pH-Tuning a Solar Redox Flow Battery for Integrated Energy Conversion and Storage

The intermittent nature of renewable energy sources such as solar and wind requires an energy storage method for future viability. Integrated solar energy conversion and storage devices such as solar redox flow batteries offer an innovative approach to this problem. Herein, we demonstrate electrolyte pH to be a valuable and tunable parameter for optimization of aqueous solar redox flow batteries. This can be accomplished by utilizing a pH-dependent redox anolyte and pH-independent catholyte to effectively tune the cell voltage by varying the operating pH, which allows direct integration of a dye-sensitized photoelectrode. A quinone–iodine redox flow battery can achieve high columbic efficiency over ∼90% for 50 cycles under mild pH conditions (pH ∼ 2–8). Furthermore, a pH-tunable solar redox flow battery can be charged using only solar illumination, thus allowing for integrated energy conversion and storage within a single devic

Understanding the Crystallization Mechanism of Delafossite CuGaO₂ for Controlled Hydrothermal Synthesis of Nanoparticles and Nanoplates

The delafossite CuGaO₂ is an important p-type transparent conducting oxide for both fundamental science and industrial applications. An emerging application is for p-type dye-sensitized solar cells. Obtaining delafossite CuGaO₂ nanoparticles is challenging but desirable for efficient dye loading. In this work, the phase formation and crystal growth mechanism of delafossite CuGaO₂ under low-temperature (<250 °C) hydrothermal conditions are systematically studied. The stabilization of Cu^I cations in aqueous solution and the controlling of the hydrolysis of Ga^III species are two crucial factors that determine the phase formation. The oriented attachment (OA) growth is proposed as the crystal growth mechanism to explain the formation of large CuGaO₂ nanoplates. Importantly, by suppressing this OA process, delafossite CuGaO₂ nanoparticles that are 20 nm in size were successfully synthesized for the first time. Moreover, considering the structural and chemical similarities between the Cu-based delafossite series compounds, the understanding of the hydrothermal chemistry and crystallization mechanism of CuGaO₂ should also benefit syntheses of other similar delafossites such as CuAlO₂ and CuScO₂

2H-CuScO₂ Prepared by Low-Temperature Hydrothermal Methods and Post-Annealing Effects on Optical and Photoelectrochemical Properties

The delafossite structured CuScO₂ is a p-type, wide band gap oxide that has been shown to support significant oxygen intercalation, leading to darkened color and increased conductivity. Control of this oxidation proves difficult by the conventional high-temperature solid-state syntheses. In addition, a pure hexagonal (2H) or rhombohedral (3R) polytype of CuScO₂ requires careful control of synthetic parameters or intentional doping. Lower-temperature hydrothermal syntheses have thus far led to only a mixed 2H/3R product. Herein, control of hydrothermal conditions with the consideration of copper and scandium hydrolysis led to the synthesis of light beige, hierarchically structured particles of 2H-CuScO₂. Absorption of the particles in the visible range was found to increase upon annealing of the sample in air, most likely due to the Cu^II formation from oxygen interstitials. X-ray photoelectron spectroscopy confirmed purely Cu^I in the as-synthesized 2H-CuScO₂ and increased Cu^II amounts upon annealing. Oxidation of the samples also led to shifts of the Fermi level toward the valence band as observed by increases in the measured flat band potentials versus normal hydrogen electrode, confirming increased hole carrier densities

p-Type Dye-Sensitized Solar Cells Based on Delafossite CuGaO₂ Nanoplates with Saturation Photovoltages Exceeding 460 mV

Exploring new p-type semiconductor nanoparticles alternative to the commonly used NiO is crucial for p-type dye-sensitized solar cells (p-DSSCs) to achieve higher open-circuit voltages (<i>V</i>_oc). Here we report the first application of delafossite CuGaO₂ nanoplates for p-DSSCs with high photovoltages. In contrast to the dark color of NiO, our CuGaO₂ nanoplates are white. Therefore, the porous films made of these nanoplates barely compete with the dye sensitizers for visible light absorption. This presents an attractive advantage over the NiO films commonly used in p-DSSCs. We have measured the dependence of <i>V</i>_oc on the illumination intensity to estimate the maximum obtainable <i>V</i>_oc from the CuGaO₂-based p-DSSCs. Excitingly, a saturation photovoltage of 464 mV has been observed when a polypyridyl Co^3+/2+(dtb-bpy) electrolyte was used. Under 1 Sun AM 1.5 illumination, a <i>V</i>_oc of 357 mV has been achieved. These are among the highest values that have been reported for p-DSSCs

p-Type Dye-Sensitized Solar Cells Based on Delafossite CuGaO₂ Nanoplates with Saturation Photovoltages Exceeding 460 mV

Exploring new p-type semiconductor nanoparticles alternative to the commonly used NiO is crucial for p-type dye-sensitized solar cells (p-DSSCs) to achieve higher open-circuit voltages (<i>V</i>_oc). Here we report the first application of delafossite CuGaO₂ nanoplates for p-DSSCs with high photovoltages. In contrast to the dark color of NiO, our CuGaO₂ nanoplates are white. Therefore, the porous films made of these nanoplates barely compete with the dye sensitizers for visible light absorption. This presents an attractive advantage over the NiO films commonly used in p-DSSCs. We have measured the dependence of <i>V</i>_oc on the illumination intensity to estimate the maximum obtainable <i>V</i>_oc from the CuGaO₂-based p-DSSCs. Excitingly, a saturation photovoltage of 464 mV has been observed when a polypyridyl Co^3+/2+(dtb-bpy) electrolyte was used. Under 1 Sun AM 1.5 illumination, a <i>V</i>_oc of 357 mV has been achieved. These are among the highest values that have been reported for p-DSSCs

Potassium-Ion Oxygen Battery Based on a High Capacity Antimony Anode

Recent investigations into the application of potassium in the form of potassium–oxygen, potassium–sulfur, and potassium-ion batteries represent a new approach to moving beyond current lithium-ion technology. Herein, we report on a high capacity anode material for use in potassium–oxygen and potassium-ion batteries. An antimony-based electrode exhibits a reversible storage capacity of 650 mAh/g (98% of theoretical capacity, 660 mAh/g) corresponding to the formation of a cubic K₃Sb alloy. The Sb electrode can cycle for over 50 cycles at a capacity of 250 mAh/g, which is one of the highest reported capacities for a potassium-ion anode material. X-ray diffraction and galvanostatic techniques were used to study the alloy structure and cycling performance, respectively. Cyclic voltammetry and electrochemical impedance spectroscopy were used to provide insight into the thermodynamics and kinetics of the K–Sb alloying reaction. Finally, we explore the application of this anode material in the form of a K₃Sb–O₂ cell which displays relatively high operating voltages, low overpotentials, increased safety, and interfacial stability, effectively demonstrating its applicability to the field of metal oxygen batteries

Probing the Low Fill Factor of NiO p‑Type Dye-Sensitized Solar Cells

p-Type dye-sensitized solar cells (<i>p</i>-DSCs) have attracted increasing attention recently, but they suffer from low fill factors (FFs) and unsatisfactory efficiencies. A full comprehension of the hole transport and recombination processes in the NiO <i>p</i>-DSC is of paramount importance for both the fundamental study and the practical device optimization. In this article, NiO <i>p</i>-DSCs were systematically probed under various bias and illumination conditions using electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent spectroscopy (IMPS), and intensity modulated photovoltage spectroscopy (IMVS). Under the constant 1 sun illumination, the recombination resistance (<i>R</i>_rec) of the cell deviates from an exponential relationship with the potential and saturates at ∼130 Ω cm² under the short circuit condition, which is ascribed to the overwhelming recombination with the reduced dye anions. Such a small <i>R</i>_rec results in the small dc resistance, which decreases the “flatness” of the <i>J–V</i> curve. The quantitative analysis demonstrates that the FF value is largely attenuated by the recombination of holes in NiO with the reduced dyes. Our analysis also shows that if this recombination can be eliminated, then an FF value of 0.6 can be reached, which agrees with the theoretical calculation with a <i>V</i>_oc of 160 mV

Understanding Side Reactions in K–O₂ Batteries for Improved Cycle Life

Superoxide based metal–air (or metal–oxygen) batteries, including potassium and sodium–oxygen batteries, have emerged as promising alternative chemistries in the metal–air battery family because of much improved round-trip efficiencies (>90%). In order to improve the cycle life of these batteries, it is crucial to understand and control the side reactions between the electrodes and the electrolyte. For potassium–oxygen batteries using ether-based electrolytes, the side reactions on the potassium anode have been identified as the main cause of battery failure. The composition of the side products formed on the anode, including some reaction intermediates, have been identified and quantified. Combined experimental studies and density functional theory (DFT) calculations show the side reactions are likely driven by the interaction of potassium with ether molecules and the crossover of oxygen from the cathode. To inhibit these side reactions, the incorporation of a polymeric potassium ion selective membrane (Nafion-K⁺) as a battery separator is demonstrated that significantly improves the battery cycle life. The K–O₂ battery with the Nafion-K⁺ separator can be discharged and charged for more than 40 cycles without increases in charging overpotential

Increasing expression of TRPV4 mRNA and protein during HSC activation.

<p>A. Total RNAs were isolated from TGF-β1-treated HSC-T6 cells, and subjected to qRT-PCR analyses. Representative images of three independent experiments are shown. *p<0.05 vs. non-treated cells. B. Whole-cell extracts were isolated from TGF-β1-treated HSC-T6 cells, and subjected to Western blot analyses with TRPV4 and β-actin antibodies. Representative blots of three independent experiments are shown. **p<0.01 vs. non-treated cells. C. Total RNAs were isolated from TGF-β1 treated HSC-T6 cells at different time points. The expression of α-SMA and Col1a1 mRNA was assessed by RT-PCR. Representative images of three independent experiments are shown. **p<0.01 vs. non-treated cells.</p

Blockade of TRPV4 inhibited the proliferation and decreased α-SMA expression in activated HSC-T6 cells.

<p>A. Total RNA extracts were made from HSC-T6 cells treated with or without TGF-β1 and Ru, and subjected to qRT-PCR analyses of TRPV4. Representative images of three independent experiments are shown. ^#p<0.05 vs. TGF-β1-treated cells. B. HSC-T6 cells were seeded in triplicate on day 0 and incubated in DMEM containing 10% fetal bovine serum or same media supplemented with Ru for further 24 h. Proliferation was measured by adding 5 mg/ml MTT reagent per well and incubating it for 4 h. ^#p<0.05 vs. TGF-β1-treated cells. C. Total RNA extracts were made from HSC-T6 cells treated with or without TGF-β1 and Ru, and subjected to qRT-PCR analyses of α-SMA. Representative images of three independent experiments are shown. ^#p<0.05 vs. TGF-β1-treated cells. D. Whole-cell protein extracts were made from HSC-T6 cells treated with or without TGF-β1 and Ru, and subjected to Western blot analyses of TRPV4. Representative images of three independent experiments are shown. ^##p<0.01 vs. TGF-β1-treated cells. E. HSC-T6 cells were treated with TGF-β1 for 48 h, followed by transfection with TRPV4-siRNA for an additional 48 h, and cell viability was determined by MTT assay. Mean±SE of two HSC preparations in quadruplets is shown; *p<0.05 vs. non-treated cells, ^#p<0.05 vs. TGF-β1-treated cells. F. Whole cell extracts were isolated from TGF-β1-treated HSC-T6 cells with RNAi transfection, and subjected to Western blot analyses. Representative images of three independent experiments are shown. **p<0.01 vs. non-treated cells, ^##p<0.01 vs. TGF-β1-treated cells.</p