Research Overview

Research in our group is aimed at (i) understanding the synthesis, unique structures and distinct properties of nanostructured transition metal oxides and related compounds and (ii) developing materials with improved properties for electrochemical energy conversion and storage devices. Our research involves studying the structure and properties of nanomaterials using a variety of materials characterization, electrochemical, and spectroscopic methods and  developing correlations between structure and electrochemical properties (e.g. activity, stability, capacity, etc.) to enable the development of improved electrochemical energy materials. Below is a description of our active research areas and representative publications.

Nanostructured transition metal oxides: (A) Representation of interconnected three-dimensional (3D) network of solid particles and pores; (B) scanning transmission electron microscopy (STEM) image of hydrous iridium-nickel oxide nanostructure

Nanostructured transition metal oxides: (A) Representation of interconnected three-dimensional (3D) network of solid particles and pores; (B) scanning transmission electron microscopy (STEM) image of hydrous iridium-nickel oxide nanostructure (ECM, Reference 1).

Electrochemical Energy Storage Materials. Electrochemical energy storage materials that provide high capacities, long cycle life, lower cost and improved safety are needed for batteries for numerous applications including electric vehicles, consumer devices, and grid-level energy storage. Research in the Rhodes group has explored designing electrode materials using nanosheet architectures, inorganic-polymer nanocomposites, disordered structures, and multi-electron processes.  Our research group has recently explored creating two-dimensional (2D) nanoarchitectures for energy storage materials. 2D nanoarchitectures can express the unique and desirable features of 2D materials (e.g. quantum confined electrons, exposure of the entire surface of the material to the electrolyte, enhanced expression of specific surface facets, and the ability to accommodate structural strain) within a practical 3D electrode structure that provides molecular accessibly to the reactive surface.  Our research has demonstrated iron oxide (γ-Fe2O3) nanosheets provide improved lithium-ion charge storage compared with nanoparticles (ESM, Reference 1). The γ-Fe2O3 nanosheets are stabilized by surface interactions and exhibit a surface-based charge storage mechanism. Layered materials can be rethought of as assemblies of 2D materials. Incorporating an ion-conducting polymer between V2O5 layers provides improved transport and storage of divalent Mg2+ cations, which shows that the structure and dynamics of the interlayer (or “inner surface”) can be tuned to enhance ion transport and storage and be used to develop improved multivalent cation battery materials (ESM, Reference 2). Representative energy storage publications are listed below.

Representation of structure of iron oxide (g-Fe2O3) nanosheets; transmission electron microscopy (TEM) image of iron oxide nanosheets, and galvanostatic charge and discharge profiles that show iron oxide nanosheets have significantly higher capacities than nanoparticles.

(left) Representation of structure of iron oxide (gamma-Fe2O3) nanosheets; (center) transmission electron microscopy (TEM) image of iron oxide nanoshee; (right) galvanostatic charge and discharge profiles that show iron oxide nanosheets have significantly higher capacities than nanoparticles (ESM, Reference 1).

Controlling the interlayer structure and dynamics within layered vanadium pentoxide (V2O5) results in significantly improved transport and storage of divalent Mg2+ , providing enhanced cathodes for lower cost and improved safety magnesium batteries; (A) interlayer distance and composition can be controlled by using poly(ethylene oxide) (PEO) and H2O within V2O5 layers; (B) transmission electron microscopy (TEM) image layered V2O5 showing interlayer distance; (C) galvanostatic charge and discharge profiles that show V2O5-polymer nanocomposites show significantly higher Mg-ion capacities than V2O5.

Controlling the interlayer structure and dynamics within layered vanadium pentoxide (V2O5) results in significantly improved transport and storage of divalent Mg2+ , providing enhanced cathodes for lower cost and improved safety magnesium batteries; (A) interlayer distance and composition can be controlled by using poly(ethylene oxide) (PEO) and H2O within V2O5 layers; (B) transmission electron microscopy (TEM) image layered V2O5 showing interlayer distance; (C) galvanostatic charge and discharge profiles that show V2O5-polymer nanocomposites show significantly higher Mg-ion capacities than V2O5 (ESM, Reference 2).

Electrochemical Energy Conversion Materials. Electrochemical energy conversion materials are critical components of systems used for chemical synthesis (e.g. hydrogen/oxygen generation in electrolyzers), power generation (e.g. fuel cells), and other applications.  Electrocatalysts are key components of fuel cells and water electrolyzers, and electrocatalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) that provide high activity, high stability and lower cost remain a key challenge.  Research in the Rhodes group has explored designing high activity and stability oxygen reduction and oxygen evolution electrocatalysts using nanostructured transition metals and metal oxides. Beyond typical 2D materials such as graphene and metal sulfides, our group has shown that metallic 2D nanoarchitectures can be created by controlled temperature/atmosphere treatments of metal hydroxide nanosheets. Metallic Ni-Pt “2D nanoframes” exhibit active surface sites within an interconnected carbon-free network that provides one of the highest electrochemical oxygen reduction specific activity and enhanced stability at high potentials reported to date (ECM, Reference 2). In addition, we have recently shown that controlled surfaces within hydrous iridium nickel oxide 2D nanoframes provide oxygen evolution reaction (OER) electrocatalysts with 15x higher activity compared with IrO2 (ECM, Reference 1).  Representative electrochemical energy conversion publications are listed below.

Scanning electron microscopy (SEM) image of Ni-Pt two-dimensional (2D) nanoframes; scanning transmission electron microscopy (STEM) image of Ni-Pt two-dimensional (2D) nanoframes showing atomic-level structure and model representation; oxygen reduction reaction (ORR) activity and specific activity and stability of Ni-Pt two-dimensional (2D) nanoframes compared with Pt/C.

(left) Scanning electron microscopy (SEM) image of Ni-Pt two-dimensional (2D) nanoframes; (center) scanning transmission electron microscopy (STEM) image of Ni-Pt two-dimensional (2D) nanoframes showing atomic-level structure and model representation; (right) oxygen reduction reaction (ORR) activity and specific activity and stability of Ni-Pt two-dimensional (2D) nanoframes compared with Pt/C (ECM, Reference 2).

(A) Scanning transmission electron microscopy (STEM) image of hydrous iridium-nickel oxide two-dimensional (2D) nanoframes showing atomic-level structure; (B) model surface structure and oxygen evolution reaction (OER) at hydrous iridium-nickel oxide electrocatalysts; (C) comparison of OER mass activities of hydrous iridium-nickel oxide treated at either 200 °C (NiIr-200-CL-EO) or 300 °C (NiIr-200-CL-EO) with commercial IrO2; NiIr-200-CL-EO showed 15x higher OER mass activity than commercial IrO2. (ECM, Reference 1).

 

Selected Representative Publications

Electrochemical Energy Storage Materials (ESM)

  1. Niu, S.; McFeron, R.; Godínez-Salomón, F.; Chapman, B.S.; Damin, C.A.; Tracy, J.B.; Augustyn, V.; Rhodes, C.P. Enhanced Electrochemical Lithium-Ion Charge Storage of Iron Oxide Nanosheets. Chemistry of Materials 2017, 9, 7794–7807. DOI: 10.1021/acs.chemmater.7b02315
  2. Perera, S.D.; Archer, R.; Damin, C.A.; Mendoza-Cruz, R.; Rhodes, C.P. Controlling interlayer interactions in vanadium pentoxide-poly(ethylene oxide) nanocomposites for enhanced magnesium-ion charge transport and storage, Journal of Power Sources 2017, 343, 580-591.DOI:10.1016/j.jpowsour.2017.01.052
  3. Duraia, E.M.; Niu, S.; Beall, G.W.; Rhodes, C.P. Humic Acid-Derived Graphene-SnO2 Nanocomposites for High Capacity Lithium-Ion Battery Anodes. Journal of Materials Science: Materials in Electronics 2018, 29, 8456–8464. DOI: 10.1007/s10854-018-8858-x
  4. Stein, M.; Chen, C.; Mullings, M.; Jamie, D.J.; Zaleski, A.; Mukherjee, P.; Rhodes, C.P. Probing the Effect of High Energy Ball Milling on the Structure and Properties of LiNi1/3Mn1/3Co1/3O2 Cathodes. Journal of Electrochemical Energy Conversion and Storage, 2016, 13, 031001. DOI:10.1115/1.4034755
  5. Stuart, J.; Hohenadel, A.; Li, X.; Xiao, H.; Parkey, J.; Rhodes, C.P.; Licht, S. The Net Discharge Mechanism of the VB2/Air Battery. Journal of the Electrochemical Society 2015, 162, A1-A6. DOI: 10.1149/2.0801501jes

Electrochemical Energy Conversion Materials (ECM)

  1. Godínez-Salomón, F.; Albiter, L.; Alia, S.M.; Pivovar, B.S.; Camacho-Forero, L.E.; Balbuena, P.B.; Mendoza-Cruz, R.; Arellano-Jimenez, M.J.; Rhodes, C.P. Self-Supported Hydrous Iridium-Nickel Oxide Two-dimensional Nanoframes for High Activity Oxygen Evolution Electrocatalysts. ACS Catalysis 2018, 8, 10498-10520. DOI: 10.1021/acscatal.8b02171
  2. Godínez-Salomón, F.; Mendoza-Cruz, R; Arellano-Jimenez, M.J., Jose-Yacaman, M.; Rhodes, C.P. Metallic Two-dimensional Nanoframes: Design of Carbon-free Hierarchical Nickel-Platinum Alloy Electrocatalyst Nanoarchitecture with Enhanced Oxygen Reduction Activity and Stability. ACS Applied Materials & Interfaces, 2017, 9, 18660-18674. DOI: 10.1021/acsami.7b00043
  3. Godínez-Salomón, F.; Rhodes, C.P.; Alcantara, K.S.; Zhu, Q.; Canton, S.E.; Calderon, H.A.; Reyes-Rodríguez, J.L.; Leyva, M.A.; Solorza-Feria, O., Tuning the Oxygen Reduction Activity and Stability of Ni(OH)2@Pt/C Catalysts through Controlling Pt Surface Composition, Strain, and Electronic Structure, Electrochimica Acta 2017, 247, 958-969. DOI: 10.1016/j.electacta.2017.06.073
  4. Rolison, D. R.; Long, R. W.; Lytle, J. C.; Fischer, A. E.; Rhodes, C. P.; McEvoy, T. M.; Bourga, M. E.; Lubers, A. M., Multifunctional 3D Nanoarchitectures for Energy Storage and Conversion. Chemical Society Reviews 2009, 38, 226-252. DOI: 10.1039/b801151f