Catalytic Decomposition of an Organic Electrolyte to Methane by a Cu Complex-Derived In Situ CO2 Reduction Catalyst.

Metal complexes are often transformed to metal complex-derived catalysts during electrochemical CO2 reduction, enhancing the catalytic performance of CO2 reduction or changing product selectivity. To date, it has not been investigated whether metal-complex derived catalysts also enhance the decomposition of the solvent/electrolyte components as compared to an uncoated electrode. Here, we tested the electrochemical stability of five organic solvent-based electrolytes with and without a Cu complex-derived catalyst on carbon paper in an inert atmosphere. The amount of methane and hydrogen produced was monitored using gas chromatography. Importantly, the onset potential for methane production was reduced by 300 mV in the presence of a Cu complex-derived catalyst leading to a significant amount of methane (417.7 ppm) produced at -2.17 V vs Fc/Fc+ in acetonitrile. This suggests that the Cu complex-derived catalyst accelerated not only CO2 reduction but also the reduction of the electrolyte components. This means that Faradaic efficiency (FE) measurements under CO2 in acetonitrile may significantly overestimate the amount of CH4. Only 28.8 ppm of methane was produced in dimethylformamide under an inert atmosphere, much lower than that produced under CO2 (506 ppm under CO2) at the same potential, suggesting that dimethylformamide is a more suitable solvent. Measurements in propylene carbonate produced mostly hydrogen gas while in dimethyl sulfoxide and 3-methoxypropionitrile neither methane nor hydrogen was detected. A strong linear correlation between the measured current and the amount of methane produced with and without the Cu complex-derived catalyst confirmed that the origin of methane production is solvent/electrolyte decomposition and not the decomposition of the catalyst itself. The study highlights that in a nonaqueous system, highly active catalyst in situ deposited during electrochemical testing can significantly influence background measurements as compared to uncoated electrodes, therefore the choice of solvent is paramount for reliable testing.

Effect of the Cu2+/1+ Redox Potential of Non-Macrocyclic Cu Complexes on Electrochemical CO2 Reduction.

Cu2+/1+ complexes facilitate the reduction of CO2 to valuable chemicals. The catalytic conversion likely involves the binding of CO2 and/or reduction intermediates to Cu2+/1+, which in turn could be influenced by the electron density on the Cu2+/1+ ion. Herein we investigated whether modulating the redox potential of Cu2+/1+ complexes by changing their ligand structures influenced their CO2 reduction performance significantly. We synthesised new heteroleptic Cu2/1+ complexes, and for the first time, studied a (Cu-bis(8-quinolinolato) complex, covering a Cu2+/1+ redox potential range of 1.3 V. We have found that the redox potential influenced the Faradaic efficiency of CO2 reduction to CO. However, no correlation between the redox potential and the Faradaic efficiency for methane was found. The lack of correlation could be attributed to the presence of a Cu-complex-derived catalyst deposited on the electrodes leading to a heterogeneous catalytic mechanism, which is controlled by the structure of the in situ deposited catalyst and not the redox potential of the pre-cursor Cu2+/1+ complexes.

Static Load Characteristics of Hydrostatic Journal Bearings: Measurements and Predictions.

Hydrostatic bearings for liquid rocket engine turbopumps provide distinctive advantages, including high load capacity even with low viscosity cryogenic fluid and extending life span by minimizing friction and wear between rotor and bearing surfaces. Application of hydrostatic bearings into turbopumps demands a reliable test database with well-quantified operating parameters and experimentally validated accurate performance predictive tools. The present paper shows the comprehensive experimental data and validation of predicted static load characteristics of hydrostatic journal bearings lubricated with air, water, and liquid nitrogen. Extensive experiments for static load characteristics of hydrostatic bearings are conducted using a turbopump-rotor-bearing system simulator while increasing supply pressure (Ps) into the test bearings. The test results demonstrate notable effects of the test fluids and their temperatures, as well as Ps, on the bearing performance. In general, the measured bearing flow rate, rotor displacement, and stiffness of the test bearings steadily increase with Ps. The static load bearing characteristics predictions considering flow turbulence and compressibility matched well with the experimental results. The work with independent test data and engineering computational programs will further the implementation of hydrostatic bearings in high-performance turbopump shaft systems with improved efficiency and enhanced reusability of liquid rocket engine sub-systems.

Wearable Photo-Thermo-Electrochemical Cells (PTECs) Harvesting Solar Energy.

Solar induced thermal energy is a vital heat source supplementing body heat to realize thermo-to-electric energy supply for wearable electronics. Thermo-electrochemical cells, compared to the widely investigated thermoelectric generators, show greater potential in wearable applications due to the higher voltage output from low-grade heat and the increased option range of cheap and flexible electrode/electrolyte materials. A wearable photo-thermo-electrochemical cell (PTEC) is first fabricated here through the introduction of a polymer-based flexible photothermal film as a solar-absorber and hot electrode, followed by a systematic investigation of wearable device design. The as-prepared PTEC single device shows outstanding output voltage and current density of 15.0 mV and 10.8 A m-2 and 7.1 mV and 8.57 A m-2 , for the device employing p-type and n-type gel electrolytes, respectively. Benefiting from the equivalent performance in current density, a series connection containing 18 pairs of p-n PTEC devices is effectively made, which can harvest solar energy and charge supercapacitors to above 250 mV (1 sun solar illumination). Meanwhile, a watch-strap shaped flexible PTEC (eight p-n pairs) that can be worn on a wrist is fabricated and the realized voltage above 150 mV under light shows the potential for use in wearable applications.

Multisample Correlation Reveals the Origin of the Photocurrent of an Unstable Cu2O Photocathode during CO2 Reduction.

The reliable characterization of the photoelectrochemical (PEC) performance of unstable photoelectrodes, often the simplest devices used as a baseline, is a huge challenge. By performing a correlation analysis of more than 100 parameters of Cu2O photocathodes electrodeposited under the same conditions, we discovered a strong positive correlation (R = 0.866) between the photocurrent in argon and the deposition current peak magnitude during electrodeposition, while a strong negative correlation (R = -0.787) was found in CO2. In argon, a positive correlation between the photocurrent during PEC tests and the post-PEC dark current suggests the dominance of photodegradation. In CO2, the higher photocurrent in PEC tests correlates well with the lower post-PEC dark current, revealing the dominance of photocatalytic CO2 reduction during the rapid PEC tests. Correlation analysis provides statistically robust insights into the operation of unstable electrodes based on routinely measured parameters and thus constitutes a simple yet previously unexplored methodology for characterizing photoelectrodes within the first minutes of operation.

Self-Healing Wide and Thin Li Metal Anodes Prepared Using Calendared Li Metal Powder for Improving Cycle Life and Rate Capability.

The commercialization of Li metal electrodes is a long-standing objective in the battery community. To accomplish this goal, the formation of Li dendrites and mossy Li deposition, which cause poor cycle performance and safety issues, must be resolved. In addition, it is necessary to develop wide and thin Li metal anodes to increase not only the energy density, but also the design freedom of large-scale Li-metal-based batteries. We solved both issues by developing a novel approach involving the application of calendared stabilized Li metal powder (LiMP) electrodes as anodes. In this study, we fabricated a 21.5 cm wide and 40 µm thick compressed LiMP electrode and investigated the correlation between the compression level and electrochemical performance. A high level of compression (40% compression) physically activated the LiMP surface to suppress the dendritic and mossy Li metal formation at high current densities. Furthermore, as a result of the LiMP self-healing because of electrochemical activation, the 40% compressed LiMP electrode exhibited an excellent cycle performance (reaching 90% of the initial discharge capacity after the 360th cycle), which was improved by more than a factor of 2 compared to that of a flat Li metal foil with the same thickness (90% of the initial discharge capacity after the 150th cycle).

Elucidating the Polymeric Binder Distribution within Lithium-Ion Battery Electrodes Using SAICAS.

Polymeric binder distribution within electrodes is crucial to guarantee the electrochemical performance of lithium-ion batteries (LIBs) for their long-term use in applications such as electric vehicles and energy-storage systems. However, due to limited analytical tools, such analyses have not been conducted so far. Herein, the adhesion properties of LIB electrodes at different depths are measured using a surface and interfacial cutting analysis system (SAICAS). Moreover, two LiCoO2 electrodes, dried at 130 and 230 °C, are carefully prepared and used to obtain the adhesion properties at every 10 µm of depth as well as the interface between the electrode composite and the current collector. At high drying temperatures, more of the polymeric binder material and conductive agent appears adjacent to the electrode surface, resulting in different adhesion properties as a function of depth. When the electrochemical properties are evaluated at different temperatures, the LiCoO2 electrode dried at 130 °C shows a much better high-temperature cycling performance than does the electrode dried at 230 °C due to the uniform adhesion properties and the higher interfacial adhesion strength.

Improving the Cycling Performance of Lithium-Ion Battery Si/Graphite Anodes Using a Soluble Polyimide Binder.

Herein, we improved the performance of Si/graphite (Si/C) composite anodes by introducing a highly adhesive co-polyimide (P84) binder and investigated the relationship between their electrochemical and adhesion properties using the 90° peel test and a surface and interfacial cutting analysis system. Compared to those of conventional poly(vinylidene fluoride) (PVdF)-based electrodes, the cycling performance and rate capability of P84-based Si/C anodes were improved by 47.0% (372 vs 547 mAh g-1 after 100 cycles at a 60 mA g-1 discharge condition) and 33.4% (359 vs 479 mAh g-1 after 70 cycles at a 3.0 A g-1 discharge condition), respectively. Importantly, the P84-based electrodes exhibited less pronounced morphological changes and a smaller total cell resistance after cycling than the PVdF-based ones, also showing better interlayer adhesion (F mid) and interfacial adhesion to Cu current collectors (F inter).

Three-Dimensional Adhesion Map Based on Surface and Interfacial Cutting Analysis System for Predicting Adhesion Properties of Composite Electrodes.

Using a surface and interfacial cutting analysis system (SAICAS) that can measure the adhesion strength of a composite electrode at a specific depth from the surface, we can subdivide the adhesion strength of a composite electrode into two classes: (1) the adhesion strength between the Al current collector and the cathode composite electrode (FAl-Ca) and (2) the adhesion strength measured at the mid-depth of the cathode composite electrode (Fmid). Both adhesion strengths, FAl-Ca and Fmid, increase with increasing electrode density and loading level. From the SAICAS measurement, we obtain a mathematical equation that governs the adhesion strength of the composite electrodes. This equation revealed a maximum accuracy of 97.2% and 96.1% for FAl-Ca and Fmid, respectively, for four randomly chosen composite electrodes varying in electrode density and loading level.

Highly Adhesive and Soluble Copolyimide Binder: Improving the Long-Term Cycle Life of Silicon Anodes in Lithium-Ion Batteries.

A highly adhesive and thermally stable copolyimide (P84) that is soluble in organic solvents is newly applied to silicon (Si) anodes for high energy density lithium-ion batteries. The Si anodes with the P84 binder deliver not only a little higher initial discharge capacity (2392 mAh g(-1)), but also fairly improved Coulombic efficiency (71.2%) compared with the Si anode using conventional polyvinylidene fluoride binder (2148 mAh g(-1) and 61.2%, respectively), even though P84 is reduced irreversibly during the first charging process. This reduction behavior of P84 was systematically confirmed by cyclic voltammetry and Fourier-transform infrared analysis in attenuated total reflection mode of the Si anodes at differently charged voltages. The Si anode with P84 also shows ultrastable long-term cycle performance of 1313 mAh g(-1) after 300 cycles at 1.2 A g(-1) and 25 °C. From the morphological analysis on the basis of scanning electron microscopy and optical images and of the electrode adhesion properties determined by surface and interfacial cutting analysis system and peel tests, it was found that the P84 binder functions well and maintains the mechanical integrity of Si anodes during hundreds of cycles. As a result, when the loading level of the Si anode is increased from 0.2 to 0.6 mg cm(-2), which is a commercially acceptable level, the Si anode could deliver 647 mAh g(-1) until the 300th cycle, which is still two times higher than the theoretical capacity of graphite at 372 mAh g(-1).

Photorealistic ray tracing to visualize automobile side mirror reflective scenes.

We describe an interactive visualization procedure for determining the optimal surface of a special automobile side mirror, thereby removing the blind spot, without the need for feedback from the error-prone manufacturing process. If the horizontally progressive curvature distributions are set to the semi-mathematical expression for a free-form surface, the surface point set can then be derived through numerical integration. This is then converted to a NURBS surface while retaining the surface curvature. Then, reflective scenes from the driving environment can be virtually realized using photorealistic ray tracing, in order to evaluate how these reflected images would appear to drivers.