Low Voltage Efficiency Research Articles

A Novel Cr2O3/MnO2-x Electrode for Lithium-Oxygen Batteries with Low Charge Voltage and High Energy Efficiency.

A high energy efficiency, low charging voltage cathode is of great significance for the development of non-aqueous lithium-oxygen batteries. Non-stoichiometric manganese dioxide (MnO2-x) and chromium trioxide (Cr2O3) are known to have good catalytic activities for the discharging and charging processes, respectively. In this work, we prepared a cathode based on Cr2O3 decorated MnO2-x nanosheets via a simple anodic electrodeposition-electrostatic adsorption-calcination process. This combined fabrication process allowed the simultaneous introduction of abundant oxygen vacancies and trivalent manganese into the MnO2-x nanosheets, with a uniform load of a small amount of Cr2O3 on the surface of the MnO2-x nanosheets. Therefore, the Cr2O3/MnO2-x electrode exhibited a high catalytic effect for both discharging and charging, while providing high energy efficiency and low charge voltage. Experimental results show that the as-prepared Cr2O3/MnO2-x cathode could provide a specific capacity of 6,779 mA·h·g−1 with a terminal charge voltage of 3.84 V, and energy efficiency of 78%, at a current density of 200 mA·g−1. The Cr2O3/MnO2-x electrode also showed good rate capability and cycle stability. All the results suggest that the as-prepared Cr2O3/MnO2-x nanosheet electrode has great prospects in non-aqueous lithium-oxygen batteries.

A Concentric Arc Meander Line Slow Wave Structure Applied on Low Voltage and High Efficiency Ka-Band TWT

A concentric arc meander line (CAML) slow wave structure (SWS) was proposed for applications on low voltage and high efficiency Ka-band traveling wave tube (TWT). Due to the CAML formed with a series of concentric arcs, the electric field in the radial direction may be more uniform, which may make the beam-wave interaction more sufficient and the electron efficiency improved. The metal shielding structure with symmetrical ridges was employed for impedance matching to obtain a wide bandwidth. Simulated results demonstrate that the proposed CAML-SWS TWT has a good transmission performance in Ka-band. When the initial beam voltage and current is set to 720 V and 0.2 A, respectively, the output power of the TWT can reach 44.15 W at 35 GHz with the gain and the electron efficiency of 18.6 dB and 30.66%, respectively. Furthermore, the 3-dB bandwidth can cover 24-42 GHz and the electron efficiency is over 23.2% in Ka-band.

Graphene-coated double D-type low loss optical fiber modulator.

A graphene-coated double D-type low loss all-fiber modulator is proposed. The modulator is improved on the basis of standard fiber. Only the cladding is processed without grinding the original core structure. The upper and lower cladding are cut same distance. This can ensure that the mode field does not deviate in one direction, so that most of the mode field is still tied to the core, which greatly reduces the device loss. The existence of the double graphene layer can also ensure a very excellent modulation efficiency. The calculation results show that the mode loss of our proposed dual-D modulator under X polarization is 0.125 dB/mm, and the mode field mismatch loss is 0.25%. The mode loss in Y polarization is 0.033 dB/mm, and the mode field mismatch loss is 0.32%. When the modulation voltage is 5 V, the modulation depth is 78.4% under the condition of five-layer graphene, while the modulation speed can reach 15.38 GHz. Besides maintaining low modulation voltage and higher modulation efficiency, this structure makes full use of the advantages of good fiber coupling, and will be widely used in future fiber communications and all-fiber systems.

Efficient green electroluminescent devices with low operation voltage and slow efficiency roll-off by utilizing hole transport material as host

We reported efficient electroluminescent (EL) devices with low operation voltage and slow efficiency roll-off based on green emitter Ir1 by utilizing hole transport material TAPC as host. Experimental results revealed our designed single light-emitting layer (EML) devices exhibit even lower operation voltage and slower efficiency roll-off compared with double-EMLs devices attributed to the reduced carriers' injection barriers, balanced carriers' distribution and well confined recombination zone. Ultimately, efficient green EL device realized the highest current efficiency (CE), power efficiency (PE), external quantum efficiency (EQE) and brightness of 71.6 cd/A, 75.0 lm/W, 22.9% and 36600 cd/m2, respectively. Excitedly, turn-on voltage was only 2.5 V. Even at a given brightness of 1000 cd/m2 (3.4 V), CE of 67.2 cd/A (EQE = 21.5%) and PE of 65.8 lm/W can still be retained. Our work offers a method to prepare efficient devices with slow efficiency roll-off, low operation voltage and simultaneously simple device structure.

New hole transport styrene polymers bearing highly π-extended conjugated side-chain moieties for high-performance solution-processable thermally activated delayed fluorescence OLEDs

New polystyrene-based polymers with high π-extended hole transport pendants were synthesized to obtain a low turn-on voltage and high efficiency in solution-processed green TADF-OLEDs.

Inverted with power efficiency over 220 lm W–1

The white organic light-emitting diodes (WOLEDs) have great potential in the fields of solid-state lighting. Continued efforts have been made to catch up with the power efficiency (PE) of inorganic light-emitting diodes. Apart from low operating voltage and near unity internal quantum efficiency, improvement the efficiency of light extraction, especially suppression of surface plasmon (SP) modes is essential for realizing ultimate PE. In contrast to corrugated structure which could suffer from spectral selectivity, higher leakage current and potential degradation issue stemmed from the rough structure, increasing the distance between the emitter and the metallic electrode becomes an effective avenue towards suppressing SP modes while maintaining the planar structure. In this work, an inverted bottom-emitting structure with thick hole transport layer (HTL) composed of multi-period organic heterojunctions is demonstrated to effectively extract the SP modes without any electrical property degradation in the current density range for lighting. Investigation on electrical properties of thickened HTL with increased count of organic heterojunctions indicates no increase of driving voltage at same current density in lighting application condition. By attaching an matched high refractive index lens, a record maximum forward-viewing PE of 228.4 lm W-1 is obtained for the thick WOLED fabricated on high refractive index glass substrate, exhibiting significant enhancements of 57% compared to the counterpart of the conventional thin WOLEDs. An unambiguous picture is given to depict the regularity derived from increase of emitter-to-metal distance by combination of a full optical simulation and experimental measurements excluded the influence of electrical property degradation.

Effects of Gas Diffusion Layers on a CO2 electrolysis Cell with an Anion Exchange Membrane for Ethylene Production

The concept of an electrolysis system, where CO2 is converted into hydrocarbons using renewable electricity, has been attracting much attention because it is expected to be one solution to achieve a decarbonized society. In order to realize an economical electrolysis system, it is important to produce high-value products such as ethylene with high reaction rate (i.e. the operating current density of CO2 electrolysis), and high efficiency (low operation voltage).The anion exchange membrane (AEM) CO2 electrolysis cells using gas diffusion electrodes (GDEs) are more advantageous than the traditional flow cell using a solution purged with CO2, both in terms of higher current density and lower voltage operation. This is because of the efficient CO2 reduction occurring at the three-phase interface of a GDE (i.e. CO2 is directly fed to the vicinity of the electrocatalysts though a gas diffusion layer (GDL)), increasing the current density, and of the cell electrodes being closely spaced, lowering the voltage. However, there are only several studies of the AEM CO2 electrolysis cells for high rate of ethylene production [1].Here, we investigate ethylene production performance of an AEM CO2 electrolysis cell consisting of copper and copper oxide nanoparticles coated on GDL as a cathode, iridium oxide-coated titanium support as an anode, and an AEM. Among these components, the GDL can play a crucial role in the efficient transport of CO2 and water management, therefore we focus on understanding the effects of GDL properties such as thickness, porosity and density on ethylene production. We evaluated the electroreduction characteristics of the cells under ambient condition by a constant current method in which a constant current is supplied for a period of time. The faradaic efficiency (FE) and partial current density (PCD) of gas products such as ethylene, carbon monoxide, methane and hydrogen are examined as a function of the total current densities (TCD). We found that the FEs and PCDs depended on the density and the thickness of the GDLs. The low density and thick GDL showed high FE and PCD of ethylene due to high gas diffusibility. The FE and the PCD of ethylene at the TCD of 600 mA/cm2 reached a maximum of 50 % and 300 mA/cm2, respectively.

Electrocatalyst Layer Design of Polymer Electrolyte Membrane Electrolyzer for Simultaneous Hydrogenation of Organic Chemical Hydride Energy Carrier and Water Decomposition

Introduction To utilize renewable electricity with fluctuation and localization, large-scale energy storage and transportation technologies using hydrogen energy carrier have been expected. In order to improve hydrogen energy carrier synthesis, we have studied one-step electrolysis for toluene electrohydrogenation and water decomposition, which has cathode side of PEFC’s MEA like structure using PtRu/C and anode side of industrial electrolyzer like structure using mesh shape of DSE® electrode for oxygen evolution reaction. This process has 1.09 V of theoretical decomposition voltage for simultaneous water electrolysis and toluene hydrogenation. We had optimized the electrolyzer with stacked anode of fine and conventional mesh to get high faraday efficiency and low cell voltage [1]. However, ultra fine anode, which decreased cell voltage a lot, based on sintered titanium fiber porous plate significantly decreased faraday efficiency.In this study, layered catalyst layer of dot shape and whole surface coating had been investigated to enhance mass transportation of toluene into the catalyst layer to improve faraday efficiency using ultra fine mesh anode, in order to develop efficient toluene direct hydrogenation electrolyzer with low cell voltage and high faraday efficiency. Experimental Figure 1 shows the schematic drawing dot shape cathode catalyst layer of square and diamond type that was consisted of 1.2 x 1.2 mm2 square dots with different direction. The dot shape was formed on a proton exchange membrane (Nafion®117, DuPont) and whole surface catalyst layer was formed on a carbon paper (35BC, SGL carbon ltd.) dispersed 0.5 mg cm-2 of Pt/C for chemical hydrogenation using by-product of hydrogen. The Pt-Ru/C (TEC61E54, TKK) loading was 0.75 mgcm-2 of metal for the layered potion of dot and whole surface coating. The type is indicated with the ratio of metal loading of dot and uniform layers on a dot as x:(10-x).The anode was ultra fine mesh and stacked anode of fine and conventional DSE® for oxygen evolution (De Nora Permelec, Ltd.), which was iridium oxide based electrocatalyst coated sintered titanium fiber plate.During electrolysis, cathode reactant of 10% toluene – methylcyclohexane or 100% toluene, and anolyte of 1 M (=moldm-3) H2SO4 was circulated at a 10 mL min-1 of flow rate, respectively at 60oC. Current efficiency was determined with the volume ratio of generated hydrogen gas and toluene-methylcyclohexane solution. Results and discussion Figure 2 shows the iR-free cell voltage, current efficiency and internal resistance as a function of current density for various electrolyzers. Internal resistances determined by EIS measurement were in the range from 0.4 to 0.5 Wcm2 in variation. The cell voltage of the conventional type with the double mesh anode was significantly higher than others, although current efficiency was higher than others. The uniform electrocatalyst layer electrolyzer with ultra fine mesh anode showed the lowest current efficiency in these. Here, only difference between these two cells were only anode structure, therefore anode structure would affect to mass transfer of toluene into cathode catalyst layer through current distribution corresponded to the anode shape. Patterned catalyst layers make current distribution by themselves, and their current efficiency were higher than that with uniform catalyst layer, so the effectiveness of the dot shape cathode catalyst layer was confirmed. The current efficiency of the diamond shape was higher than that of square shape, especially the current efficiency of 3:7 of the diamond shape was close to the fine mesh electrolyzer. From the comparison among square, diamond, and double layer catalyst, the current efficiency was affected not only current distribution by a shape of dot but also reactant flow distribution in cathode side flow field.Figure 3 shows current density and cathode potential as a function of the metal loading ratio of dot and uniform layers on a dot: r dot at a current hydrogenation current density of 90, 95, and 100%. The current density was the highest at 30% of the ratio with the lowest cathode potential. Therefor, the selectivity of hydrogenation should not be controlled by kinetics of charge transfer of the electrocatalyst, and strongly affected by mass transfer process of toluene in the catalyst layer. The optimized shape catalyst layer of this study was the stack of the dot layer and thinner whole surface layer of 3:7. Acknowledgement DSE® anodes for oxygen evolution were supplied from De Nora Permelec (DNJ). Authors appreciate to Dr. A. Kato and Dr. Y. Nishiki, DNJ for the distribution of the anodes.

High performance doping-free WOLEDs based on rationally designed asymmetric orange-red Ir(III) emitter with balanced charge mobility

Doping-free organic light-emitting diodes (OLEDs) have attracted continuous attention owing to reduced phase separation, better repeatability, and low cost. Despite demonstrating great potential for white OLEDs (WOLEDs), development of phosphorescent materials capable of achieving high performance with low voltage, high luminance, and low efficiency roll-off simultaneously, still remains a significant challenge. Herein, we design three orange-red Ir(III) phosphors employing functionalized 1,2-diphenylbenzimidazole as main ligands. Clear relationship between structures and electroluminescence (EL)-performances has been established by comprehensively studying their emission properties and intrinsic carrier transporting abilities. Designed phosphor SFIrbiq with spirobifluorene moiety showing negligible intermolecular interactions and balanced carrier transporting ability, not only achieves favorable monochromatic doping-free device but also high-performance doping-free WOLEDs. Optimized WOLED realizes low voltages (2.5 V at 1 cd m−2, 3.3 V at 100 cd m−2, and 4.2 V at 1000 cd m−2), maximum brightness of 34 505 cd m−2 and efficiencies of 24.2 cd A−1, 21.7 lm W−1, 10.3%. Such doping-free hybrid WOLED also achieves low efficiency roll-off of 5% for external quantum efficiency (EQE) at 1000 cd m−2. The device performance can be further improved by employing doping-free all-phosphorescent device structure, achieving maximum efficiencies of 33.3 cd A−1, 32.4 lm W−1, and 16.9%. The results are promising among reported doping-free three-color WOLEDs, paving a feasible way to development of efficient Ir(III) phosphors and doping-free WOLEDs.

Controllable and efficient hole-injection layers with molybdenum oxide units by solution-processed procedure for OLEDs

Since the low work function of ITO, introducing hole injection layer (HIL) with controllable and efficient property is an effective way to improve the performance of organic light-emitting diodes (OLEDs). In this work, films, containing molybdenum oxide units by employing H 2 O 2 treated ammonium phosphomolybdate (AMP) as precursors, are fabricated through solution-processed procedure. The hole injection property of the HILs can be modulated by the gap-state density, which is negatively correlated with the molar ratio of AMP/H 2 O 2 . Green fluorescent and phosphorescent OLEDs based on the HILs are endowed with reduced turn-on voltage from 3.4 to 2.5 V and 4.1 to 3.4 V, respectively. Furthermore, fluorescent OLEDs based on the HIL with AMP/H 2 O 2 of 1:14 show a maximum current efficiency of 6.82 cd/A, 1.2-flod higher than that of PEDOT:PSS based devices. This method opens up a new path to obtain HIL with adjustable property in mild prepare condition for various electroluminescent devices. • Controllable HILs with MoO 3 units were fabricated by solution-processed procedure. • Hole injection property of HILs was modulated by gap-state density, negatively correlated with AMP/H 2 O 2 molar ratio. • Green fluorescent and phosphorescent OLEDs based on the HILs were endowed with low turn-on voltage and high efficiency.

Experimental Study on the Design and Characteristics of a Laminar Plasma Torch With Medium Working Power and its Applications for Surface Hardening

Due to its favorable temperature and velocity distributions, a lamina plasma jet, generated by a laminar plasma torch (LPT), is superior to a turbulent plasma jet on some applications. However, most of the reported LPTs usually work at a relatively low output power with a relatively low arc voltage and thermal efficiency, limiting its capability in the applications such as the surface hardening, synthesis of nanoparticles, remanufacturing of large components, and so on. Therefore, this article aims at designing an LPT with medium level output power and a relatively low arc current but a high thermal efficiency. The characteristics and applications of the proposed LPT have been obtained by experiments. The experimental results show the following characteristics: 1) the mean arc voltage of the proposed LPT is higher than 190 V with a maximum working power larger than 25 kW; 2) its mean thermal efficiency and jet length arrive at 50% and 450 mm, respectively; 3) the experimental data of the proposed LPT were used to fit its theoretical characteristics by using the least squares method. According to these fitted curves, the theoretical characteristics of the proposed LPT at a specified working conditions can be predicted; and 4) in addition, the surface of 45# steel was hardened by using the laminar plasma jet to obtain a hardening surface. The maximum hardness of the treated substrate arrives at about 600 HV, which is three times of the untreated substrate.

In situ construction of porous hierarchical (Ni3-xFex)FeN/Ni heterojunctions toward efficient electrocatalytic oxygen evolution

As a choke point in water electrolysis, the oxygen evolution reaction (OER) suffers from the severe electrode polarization and large overpotential. Herein, the porous hierarchical hetero-(Ni3-xFex)FeN/Ni catalysts are in situ constructed for the efficient electrocatalytic OER. X-ray absorption fine structure characterizations reveal the strong Ni-Fe bimetallic interaction in (Ni3-xFex)FeN/Ni. Theoretical study indicates the heterojunction and bimetallic interaction decrease the free-energy change for the rate-limiting step of the OER and the overpotential thereof. In addition, the high conductivity and porous hierarchical morphology favor the electron transfer, electrolyte access and O2 release. Consequently, the optimized catalyst achieves a low overpotential of 223 mV at 10 mA·cm-2, a small Tafel slope of 68 mV·dec-1, and a high stability. The excellent performance of the optimized catalyst is also demonstrated by the overall water electrolysis with a low working voltage and high Faradaic efficiency. Moreover, the correlation between the structure and performance is well established by the experimental characterizations and theoretical calculations, which confirms the origin of the OER activity from the surface metal oxyhydroxide in situ generated upon applying the current. This study suggests a promising approach to the advanced OER electrocatalysts for practical applications by constructing the porous hierarchical metal-compound/metal heterojunctions.

Design and characteristics of a new type laminar plasma torch for materials processing

Laminar plasma jet (LPJ) generated by laminar plasma torch (LPT) has a favorable temperature and velocity distribution. Thus, it is superior to the turbulent plasma jet in material processing. However, most of the reported LPTs usually operate at a relatively low output power with a relatively low arc voltage and thermal efficiency, which limits its capabilities. In this context, this paper attempts to design a new type of high-power LPT with a relatively low arc current and a high thermal efficiency. In the first section, the design principle of the main components is studied and discussed in detail, and a new high-power LPT is proposed. Then, the experimental characteristics of the proposed high-power LPT are examined. Experimental results reveal the following characteristics of the proposed LPT. (1) The max jet length of the proposed LPT reaches at 540 mm. (2) Its mean arc voltage is higher than 290 V when the LPT works with arc currents lower than 200 A, leading to an output power greater than 50 kW. (3) The mean thermal efficiency is higher than 50%. Lastly, the proposed LPT has been applied to spheroidize the aluminum oxide powers. The experiment results for the production of spherical powders show that the proposed LPT has a good characteristic for material processing.

Efficient blue organic light-emitting diodes with low operation voltage by improving the injection and transport of holes

In this work, we reported the highly efficient organic electroluminescent (EL) devices based on blue phosphorescent material FIr6. By utilizing p-type dopant HAT-CN as hole injection layer material, the injection of holes from the anode was significantly improved. In addition, doping HAT-CN into hole transport layer (HTL) and inserting thin TcTa film between HTL and light-emitting layer (EML) improved the transport of holes. The stepwise energy levels between functional layers reduced the injection barriers of carriers, thus improving the balance of carriers within EML. Finally, highly efficient blue EL device realized the maximum current efficiency, power efficiency, external quantum efficiency (EQE) and brightness up to 39.14 cd/A, 38.68 lm/W, 24.6% and 17201 cd/m2, respectively. Even at the high brightness of 1000 cd/m2 (3.7 V), current efficiency and EQE as high as 36.73 cd/A and 23.1%, respectively, can still be retained by the same device. Our investigation provides an idea for the design of high-performance devices with low operation voltage and slow efficiency roll-off.

Novel Sulfonated Aromatic Polymer Membranes for Breaking the Coulombic and Voltage Efficiency Trade-Off Limitation in Vanadium Redox Flow Battery

Vanadium redox flow batteries (VRFBs) have received extensive attention due to its attractive features for the large-scale energy storage because of their design flexibility, absence of intercalation/deintercalation and stress build-up in electrodes, and safe operation. One of the most critical components in VRFB is an ion exchange membrane which can prevent cross mixing of the multivalence vanadium ions, while it still allows the transport of protons (or anions) to complete the circuit. However, the trade-off relationship of proton exchange membrane limits the energy efficiency (EE) of the VRFB due to low coulombic efficiency (CE) caused by vanadium ion cross over through the membrane or high membrane resistances. Anion exchange membrane suffers from poor chemical stability and low voltage efficiency due to low ion conductivity. In this study, we synthesized a series of novel sulfonated aromatic polymer membranes having high proton conductivity as well as selectivity which surpass the proton conductivity-selectivity trade-off relationship. The effect of the pendent group structure on the membrane ion selectivity and battery performance was investigated. It was found that the incorporation of aromatic structures on the pendent groups effectively improved the proton conductivity and selectivity. The membrane with aromatic pendent groups (BPAr-F4) shows 3 times higher vanadium/proton ion selectivity than Nafion 212. As a result, the VRFB single cell equipped with the 80um-thick BPAr-F4 membrane shows significantly better performance in comparison to the cell with Nafion membranes, as high as 97.18% CE, 95.91% VE and 93.20% EE (vs. 75.14% CE, 96.12% VE and 72.22% EE of Nafion 212; 91.30% CE, 95.63% VE and 87.62% EE of Nafion 117) at 20 mA/cm2. Small-angle X-ray scattering (SAXS) studies indicates that their unique morphologies with narrow aqueous ionic domains which are well organized with acidic -SO3H groups results in the high proton selectivity and VRFB performance.

Review of experimental and modelling developments for ceria-based solid oxide fuel cells free from internal short circuits

Ceria-based solid oxide fuel cells (SOFCs) are the promising candidates for the low- and intermediate-temperature SOFCs. However, the Ce4+ in the ceria-based electrolyte materials is likely reduced to Ce3+ under low oxygen partial pressure, leading to high electronic conductivity. Therefore, ceria-based SOFCs commonly show low open-circuit voltage and low efficiency due to the leakage current. While extensive studies of the electron transport mechanism and the methods for the prevention of leakage current in ceria-based electrolytes have been conducted, systematic reviews of the relevant literature have been notably rare. In this review, the formation mechanism and factors affecting electronic conductivity in doped ceria are clearly described. Additionally, two kinds of methods including the optimization of the single ceria-doped electrolyte and the use of the various electron blocking layers (e.g., ZrO2-based, doped BaCeO3/SrCeO3 and doped Bi2O3 materials) are systematically summarized. Finally, mathematical models describing the electrochemical characteristics of ceria-based SOFCs based on different assumptions are reviewed. This review can provide useful guidance for the further development and application of internal short-circuit-free ceria-based SOFCs.

Highly efficient yellow nondoped thermally activated delayed fluorescence OLEDs by utilizing energy transfer between dual conformations based on phenothiazine derivatives

The nondoped thermally activated delayed fluorescence (TADF) devices are increasingly attracting attention due to the superior performances and simple fabrication process. By incorporating two acceptors with phenothiazine, two materials 2-(10H-phenothiazine-10-yl)-10-phenyl-10H-phenothiazine-5,5-dioxide (PTZ-2PTO) and 3-(10H-phenothiazin-10-yl)-10-phenylacridin-9(10H)-one (PTZ-AD) are designed and investigated. Both the two materials possess dual conformations, whereas the quasi-axial conformer is the main configuration of PTZ-2PTO and quasi-equatorial conformer of PTZ-AD is more stable. The quasi-axial conformers show classical fluorescence emission, and the quasi-equatorial conformers exhibit TADF characteristic. Fascinatingly more, efficient energy transfer can be achieved between quasi-axial conformers and quasi-equatorial conformers, exhibiting similar mechanism to the traditional host-guest system. Based on this characteristic, yellow nondoped TADF-OLED device of PTZ-AD has realized the efficiency of up to 17.08%, 50.48 cd A−1 and 60.04 lm W−1. Meanwhile, the PTZ-AD based nondoped device exhibits low turn-on voltage and low efficiency roll-off, which is among the best performance for yellow nondoped TADF devices. In addition, PTZ-AD based doped device realizes high efficiency of 20.23%, 61.04 cd A−1 and 68.45 lm W−1. This dual conformations forming host-guest system provides a new strategy for obtaining highly efficient nondoped OLEDs devices.

(Invited) Fuel Cells Fueled By Sustainable Liquid Fuels

The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical technologies for energy transformation and storage for distributed, grid scale and automotive applications. Recently hydrogen PEM fuel cells (FC) made great progress in performance, durability and cost that reflected in the emerging of multiple commercial vehicles powered by FCs. However their market penetration is hampered mostly by the absence of hydrogen infrastructure including transportation and storage, and high cost of its implementation. On the other side, carbon-neutral liquid fuels (CNLFs) have energy density higher than of liquid hydrogen, better safety, low footprint and cost of transportation and storage. Easily liquefied ammonia and dimethyl ether as well as more traditional lower alcohols are the most promising CNLFs. They can be used with or without internal reforming in direct liquid fuel cells (DLFCs) or as a hydrogen carrier for PEM fuel cells thus allowing the use of existing liquid fuels infrastructure. History of DLFCs started in 1960s from first GE attempts to use diesel fuel in a FC and continued with development of direct methanol fuel cells (DMFCs). In spite intensive research, the latter found very limited application because of low efficiency and power density. As conventional low temperature PEMs and AEMs content a lot of water to support high H+ or OH- conductivity, high crossover rate of most CNLFs is inevitable and leads to low cell voltage and energy efficiency. In addition, traditional platinum group metal catalysts are easily poisoned by CNLFs or by intermediate oxidation products. Therefore, to realize high energy density of CNLFs and provide high FC power density, it is necessary to increase operation temperature of DLFCs, develop more active and less expensive electrocatalysts, develop selective ion conducting membranes and design electrodes and cells for using liquid fuels. Recent advances in the development of novel DLFCs that is being funded by ARPA-E via REFUEL and OPEN 2018 programs will be presented. Possible future ARPA-E program targeting the use of such fuel cells for transportation (in hybrids, range extenders, APUs for aviation and ground transportation) will be also discussed.

2D-σ-2A type cruciform host material with silane core for highly efficient solution-processable green thermally activated delayed fluorescence organic light emitting diodes

A new solution processable cruciform tetraphenylsilane-based bipolar host material, bis(4-(9H-carbazol-9-yl)phenyl)bis(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)silane (SiCT), was designed and synthesized. Two carbazoles as donors and two diphenyl triazine moieties as acceptors were tethered to the tetraphenylsilane. SiCT showed great solubility in common organic solvents, high thermal stability, high triplet energy (T1 ∼3.0 eV), and a superior bipolar electronic nature, which are sufficient for it to function as a host material in thermally activated delayed fluorescence organic light emitting diodes (TADF-OLEDs). Consequently, the solution-processed green TADF-OLEDs employed SiCT as a bipolar host exhibited a low turn-on voltage and high external quantum efficiency (EQE) of 19.17% with a high power efficiency (PE) of 41.13 lm W−1, while control device based-on SiC as unipolar host showed a low EQE of 12.74% with a low PE of 16.13 lm W−1. This work highlights the potential of a bipolar tetraphenylsilane derivative as a host material in solution-processable green TADF-OLEDs.

A deep eutectic solvent (DES) electrolyte-based vanadium-iron redox flow battery enabling higher specific capacity and improved thermal stability

Compared with conventional aqueous electrolyte, due to unique merits of deep eutectic solvents including a wide electrochemical window, ease in preparation, low vapor pressure and low cost, they have been used as electrolyte in the non-aqueous flow battery. This work reports a reline deep eutectic solvent, which is prepared as the anolyte and catholyte of a vanadium-iron redox flow battery. Since the solubility of the vanadium and iron species in deep eutectic solvent has been improved, an increased specific capacity can be obtained, up to 54.6% compared with the aqueous electrolyte one. However, the viscosity of this electrolyte is much larger than that of aqueous electrolyte, which causes more pumping losses. With the increase of operating temperature, the viscosity experiences a huge drop. The open-circuit voltage of such an non-aqueous system begins near 0.9 V with a decrease rate of 0.005 V h−1, suggesting a better capacity retention ability than does the aqueous flow battery. The cycling performance of this redox flow battery is evaluated at a current density of 2.0 mA cm−2 under the temperature of 30 °C. The coulombic efficiency is up to 94.8%, while voltage efficiency and energy efficiency are just 68.3% and 64.7%, respectively. The low voltage efficiency stems from the sluggish redox kinetics of the vanadium ions, and large internal ohmic resistance. With an improved thermal stability, this vanadium-iron redox flow battery is preferred to be operated at elevated temperature, which helps to greatly reduce the ohmic loss and pumping loss, such that to increase the system energy efficiency.