@article{fortunato_shin_spencer_duin_augustyn_2023, title={Choice of Electrolyte Impacts the Selectivity of Proton-Coupled Electrochemical Reactions on Hydrogen Titanate}, ISSN={["1932-7455"]}, DOI={10.1021/acs.jpcc.3c01057}, abstractNote={Proton-coupled electron transfer (PCET) reactions involving transition metal oxides are prevalent in aqueous electrochemical systems used for energy storage and conversion. Here, we elucidate the role of electrolyte on PCET mechanisms in transition metal oxides in aqueous acidic electrolytes using layered hydrogen titanate (H2Ti3O7) as an example. We identify three processes by which electrolyte protons interact with hydrogen titanate at the electrochemical interface: (1) adsorption at the surface and/or insertion into the bulk, (2) adsorption as part of the hydrogen evolution reaction (HER) at the surface, and (3) dissolution of the hydrogen titanate. We utilize a combined experimental and computational (ReaxFF) approach to probe how the competition for protons and electrons among these processes influences electrochemical properties, including the energy storage, Coulombic efficiency (CE), rate capability, and lifetime. In an acidic buffered electrolyte (1 M H3PO4), the CE increases from an average of 48% to 71% and the specific capacity increases from 83 to 90 mAh g–1 as compared to a strong acid electrolyte (1 M H2SO4). We propose that H3PO4 mitigates the HER and hydrogen titanate dissolution, thereby increasing the operating potential window for proton adsorption/insertion for charge storage in hydrogen titanate. Material characterization and computational results indicate that adsorption of phosphate species onto the surface of hydrogen titanate may decrease its dissolution upon reduction, thereby improving electrode performance. We offer a preliminary solution to improve energy storage performance via electrolyte tuning by decreasing the prevalence of the HER and electrode dissolution.}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Fortunato, Jenelle and Shin, Yun Kyung and Spencer, Michael A. A. and Duin, Adri C. T. and Augustyn, Veronica}, year={2023}, month={Jun} }
 @article{fortunato_zydlewski_lei_holzapfel_chagnot_mitchell_lu_jiang_milliron_augustyn_2023, title={Dual-Band Electrochromism in Hydrous Tungsten Oxide}, ISSN={["2330-4022"]}, DOI={10.1021/acsphotonics.3c00921}, abstractNote={The independent modulation of visible and near-infrared light by a single material, termed dual-band electrochromism, is highly desirable for smart windows to enhance the energy efficiency of buildings. Tungsten oxides are commercially important electrochromic materials, exhibiting reversible visible and near-infrared absorption when electrochemically reduced in an electrolyte containing small cations or protons. The presence of structural water in tungsten oxides has been associated with faster electrochromic switching speeds. Here, we find that WO3·H2O, a crystalline hydrate, exhibits dual-band electrochromism unlike the anhydrous WO3. This provides a heretofore unexplored route to tune the electrochromic response of tungsten oxides. Absorption of near-infrared light is achieved at low Li+/e– injection, followed by the absorption of visible light at higher Li+/e– injection as a result of an electrochemically induced phase transition. We propose that the dual-band modulation is possible due to the more open structure of WO3·H2O as compared to WO3. This facilitates a more extended solid-solution Li+ insertion regime that benefits the modulation of near-infrared radiation via plasmon absorption. Higher degrees of Li+/e– insertion lead to polaronic absorption associated with localized charge storage. These results inform how structural factors influence the electrochemically induced spectral response of transition-metal oxides and the important role of structural water beyond optical switching speed.}, journal={ACS PHOTONICS}, author={Fortunato, Jenelle and Zydlewski, Benjamin Z. and Lei, Ming and Holzapfel, Noah P. and Chagnot, Matthew and Mitchell, James B. and Lu, Hsin-Che and Jiang, De-en and Milliron, Delia J. and Augustyn, Veronica}, year={2023}, month={Sep} }
 @article{spencer_fortunato_augustyn_2022, title={Electrochemical proton insertion modulates the hydrogen evolution reaction on tungsten oxides}, volume={156}, ISSN={["1089-7690"]}, DOI={10.1063/5.0082459}, abstractNote={The development of new electrocatalysts for the hydrogen evolution reaction (HER) could reduce the dependence on Pt and other rare metals and enable large-scale production of hydrogen with near-zero carbon emissions. Mechanistic insight into the electrocatalytic activity of a material helps to accelerate the development of new electrocatalysts. Alternative electrocatalyst materials such as transition metal oxides and sulfides can undergo insertion reactions that change their properties. Recent reports indicate that the presence of inserted ions can influence the electrocatalytic activity. Here, we utilized a materials chemistry approach to understand the role of proton insertion in the HER activity of the layered tungsten oxide hydrates (WO3·xH2O, x = 1, 2). We synthesized a series of tungsten oxide hydrates along with an octylamine-pillared tungsten oxide (OA-WO3). We used cyclic voltammetry to study the electrochemical reactivity of each material and performed ex situ x-ray diffraction and Raman spectroscopy to understand bulk and surface structural changes during electrochemical cycling. We show an inverse relationship between the degree of proton insertion and HER overpotential in tungsten oxides: the lack of proton insertion leads to a high overpotential for the HER. We discuss three hypotheses for how proton insertion leads to the HER activity in WO3·xH2O: (1) proton insertion changes the electronic band structure of WO3·xH2O, (2) the presence of bulk protons can influence ΔGH,ads at the surface sites, and (3) the inserted protons may participate in the HER mechanism on WO3·xH2O. Overall, this work shows the critical role of proton insertion in enabling the high HER activity in tungsten oxides.}, number={6}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={Spencer, Michael A. and Fortunato, Jenelle and Augustyn, Veronica}, year={2022}, month={Feb} }
 @misc{fortunato_jordan_newton_walsh_augustyn_2022, title={Electrochemical reactivity of atomic and molecular species under solid-state confinement}, volume={34}, ISSN={["2451-9103"]}, DOI={10.1016/j.coelec.2022.101014}, abstractNote={The nanoconfinement of electrochemically-active guest species in host solid state electrode materials provides opportunities to tune mass transport between the bulk electrolyte and inner surface of the electrode, enhance electron-transfer rates, and/or improve the stability and dispersion of active material. This review summarizes recent experimental and theoretical electrochemical studies of three types of nanoconfined guest species: (1) ion adsorption of electrolyte ions, (2) confined redox-active molecules, and (3) electrocatalytic reactions of confined ions/solvents and catalytic particles. The examples discussed in this review illustrate how the confinement of guest species within enclosed spaces with nanoscale dimensions – such as pores, pockets, channels, and interlayers – can lead to improved electrochemical performance.}, journal={CURRENT OPINION IN ELECTROCHEMISTRY}, author={Fortunato, Jenelle and Jordan, Jack W. and Newton, Graham N. and Walsh, Darren A. and Augustyn, Veronica}, year={2022}, month={Aug} }
 @article{saeed_fortunato_ganeshan_duin_augustyn_2021, title={Decoupling Proton and Cation Contributions to Capacitive Charge Storage in Birnessite in Aqueous Electrolytes}, volume={8}, ISSN={["2196-0216"]}, DOI={10.1002/celc.202100992}, abstractNote={Nanostructured birnessite is of interest as an electrode material for aqueous high power electrochemical energy storage as well as desalination devices. In neutral pH aqueous electrolytes, birnessite exhibits a capacitive response attributed to the adsorption of cations and protons at the outer surface and within the hydrated interlayer. Here, we utilize the understanding of proton-coupled electron transfer (PCET) in buffered electrolytes to decouple the role of protons and cations in the capacitive charge storage mechanism of birnessite at neutral pH. We find that without buffer, birnessite exhibits primarily potential-independent (capacitive) behavior with excellent cycling stability. Upon the addition of buffer, the capacity initially increases and the cyclic voltammograms become more potential-dependent, features attributed to the presence of PCET with the birnessite. However, long-term cycling in the buffered electrolyte leads to significant capacity fade and dissolution, which is corroborated through ex situ characterization. ReaxFF atomistic scale simulations support the observations that proton adsorption leads to birnessite degradation and that capacitive charge storage in birnessite is primarily attributed to cation adsorption at the outer surface and within the interlayer.}, number={22}, journal={CHEMELECTROCHEM}, author={Saeed, Saeed and Fortunato, Jenelle and Ganeshan, Karthik and Duin, Adri C. T. and Augustyn, Veronica}, year={2021}, month={Nov}, pages={4371–4379} }