Ryan Hannagan

All Publications

• Multimodal In Situ Characterization Uncovers Unexpected Stability of a Cobalt Electrocatalyst for Acidic Sustainable Energy Technologies. Journal of the American Chemical Society Aleman, A. M., Crago, C. F., Kamat, G. A., Mule, A. S., Avilés Acosta, J. E., Matthews, J. E., Keyes, N., Hannagan, R. T., Nielander, A. C., Stevens, M. B., Jaramillo, T. F. 2025

  Abstract

  An accelerated development of durable and affordable sustainable energy technologies is often hindered by a limited understanding of how nonprecious materials within these systems degrade. In acidic proton exchange membrane fuel cells and water electrolyzers, metallic cobalt (Co) is considered an unstable component that is often combined with precious metals or other stabilizers. To understand the mechanisms behind Co instability, we employ an experimental platform that quantifies dissolution with on-line inductively coupled plasma mass spectrometry and product formation with electrochemical mass spectrometry during electrochemical testing, along with ex situ characterization. Under varied conditions (electrocatalysis, time, gas-type saturation, and ion concentration), windows of Co stability are observed that are different than predicted with classical chemical thermodynamics, suggesting new stabilization and degradation mechanisms than previously understood. Notably, Co is active for the hydrogen evolution reaction (HER), with prolonged stability that is ∼300 mV greater than thermodynamically projected. Additionally, in an oxygenated environment, Co concurrently performs the HER and the oxygen reduction reaction (ORR) yet undergoes different morphology changes and dissolution mechanisms. Interestingly, at open-circuit voltage, there is a 22× decrease in dissolution in an oxygen-free environment, proposing a route to decrease Co losses during device shutdown protocols. Lastly, under more extreme operating conditions, Co becomes stable after a substantial amount of dissolution, suggesting that high concentrations of Co2+ ions in the microenvironment induce the formation of a stable CoHO2 surface. Altogether, these results can be leveraged to improve the design and development of more robust and cost-effective sustainable energy technologies, as well as promote strategic strategies for prolonged material utilization.

  View details for DOI 10.1021/jacs.4c16707

  View details for PubMedID 40079839

• On-line Inductively Coupled Plasma Mass Spectrometry Reveals Material Degradation Dynamics of Au and Cu Catalysts during Electrochemical CO2 Reduction. Journal of the American Chemical Society Yan, K., Lee, S. W., Yap, K. M., Mule, A. S., Hannagan, R. T., Matthews, J. E., Kamat, G. A., Lee, D. U., Stevens, M. B., Nielander, A. C., Jaramillo, T. F. 2025

  Abstract

  A significant challenge in commercializing electrochemical CO2 reduction (CO2R) is achieving catalyst durability. In this study, online inductively coupled mass spectrometry (ICP-MS) was used to investigate catalyst degradation via nanoparticle detachment and/or dissolution into metal ions under CO2R operating conditions in 0.1 M KHCO3. We developed an experimental framework with ex situ characterization to validate the online ICP-MS method for in situ evaluation of degradation from metal foils. By varying the applied potential and microenvironment (CO2 vs N2-saturated electrolyte), we gained insights into the degradation of Au and Cu foils under CO2R and hydrogen evolution reaction (HER) conditions. While both Au and Cu foils were observed to be stable to dissolution in these regimes, degradation via nanoparticle detachment from the foil surface at the femtogram scale was observed as a function of reaction conditions, providing new insights into material degradation mechanisms. When applying potential steps at -0.1 and -1.0 V vs the reversible hydrogen electrode (RHE), Au was found to degrade via nanoparticle detachment under CO2R operating conditions more than under HER conditions, while Cu was found to degrade via nanoparticle detachment in similar amounts during both reactions. Au lost ∼1.8× more mass and ∼7.5× more nanoparticles than Cu under CO2R operating conditions. This study demonstrates the use of online ICP-MS to gain insight into the degradation of Au and Cu, the importance of studying unconventional degradation mechanisms such as nanoparticle detachment, and that online ICP-MS can be further utilized to gain fundamental understanding of catalyst durability for a variety of reaction systems.

  View details for DOI 10.1021/jacs.4c13233

  View details for PubMedID 39871661

• Understanding the Effects of Anode Catalyst Conductivity and Loading on Catalyst Layer Utilization and Performance for Anion Exchange Membrane Water Electrolysis. ACS catalysis Kreider, M. E., Yu, H., Osmieri, L., Parimuha, M. R., Reeves, K. S., Marin, D. H., Hannagan, R. T., Volk, E. K., Jaramillo, T. F., Young, J. L., Zelenay, P., Alia, S. M. 2024; 14 (14): 10806-10819

  Abstract

  Anion exchange membrane water electrolysis (AEMWE) is a promising technology to produce hydrogen from low-cost, renewable power sources. Recently, the efficiency and durability of AEMWE have improved significantly due to advances in the anion exchange polymers and catalysts. To achieve performances and lifetimes competitive with proton exchange membrane or liquid alkaline electrolyzers, however, improvements in the integration of materials into the membrane electrode assembly (MEA) are needed. In particular, the integration of the oxygen evolution reaction (OER) catalyst, ionomer, and transport layer in the anode catalyst layer has significant impacts on catalyst utilization and voltage losses due to the transport of gases, hydroxide ions, and electrons within the anode. This study investigates the effects of the properties of the OER catalyst and the catalyst layer morphology on performance. Using cross-sectional electron microscopy and in-plane conductivity measurements for four PGM-free catalysts, we determine the catalyst layer thickness, uniformity, and electronic conductivity and further use a transmission line model to relate these properties to the catalyst layer resistance and utilization. We find that increased loading is beneficial for catalysts with high electronic conductivity and uniform catalyst layers, resulting in up to 55% increase in current density at 2 V due to decreased kinetic and catalyst layer resistance losses, while for catalysts with lower conductivity and/or less uniform catalyst layers, there is minimal impact. This work provides important insights into the role of catalyst layer properties beyond intrinsic catalyst activity in AEMWE performance.

  View details for DOI 10.1021/acscatal.4c02932

  View details for PubMedID 39050897

  View details for PubMedCentralID PMC11264204

• Protocol for assembling and operating bipolar membrane water electrolyzers. STAR protocols Rios Amador, I., Hannagan, R. T., Marin, D. H., Perryman, J. T., Rémy, C., Hubert, M. A., Lindquist, G. A., Chen, L., Stevens, M. B., Boettcher, S. W., Nielander, A. C., Jaramillo, T. F. 2023; 4 (4): 102606

  Abstract

  Renewable energy-driven bipolar membrane water electrolyzers (BPMWEs) are a promising technology for sustainable production of hydrogen from seawater and other impure water sources. Here, we present a protocol for assembling BPMWEs and operating them in a range of water feedstocks, including ultra-pure deionized water and seawater. We describe steps for membrane electrode assembly preparation, electrolyzer assembly, and electrochemical evaluation. For complete details on the use and execution of this protocol, please refer to Marin et al. (2023).1.

  View details for DOI 10.1016/j.xpro.2023.102606

  View details for PubMedID 37924520