Exploration Of Electrochemical Applications Based On Deep Eutectic Solvents

With the deterioration of the natural environment,people gradually realized the importance of protecting the natural ecological environment and sustainable development,and the concept of "green chemistry" has gained more and more attention and development in chemical research and chemical production.The solvent is the most used component in the chemical reaction of solution phase.Whether the green solvent is used or not largely determines whether the chemical process is "green".At present,there are five types of green solvents recognized by scientists,including water,supercritical liquid,ionic liquid,deep eutectic solvent(DES)and biomass based green solvent.DES is a new type of green solvent and was proposed by Abbott in 2002.A DES usually comprises two or several components which interact via hydrogen bond interactions to form the eutectic mixtures with the melting point lower 100?.The DES maintains the green characteristics,but also has low vapor pressure,good conductivity,excellent biocompatibility and biodegradability,low or non-toxicity,non-flammability,unique solubility,low price and easy synthesis.DESs are also widely used in more and more fields,such as extraction and separation,inorganic or organic synthesis,gas adsorption,electrochemical reaction electrolyte,biomass dissolution and processing,biological and medical applicants.In this paper,we introduced the definition,classification,development history,synthesis methods,physical and chemical properties,theoretical calculation and practical application of DES.Thereafter,four researches based on our work in the field of electrochemistry are introduced in detail:1.An electrochemical method was developed to fabricate nanoporous gold electrodes by alloying and dealloying Au-Zn alloy in ZnCl2-urea deep eutectic solvent.Zinc was electrodeposited on gold electrode in DES at high temperature and an Au-Zn alloy layer was formed.When the zinc in the alloy was continuously electrochemically oxidized,the nanoporous gold electrode was obtained.The electrochemical reaction temperature is the key factor affecting the porosity of porous gold electrode.As the electrodeposition temperature was set to 120 ?,the nanoporous gold electrode has the highest electrochemical specific surface area and electrochemical activity.The as-prepared active nanoporous gold electrodes facilitated the electrochemical detections of water pollutants(mercury(?),hydrazine and nitrobenzene)with superior sensitivities.2.Here choline chloride(ChCl)-urea DES was used as the electrolyte for electrochromic reactions of two inorganic electrochromic materials(Prussian blue(PB)and tungsten trioxide(WO3)).Starting from the evaluations of thermal and electrochemical properties of ChCl-urea DES,we found the DES electrolyte can be used in the electrochromic experiments at a wide temperature range(from 25 to 100?)and potential range(from-0.8 to 1.0 V vs.Ag).And as the temperature increased,both coloring and bleaching time dramatically decreased but efficiency slightly decreased.A complementary electrochromic device with PB-DES-WO3 was also fabricated to demonstrate the feasibility for electrochromic applications with the combination of green and cheap DES and inorganic electrochromic materials.3.Here we develop a direct DES calcining method to prepare low-dimensional and highly active TMOs for electrochemical oxygen evolution reaction(OER).Glucose monohydrate and urea can form glucose-urea DES,which was calcined in N2 atmosphere to produce 2D N,O-doped graphene.When metal precursors were introduced into glucose-urea DES and calcined together,TMOs were templated by the graphene flakes and exhibited low-dimensional morphologies.With this method,a series of metal oxides were readily synthesized,and the thickness and porosity can be conveniently tuned by the concentrations of metal salts.Our nanostructured TMOs were further applied for OER,and they showed quite competitive activities over the counterparts from other methods.2D porous LSCF20-DES exhibited the largest specific surface area(28.9 m2/g)and the highest OER electrocatalytic activities(0.304 V overpotential at current density of 10 mA/cm2).4.We used choline chloride-lactic acid DES to dissolve lignin as the electrospinning solution to synthesize three-dimensional lignin aerogels by vertical electrospinning method.The lignin fiber aerogel has a specific weight of 5 mg/cm3 and is lighter than cotton.The lignin fiber aerogels can be carbonized at high temperature under N2 protection to form three-dimensional porous carbon fiber aerogels.The aerogels have high specific surface areas and conductivities.It can be used as electrode material to make supercapacitors which performances are better than that of commercial carbon nanotubes.In this experiment,the used pure water,lignin,DES can be cycled.This work is atomic economy and accords with the principle of green chemistry.