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Öğe Carbon Pseudocubes from Iron Oxide Templates for Capacitive Energy Storage(Electrochemical Soc Inc, 2020) Sinan, Neriman; Ünür Yılmaz, EceA surface-protected etching approach was used to synthesize monodisperse partially hollow carbon nanostructures with pseudocubic shapes. Monodisperse chemical templates (alpha-Fe2O3, MF) were synthesized by the gel-sol method and coated with a polyvinylpyrrolidone (PVP) protective layer. Pyrrole monomers were dispersed around the PVP-protected alpha-Fe2O3 templates. Upon acidic etching, Fe3+ ions were released to initiate in situpolymerization of pyrrole to form Fe2O3@PPy (MFP) core-shell intermediates. The MFP particles were calcined to obtain partially hollow 3D pseudocubic carbon nanoparticles (PCC). The PCC delivered a high specific capacitance (395 F g(-1) at 0.2 A g(-1)) and enhanced cycling stability (5000 cycles at 4 A g(-1)). The superior electrochemical properties of the PCC is attributed to its cubic and partially hollow structure, which increases electric double layer capacitance by increasing charge storage surface, facilitates effective ion diffusion by reducing interparticle distances, and buffers volumetric changes associated with ion insertion through void space/pores. The simple and highly reproducible method presented in this work can be extended to produce various hollow or yolk-shell nanostructures as high-performance supercapacitor electrode materials. (C) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.Öğe Fe3O4/carbon nanocomposite: Investigation of capacitive & magnetic properties for supercapacitor applications(Elsevier Science Sa, 2016) Sinan, Neriman; Ünür Yılmaz, EceFe3O4 nanoparticles with similar to 10 nm diameters were synthesized by an extremely low-cost, scalable and relatively biocompatible chemical co-precipitation method. Magnetic measurements revealed that Fe3O4 nanoparticles have bifunctional superparamagnetic and ferromagnetic character with saturation magnetization (Ms) values of 64 and 71 emu g(-1) at 298 K and 10 K, respectively. Pseudocapacitive Fe3O4 nanoparticles were then integrated into hazelnut shells - an abundant agricultural biomass - by an energy efficient hydrothermal carbonization method. Presence of magnesium oxide (MgO) ceramic template or its precursor in the hydrothermal reactor allowed simultaneous introduction of pores into the composite structure. Hierarchically micro-mesoporous Fe3O4/C nanocomposite possesses a high specific surface area of 344 m(2) g(-1). Electrochemical properties of Fe3O4/C nanocomposite were investigated by cyclic voltammetry and galvanostatic charge-discharge measurements in a conventional three-electrode cell. The Fe3O4/C nanocomposite is able to operate in a large negative potential window in 1 M Na2SO4 aqueous electrolyte (-1.2-0 V vs. Ag/AgCl). Synergistic effect of the Fe3O4 and carbon leads to enhanced specific capacitance, rate capability and cyclability making Fe3O4/C nanocomposite a very promising negative electrode material for asymmetric supercapacitors. (C) 2016 Elsevier B.V. All rights reserved.Öğe Hydrothermal conversion of lignocellulosic biomass into high-value energy storage materials(Elsevier Science Bv, 2017) Sinan, Neriman; Ünür Yılmaz, EcePreparation of hierarchically porous, heteroatom-rich nanostructured carbons through green and scalable routes plays a key role for practical energy storage applications. In this work, naturally abundant lignocellulosic agricultural waste with high initial oxygen content, hazelnut shells, were hydrothermally carbonized and converted into nanostructured 'hydrochar'. Environmentally benign ceramic/magnesium oxide (MgO) templating was used to introduce porosity into the hydrochar. Electrochemical performance of the resulting material (HM700) was investigated in aqueous solutions of 1 M H2SO4, 6 M KOH and 1 M Na2SO4, using a three-electrode cell. HM700 achieved a high specific capacitance of 323.2 F/g in 1 M H2SO4 (at 1 A/g, -0.3 to 0.9 V vs. Ag/AgCl) due to the contributions of oxygen heteroatoms (13.5 wt%) to the total capacitance by pseudo-capacitive effect. Moreover, a maximum energy density of 11.1 Wh/kg and a maximum power density of 3686.2 W/kg were attained for the symmetric supercapacitor employing HM700 as electrode material (1 M Na2SO4, Delta E = 2 V), making the device promising for green supercapacitor applications. (C) 2017 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.Öğe PEDOT:PSS Enhanced Electrochemical Capacitive Performance of Graphene-Templated delta-MnO2(Korean Electrochemistry Soc, 2020) Sinan, Neriman; Ünür Yılmaz, EceBirnessite-type manganese dioxide (delta-MnO2) with hierarchical micro-/mesoporosity was synthesized via sacrificial graphene template approach under mild hydrothermal conditions for the first time. Graphene template was obtained by a surfactant (cetyltrimethylammonium bromide, CTAB) assisted liquid phase exfoliation (LPE) in water. A thin PEDOT:PSS (poly (3,4-ethylene dioxythiophene): poly (styrene sulfonate)) layer was applied to improve electrical conductivity and rate capability of MnO2. The MnO2 (535 F g(-1) at 1 A g(-1) and 45 F g(-1) at 10 A g(-1) ) and MnO2/PEDOT:PSS nanocomposite (550 F at 1 A g(-1) and 141 F g(-1) at 10 A g(-1) ) delivered electrochemical performances superior to their previously reported counterparts. An asymmetric supercapacitor, composed of MnO2 /PEDOT:PSS (positive) and Fe3O4/Carbon (negative) electrodes, provided a maximum specific energy of 18 Wh kg(-1) and a maximum specific power of 4.5 kW kg(-1) (Delta V= 2 V, 1M Na2SO4) with 85% capacitance retention after 1000 cycles. The graphene-templated MnO2 /PEDOT:PSS nanocomposite obtained by a simple and green approach promises for future energy storage applications with its remarkable capacitance, rate performance and cycling stability.Öğe Yüksek performanslı karbon/metal-oksit nanokompozit süperkapasitörlerin üretim ve karakterizasyonu(Bursa Teknik Üniversitesi, 2016) Sinan, Neriman; Yılmaz, Ece ÜnürEnerji ihtiyacımızın büyük bölümünü karşılayan fosil yakıt rezervleri hızla tükenmektedir. Bu durum alternatif enerji kaynakları kullanımına yönelik bilimsel çalışmaları hızlandırmıştır. Alternatif enerji kaynaklarının etkili şekilde kullanılabilmesi için sürdürülebilir ve çevre dostu enerji depolama/dönüşüm sistemlerine gereksinim duyulmaktadır. Süperkapasitörler, yüksek güç ve enerji yoğunlukları ve uzun ömürleri ile alternatif enerji kaynaklarından değişken zamanlarda elde edilen yüksek yoğunluklu enerjinin çok hızlı bir şekilde depolanması için en iyi çözümü sunmaktadır. Süperkapasitörler enerji depolama mekanizmalarına göre ikiye ayrılır: elektriksel çift tabaka (EDL)- ve pseudo-kapasitörler. EDL-kapasitörlerde yüklerin elektrostatik olarak ayrışması söz konusudur ve geniş yüzey alanlı (1000-2000 m2 g-1) aktif karbonlar kullanılır. Pseudo-kapasitörlerde ise faradaik redoks tepkimeleri görülür ve redoks-aktif geçiş metal oksitleri kullanılmaktadır. Rutenyum oksit (RuO2) elektrot malzemesi olarak sıklıkla incelenmiş ancak yüksek maliyetli, toksik ve az bulunur olması nedeniyle alternatif pseudo-kapasitif malzemelerin geliştirilmesine ihtiyaç duyulmuştur. Nanokompozit elektrotlardan oluşan hibrit süperkapasitörler, aktif karbonun yüksek güç yoğunluğundan (hızlı şarj-deşarj) ve metal oksitlerin yüksek enerji yoğunluğundan aynı anda faydalanırlar. Bu çalışmada, karbon kaynağı olarak fındıkkabukları (biyokütle) kullanılmıştır. Kimyasal birlikte çöktürme metodu ile sentezlenen Fe3O4 nanopartikülleri tek adımda hidrotermal karbonizasyon ve seramik (MgO) şablonlama ile biyokütleye entegre edilerek gözenekli Fe3O4/C nanokompozit elektrotlar üretilmiştir. Fiziksel karakterizasyonların ardından elektrokimyasal performanslar üç-elektrotlu hücrede 1M Na2SO4 sulu çözeltisi içinde ve bu çözeltiye farklı konsantrasyonlarda Triton X-100 surfaktant katkılanarak incelenmiştir. En iyi spesifik kapasitans 0.0025M surfaktant katkılandığında elde edilmiştir (1 A g-1' da 161 F g-1, ?V=1.2 V). Daha sonra simetrik süperkapasitör üretilmiş ve maksimum enerji yoğunluğu 4 Wh kg-1 olarak hesaplanmıştır (?V=1.8 V).
