Development of Transition Metal Hydroxides and Chalcogenides Based Electrodes for Supercapacitor Application

Abstract

v newlineABSTRACT newlineAdvancements in energy storage devices like supercapacitors and batteries are newlineaccelerating fast. These devices rely on electrochemical reactions to store energy, but newlineboosting their capacity and durability remains a major hurdle. This research focuses on newlineusing nanostructured materials based on transition metals and chalcogenides to overcome newlinethese challenges and unlock better performance. One promising approach involves the newlinedevelopment of hybrid-type super capacitive electrodes, which offer higher specific newlinecapacities than conventional electrochemical double-layer capacitors (EDLCs) and newlinetraditional pseudocapacitors. This enhanced performance arises from their dual charge newlinestorage mechanism that combines surface redox reactions with intercalation processes, newlineunlike conventional supercapacitors where charge storage is primarily surface-limited. newlineAdditionally, assembling hybrid devices by integrating EDLCs with battery-type newlineelectrodes in a series configuration can extend the operating voltage window (V), further newlineimproving overall energy performance. Although lithium-ion batteries offer high energy newlinedensities (approximately 150-200 Wh kg-1), they are limited by relatively low power newlinedensities (charging/discharging rates typically below 1000 W kg-1) and limited cycle life. newlineIn contrast, supercapacitors provide significantly higher power densities (up to 10 kW newlinekg-1) and excellent cycle stability (gt105 cycles), but their energy densities (~5-10 Wh kg- newline1) remain much lower than those of batteries. As a result, there is considerable ongoing newlineresearch aimed at enhancing the energy density of supercapacitors without compromising newlinetheir power delivery and long-term stability for broader practical applications. newlineIn response to the challenges outlined above, this dissertation focuses on designing and newlinedeveloping high-performance hybrid supercapacitor electrodes based on multicomponent newlinetransition metal compounds. The main objective is to enhance energy density while newlineretaining power delivery and cycling stability. To achieve this, a range of strategies were newlineinvestigated, including direct growth techniques, multicomponent material design, and newlinehybrid configuration assembly. The materials were successfully synthesized and newlineintegrated into asymmetric supercapacitor electrodes, yielding improved electrochemical newlineperformance, which underscores their potential for use in future energy storage newlinetechnologies. newlineIn the first strategy, a trimetallic CoNiMo hydroxide was successfully grown directly on newlinecarbon cloth, yielding a high specific capacitance of 293.4 F g-1 at 1 A g-1, which was newlinesignificantly greater than its bimetallic counterparts. Furthermore, the electrode newlinevi newlinedemonstrated remarkable cyclic stability, retaining about 80% of its capacitance after newline1,200 cycles. To further enhance its electrochemical performance, the same material was newlinedirectly grown in situ on a nickel foam current collector, which resulted in a dramatic newlineincrease in capacitance to 1444 F g-1 at 1 A g-1. To exploit the benefits of metal newlinechalcogenides, which typically exhibit higher conductivity and rich redox-active sites, newlinethe trimetallic CoNiMo precursor was converted into CoNiMoS through a one-pot newlinesolvothermal process. The electrodes were fabricated by drop casting on NF, as a result newlineof which CoNiMoS displayed a superior capacitance of 1537.8 F g-1 at 1 A g-1. Among newlineall the electrodes investigated yet, CoNiMoS exhibited the most promising performance. newlineTo maximize its electrochemical properties, CoNiMoS was further synthesized by in situ newlinedeposition through a two-step hydro/solvothermal method, yielding a capacitance of newline1,940 F g-1 at 1 A g-1. Additionally, an asymmetric supercapacitor (ASC) constructed newlineusing this material demonstrated a specific capacitance of 181.8 F g-1 at 1 A g-1, with a newlinehigh energy density of 232.8 Wh kg-1 and a power density of 2903 W kg-1. Furthermore, newlineconsidering the desirable properties of Fe including its multiple valence states, abundant newlineredox-active sites, and robust structural stability, Mo was replaced by Fe in the CoNiMo newlinechalcogenides combination. The resultant CoNiFeSe electrode demonstrated a high newlinecapacitance of 1442.2 F g-1 at 1 A g-1, alongside 82.1% capacitance retention after 10,000 newlinecycles, reflecting its remarkable stability. newlineKeywords: Bimetallic, Trimetallic, Ternary, Hydroxide, Chalcogenides, newlinesupercapacitor, Energy storage, Hydrothermal, Solvothermal, In situ newline