Architected functional materials with emphasis on sustainable electrochemical energy storage and sensing

Abstract

Investigations embodied in thesis entitled “ARCHITECTED FUNCTIONAL MATERIALS WITH EMPHASIS ON SUSTAINABLE ELECTROCHEMICAL ENERGY STORAGE AND SENSING” were initiated from December 29, 2014 in the Discipline of Metallurgy Engineering and Materials Science (MEMS), Indian Institute of Technology Indore, Indore, India. Objectives and Scope  Design and construction of nanostructured materials of different metal oxides/sulfides, metal organic frameworks (MOFs), reduced graphene oxide (rGO) and their composites.  Probing physico-chemical properties of these materials by various advanced characterization techniques.  Fabrication of electrodes for supercapacitors and electrochemical sensors.  Analyzing supercapacitor and sensing properties by various electrochemical techniques. The present thesis contains eight chapters and it begins with a general introduction, followed by synthesis of different nanomaterials and their applications in electrochemical energy storage and sensing as subsequent chapters. In the introduction, the basic fundamentals of supercapacitors along with its categories based on energy storage mechanisms have been discussed (Chapter 1). A recent background in the supercapacitor field has been provided and the research gaps in the literature has been summarized. Some recent reports on different types of supercapacitors along withresults have been discussed. Similarly, the background of electrochemical sensing has been provided and various sensors such as glucose, peroxide and nitrite has been discussed with recent examples. In addition, various methods of nanomaterials synthesis, characterization and electrochemical techniques have been introduced, which are within the scope of this thesis.The initial work is focused on non-enzymatic amperometric sensing of glucose based on copper oxide microspheres (CMS), which were produced by a facile hydrothermal technique (Chapter 2). The prepared CMS were characterized by various techniques and subsequently grafted onto the working area of a carbon screen printed electrode (CSPE) and covered with a thin Nafion layer (Nafion/CMS/CSPE), to form a modified carbon screen printed electrode (MCSPE), which acts as a working electrode. Further, the glucose sensing properties of MCSPE was investigated under optimized conditions and the results showed a drastic enhancement of the current response in the presence of glucose. The amperometry results revealed a good glucose sensing ability of CMS with a notable limit of detection (LOD) of 20.6 μM, in awide linear range of 2–9 mM with a high sensitivity of 26.59 μA mM−1 cm−2. Moreover, the selectivity of the fabricated sensor towards glucose was observed in the presence of various interfering agents. In another part of this work, CMS were integrated with conducting reduced graphene oxide nanosheets (CRGO), through a facile and effective ultra-sonication assisted approach, which yields a new composite material (CSCO). This composite materials was incorporated to study its energy storage properties. The results revealed a notable specific capacitance of 244 F g‒1 at a current density of 0.125 A g‒1 of CSCO (more than six times higher than CMS and CRGO). Additionally, itexhibited high rate performance (retains 82.78% of its initial capacitance even at a high current density of 0.5 A g‒1) and long cycle life (~ 90% up to 1000 cycles), confirming the robustness and high stability of the composite on the electrode surface. The distinguishing features such as facile and binder-free electrode preparation, define CSCO as an emerging candidate for high performance supercapacitors. In another work, a multitasking Cu-MOF/rGO hybrid was employed for supercapacitors and electrochemical determination of nitrite (Chapter 3). This hybrid was synthesized by a simple ultra-sonication of slow-diffusion driven Cu-MOF and reduced graphene oxide (rGO). The molecular structure of the Cu-MOF was authenticated by single crystal Xray studies. The positive synergistic effects between Cu-MOF and rGO leads to a specific capacitance (685.33 F g‒1 at 1.6 Ag‒1) with excellent rate performance (retains 71.01% up to 8 A g‒1). Furthermore, we observed long cycle life (91.91% after 1000 cycles) of this hybrid, which indicates its high stability on the electrode surface. In another application, the Cu-MOF/rGO hybrid was employed for nitrite detection. The electrode can sense nitrite in a wide linear range with a notable detection limit of 33 nm, high sensitivity and with distinguished selectivity. In another part of this work, solvothermally grown ZIF-67 MOF crystals were utilized to produce porous Co3O4 nanoparticles through a simple calcination treatment. The crystal structure of ZIF-67 was also authenticated by single crystal x-ray analysis. Further, obtained Co3O4 nanoparticles were incorporated as supercapacitor electrode. The results show that ZIF-67 derived Co3O4 nanoparticles deliver an appreciable specific capacitance with good capacitance retention.The next work is focused on supercapacitors based on an rGO–Fe2O3 composite, which was synthesized by a facile two-step method, including homogenous precipitation followed by microwave assisted reduction (Chapter 4). This composite was characterized by various analytical techniques and its application as an electrode material for supercapacitors was evaluated. The electrochemical investigations revealed an excellent supercapacitor performance of composite (577.5 F g‒1 at 2 A g‒1), with a high rate performance (437.5 F g‒1 up to 10 A g‒1). Finally, charge transfer characteristics of the electrode were probed by electrochemical impedance spectroscopy (EIS), and the results were found to be consistent with other electrochemical measurements.