Micropumping of liquid by directional growth and selective venting of gas bubbles

We introduce a new mechanism to pump liquid in microchannels based on the directional growth and displacement of gas bubbles in conjunction with the non-directional and selective removal of the bubbles. A majority of the existing bubble-driven micropumps employs boiling despite the unfavorable scaling of energy consumption for miniaturization because the vapor bubbles can be easily removed by condensation. Other gas generation methods are rarely suitable for micropumping applications because it is difficult to remove the gas bubbles promptly from a pump loop. In order to eradicate this limitation, the rapid removal of insoluble gas bubbles without liquid leakage is achieved with hydrophobic nanopores, allowing the use of virtually any kind of bubbles. In this paper, electrolysis and gas injection are demonstrated as two distinctively different gas sources. The proposed mechanism is first proved by circulating water in a looped microchannel. Using H(2) and O(2) gas bubbles continuously generated by electrolysis, a prototype device with a looped channel shows a volumetric flow rate of 4.5-13.5 nL s(-1) with a direct current (DC) power input of 2-85 mW. A similar device with an open-ended microchannel gives a maximum flow rate of approximately 65 nL s(-1) and a maximum pressure head of approximately 195 Pa with 14 mW input. The electrolytic-bubble-driven micropump operates with a 10-100 times higher power efficiency than its thermal-bubble-driven counterparts and exhibits better controllability. The pumping mechanism is then implemented by injecting nitrogen gas bubbles to demonstrate the flexibility of bubble sources, which would allow one to choose them for specific needs (e.g., energy efficiency, thermal sensitivity, biocompatibility, and adjustable flow rate), making the proposed mechanism attractive for many applications including micro total analysis systems (microTAS) and micro fuel cells.     

A dyadic sensitizer for dye solar cells with high energy-transfer efficiency in the device.

A new bichromophoric dyad based on an alkyl-functionalized aminonaphthalimide as energy-donor chromophore and [Ru(dcbpy)2(acac)]Cl (dcbpy=4,4'-dicarboxybipyridine, acac=acetylacetonato) as energy acceptor and sensitizing chromophore is synthesized. Efficient quenching of the donor-chromophore emission is observed in solution, presumably due to resonant energy transfer. This dyad is then used as a sensitizer in a dye solar cell. By comparing the spectral properties of transparent dye solar cells sensitized with the dyad and [Ru(dcbpy)2(acac)]Cl, it is possible to demonstrate that photons absorbed by the donor moiety also contribute significantly to the generation of current. Instead of using acceptor luminescence as a probe, enhanced photocurrent generation is employed to estimate the energy-transfer efficiency. Fitting theoretical to experimental external quantum efficiency functions gives a value for the energy-transfer efficiency of 85 %. Evaluation of the maximum output power of dye solar cells sensitized with the dyad and [Ru(dcbpy)2(acac)]Cl showed, under selective illumination at the absorption maximum of the donor chromophore, that the introduction of the energy-donor moiety leads to a significant increase in the monochromatic maximum output power under blue illumination. This result demonstrates the usefulness of energy transfer for the generation of current in dye-sensitized solar cells.     

Carbon‐Electrode‐Tailored All‐Inorganic Perovskite Solar Cells To Harvest Solar and Water‐Vapor Energy

Moisture is the worst enemy for state‐of‐the‐art perovskite solar cells (PSCs). However, the flowing water vapor within nanoporous carbonaceous materials can create potentials. Therefore, it is a challenge to integrate water vapor and solar energies into a single PSC device. We demonstrate herein all‐inorganic cesium lead bromide (CsPbBr₃) solar cells tailored with carbon electrodes to simultaneously harvest solar and water‐vapor energy. Upon interfacial modification and plasma treatment, the bifunctional PSCs yield a maximum power conversion efficiency up to 9.43 % under one sun irradiation according to photoelectric conversion principle and a power output of 0.158 μW with voltage of 0.35 V and current of 0.45 μA in 80 % relative humidity through the flowing potentials at the carbon/water interface. The initial efficiency is only reduced by 2 % on exposing the inorganic PSC with 80 % humidity over 40 days. The successful realization of physical proof‐of‐concept multi‐energy integrated solar cells provides new opportunities of maximizing overall power output.     

Chemical and Physical Characteristics of Pulsed Electrical Discharge Within Gas Bubbles in Aqueous Solutions

The chemical and physical characteristics of pulsed electrical discharge within gas bubbles immersed in an aqueous solution were investigated using a reactor with long protrusion length high voltage needle electrodes. Argon gas was introduced at the base of the needle electrode causing gas bubbles to flow upwards in contact with the needle. The effects of needle protrusion length were evaluated by using 2, 4, and 6 cm length needles under a wide range of power input (3–78 W). No significant differences in chemical or electrical characteristics were found among the different protrusion lengths. H₂ and H₂O₂ generation rates were proportional to input power and the energy yield efficiency for these species was not affected dramatically by input power. The results of discharge within bubbles in aqueous solution were also compared with those for direct liquid phase discharge and gas phase discharge above the liquid surface.     

Mini‐Generator Based on Self‐Propelled Vertical Motion of a Functionally Cooperating Device Driven by H2‐Forming Reaction

Mini‐generators based on locomotion of small objects have aroused widespread attention because of their potential application in powering small‐scale electronic devices. Although improvements have been made in the development of mini‐generators, there are still some key challenges such as low power output and energy conversion efficiency, which limit the potential application of mini‐generators. Herein, through integrating a superhydrophobic surface, chemical reaction and solenoid coil/magnet into a system, an innovative mini‐generator is designed, which can convert chemical energy into electrical energy through mechanical form. As a result, the energy conversion efficiency and output power are both three hundred times higher than previously reported results and can be applied to power light‐emitting diodes without amplification. We believe that the proposed mini‐generator provides more chance for the application of self‐supplying power sources for electronic devices.     

Effect of contact barrier heights on the power conversion efficiency of a perovskite photovoltaic element

The influence of contact barrier heights on the principal characteristics (open circuit voltage, short circuit current, fill factor, and power conversion efficiency) of a perovskite photovoltaic element was examined by numerical simulations in order to reach a maximum efficiency of the element. The role of crystal fields at the perovskite boundaries was pointed out.     

仿生智能纳米通道在能量转换中的应用

智能纳米通道由于独特的纳米结构,导致对离子的通过具有选择性、整流性和门控性,从而在能量转换领域具有重要的应用前景。本文根据能量转换原理的不同,将纳米通道在能量转换中的应用分为:模仿电鳗鱼将化学能转换为电能,模仿绿叶将光能转换为化学能,模仿菌紫质将光能转换为电能,模仿水力发电机将流体机械能转换为电能。其中,模仿电鳗鱼系统由于广泛的能量来源、高的能量转换效率以及输出的能量形式为电能,应用前景最为广阔。能量转换的性能受纳米通道自身的几何结构以及内表面电荷密度的影响。除此之外,还受外界条件的影响,比如电解质溶液类型和浓度,浓差和气压差的大小以及pH值等。     

Enhancing the Photocurrent in Diketopyrrolopyrrole-Based Polymer Solar Cells via Energy Level Control

A series of diketopyrrolopyrrole (DPP)-based small band gap polymers has been designed and synthesized by Suzuki or Stille polymerization for use in polymer solar cells. The new polymers contain extended aromatic π-conjugated segments alternating with the DPP units and are designed to increase the free energy for charge generation to overcome current limitations in photocurrent generation of DPP-based polymers. In optimized solar cells with [6,6]phenyl-C(71)-butyric acid methyl ester ([70]PCBM) as acceptor, the new DPP-polymers provide significantly enhanced external and internal quantum efficiencies for conversion of photons into collected electrons. This provides short-circuit current densities in excess of 16 mA cm(-2), higher than obtained so far, with power conversion efficiencies of 5.8% in simulated solar light. We analyze external and internal photon to collected electron quantum efficiencies for the new polymers as a function of the photon energy loss, defined as the offset between optical band gap and open circuit voltage, and compare the results to those of some of the best DPP-based polymers solar cells reported in the literature. We find that for the best solar cells there is an empirical relation between quantum efficiency and photon energy loss that presently limits the power conversion efficiency in these devices.     

脉冲电晕放电-催化转化CO2为CO

在常温、常压下，较系统地研究了CO2在脉冲电晕等离子体条件下的活化与转化，考察了反应器参数、脉冲成形电容、应用电压、气体流量、电晕极性对二氧化碳转化的影响。在本实验条件下，最佳反应器的有效长度为125mm,内径为22mm。二氧化碳转化率和一氧化碳产率随应用电压的增加而增加。另外，随着应用电压的增加，脉冲反应器的能量利用效率反而降低。随着气体流量的增大，二氧化碳的转化率及一氧化碳的产率下降。γ-Al2O3的存在大大促进了二氧化碳的转化，CO2的最高转化率达23％。由于γ-Al2O3在物化性质方面的特性，γ－Al2O3的存在对二氧化碳的转化有重要的作用。研究表明：脉冲电晕放电－催化转化CO2为CO是可行的。     

Bubble formation in lattice Boltzmann immiscible shear flow

Bubble formation and the effect of shear on bubble formation in a van der Waals fluid is investigated by means of lattice Boltzmann mesoscale simulations. In the absence of shear, the maximum number of formed bubbles increases with undercooling but the incubation time before bubble formation decreases dramatically. The results are in agreement with classical phase transition theory. In shear flow, the maximum number of bubbles is not affected by shear but the bubble growth rate is accelerated. The effect of shear on bubble growth rate weakens at large undercoolings. The reasons are twofold. On the one hand the highly undercooled system takes less time to complete phase transition due to the large driving force so that there is less time to accumulate the flow effect. On the other hand the mechanism for bubble growth changes from coarsening to coalescence at large undercoolings.     

Optimizing Membranes for Osmotic Power Generation

The design of ion-selective membranes is the key towards efficient reverse electrodialysis-based osmotic power conversion. The tradeoff between ion selectivity (output voltage) and ion permeability (output current) in existing porous membranes, however, limits the upgradation of power generation efficiency for practical applications. Thus, we provide the simple guidelines based on fundamentals of ion transport in nanofluidics for promoting osmotic power conversion. In addition, we discuss strategies for optimizing membrane performance through analysis of various material parameters in membrane design, such as pore size, surface charge, pore density, membrane thickness, ion pathway, pore order, and ionic diode effect. Lastly, a perspective on the future directions of membrane design to further maximize the efficiency of osmotic power conversion is outlined.     

Overcoming Kinetic Limitations of Electron Injection in the Dye Solar Cell via Coadsorption and FRET

A new, extremely simple concept for the use of energy transfer as a means to the enhancement of light absorption and current generation in the dye solar cell (DSC) is presented. This model study is based upon a carboxy‐functionalized 4‐aminonaphthalimide dye (carboxy‐fluorol) as donor, and (NBu₄)₂[Ru(dcbpy)₂(NCS)₂] (N719) as acceptor chromophores. A set of three different devices is assembled containing either exclusively carboxy‐fluorol or N719, or a mixture of both. This set of transparent devices is characterized via IV‐measurements under AM1.5G and monochromatic illumination and their light‐harvesting and external quantum efficiencies (LHE and EQE, respectively) are determined as well. It is shown that the device containing only the donor chromophore has a marginal power conversion efficiency, thus indicating that carboxy‐fluorol is a poor sensitizer for the DSC. Cyclovoltametric measurements show that the poor sensitization ability arises from the kinetic inhibition of electron injection into the TiO₂ conduction band. Comparing the spectral properties of the DSCs assembled presently, however, demonstrates that light absorbed by carboxy‐fluorol is almost quantitatively contributing to the photocurrent if N719 is present as an additional sensitizer. In this case, N719 acts as a catalyst for the sensitization of TiO₂ by carboxy‐fluorol in addition to being a photosensitizer. Evaluation of the maximum output power under blue illumination shows that the introduction of an energy‐donor moiety via coadsorption, leads to a significant increase in the monochromatic maximum output power. This result demonstrates that energy transfer between coadsorbed chromophores could be useful for the generation of current in dye‐sensitized solar cells.     

A Highly Conjugated Benzimidazole Carbene‐Based Ruthenium Sensitizer for Dye‐Sensitized Solar Cells

A new type of carbene‐based ruthenium sensitizer, CB104, with a highly conjugated ancillary ligand, diphenylvinylthiophene‐substituted benzimidazolepyridine, was designed and developed for dye‐sensitized solar cell applications. The influence of the thiophene antenna on the performance of the cell anchored with CB104 was investigated. Compared with the dye CBTR, the conjugated thiophene in the ancillary ligand of CB104 enhanced the molar extinction coefficient of the intraligand π–π* transition and the intensity of the lower energy metal‐to‐ligand charge‐transfer band. However, the incident photon‐to‐current conversion efficiency spectrum of the cell anchored with CB104 (0.15 mM ) showed a maximum of 63 % at 420 nm. The cell sensitized with the dye CB104 attained a power conversion efficiency of 7.30 %, which was lower than that of the cell with nonconjugated sensitizer CBTR (8.92 %) under the same fabrication conditions. The variation in the performance of these two dyes demonstrated that elongating the conjugated light‐harvesting antenna resulted in the reduction of short‐circuit photocurrent density, which might have been due to the aggregation of dye molecules. In the presence of a coabsorbate, chenodeoxycholic acid, the CB104‐sensitized cell exhibited an enhanced photocurrent density and achieved a photovoltaic efficiency of 8.36 %.     

Biomass conversion to hydrogen-rich synthesis fuels using water steam plasma

In this study, an experimental plasma-chemical reactor equipped with an arc discharge water steam plasma torch was used for biomass conversion to hydrogen-rich synthesis fuels. Glycerol and crushed wood were used as biomass sources. The effects of different conversion parameters including the water steam flow rate, treated material flow rate, and plasma torch power were studied. The experimentally obtained results were compared with the model based on the thermodynamic equilibrium. Additionally, the quantification of the plasma conversion system in terms of energy efficiency and specific energy requirement was performed. It has been found that the synthesis gas can be effectively produced from the biomass using water steam plasma.     

常压辉光放电等离子体转化CH4制C2烃的研究

采用新型的旋转电极辉光放电反应器, 在常温常压下对辉光等离子体作用下的甲烷转化制C₂烃进行了研究. 在氢气共存条件下, 考察了反应器电极的结构、材料, 输入电场峰值电压和反应物流率等参数对甲烷转化率和C₂烃单程收率及其选择性的影响规律, 同时比较了不同反应器的能量效率. 结果表明: 在本实验条件下, 金属铜材料好于不锈钢, 螺旋形结构优于三排圆盘结构. CH₄转化率和C₂烃选择性和收率均随输入电场峰值电压的升高而增大, 随反应物流量的增加而减小. 从CH₄转化率、C₂烃的收率和选择性的指标来评价这些反应器, 采用旋转螺旋状铜电极反应器时最好, 当反应物流量为60 mL/min时, 甲烷最高转化率为77.31%, 对应的C₂烃收率和选择性分别为75.66%和97.88%; 当能量密度为800 kJ/mol时, 能效最高为13.5%.     

YSZ中温燃料电池的稳态模拟

依据同时考虑电化学及热平衡耦合的二维模拟软件 ,计算了薄膜钇稳氧化锆 (YSZ)中温燃料电池在不同工作条件下的稳态特性 .通过电流～电压关系参数进行自拟合实验 ,格点选取由平衡收敛性和计算效率而得 ,研究了不同连接体、气流流向设计等工作条件下的温度场 ,给出了不同工作温度下输出功率及电池效率与工作电压的关系 .对温度场的分析表明 :电池板内最高温度及最大温差以并流为最小 ,交叉流为最大 ,并流是最好的气流流向设计 .与以陶瓷材料作连接体相比 ,使用金属连接体能显著减小热应力和电池板内最高温度 ,受益最大的是交叉流 ,其最高温度及最大温差均小于陶瓷连接体的并流设计 .不同的气流流向对于输出功率及电池效率影响很小 ,对并流和金属连接体组合 ,给出了工程设计的燃料分布、电流密度、Nernst势及温度梯度在典型工作条件下的情形     

Alkyl-Chain-Regulated Charge Transfer in Fluorescent Inorganic CsPbBr3 Perovskite Solar Cells

Improved charge extraction and wide spectral absorption promote power conversion efficiency of perovskite solar cells (PSCs). The state-of-the-art carbon-based CsPbBr₃ PSCs have an inferior power output capacity because of the large optical band gap of the perovskite film and the high energy barrier at perovskite/carbon interface. Herein, we use alkyl-chain regulated quantum dots as hole-conductors to reduce charge recombination. By precisely controlling alkyl-chain length of ligands, a balance between the surface dipole induced charge coulomb repulsive force and quantum tunneling distance is achieved to maximize charge extraction. A fluorescent carbon electrode is used as a cathode to harvest the unabsorbed incident light and to emit fluorescent light at 516 nm for re-absorption by the perovskite film. The optimized PSC free of encapsulation achieves a maximum power conversion efficiency up to 10.85 % with nearly unchanged photovoltaic performances under 80 %RH, 80 °C, or light irradiation in air.     

New Bithiazole‐Based Sensitizers for Efficient and Stable Dye‐Sensitized Solar Cells

A series of new push–pull organic dyes ( BT‐I – VI ), incorporating electron‐withdrawing bithiazole with a thiophene, furan, benzene, or cyano moiety, as π spacer have been synthesized, characterized, and used as the sensitizers for dye‐sensitized solar cells (DSSCs). In comparison with the model compound T1 , these dyes containing a thiophene moiety between triphenylamine and bithiazole display enhanced spectral responses in the red portion of the solar spectrum. Electrochemical measurement data indicate that the HOMO and LUMO energy levels can be tuned by introducing different π spacers between the bithiazole moiety and cyanoacrylic acid acceptor. The incorporation of bithiazole substituted with two hexyl groups is highly beneficial to prevent close π–π aggregation, thus favorably suppressing charge recombination and intermolecular interaction. The overall conversion efficiencies of DSSCs based on bithiazole dyes are in the range of 3.58 to 7.51 %, in which BT‐I ‐based DSSCs showed the best photovoltaic performance: a maximum monochromatic incident photon‐to‐current conversion efficiency (IPCE) of 81.1 %, a short‐circuit photocurrent density (J_sc) of 15.69 mA cm^?2, an open‐circuit photovoltage (V_oc) of 778 mV, and a fill factor (ff) of 0.61, which correspond to an overall conversion efficiency of 7.51 % under standard global AM 1.5 solar light conditions. Most importantly, long‐term stability of the BT‐I – III ‐based DSSCs with ionic‐liquid electrolytes under 1000 h of light soaking was demonstrated and BT‐II with a furan moiety exhibited better photovoltaic performance of up to 5.75 % power conversion efficiency.     

The Open Circuit Voltage in Biofuel Cells: Nernstian Shift in Pseudocapacitive Electrodes

In the development of biofuel cells great effort is dedicated to achieving outstanding figures of merit, such as high stability, maximum power output, and a large open circuit voltage. Biofuel cells with immobilized redox mediators, such as redox polymers with integrated enzymes, show experimentally a substantially higher open circuit voltage than the thermodynamically expected value. Although this phenomenon is widely reported in the literature, there is no comprehensive understanding of the potential shift, the high open circuit voltages have not been discussed in detail, and hence they are only accepted as an inherent property of the investigated systems. We demonstrate that this effect is the result of a Nernstian shift of the electrode potential when catalytic conversion takes place in the absence or at very low current flow. Experimental evidence confirms that the immobilization of redox centers on the electrode surface results in the assembled biofuel cell delivering a higher power output because of charge storage upon catalytic conversion. Our findings have direct implications for the design and evaluation of (bio)fuel cells with pseudocapacitive elements.     

Enhanced β‐phase in PVDF polymer nanocomposite and its application for nanogenerator

Harvesting energy from the ambient mechanical energy by using flexible piezoelectric nanogenerator is a revolutionary step toward achieving reliable and green energy source. Polyvinylidene fluoride (PVDF), a flexible polymer, can be a potential candidate for the nanogenerator if its piezoelectric property can be enhanced. In the present work, we have shown that the polar crystalline β‐phase of PVDF, which is responsible for the piezoelectric property, can be enhanced from 48.2% to 76.1% just by adding ZnO nanorods into the PVDF matrix without any mechanical or electrical treatment. A systematic investigation of PVDF‐ZnO nanocomposite films by using X‐ray diffractometer, Fourier transform infrared spectroscopy, and polarization‐electric field loop measurements supports the enhancement of β‐phase in the flexible nanocomposite polymer films. The piezoelectric constant (d₃₃) of the PVDF‐ZnO (15 wt%) film is found to be maximum of approximately −1.17 pC/N. Nanogenerators have been fabricated by using these nanocomposite films, and the piezoresponse of PVDF is found to enhance after ZnO loading. A maximum open‐circuit voltage ~1.81 V and short‐circuit current of 0.57 μA are obtained for 15 wt% ZnO‐loaded PVDF nanocomposite film. The maximum instantaneous output power density is obtained as 0.21 μW/cm² with the load resistance of 7 MΩ, which makes it feasible for the use of energy harvesting that can be integrated to use for driving small‐scale electronic devices. This enhanced piezoresponse of the PVDF‐ZnO nanocomposite film‐based nanogenerators attributed to the enhancement of electroactive β‐phase and enhanced d₃₃ value in PVDF with the addition of ZnO nanorods.