Lithium-oxygen cells:an analytical model to explain the key features in the discharge voltage profiles

Sodium-oxygen Lithium-oxygen (Li-O2) cells are popular due to their potentially high energy density. A characteristic fingerprint of a given cell is the voltage profile during constant-current discharge. We suggest that the typical initial dip and the following increase of the voltage result from a temporary increase and slow decrease in the concentration of dissolved superoxide, respectively, feeding into the Nernst equation. The steady-state superoxide concentration decreases as the surface area of the solid precipitation product (Li2O2) increases. Importantly, these products bury the electrochemically active carbon surface. Assuming that the electrochemical step only occurs on bare carbon, the Tafel equation provides an expression for the increasing overpotential as a result of the shrinking effective electrode area. This boils the discharge voltage profile down to the sum of two logarithms, grasping all relevant features in recorded discharge voltage profiles

CHLORIDE SENSOR FABRICATION BASED ON SPE Ag/AgCl THROUGH CYCLIC VOLTAMMETRIC TECHNIQUE: SCAN RATE EFFECT

The Cyclic Voltammetric (CV) technique is one of the Ag/AgCl fabrication processes. In electrochemical processes using this CV technique, the microstructure of the surface of a substrate or electrode can affect the scan rate. Thus, this study aims to identify the scan rate effect of the Cl-ion sensor fabrication process using the CV technique on the performance of the Cl-ion sensor. First, the CV process was carried out in one cycle to grow the AgCl layer on the Ag surface. Then, this process was carried out at varied scan rates of 20, 40, 60, 80, and 100 mV/s. After completing the Ag/AgCl fabrication process, it was followed by the characterization process, selectivity coefficient test, lifetime test, and validation test to compare the test results of the Cl SPE Ag/AgCl ion sensor with Ag/AgCl commercial. The results showed that the optimum Cl-ion sensor response was obtained at the scan rate of 60 mV/s. Then, based on the validation test, the Cl-ion in the two samples did not show significant differences. Therefore, it indicates that the SPE Ag/AgCl ion sensor has the same performance as the Ag/AgCl commercial

Sistem Kendali Sensor Tanah Sebagai Pemonitor Tingkat Kelembaban Media Tanam Padi

Wabah pandemi Corona Virus Disease 2019  atau Covid-19 yang menyebar kebeberapa negara termasuk indonesia. Sektor pertanian menjadi tumpuan dalam memenuhi kebutuhan bahan pokok masyarakat. Pertanian di indonesia khusus di wilayah Indramayu Jawa Barat memiliki dua musim yaitu musim penghujan dan musim kemarau, sedangkan pengamatan masa tanam padi bergantung pada kesediaan air. Kekurangan air akan menyebabkan pertumbuhan padi terganggu, sedangkan kelebihan air akan menimbulkan banyak hama sehingga padi akan rusak. Keseimbangan dan ketersediaan air sangat membantu pertumbuhan padi secara baik sehingga akan menghasilkan panen yang melimpah. Sistem kedali sensor tanah dengan arduino dapat membantu petani dalam menggukur kelembaban tanah secara akurat, sensor akan di tanam dibeberapa petak sawah memberikan data-data, dari data tersebut di analisa dan dilakukan uji. Jika hasil data uji menunjukan nilai kekeringan maka akan mengalirkan air, jika hasil data uji menunjukan kelembaban yang sangat tinggi maka membagi air sawah ke petak yang lain. Hasil Penelitian sistem kendali sangat berguna dalam menerapkan teknologi pertanian terlihat dari uji kefektifan kelembaban tanah

The Effect of Substrate Pre-treatment on Hydroxy-apatite Coated Titanium Alloy by High-velocity Oxy-fuel Process

In order to fully meet bio-compatibility requirement of titanium alloy as implant material, coating with hydroxyapatite (HA) is normally applied. The present research concerns on the effect of substrate pre-treatment on the coating of HA on titanium alloy by high-velocity oxy fuel process (HVOF). Before the coating, all samples were pre-treated by thermo-mechanical treatment in order to obtain fine grain structure. Three type of substrate pre-treatment is then applied on different substrates, including, sand-blasting, sand-blasting+etching, and sand-blasting+etching+CNT intermediate layer. After coating, post-annealing treatment was applied on each sample and characterization was performed on the sample after the treatment. It was obtained that the sand-blasted sample has relatively rougher surface (SEM observation), lower degree of crystallinity (XRD characterization) and higher residual strain (XRD data calculation by Mud Master software) as compared with other samples. From FTIR characterization it can be obtained that all samples show no differences in orbital function

Controlling the yield and structure of carbon nanofibers grown on a nickel/activated carbon catalyst

Carbon nanofibers (CNFs) were grown via the chemical vapor deposition of C2H4 on an activated carbon (AC)-supported Ni catalyst. The texture of the CNF/AC composites can be tuned by varying the growth temperature and by treatment in reducing atmosphere prior to C2H4/H2 exposure. The Ni-catalyzed gasification of the AC support increases the microporosity of the composite and shown to be dominant throughout the composite synthesis especially during reduction, subsequent treatment in reducing atmosphere, and CNF growth at low temperatures. N2 isotherm and scanning electron microscope were used to characterize the texture and morphology of the composites. Subsequent treatment in reducing atmosphere were shown to increase the Ni catalyst activity to grow CNFs. High resolution transmission electron microscope however did not reveal any microstructural difference for Ni catalyst with and without the subsequent reduction treatment. We propose in this paper that the carbon dissolutions during treatment of the catalyst might have an implication on the CNF growth

Influence of carbon microstructure on the Li–O2 battery first-discharge kinetics

Defects in the carbon microstructure have been reported to enhance the discharge performance of Li–O2 battery. However, systematic studies correlating the presence of defects with the discharge kinetics have not addressed the variation of carbon electrode surface areas. In this work, carbon blacks and carbon nanofibers with different defect densities were investigated for their discharge properties. The electrolyte-accessible areas of the carbon electrodes were obtained from Cyclic voltammetry measurements. The microstructure and surface areas of the carbons were characterized by Raman spectroscopy, electron microscopy, and N2 isotherm. Linear sweep voltammetry and galvanostatic discharge experiments consistently demonstrated that graphitic carbons have more negative onset potentials and more negative discharge potentials at the same current density than defective carbons. The linear sweep voltammetry data were normalized to the carbon masses, Brunauer–Emmet–Teller surface areas, and double layer capacitance-derived areas for comparison. Plot of inverse charge transfer resistance and double layer capacitance from electrochemical impedance spectroscopy measurements were used to extract current density values without knowledge of electrode areas. The current densities from impedance measurements exhibited good agreement with the data from linear sweep experiments. The electrochemical experiments conclusively showed that defects on the graphitic microstructure increase the discharge kinetics of the Li–O2 battery

Pengaruh Supervisi Kepala Sekolah Terhadap Kinerja Guru Di SMAS CERDAS MURNI

Dalam penelitian ini tujuan utamanya adalah untuk mengetahui pengaruh supervisi dan motivasi guru secara bersama-sama terhadap kinerja guru di SMAS CERDAS MURNI yang terletak di JL. BERINGIN NO. 33, Tembung, Kec. Percut Sei Tuan, Kab. Deli Serdang, Sumatera Utara. Metode yang akan digunakan adalah kualitatif dengan teknik wawancara dan analisis dokumen. Selain itu, penelitian ini juga bertujuan untuk mengidentifikasi peran pengawas dalam mengelola kinerja guru, serta meningkatkan kinerja guru agar mencapai hasil yang optimal. Penting untuk dicatat bahwa kebijakan pendidikan harus didukung oleh para praktisi pendidikan yang berada di garda terdepan, yaitu para guru, melalui interaksinya dalam dunia pendidikan. Oleh karena itu, keterlibatan seluruh komponen pendidikan seperti guru, kepala sekolah, masyarakat dan komite sekolah melalui perencanaan yang matang dan pelaksanaan program pendidikan yang terukur menjadi sangat penting. Data yang diperoleh dalam penelitian ini akan dianalisis dengan cermat untuk memastikan kesimpulan yang objektif dan dapat diandalkan. Kata Kunci: Supervisi, Kepala Sekolah, Kinerja Guru