Person: Gordon, Roy
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Gordon, Roy
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Publication Atomic layer deposition of energy band tunable tin germanium oxide electron transport layer for the SnS-based solar cells with 400 mV open-circuit voltage(AIP Publishing, 2019-05-27) Chua, Danny; Kim, Sang Bok; Sinsermsuksakul, Prasert; Gordon, RoyTin germanium oxide, (Sn,Ge)O2, films were prepared using atomic layer deposition and tailored to SnS absorber layer by incorporating various amounts of germanium into tin oxide to adjust band alignments at the interfaces of SnS/(Sn,Ge)O2 photovoltaic devices. Carrier concentrations of (Sn,Ge)O2 were suppressed from 1020 to 1018 cm-3 with germanium incorporation, with nitrogen doping of further reducing carrier concentrations by another order of magnitude. Excellent tunability of both band energy levels and carrier concentrations of (Sn,Ge)O2 allowed optimizing SnS-based solar cells. SnS/(Sn,Ge)O2:N devices were demonstrated, with an open-circuit voltage as high as 400 mV, due to effective mitigation of interfacial recombination of photogenerated carriers at the SnS/(Sn,Ge)O2:N absorber-buffer heterojunction interface.Publication Effect of Molecular Structure of Quinones and Carbon Electrode Surfaces on the Interfacial Electron Transfer Process(American Chemical Society (ACS), 2020-01-28) De Porcellinis, Diana; Jing, Yan; Kerr, Emily; Mejia-Mendoza, Luis Martin; Vazquez-Mayagoitia, Álvaro; Aspuru-Guzik, Alán; Sedenho, Graziela Cristina; Gordon, Roy; Crespilho, Frank; Aziz, MichaelQuinones can undergo thermodynamically reversible proton-coupled electron transfer reactions and are being applied as electroactive compounds in aqueous organic batteries. However, the electrochemical reversibility of these compounds is affected not only by their molecular structure but also by the properties of a carbon-based electrode surface. This study combines experimental and theoretical approaches to understand this dependence. We study the electron transfer kinetics of two synthesized quinone derivatives and two commercially available ones with a glassy carbon, a highly ordered pyrolytic graphite, and a high-edge-density graphite electrode (HEDGE). The electrochemical reversibility is notably improved on the HEDGE, which shows a higher density of defects and presents oxygenated functional groups at its surface. The electron transfer kinetics are controlled by adsorbed species onto the HEDGE. Molecular dynamics simulation and quantum mechanics calculations suggest defects with oxygen-containing functional groups, such as C–O and C═O, on HEDGE surfaces drive the interaction with the functional groups of the molecules, during physisorption from van der Waals forces. The presence of sulfonic acid side groups and a greater number of aromatic rings in the molecular structure may contribute to a higher stabilization of quinone derivatives on HEDGEs. We propose that high-performance carbon-based electrodes can be obtained without catalysts for organic batteries, by the engineering of carbon-based surfaces with edge-like defects and oxygenated functional groups.Publication Non-corrosive, Low-Toxicity Gel-based Microbattery from Organic and Organometallic Molecules(Royal Society of Chemistry (RSC), 2019) Crespilho, Frank; Sedenho, Graziela Cristina; De Porcellinis, Diana; Kerr, Emily; Granados-Focil, Sergio; Gordon, Roy; Aziz, MichaelMicrobatteries with safe, non-corrosive electrolyte chemistries can have an immediate positive impact on modern life applications, such as ingestible electronic pills and system-on-chip bioelectronics. Here a safe, non-corrosive and non-flammable microbattery is reported. A natural agarose hydrogel is the electrolyte-supporting matrix, and organic and organometallic molecules are the redox-active species. This device can safely meet the needs of ingestible medical microdevices as a primary battery. Additionally, this redox gel system can be used as a secondary battery for on-chip electronics applications, potentially enabling safe and cost-effective small-scale energy storage.Publication Electrostatically Doped Silicon Nanowire Arrays for Multispectral Photodetectors(American Chemical Society (ACS), 2019-10-02) Um, Han-Don; Solanki, Amit; Jayaraman, Ashwin; Gordon, Roy; Habbal, FawwazNanowires have promising applications as photodetectors with superior ability to tune absorption with morphology. Despite their high optical absorption, the quantum efficiencies of these nanowire photodetectors remain low due to difficulties in fabricating a shallow junction using traditional doping methods. As an alternative, we report non-conventional radial heterojunction photodiodes obtained by conformal coating of indium oxide layer on silicon nanowire arrays. The indium oxide layer has a high work function which induces a strong inversion in the silicon nanowire and creates a virtual p-n junction. The resulting nanowire photodetectors show efficient carrier separation and collection leading to an improvement of quantum efficiency up to 0.2. In addition, by controlling the nanowire radii, the spectral response of the In2O3/Si nanowire photodetectors are tuned over several visible light wavelengths, creating a multispectral detector. Our approach is promising for the development of highly-efficient wavelength selective photodetectors.Publication Near Neutral pH Redox Flow Battery with Low Permeability and Long‐Lifetime Phosphonated Viologen Active Species(Wiley, 2020-04-06) Jin, Shijian; Fell, Eric; Vina-Lopez, Lucia; Jing, Yan; Michalak, Winston; Gordon, Roy; Aziz, MichaelA highly stable phosphonate‐functionalized viologen is introduced as the redox‐active material in a negative potential electrolyte for aqueous redox flow batteries (ARFBs) operating at nearly neutral pH. The solubility is 1.23 m and the reduction potential is the lowest of any substituted viologen utilized in a flow battery, reaching −0.462 V versus SHE at pH = 9. The negative charges in both the oxidized and the reduced states of 1,1′‐bis(3‐phosphonopropyl)‐[4,4′‐bipyridine]‐1,1′‐diium dibromide (BPP−Vi) effect low permeability in cation exchange membranes and suppress a bimolecular mechanism of viologen decomposition. A flow battery pairing BPP−Vi with a ferrocyanide‐based positive potential electrolyte across an inexpensive, non‐fluorinated cation exchange membrane at pH = 9 exhibits an open‐circuit voltage of 0.9 V and a capacity fade rate of 0.016% per day or 0.00069% per cycle. Overcharging leads to viologen decomposition, causing irreversible capacity fade. This work introduces extremely stable, extremely low‐permeating and low reduction potential redox active materials into near neutral ARFBs.Publication A Phosphonate‐Functionalized Quinone Redox Flow Battery at Near‐Neutral pH with Record Capacity Retention Rate(Wiley, 2019-02-06) Ji, Yunlong; Goulet, Marc-Antoni; Pollack, Daniel; Kwabi, David; Jin, Shijian; De Porcellinis, Diana; Kerr, Emily; Gordon, Roy; Aziz, MichaelA highly stable phosphonate‐functionalized anthraquinone is introduced as the redox‐active material in a negative potential electrolyte (negolyte) for aqueous redox flow batteries operating at nearly neutral pH. The design and synthesis of 2,6‐DPPEAQ, (((9,10‐dioxo‐9,10‐dihydroanthracene‐2,6‐diyl)bis(oxy))bis(propane‐3,1‐diyl))bis(phosphonic acid), which has a high solubility at pH 9 and above, is described. Chemical stability studies demonstrate high stability at both pH 9 and 12. By pairing 2,6‐DPPEAQ with a potassium ferri/ferrocyanide positive electrolyte across an inexpensive, nonfluorinated permselective polymer membrane, this near‐neutral quinone flow battery exhibits an open‐circuit voltage of 1.0 V and a capacity fade rate of 0.00036% per cycle and 0.014% per day, which is the lowest ever reported for any flow battery in the absence of rebalancing processes. It is further demonstrated that the negolyte pH drifts upward upon atmospheric oxygen penetration but, when oxygen is excluded, oscillates reversibly between 9 and 12 during cycling. These results enhance the suitability of aqueous‐soluble redox‐active organics for use in large‐scale energy storage, potentially enabling massive penetration of intermittent renewable electricity.Publication A High Voltage Aqueous Zinc–Organic Hybrid Flow Battery(Wiley, 2019-05-17) Park, Minjoon; Beh, Eugene S.; Fell, Eric; Jing, Yan; Kerr, Emily; De Porcellinis, Diana; Goulet, Marc‐Antoni; Ryu, Jaechan; Wong, Andrew A.; Gordon, Roy; Cho, Jaephil; Aziz, MichaelWater‐soluble redox‐active organic molecules have attracted extensive attention as electrical energy storage alternatives to redox‐active metals that are low in abundance and high in cost. Here an aqueous zinc–organic hybrid redox flow battery (RFB) is reported with a positive electrolyte comprising a functionalized 1,4‐hydroquinone bearing four (dimethylamino)methyl groups dissolved in sulfuric acid. By utilizing a three‐electrolyte, two‐membrane configuration this acidic positive electrolyte is effectively paired with an alkaline negative electrolyte comprising a Zn/[Zn(OH)4]2− redox couple and a hybrid RFB is operated at a high operating voltage of 2.0 V. It is shown that the electrochemical reversibility and kinetics of the organic redox species can be enhanced by an electrocatalyst, leading to a cyclic voltammetry peak separation as low as 35 mV and enabling an enhanced rate capability.Publication Long Lifetime Mild pH-decoupling Aqueous Flow Battery with Practical in Situ pH Recovery(American Chemical Society (ACS), 2023-08-03) Xi, Dawei; Alfaraidi, Abdulrahman; Gao, Jinxu; Cochard, Thomas; Italiano Faria, Luana Cristina; George, Thomas; Wang, Taobo; Gordon, Roy; Liu, Richard; Aziz, MichaelAqueous redox flow batteries (ARFBs) constitute a promising technology for grid-scale electricity storage, but it is challenging to implement cell voltages exceeding the 1.23 V thermodynamic water splitting window with high Coulombic efficiency and long lifetime. pH decoupling – the creation of a pH difference between the negolyte and posolyte – can broaden the operating voltage window and improve long-term operational stability. This penalizes the efficiency, however, due to acid-base crossover induced by the pH gradient. As the voltage of the water splitting window varies linearly with pH whereas crossover fluxes vary exponentially, we employed mildly acidic and mildly basic electrolytes to develop a cell with high round-trip energy efficiency at an open-circuit voltage > 1.7 V. Moreover, we implemented an in situ acid-base regeneration system to periodically restore the negolyte and posolyte pH to their initial values. The combined system exhibits a capacity fade rate of less than 0.07% per day, a roundtrip energy efficiency of over 85%, and a Coulombic efficiency of approximately 99%. This work demonstrates principles for addressing critical issues such as lifespan, rate capability, long-term practicability, and energy efficiency in pH-decoupling ARFBs, providing guidance for the design of the next generation of high-voltage ARFBs.Publication pH swing cycle for CO2 capture electrochemically driven through proton-coupled electron transfer(Royal Society of Chemistry (RSC), 2020) Jin, Shijian; Wu, Min; Gordon, Roy; Aziz, Michael; Kwabi, DavidWe perform a thermodynamic analysis of the energetic cost of CO2 separation from flue gas (0.1 bar CO2(g)) and air (400 ppm CO2) using a pH swing created by electrochemical redox reactions involving proton-coupled electron transfer from molecular species in aqueous electrolyte. In this scheme, electrochemical reduction of these molecules results in the formation of alkaline solution, into which CO2 is absorbed; subsequent electrochemical oxidation of the reduced molecules results in the acidification of the solution, triggering the release of pure CO2 gas. We examined the effect of buffering from the CO2–carbonate system on the solution pH during the cycle, and thereby on the open-circuit potential of an electrochemical cell in an idealized four-process CO2 capture-release cycle. The minimum work input varies from 16 to 75 kJ molCO2−1 as throughput increases, for both flue gas and direct air capture, with the potential to go substantially lower if CO2 capture or release is performed simultaneously with electrochemical reduction or oxidation. We discuss the properties required of molecules that would be suitable for such a cycle. We also demonstrate multiple experimental cycles of an electrochemical CO2 capture and release system using 0.078 M sodium 3,3′-(phenazine-2,3-diylbis(oxy))bis(propane-1-sulfonate) as the proton carrier in an aqueous flow cell. CO2 capture and release are both performed at 0.465 bar at a variety of current densities. When extrapolated to infinitesimal current density we obtain an experimental cycle work of 47.0 kJ molCO2−1. This result suggests that, in the presence of a 0.465 bar/1.0 bar inlet/outlet pressure ratio, a 1.9 kJ molCO2−1 thermodynamic penalty should add to the measured value, yielding an energy cost of 48.9 kJ molCO2−1 in the low-current-density limit. This result is within a factor of two of the ideal cycle work of 34 kJ molCO2−1 for capturing at 0.465 bar and releasing at 1.0 bar. The ideal cycle work and experimental cycle work values are compared with those for other electrochemical and thermal CO2 separation methods.Publication Alkaline Quinone Flow Battery with Long Lifetime at pH 12(Elsevier BV, 2018-09) Kwabe, David G.; Ji, Yunlong; Lin, Kaixiang; Kerr, Emily F.; Goulet, Marc-Antoni; De Porcellinis, Diana; Tabor, Daniel P.; Pollack, Daniel A.; Aspuru-Guzik, Alán; Gordon, Roy; Aziz, MichaelWe demonstrate a long-lifetime, aqueous redox-flow battery that can operate at a pH as low as 12 while maintaining an open-circuit voltage of over 1 V. We functionalized 2,6-dihydroxyanthraquinone (2,6-DHAQ) with highly alkali-soluble carboxylate terminal groups. The resulting negative electrolyte material 4,4′-((9,10-anthraquinone-2,6-diyl)dioxy)dibutyrate (2,6-DBEAQ) was six times more soluble than 2,6-DHAQ at pH 12. Symmetric cell cycling with 2,6-DBEAQ on both sides of the cell demonstrates a capacity fade rate of <0.01%/day and <0.001%/cycle. By pairing 2,6-DBEAQ with a potassium ferri-/ferrocyanide positive electrolyte and utilizing a non-fluorinated membrane, this near-neutral flow battery shows a capacity fade rate that is the lowest of any quinone and rivals the lowest ever reported for any flow battery in the absence of rebalancing processes. This result adds the important attribute of long calendar life to quinone-based redox-flow batteries, which may enable massive penetration of intermittent renewable electricity.