مقاله انگلیسی رایگان در مورد الکترودهای کربنی در فناوری خازن – الزویر 2019

An overview of capacitive technologies based on carbon materials (energy storage in electrical double-layer capacitors (EDLCs), capacitive deionization (CDI), energy harvesting, capacitive actuation, and potential controlled chromatography) is presented. The review reveals the role of carbon for these scientific and industrial purposes with disclosing the benefits and limitations of various nanostructured carbons for a certain application. A special attention is placed on the electrical double-layer (EDL) formation mechanisms affected by the porous texture of carbon and the electrode architecture. The importance of a careful selection of the electrolytic solution for the EDL formation inside the intraparticle pores of carbon electrodes is also enlightened.

Introduction

During the last fifty years, the worldwide industrial development accompanied by improving wealth in emerging markets and growth of the human population have driven a steadily increasing demand for new energy and fresh water supplies. The emission of noxious gases during fossil fuel consumption and the depletion of their reserves have led to introduce renewables (sun and wind) in the energy mix. Unfortunately, due to their intermittent character, the renewable technologies are not able to ensure a real-time balance of electricity supply.[1] Therefore, in order to adapt the energy delivery to the demand and improve the energy efficiency, current researches are focused on introducing energy-storage technologies which would meet sustainability, environmental requirements and be cost-effective. What is more, the automotive industry faces the challenge to reduce the exhaust gases emission and amount of energy dissipated in urban areas by internal combustion engine powered vehicles. Encouraging efficient energy management should accelerate commercialization of the powertrain technologies to be applied in low carbon vehicles (LCV), fast-charging infrastructures in the stations, wireless monitoring systems or electricity load leveling in stationary and transportation systems. Apart from energy related issues, another critical problem worldwide concerns the shrinking access to potable water sources. It is commonly known that sea or brackish water is not suitable to drink without being desalinated. Therefore, alternative options to i.e. expensive vacuum distillation processes, reverse osmosis and cogeneration desalination plants, using either fossil fuels or nuclear power, are still highly sought in order to meet the global needs for clean water with reduced carbon footprint. Electrochemical technologies are able to bring some response to the issues related with efficient energy management, reduction of greenhouse gases emissions and water desalination by utilizing the concept of electrical double-layer (EDL) created at the surface of nanoporous electrodes.[2-4] When an electrode is polarized, the ions of opposite charge present in the electrolyte migrate to the electrode surface, where they create an EDL.[5] The double-layer capacitance depends on the electrode surface area able to accumulate electrical charge by pure electrostatic forces and on the charge separation distance imposed by dimensions of the charge carriers. Therefore, electrodes made from nanostructured carbon materials (also called carbons further in the text), characterized by a highly extended surface area and pores which match with the size of electrolyte ions, are generally considered to be capacitive.[4, 6-13] The capacitive technologies include: i) capacitive energy storage in electrical double-layer capacitors (EDLCs);[14, 15] ii) capacitive energy harvesting where small amount of ambient energy is captured, accumulated, and converted into electrical energy;[16, 17] and iii) capacitive deionization (CDI) of sea or brackish water where the salt ions are removed from the feed water, electrostatically held in the EDL and released in a brine stream during discharge.[18-20] Besides, the chargedependent ions separation can be also employed in a new type of liquid chromatography (called potentialcontrolled chromatography) to enhance the anolyte concentration or to introduce withholding of certain species.[21] What is more, the distribution of electric charges within the porosity of carbon material entails changes of geometric surface area of the electrodes triggered by charging and discharging, so-called capacitive actuation. The flexible capacitive devices where the electrodes deformation is controlled by a voltage stimulation can be used in soft robotics to make shape-changing robots.[22] In this context, the paper reveals the benefits and limitations of various nanostructured carbons, with a special attention to the charge storage mechanism in EDLCs affected by the porous texture of carbon electrodes. It then reviews the state-of-the-art of capacitive technologies based on carbon materials with discussing in some detail how the double-layer concept is being utilized for their development.