal hydride corrosion intermediate. In contrast to anodic corrosion, the (111) facet corrodes the fastest, and the (110) facet corrodes the slowest. For cathodic corrosion on the (100) facet and on higher-index surfaces close to the (100) plane, the etch pit destabilizes in a second growth stage, by etching faster in the (111) direction, leading to arms in the etch pit, yielding a concave octagon-shaped pit. In a third growth stage, these arms develop side arms, leading to a structure that strongly resembles a self-similar diffusion-limited growth pattern, with strongly preferred growth directions.

  View details for DOI 10.1073/pnas.2017086117

  View details for Web of Science ID 000601315200017

  View details for PubMedID 33288700

  View details for PubMedCentralID PMC7768681

• Tailoring the Electrocatalytic Activity and Selectivity of Pt(111) through Cathodic Corrosion ACS CATALYSIS Hersbach, T. P., Ye, C., Garcia, A. C., Koper, M. M. 2020; 10 (24): 15104–13

  View details for DOI 10.1021/acscatal.0c04016

  View details for Web of Science ID 000608850500063

• Alkali Metal Cation Effects in Structuring Pt, Rh, and Au Surfaces through Cathodic Corrosion ACS APPLIED MATERIALS & INTERFACES Hersbach, T. P., McCrum, I. T., Anastasiadou, D., Wever, R., Calle-Vallejo, F., Koper, M. M. 2018; 10 (45): 39363–79

  Abstract

  Cathodic corrosion is an electrochemical etching process that alters metallic surfaces by creating nanoparticles and a variety of etching features. Because these features typically have a preferential orientation, cathodic corrosion can be applied to modify and nanostructure electrode surfaces. However, this application of cathodic corrosion is currently limited by an insufficient chemical understanding of its underlying mechanism. This includes the role of alkali metal cations, which are thought to be crucial in both enabling cathodic corrosion and controlling its final facet preference. This work addresses this knowledge gap by exploring the cathodic corrosion of Pt, Rh, and Au in LiOH, NaOH, and KOH through both experimental and theoretical methods. These methods demonstrate that cations are adsorbed during cathodic corrosion and play a major role in controlling the onset potential and final surface morphology in cathodic corrosion. Interestingly, an equally significant role appears to be played by adsorbed hydrogen, based on calculations using literature density functional theory data. Considering the significance of both hydrogen and electrolyte cations, it is hypothesized that cathodic corrosion might proceed via an intermediate ternary metal hydride. This fundamental insight leads to both metal-specific recommendations and more general guidelines for applying cathodic corrosion to structure metallic surfaces.

  View details for DOI 10.1021/acsami.8b13883

  View details for Web of Science ID 000451100500078

  View details for PubMedID 30351902

• Hydrogen adsorption on nano-structured platinum electrodes FARADAY DISCUSSIONS Diaz-Morales, O., Hersbach, T. P., Badan, C., Garcia, A. C., Koper, M. M. 2018; 210: 301–15

  Abstract

  The "hydrogen region" of platinum is a powerful tool to structurally characterize nanostructured platinum electrodes. In recent years, the understanding of this hydrogen region has improved considerably: on Pt(111) sites, there is indeed only hydrogen adsorption, while on step sites, the hydrogen region involves the replacement of adsorbed hydrogen by adsorbed hydroxyl which interacts with co-adsorbed cations. However, the hydrogen region features an enigmatic and less well-understood "third hydrogen peak", which develops on oxidatively roughened platinum electrodes as well as on platinum electrodes with a high (110) step density that have been subjected to a high concentration of hydrogen. In this paper, we present evidence that the peak involves surface-adsorbed hydrogen (instead of subsurface hydrogen) on a locally "reconstructed" (110)-type surface site. This site is unstable when the hydrogen is oxidatively removed. The cation sensitivity of the third hydrogen peak appears different from other step-related peaks, suggesting that the chemistry involved may still be subtly different from the other features in the hydrogen region.

  View details for DOI 10.1039/c8fd00062j

  View details for Web of Science ID 000449765000009

  View details for PubMedID 29987308

• Local structure and composition of PtRh nanoparticles produced through cathodic corrosion PHYSICAL CHEMISTRY CHEMICAL PHYSICS Hersbach, T. P., Kortlever, R., Lehtimaki, M., Krtil, P., Koper, M. M. 2017; 19 (16): 10301–8

  Abstract

  Alloy nanoparticles fulfill an important role in catalysis. As such, producing them in a simple and clean way is much desired. A promising alloy nanoparticle production method is cathodic corrosion, which generates particles by applying an AC voltage to an alloy electrode. However, this harsh AC potential program might affect the final elemental distribution of the nanoparticles. In this work, we address this issue by characterizing the time that is required to create 1 μmol of Rh, Pt12Rh88, Pt55Rh45 and Pt nanoparticles under various applied potentials. The corrosion time measurements are complemented by structural characterization through transmission electron microscopy, X-ray diffraction and X-ray absorption spectroscopy. The corrosion times indicate that platinum and rhodium corrode at different rates and that the cathodic corrosion rates of the alloys are dominated by platinum. In addition, the structure-sensitive techniques reveal that the elemental distributions of the created alloy nanoparticles indeed exhibit small degrees of elemental segregation. These results indicate that the atomic alloy structure is not always preserved during cathodic corrosion.

  View details for DOI 10.1039/c7cp01059a

  View details for Web of Science ID 000400117700011

  View details for PubMedID 28393941

• Anisotropic etching of platinum electrodes at the onset of cathodic corrosion NATURE COMMUNICATIONS Hersbach, T. P., Yanson, A. I., Koper, M. M. 2016; 7: 12653

  Abstract

  Cathodic corrosion is a process that etches metal electrodes under cathodic polarization. This process is presumed to occur through anionic metallic reaction intermediates, but the exact nature of these intermediates and the onset potential of their formation is unknown. Here we determine the onset potential of cathodic corrosion on platinum electrodes. Electrodes are characterized electrochemically before and after cathodic polarization in 10 M sodium hydroxide, revealing that changes in the electrode surface start at an electrode potential of -1.3 V versus the normal hydrogen electrode. The value of this onset potential rules out previous hypotheses regarding the nature of cathodic corrosion. Scanning electron microscopy shows the formation of well-defined etch pits with a specific orientation, which match the voltammetric data and indicate a remarkable anisotropy in the cathodic etching process, favouring the creation of (100) sites. Such anisotropy is hypothesized to be due to surface charge-induced adsorption of electrolyte cations.

  View details for DOI 10.1038/ncomms12653

  View details for Web of Science ID 000382456300001

  View details for PubMedID 27554398

  View details for PubMedCentralID PMC4999510

• Reactions at the nanoscale: general discussion FARADAY DISCUSSIONS Hersbach, T., MacPherson, J., Magnussen, O., Crooks, R., Higgins, S., Fermin, D., Kanouii, F., Schuhmann, W., Nichols, R., Mitra, S., Schmickler, W., Tschulik, K., Bartlett, P., Faez, S., Nogala, W., Eikerling, M., Kranz, C., Unwin, P., Koper, M., Lemay, S., Mount, A., Ewing, A., Tian, Z., White, H., Chen, S., Clausmeyer, J., Krischer, K. 2016; 193: 265-292

  View details for DOI 10.1039/C6FD90067D

  View details for Web of Science ID 000390786000016

  View details for PubMedID 27892968

• Electrochemistry of single nanoparticles: general discussion FARADAY DISCUSSIONS Albrecht, T., MacPherson, J., Magnussen, O., Fermin, D., Crooks, R., Gooding, J., Hersbach, T., Kanoufi, F., Schuhmann, W., Bentley, C., Tao, N., Mitra, S., Krischer, K., Tschulik, K., Faez, S., Nogala, W., Unwin, P., Long, Y., Koper, M., Tian, Z., Alpuche-Aviles, M. A., White, H., Brasiliense, V., Kranz, C., Schmickler, W., Stevenson, K., Jing, C., Edwards, M. 2016; 193: 387-413

  View details for DOI 10.1039/c6fd90068b

  View details for Web of Science ID 000390786000023

  View details for PubMedID 27892971

• Anisotropic etching of rhodium and gold as the onset of nanoparticle formation by cathodic corrosion FARADAY DISCUSSIONS Hersbach, T. P., Mints, V. A., Calle-Vallejo, F., Yanson, A. I., Koper, M. M. 2016; 193: 207–22

  Abstract

  Cathodic corrosion is a phenomenon in which negatively polarized metal electrodes are degraded by cathodic etching and nanoparticle formation. Though these changes are dramatic and sometimes even visible by eye, the exact mechanisms underlying cathodic corrosion are still unclear. This work aims to improve the understanding of cathodic corrosion by studying its onset on rhodium and gold electrodes, which are subjected to various constant cathodic potentials in 10 M NaOH. After this polarization, the electrodes are studied using cyclic voltammetry and scanning electron microscopy, allowing a corrosion onset potential of -1.3 V vs. NHE for rhodium and -1.6 V vs. NHE for gold to be defined. The mildness of the potentials on both metals suggests that cathodic corrosion is less extreme and more ubiquitous than expected. Furthermore, we are able to observe well-defined rectangular etch pits on rhodium. Combined with rhodium cyclic voltammetry, this indicates a strong preference for forming (100) sites during corrosion. In contrast, a (111) preference is indicated on gold by voltammetry and the presence of well-oriented quasi-octahedral nanoparticles. This different etching behavior is suggested to be caused by preferential adsorption of sodium ions to surface defects, as is confirmed by density functional theory calculations.

  View details for DOI 10.1039/c6fd00078a

  View details for Web of Science ID 000390786000012

  View details for PubMedID 27722596

• Enhancement Effect of Noble Metals on Manganese Oxide for the Oxygen Evolution Reaction JOURNAL OF PHYSICAL CHEMISTRY LETTERS Seitz, L. C., Hersbach, T. J., Nordlund, D., Jaramillo, T. F. 2015; 6 (20): 4178-4183

  Abstract

  Developing improved catalysts for the oxygen evolution reaction (OER) is key to the advancement of a number of renewable energy technologies, including solar fuels production and metal air batteries. In this study, we employ electrochemical methods and synchrotron techniques to systematically investigate interactions between metal oxides and noble metals that lead to enhanced OER catalysis for water oxidation. In particular, we synthesize porous MnOx films together with nanoparticles of Au, Pd, Pt, or Ag and observe significant improvement in activity for the combined catalysts. Soft X-ray absorption spectroscopy (XAS) shows that increased activity correlates with increased Mn oxidation states to 4+ under OER conditions compared to bare MnOx, which exhibits minimal OER current and remains in a 3+ oxidation state. Thickness studies of bare MnOx films and of MnOx films deposited on Au nanoparticles reveal trends suggesting that the enhancement in activity arises from interfacial sites between Au and MnOx.

  View details for DOI 10.1021/acs.jpclett.5b01928

  View details for Web of Science ID 000363083900031

• Electro-Oxidation of Glycerol on Platinum Modified by Adatoms: Activity and Selectivity Effects TOPICS IN CATALYSIS Kwon, Y., Hersbach, T. P., Koper, M. M. 2014; 57 (14-16): 1272–76

  View details for DOI 10.1007/s11244-014-0292-6

  View details for Web of Science ID 000344157900018

• Electrochemical and Spectroelectrochemical Characterization of an Iridium-Based Molecular Catalyst for Water Splitting: Turnover Frequencies, Stability, and Electrolyte Effects JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Diaz-Morales, O., Hersbach, T. P., Hetterscheid, D. H., Reek, J. H., Koper, M. M. 2014; 136 (29): 10432–39

  Abstract

  We present a systematic electrochemical and spectroelectrochemical study of the catalytic activity for water oxidation of an iridium-N-dimethylimidazolin-2-ylidene (Ir-NHC-Me2) complex adsorbed on a polycrystalline gold electrode. The work aims to understand the effect of the electrolyte properties (anions and acidity) on the activity of the molecular catalyst and check its stability toward decomposition. Our results show that the iridium complex displays a very strong dependence on the electrolyte properties such that large enhancements in catalytic activity may be obtained by adequately choosing pH and anions in the electrolyte. The stability of the adsorbed compound was investigated in situ by Surface Enhanced Raman Spectroscopy and Online Electrochemical Mass Spectrometry showing that the catalyst exhibits good stability under anodic conditions, with no observable evidence for the decomposition to iridium oxide.

  View details for DOI 10.1021/ja504460w

  View details for Web of Science ID 000339471900040

  View details for PubMedID 24977640