Key Engineering Materials Vol. 950

Abstract: Recently, dye sensitized solar cell (DSSC) are considered to replace the previous generation of solar cells. DSSC uses an organic dye to absorb light and convert it to electricity. One-dimensional morphological structure of photoanode that provides a straight pathway for electron transport can improve the efficiency of DSSC. TiO₂ nanofibers is one-dimensional structure of oxide semiconductor material commonly used as photoanode in DSSC. A simple method to synthesis continuous nanofiber is electrospinning method that use the influence of electrostatic forces. The nanofiber’s diameter that produced by electrospinning method depends on several parameters, one of which is the applied voltage. This study reports the synthesis of TiO₂ nanofibers with varying the applied voltages from 10 kV to 14 kV and their performance as photoanode in DSSC. TiO₂ nanofibers were electrospun directly onto a TiO₂-coated fluorine tin oxide (FTO) substrate from a mixture of titanium (IV) propoxide (TTIP), triton X-100, acetic acid, poly (vinyl) acetate (PVAc) that were dissolved in dimethyl formamide (DMF). TiO₂ nanofiber photoanodes were then immersed in ruthenium (II) dye, stacked with a counter electrode, and finally the electrolyte was injected between them. Based on the SEM results, we found that the beads disappeared with increasing applied voltage. The XRD pattern of TiO₂ nanofibers indicates the presence of the anatase phase. Based on the photocurrent-voltage characteristic, TiO₂ nanofibers produced by applied voltage of 14 kV shows the highest efficiency of 1.11% with J_SC 4.78 mA/cm², V_OC 0.74 Volt and fill factor (FF) of 31.37%.

Abstract: Carrageenan is a generic name for a family of natural, water-soluble, sulphated galactans isolated from red seaweeds and exploited commercially. The biopolymer of kappa carrageenan has been known to be used as electrolyte in electrochemical device since it shows good ionic conductivity characteristic. In this study, we attempt to study the chemical, morphology, and electric properties of biopolymer kappa carrageenan. We developed a free-standing film of kappa carrageenan with addition of ammonium chloride as an electrolyte for an organic battery prototype. We prepared the solution by mixing kappa carrageenan, ammonium chloride and water to form a gel with a particular concentration. Then, the gel was coated on the substrate and cured at 50°C for 4 hours. The final free-standing film product reveals a thickness about 100-200 mm as captured by SEM image in cross-section view. The morphology of kappa carrageenan with or without ammonium chloride clearly shows a non-homogeneous surface that attributed to the nature characteristics of kappa carrageenan immiscible. The addition of ammonium chloride into kappa carrageenan forms a smoother surface that show good mixture of kappa carrageenan. FTIR spectra of the samples show the interaction of ammonium chloride to the host polymer of kappa carrageenan as indicated by the shifted of the O-H peak from 3448 to 3446 cm^-1 and from 3288 to 3207 cm^-1 while the peak of 2924 cm^-1 is disappeared after addition of the ammonium chloride. The implementation of this film in an organic C_Zn battery prototype shows that battery’s voltage reached 2.1 Volt by charging. Then, the battery can be used to emit an LED with 20 µA electrical current for about 1 hour in discharging process.

Abstract: NaFePO₄, which is analogue to LiFePO_4, has been expected to show similar properties as LiFePO₄ that has a good cycle stability and excellent electrochemical performances. Here we report the synthesis of NaFePO₄ via sol-gel method and the structural study of NaFePO₄ as a cathode material for sodium-ion battery (SIB). The as-synthesized NaFePO₄ samples were calcined under air and argon atmosphere at the constant holding time of 10 hours with the variation of calcined temperature. In this report, we present the successfully synthesized NaFePO₄ based on XRD and SEM result. XRD results show the presence of NaFePO₄ as a major phase and some amount of secondary phase. SEM result indicates the plate-like particle which tends to agglomerate with the size range 2-5 .

Abstract: TiO₂ are usually used as photoanode to get high-performance dye-sensitized solar cells (DSSCs). TiO₂ has good chemical stability, but still has poor electron mobility so that the DSSC efficiency is low. An alternative semiconductor metal-oxides such as ZnO currently are being explored due to ease of processing, higher electron mobility, interface band energetics, and can be utilized as photoanode also, but the chemical stability is low. Based on these facts, by combining the advantages of TiO₂ and ZnO, the TiO₂:ZnO composite can be an ideal material as a photoanode in DSSC. In this study, composite of TiO₂:ZnO was synthesized using sol-gel method with ratio of TiO₂ to ZnO were varied from 80:20, 60:40, 50:50, 40:60, and 20:80 in atomic percent. DSSCs were fabricated by coating the photoanode using screen-printing technique on a FTO-glass substrate. Composite of TiO₂:ZnO photoanodes were then sensitized in a solution of N719 dye for several hours. Finally, the DSSCs were assembled and the power conversion efficiency was measured using an I–V measurement system. The highest power conversion efficiency of 2.30% was obtained from the cell fabricated with TiO₂:ZnO (50:50) photoanode. This result indicated that the balanced composition allowed to increase J_sc along with reducing recombination process and retaining high dye-loading capability.

Abstract: The main limitation of LiFePO₄ (LFP) as a cathode material for lithium-ion battery (LIB) is its poor rate performance due to its low electronic conductivity values. At present, there are three main efforts being intensively carried out to overcome this: cation doping, crystal morphology adjustment, and LFP surface modification. Surface modification of LFPs has become a major concern in efforts to improve battery performance. The use of zeolitic imidazolate frameworks 8 (ZIF-8) and 67 (ZIF 67) as N-doped C sources for surface modification of LIB cathodes carried out in several studies has shown an improvement in the electrochemical performance of LIB. However, the thermal, solvothermal and chemical stability of ZIF-8 and ZIF-67, which adopt the sodalite (SOD) topology, is still not enough for this purpose. Zeolitic imidazolate frameworks 14 (ZIF-14), which is homologous to ZIF-8 and ZIF-67 with its crystals adopting analcime (ANA) topology, has better thermal, solvothermal, and chemical stability than ZIF-8 and ZIF-67. Apart from its topology, ZIF-14 cobalt (ZIF-14 Co) can be synthesized rapidly in a water-based system at room temperature, so that its use becomes more effective and efficient. This paper will describe the synthesis and characterization procedure of ZIF-14 Co for use as a modification material for the cathode surface of LIB.

Abstract: Currently humans are still very dependent on resources derived from fossil fuels. Even though fossil fuels are no longer sufficient to meet energy needs. For this reason, renewable energy technology is developed in the form of energy harvesting from mechanical energy in the form of ferrofluid vibrations. The ferrofluid used in this study is composed of filler Mn_0.5Zn_0.5Fe₂O₄ where Zn doping is used to increase magnetization, surfactant tetramethylammonium hydroxide (TMAH), and H₂O as a liquid carrier. This study aims to study ferrofluid Mn_0.5Zn_0.5Fe₂O₄ as energy harvesting. Mn_0.5Zn_0.5Fe₂O₄ nanoparticles were synthesized using the coprecipitation method accompanied by nanostructure studies in the form of XRD, FTIR and VSM tests to determine the diffraction peaks, functional groups and magnetic properties of the sample. The diffraction peaks of Mn_0.5Zn_0.5Fe₂O₄ are at the peaks (2 2 0), (3 1 1), (2 2 2), (4 0 0), (4 2 2), (5 1 1), and (4 4 0). The FTIR spectrum of Mn_0.5Zn_0.5Fe₂O₄ nanoparticles is shown in the wavelength range of 4000-500 cm⁻¹. The band vibration peaks of O-H stretching, CO₂, O-H, Mn-O, Zn-O, and Fe-O particles Mn_0.5Zn_0.5Fe₂O₄ are respectively at 3392 cm⁻¹, 2309 and 2376 cm⁻¹, 1635 cm⁻¹, 861 and 1636 cm⁻¹, 686 cm⁻¹ and 539 cm⁻¹. The functional group of the metal-oxygen group (M–O) originates from magnetic particles as fillers to form ferrofluids. The competition of Mn and Zn ions at octahedral and tetrahedral sites in the spinel system tends to change the lattice parameters of the Mn_0.5Zn_0.5Fe₂O₄ ferrofluid. The magnetization curve of the Mn_0.5Zn_0.5Fe₂O₄ ferrofluid has superparamagnetic characteristics with a saturation magnetization value of 31,727 emu/g so it can be used as an energy harvester. Based on the IV electrical test, the Mn_0.5Zn_0.5Fe₂O₄ ferrofluid has the potential for energy harvesting with a voltage value of 1.67 µV and a current of 136.6 µA.

Abstract: The a-C/a-C:B homojunction of palmyra sugar has been successfully fabricated using the nanospray method. Palmyra sugar was chosen as the main source of carbon because it is cheap, renewable, abundant and available around the clock. nanospray is used as a deposition method on glass ITO substrates because of several advantages, namely cheap, easy, portable, low power consumption, the deposited layer is more evenly distributed and thinner. Junction samples when in bright conditions [emitted light] showed an increase in current and voltage values ​​compared to dark conditions. Testing the current and voltage of the junction sample shows the characteristics of a rectifier diode. This confirms the results of the test using PES as a doping process with amorphous carbon with boron capable of changing the conduction type from a-C from an intrinsic semiconductor to a p-type semiconductor. Testing the junction sample when irradiated with visible light using a lamp shows symptoms of the photovoltaic effect. Tests directly on the sun when conditions AM 1.5 samples showed symptoms of the photovoltaic effect. This indicates that the a-C/a-C:B amorphous carbon homojunction junction sample functions as a solar cell.

Abstract: Photoelectrochemical cell (PEC) has the same working principle as solar cell which convert solar energy into electricity. PEC consists of photoanode, electrolyte, and counter electrode, where electrolyte plays an important role in determining PEC performance. Yttria-stabilized zirconia (YSZ) is the most suitable electrolyte used due to its high ionic conductivity and chemically stable. In this study, YSZ was deposited to ZnO Nanorods (NRs) by doctor blade method with thickness variation of 100 μm (PEC10) and 120 μm (PEC12). X-ray diffraction (XRD), scanning electron microscope (SEM), and UV-Vis spectroscopy were used to distinguish the phase, morphology, and band gap of the formed materials, respectively. Moreover, I-V test was also conducted to evaluate the performance of the fabricated PEC with different YSZ thickness. SEM image confirmed the deposition thickness of YSZ layer on NRs which formed rough and irregular interface due to grain boundary fusion of YSZ and NRs. In addition, there is little difference XRD pattern from PEC10 and PEC12 which shows ZnO and YSZ peaks with peak shifting observed. Meanwhile, slightly difference noticed on band gap value where PEC10 has 3.25 eV and PEC12 has 3.58 eV. Even though, the characteristic of PEC10 and PEC12 is similar, the I-V test shown a significant difference of solar efficiency where PEC10 has higher efficiency of about 0.328% than PEC12. This difference is contributed by smaller grain size which has higher specific surface area and porosity. Based on this study, the thickness of electrolyte layer YSZ doesn’t affect the basic characteristic of PEC but affect the efficiency of PEC significantly.

Abstract: This research uses the Solid State method to produce LiNi_xFe_1-xPO₄ /C Composite Materials with variation Ni ion doping are x= 0.01, 0.02, and 0.03, Characterization was carried out using XRD, PSA, SEM and EIS. The results of XRD analysis showed that LiFePO₄, Li₃Fe₂PO₄ and Fe₂O₃ phases were formed. The conductivity test results show that the conductivity of the LFP/C precursor is 10.24x10^-4 S/cm, the LiNi_0.01Fe_0.99PO₄/C precursor is 7.75 x10^-4 S/cm, the LiNi_0.02Fe_0.98PO₄/C precursor is 10.334 x10^-4 S/cm, and the precursor LiNi_0.03Fe_0.97PO₄/C was 4.87 x10^-4 S/cm . With the highest conductivity value at LiNi_0.02Fe_0.98PO₄/C precursor.