Group Research Focuses

	Ion-exchange membranes are critical to electrolyzers, fuel cells, artificial photosynthetic systems, and electrodialysis devices, by providing a barrier to fuel crossover and maintaining pressure differentials while still affording rapid ion conduction. If the membranes could also generate ionic voltages upon sunlight absorption or function as electrochemical ion-pumping ratchets, they would boost the power output and efficiency of these devices, as well as enable game-changing solar desalination innovations. The Ardo Group is characterizing excited-state ion-transfer photochemistry and photophysics and functionalizing ion-exchange materials with photoacid dyes for this purpose. The Ardo Group is also embarking on research related to other new concepts in small-scale clean water generation, including electricity-driven ratchet-based ion pumping, solar thermal distillation, and atmospheric water harvesting.
Select Works on Light-Driven Proton Pumps G. S. Phun, et al., Energy & Environmental Science 2023, 16(10), 4593-4611; DOI: 10.1039/D3EE00710C.  Detailed-balance limits for sunlight-to-protonic energy conversion from aqueous photoacids and photobases based on reversible mass-action kinetics. S. Luo, et al., Energy & Environmental Science 2021, 14(9), 4961-4978; DOI: 10.1039/D1EE00482D.  Clarification of Mechanisms of Protonic Photovoltaic Action Initiated by Photoexcitation of Strong Photoacids Covalently Bound to Hydrated Nafion Cation-Exchange Membranes Wetted by Aqueous Electrolytes. L. Schulte, et al., Joule 2021, 5(9), 2380-2394; DOI: 10.1016/j.joule.2021.06.016.  Turning Water into a Protonic Diode and Solar Cell via Doping and Dye Sensitization. C. D. Sanborn, et al., Chem 2019, 5(6), 1648-1670; DOI: 10.1016/j.chempr.2019.04.022.  Interfacial and Nanoconfinement Effects Decrease the Excited-State Acidity of Polymer-Bound Photoacids. W. White, et al., Joule 2018, 2(1), 94-109; DOI: 10.1016/j.joule.2017.10.015.  Conversion of Visible Light into Ionic Power Using Photoacid-Dye-Sensitized Bipolar Ion-Exchange Membranes. W. White, et al., Journal of the American Chemical Society 2017, 139(34), 11726-11733; DOI: 10.1021/jacs.7b00974.  Observation of Photovoltaic Action from Photoacid-Modified Nafion Due to Light-Driven Ion Transport. Select Works on Electrochemical Ion Pumps A. Herman, et al., PRX Energy 2023, 2(2), 23001; DOI: 10.1103/PRXEnergy.2.023001.  Ratchet-Based Ion Pumps for Selective Ion Separations. Z. M. Bhat, et al., Joule 2020, 4(8), 1730-1742; DOI: 10.1016/j.joule.2020.07.001.  An Electrochemical Neutralization Cell for Spontaneous Water Desalination. S. Ardo, et al., Intellectual Property, University of California, Irvine 2019; Publication number: US20210187442 A1.  Ratchet-based ion pumping membrane systems.
This work is supported by funding from the U.S. Department of Energy and a Private Investor, and was previously supported by funding from the Gordon and Betty Moore Foundation, the Research Corporation for Science Advancement, Nissan Chemical Corporation, the Beall Family Foundation, a U.S. National Science Foundation graduate-student research fellowship, and a U.S. Department of Energy graduate-student research award.                                 Graduate-Student Support

	Controlling rates of water dissociation and formation are critical to the effective function of several environmentally important processes, including proton transfer in electrochemical reactions, CO2 capture from air, and CO2 release from oceanwater. For example, fuel cells and solar fuels devices each require electrocatalysts and ion-exchange membranes that are stable in a single electrolyte. State-of-the-art ion-exchange membranes are highly acidic, yet most scalable and inexpensive electrocatalysts are either unstable in acidic conditions or incompatible with desired redox chemistries. The Ardo Group is leveraging materials synthesis and engineering of ion-exchange membranes and synthesis of molecular proton-transfer catalysts to speed the rates of critical proton-transfer reactions.
Select Works on Proton-Transfer Catalysis R. Bhide, et al., Journal of the American Chemical Society 2022, 144(32), 14477-14488; DOI: 10.1021/jacs.2c00554.  Quantification of Excited-State Brønsted–Lowry Acidity of Weak Photoacids Using Steady-State Photoluminescence Spectroscopy and a Driving-Force-Dependent Kinetic Theory. S. Ardo, et al., Intellectual Property, University of California, Irvine 2019; Publication number: US20210046423 A1.  Membranes for enhancing rates of water dissociation and water formation. S. Z. Oener, et al., ACS Energy Letters 2017, 2(11), 2625-2634; DOI: 10.1021/acsenergylett.7b00764.  Ionic Processes in Water Electrolysis: The Role of Ion-Selective Membranes. Select Works on Fluorescence Sensing A. E. Böhme, et al., Intellectual Property, California Institute of Technology 2022; Publication number: US20230358677 A1.  Reversible excited-state photoacids and photobases as dynamic fluorescence sensors of protonic species. A. Böhme, et al., Energy & Environmental Science 2023, 16(4), 1783-1795; DOI: 10.1039/D2EE02607D.  Direct observation of the local microenvironment in inhomogeneous CO2 reduction gas diffusion electrodes via versatile pOH imaging. Select Works on Oceanic CO2 Capture H. A. Atwater, et al., Intellectual Property, California Institute of Technology 2022; Publication number: US20240133051 A1.  Systems and methods for electrochemical hydrogen looping. C. Xiang, et al., Intellectual Property, California Institute of Technology 2021; Publication number: US20230107163 A1.  Systems and methods for gas-liquid contactors for rapid carbon capture.
This work is supported by funding from the U.S. Department of Energy, the U.S. National Science Foundation, and a U.S. National Science Foundation graduate-student research fellowship, and was previously supported by funding from the Beall Family Foundation, the U.S. Department of Defense, the U.S. Department of Energy, and a U.S. Department of Energy graduate-student research award.                                         CI2 Graduate-Student Support

	Scalable technologies for solar-energy conversion and storage must be efficient, robust, and inexpensive to manufacture. Recent techno-economic analyses of solar water splitting reactors suggest that colloidal-particle-based photocatalyst suspensions would be cost competitive with current forms of H2 generation. Moreover, it is projected that the first major large-scale photovoltaic installations will utilize silicon, or an inexpensive easy-to-deposit material. The Ardo Group is exploring alternative fuel-forming chemistries, materials, and designs for disruptive innovations in grid-scale solar-energy conversion, storage, and use.
Select Works on Nanomaterials Design B. T. Zutter, et al., ACS Nano 2023, 17(10), 9405-9414; DOI: 10.1021/acsnano.3c01448.  Single-Particle Measurements Reveal the Origin of Low Solar-to-Hydrogen Efficiency of Rh-doped SrTiO3 Photocatalysts. F. Aydin, et al., ACS Applied Materials & Interfaces 2023, 15(14), 17814-17824; DOI: 10.1021/acsami.2c22865.  Mechanistic Insights on Permeation of Water over Iron Cations in Nanoporous Silicon Oxide Films for Selective H2 and O2 Evolution. W. D. H. Stinson, et al., ACS Applied Materials & Interfaces 2022, 14(5), 55480-55490; DOI: 10.1021/acsami.2c13646.  Quantifying the Influence of Defects on Selectivity of Electrodes Encapsulated by Nanoscopic Silicon Oxide Overlayers. Select Works on Reactor Innovations S. Ardo, et al., Intellectual Property, University of California, Irvine 2022; Publication number: US20230390724 A1.  Photocatalyst suspension reactor for solar fuel formation. S. Ardo, et al., Intellectual Property, University of California, Irvine 2018; Publication number: US20200140293 A1.  Optically thin light-absorbers for increasing photochemical energy-conversion efficiencies. S. Keene, et al., Energy & Environmental Science 2019, 12(1), 261-272; DOI: 10.1039/C8EE01828F.  Calculations of Theoretical Efficiencies for Electrochemically-Mediated Tandem Solar Water Splitting as a Function of Bandgap Energies and Redox Shuttle Potential. S. Ardo, et al., Energy & Environmental Science 2018, 11(10), 2768-2783; DOI: 10.1039/C7EE03639F.  Pathways to electrochemical solar-hydrogen technologies. R. Bala Chandran, et al., Energy & Environmental Science 2018, 11(1), 115-135; DOI: 10.1039/C7EE01360D.  Evaluating particle-suspension reactor designs for Z-scheme solar water splitting via transport and kinetic modeling.
This work is supported by funding from the U.S. Department of Energy, and was previously supported by funding from the U.S. Department of Energy, the Alfred P. Sloan Foundation, and the UC Irvine Research Seed Funding Program.

	If several photon absorption events could be efficiently coupled to multiple-charge-transfer catalysis in donor–chromophore–acceptor complexes, light-driven reactions to form stable chemical products would be possible. Although individual electron-transfer and energy-transfer events are efficient, successful integration into a functioning system remains elusive. The Ardo Group is evaluating various integrated geometries to demonstrate sunlight-driven charge accumulation, which is projected to enable a >20% efficiency for solar energy conversion to electricity.
Select Works J. M. Cardon, et al., ACS Applied Materials & Interfaces 2021, 13(35), 41396-41404; DOI: 10.1021/acsami.9b19096.  Reconciliation of differences in apparent diffusion coefficients measured for self-exchange electron transfer between molecules anchored to mesoporous titanium dioxide thin films. K. Tkaczibson and S. Ardo, ACS Applied Energy Materials 2020, 3(5), 4699-4707; DOI: 10.1021/acsaem.0c00336.  Numerical Monte Carlo Simulations to Evaluate the Influence That Spherical Nanoparticle Size and Arrangement Have on Interparticle Charge Transport across the Surface of Dye- and Cocatalyst-Modified Materials. K. Tkaczibson and S. Ardo, Sustainable Energy & Fuels 2019, 3(6), 1573-1587; DOI: 10.1039/C9SE00009G.  Numerical Monte Carlo Simulations of Charge Transport across the Surface of Dye and Cocatalyst Modified Spherical Nanoparticles under Conditions of Pulsed or Continuous Illumination. H. Chen and S. Ardo, Nature Chemistry 2018, 10(1), 17-23; DOI: 10.1038/nchem.2892.  Direct observation of sequential oxidations of a titania-bound molecular proxy catalyst generated through illumination of molecular sensitizers. Doctoral Work: S. Ardo and G. J. Meyer, Chemical Society Reviews 2009, 38(1), 115-164; DOI: 10.1039/b804321n.  Photodriven heterogeneous charge transfer with transition-metal compounds anchored to TiO2 semiconductor surfaces.
This work was previously supported by funding from the U.S. National Science Foundation and a U.S. National Science Foundation graduate-student research fellowship. Graduate-Student Support

	Hybrid organic–inorganic lead–halide perovskite solar cells have reached >20% sunlight-to-electrical energy conversion efficiency using small laboratory-scale devices. However, for commercialization, the materials need to be made more robust and lead should be replaced with more environmentally friendly alternatives. The Ardo Group is chemically modifying the organic moiety from a monovalent cation to a divalent cation with the goal of increasing thermal and moisture stability of one-dimensional and two-dimensional metal–halide perovskite materials.
Select Works D. M. Fabian, et al., ACS Applied Energy Materials 2019, 2(3), 2178-2187; DOI: 10.1021/acsaem.8b02134.  Demonstration of photovoltaic action and enhanced stability from a quasi-two-dimensional hybrid organic–inorganic copper–halide material incorporating divalent organic groups. D. M. Fabian, et al., ACS Applied Energy Materials 2019, 2(3), 1579-1587; DOI: 10.1021/acsaem.8b01809.  Influence of one specific carbon–carbon bond on the quality, stability, and photovoltaic performance of hybrid organic–inorganic bismuth–iodide materials. S. P. Dunfield, et al., ACS Energy Letters 2018, 3(1), 1192-1197; DOI: 10.1021/acsenergylett.8b00548.  Curtailing Perovskite Processing Limitations via Lamination at the Perovskite/Perovskite Interface. D. M. Fabian and S. Ardo, Journal of Materials Chemistry A 2016, 4(18), 6837-6841; DOI: 10.1039/C6TA00517A.  Hybrid organic–inorganic solar cells based on bismuth iodide and 1,6-hexanediammonium dication.
This work was previously supported by funding from UC MEXUS–CONACYT, the Alfred P. Sloan Foundation, a U.S. National Science Foundation graduate-student research fellowship, and a U.S. Department of Energy graduate-student research award.            Graduate-Student Support