@article{spencer_holzapfel_you_mpourmpakis_augustyn_2024, title={Participation of electrochemically inserted protons in the hydrogen evolution reaction on tungsten oxides}, ISSN={["2041-6539"]}, DOI={10.1039/d4sc00102h}, abstractNote={Tungsten oxides undergo a significant increase in their hydrogen evolution reaction activity upon proton-insertion coupled electron transfer.}, journal={CHEMICAL SCIENCE}, author={Spencer, Michael A. and Holzapfel, Noah P. and You, Kyung-Eun and Mpourmpakis, Giannis and Augustyn, Veronica}, year={2024}, month={Mar} }
 @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{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} }
 @article{spencer_yildiz_kamboj_bradford_augustyn_2021, title={Toward Deterministic 3D Energy Storage Electrode Architectures via Electrodeposition of Molybdenum Oxide onto CNT Foams}, volume={35}, ISSN={["1520-5029"]}, DOI={10.1021/acs.energyfuels.1c02352}, abstractNote={Three-dimensional (3D) deterministic design of electrodes could enable simultaneous high energy and power density for electrochemical energy storage devices. The goal of such electrode architectures is to provide adequate charge (electron and ion) transport pathways for high power, while maintaining high active material loading (>10 mg cm–2) for high areal and volumetric capacities. However, it remains a challenge to fabricate such electrodes with processes that are both scalable and reproducible. Toward this end, here, we demonstrate how the fabrication of such an electrode is made possible by combining tunable, free-standing, and aligned carbon nanotube (CNT) foams with aqueous electrodeposition of a model intercalation-type transition metal oxide, MoO3. Morphological characterization including X-ray microcomputed tomography indicates that the obtained composite is homogeneous. Electrodes with an active mass loading of up to 18 mg cm–2 reached near-theoretical Li-ion intercalation capacities within 1.7 h. The highest-mass loading electrodes also led to areal and volumetric capacities of 4.5 mA h cm–2 and 290 mA h cm–3, respectively, with 55% capacity retention for charge/discharge times of 10 min. Overall, this work demonstrates a scalable, deterministic 3D electrode design strategy using electrodeposition and free-standing, aligned CNT foams that lead to high areal and volumetric capacities and good rate performance due to well-distributed charge transport pathways.}, number={19}, journal={ENERGY & FUELS}, author={Spencer, Michael A. and Yildiz, Ozkan and Kamboj, Ishita and Bradford, Philip D. and Augustyn, Veronica}, year={2021}, month={Oct}, pages={16183–16193} }
 @article{fleischmann_spencer_augustyn_2020, title={Electrochemical Reactivity under Confinement Enabled by Molecularly Pillared 2D and Layered Materials}, volume={32}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.0c00648}, abstractNote={This perspective presents an overview of how confinement can be used to tune electrochemical reactivity and the concept of using molecularly pillared 2D and layered materials to experimentally stud...}, number={8}, journal={CHEMISTRY OF MATERIALS}, author={Fleischmann, Simon and Spencer, Michael A. and Augustyn, Veronica}, year={2020}, month={Apr}, pages={3325–3334} }
 @article{lynch_kelliher_anderson_japit_spencer_rizvi_sarac_augustyn_tracy_2021, title={Sulfidation and selenidation of nickel nanoparticles}, volume={3}, ISSN={["2637-9368"]}, url={https://doi.org/10.1002/cey2.83}, DOI={10.1002/cey2.83}, abstractNote={AbstractTransition metal chalcogenide nanoparticles (NPs) are of interest for energy applications, including batteries, supercapacitors, and electrocatalysis. Many methods have been established for synthesizing Ni NPs, and conversion chemistry to form Ni oxide and phosphides from template Ni NPs is well‐understood. Sulfidation and selenidation of Ni NPs have been much less explored, however. We report a method for the conversion of Ni template NPs into sulfide and selenide product NPs using elemental sulfur, 1‐hexadecanthiol, thiourea, trioctylphosphine sulfide, elemental selenium, and selenourea. While maintaining mole ratios of 2 mmol sulfur/selenium precursor: mmol Ni, products with phases of Ni3S2, Ni9S8, NiS, NiSO4·6H2O, Ni3S4, Ni3Se2, and NiSe have been obtained. The products have voids that form through the Kirkendall effect during interdiffusion. Trends relating the chemical properties of the precursors to the phases of the products have been identified. While some precursors contained phosphorus, there was no significant incorporation of phosphorus in any of the products. An increase of the NP size during sulfidation and selenidation is consistent with ripening. The application of Ni sulfide and selenide NPs as electrocatalysts for the hydrogen evolution reaction is also demonstrated.}, number={4}, journal={CARBON ENERGY}, publisher={Wiley}, author={Lynch, Brian B. and Kelliher, Andrew P. and Anderson, Bryan D. and Japit, Alexander and Spencer, Michael A. and Rizvi, Mehedi H. and Sarac, Mehmet F. and Augustyn, Veronica and Tracy, Joseph B.}, year={2021}, month={Aug}, pages={582–589} }
 @misc{spencer_augustyn_2019, title={Free-standing transition metal oxide electrode architectures for electrochemical energy storage}, volume={54}, ISSN={["1573-4803"]}, DOI={10.1007/s10853-019-03823-y}, number={20}, journal={JOURNAL OF MATERIALS SCIENCE}, author={Spencer, Michael A. and Augustyn, Veronica}, year={2019}, month={Oct}, pages={13045–13069} }