“ACID-SALT-SURFACTANT LYOTROPIC LIQUID CRYSTALLINE MESOPHASES:
SYNTHESIS, CHARACTERIZATION, AND ELECTROCHEMICAL PROPERTIES OF MESOPOROUS M2P2O7 AND M2-xM’xP2O7 (M AND M’= MN(II), CO(II) AND NI(II)) POWDERS AND FILMS”
By: Işıl Ulu
Advisor: Prof. Dr. Ömer Dağ
Bilkent University, Department of Chemistry
Date: 03.10.2023
Time: 10:30
Place: Chemistry Meeting Room (SB Building)
All are cordially invited to attend.
Abstract:
The mesoporous metal pyrophosphates (M2P2O7) are considered to be important as energy storage materials. A novel synthesis method for the synthesis of mesoporous metal pyrophosphates (Ni2P2O7, Co2P2O7, Mn2P2O7, and binary metal pyrophosphates) is investigated by using a modified MASA (Molten Salt Assisted Self-Assembly) method using related acid; phosphoric acid (PA, H3PO4) or pyrophosphoric acid (PPA, H4P2O7), salts ([Mn(H2O)4](NO3)2, [Co(H2O)6](NO3)2, [Ni(H2O)6](NO3)2) and surfactant (pluronic P123 (EO20PO70EO20, where EO is ethylene oxide and PO is propylene oxide)). The homogeneous solutions using a broad range of inorganic ingredients are prepared to form lyotropic liquid crystalline
(LLC) mesophases and/or mesostructured semi-solid M2HxP2O7(NO3)x∙nH2O films that can be calcined at various temperatures to synthesize the mesoporous metal pyrophosphates. The mesostructured and mesoporous materials are characterized using XRD, ATR-FTIR, POM, XPS, SEM-EDX, TEM, N2 adsorption-desorption, and electrochemical characterization techniques. The clear solutions are spin-coated onto an FTO surface and/or dip-coated over a pure graphite rod (GR) to fabricate electrodes of mesoporous metal pyrophosphates. It is important to note that the metal pyrophosphates transform to their corresponding hydroxides in an alkaline solution during the electrochemical measurements. The mesoporous spherical Ni2P2O7 material is converted into a very thin needle-like β-Ni(OH)2 (1.5 nm thick and 7 nm wide) in alkaline media, maintaining its spherical morphology. In contrast, the mesoporous spherical Co2P2O7 and Mn2P2O7 particles transform into much thicker plate-like β-Co(OH)2 and β-Mn(OH)2 particles. The transformation time differs depending on the type of metal; the Co2P2O7 and Mn2P2O7 materials transform rapidly (about 30 sec), whereas the complete transformation of Ni2P2O7 to its hydroxide takes around 1 hour. The transformation time determines the particle size and morphology, consequently influencing the capacitance values. The β-Ni(OH)2 exhibits a high charge capacity and specific capacitance (102 mA.s and 368 mF/cm2 at a current density of 1 mA/cm2). However, these values are nearly 10 times smaller in the β-Mn(OH)2 and β-Co(OH)2 electrodes. The addition of nickel ions to the cobalt system in the preparation of binary metal pyrophosphates enhances the capacity and specific capacitance values, with the sample having β-Ni0.67Co0.33(OH)2 composition displaying the highest capacity value in alkali media (170 mA.s at a current density of1 mA/cm2).
Keywords: Mesoporous metal pyrophosphates, lyotropic liquid crystalline (LLC) mesophases, molten-salt assisted self-assembly, mesostructured semi-solid materials, metal hydroxides, specific capacitance.