Design Of Function-Oriented Electrochemical Systems And Preparation Of Carbon-based Composite Electrodes

The development of electrochemical systems （electrolysis,batteries/super capacitor, electrochemical sensor） is greatly depended onthe advance in electrode material and electrode structure. It is importantto carry functional directed design and investigation for these differentelectrochemical systems. Based on the composite electrodes withnano-sized electro-catalysts on conductive carbon, several energy-savingand high efficient electrolysis methods or electrode materials in followingfields were studied.1) Electrolytic synthesis KIO₃from KI and O₂.2)Electrolysis of Na₂CO₃-H₂O to produce NaOH and NaHCO₃.3) Ultrafastcharge and discharge rate of electrode materials for battery orsuper-capacitor.4) Non-enzymatic electrochemical sensor for glucosedetection. The main work and results of this dissertation are as follows:（1） Green, energy-saving and low-cost method of electrolyticsynthesis KIO₃: The traditional electrolytic synthesis of KIO₃is limitedby the high cell voltage and high cost of ion exchange membrane. Baseon the investigation on the mechanism and electrode process of electro-oxidation of I-and electro-reduction of IO₃^-, an atom economyand energy-saving process for synthesis KIO₃by electrolysis KI and O₂isproposed in this thesis. Oxygen reduction reaction is the mainelectrochemical reaction while the electrochemical reduction of IO₃^-isnegligible on Ag catalyst-Oxygen consumption cathode, so we adopt asimple membraneless and single liquid flow electrolytic cell in theproposed method. The cell voltage is only0.7⁰.8V at the current densityof150mA cm^-2, and the current efficiency achieves96%. Thecorresponding electricity consumption is only35⁴0%as compared totraditional method.（2） Energy-saving electrolysis of sodium carbonate with oxygenreduction cathode for alkaline digestion-carbonation precipitation processof alumina production：The method of alkaline digestion-carbonationprecipitation is an efficient and advance technology for production ofalumina. The membrane electrolysis of sodium carbonate is the keyprocess in this technology but its high electricity consumption hashindered its industrialization. This thesis investigated the electrolysis ofsodium carbonate with oxygen evolution on anode and oxygen reductionon cathode. By replacing the traditional hydrogen evolution cathode withoxygen reduction cathode that work at high potential, the potential gapbetween anode and cathode is reduced and the corresponding cell voltageof electrolysis sodium carbonate is decreased. The ORR catalyst including Ag-Co₃O₄/C, Co₃O₄/C and Ag/C was prepared by simplemethod that contains impregnation step and thermal decomposition step.The kinetic parameter of the ORR of the prepared catalysts wasinvestigated through rotation disk electrode （RDE） system. The oxygendiffusion cathode was prepared, characterized and then used forelectrolysis of sodium carbonate； The constant current electrolysisindicates that the cell voltage of Ag nanoparticles catalyzed ORCelectrolysis of Na₂CO₃is as low as1.52V and the correspondingelectrical energy consumption is saved up to39.8%as compared to HECelectrolysis at the same current density of100mA cm^-2.（3） Energy-saving electrolysis of sodium carbonate with hydrogenoxidation anode： In order to decrease electricity consumption ofelectrolysis Na₂CO₃-H₂O to produce NaOH and NaHCO₃as much aspossible, the electrolysis method using hydrogen oxidation anode andhydrogen evolution cathode was established. The hydrogen oxidationelectro-catalyst and the hydrogen diffusion anode was prepared,characterized and then used for electrolysis of sodium carbonate with theoptimization of the experimental conditions. The cell voltage of andhydrogen anode electrolysis at100mA cm^-2is only0.86V, while thetraditional hydrogen evolution cathode-oxygen evolution anodeelectrolysis and oxygen reduction cathode electrolysis is2.53and1.52V,respectively. What’s more, the cell voltage of the hydrogen anode electrolysis is only1.32V at200mA cm^-2. These results demonstrate thatthe hydrogen anode takes the obvious advantages of improving thespace-time yield and decreasing the electricity consumption.（4） The Ni（OH）₂/C nanocomposite electrode with ultrafastcharge-discharge rate：Conductive carbon black with high specific surfacearea was dipped with nickel nitrate solution and then rolled into electrodeplate directly. The in-situ precipitation in KOH solution was used toloading the Ni（OH）₂inside the porous electrode. The results of XRD,SEM and TEM indicated that the porous conductive carbon substrate wasnot separate by Ni（OH）₂and the Ni（OH）₂is evenly distributed onelectrode. The ultrafast charge-discharge properties of the preparednanocomposite electrode were investigated by cyclic voltammetry andchronopotentiometry. The results indicated that the charge-discharge timeis only272-261s at40mA cm^-2even when the active material loading isas high as6mg cm^-2, and the corresponding electricity quantity exceed10C cm^-2, respectively. The capacity achieves2688F g^-1even at dischargecurrent density as high as200mA cm^-2(32.6A g^-1). its capacity keeps81.5%at super high discharge current density of1000mA cm^-2（498C）as that of40mA cm^-2. The prepared electrode shows excellent ultrafastcharge-discharge rate and high capacity.（5） Non-enzymatic glucose sensor with extended linearity based onfast conversion of Ni（OH）₂NiOOH and concentrated OH-： The Ni（OH）₂nanoparticles modified carbon （Ni（OH）₂/C） composite electrodeelectrode was prepared by in-situ precipitation of Ni（OH）₂on carbon andthen treated by cyclic voltammetry. Fast conversion of redox couple（Ni（OH）₂/NiOOH: NiII/NiIII） is established on the prepared electrodecoupling with concentrated COH-electrolyte. Continuous cyclicvoltammetry method with increasing the concentration of glucose on eachcycle step by step was employed to quickly determine linear range andappropriate potential for glucose detection in0.1,1and7M KOHelectrolyte. The amperometric measurement under the optimizedcondition （0.28V vs. SCE in7M KOH） indicates the Ni（OH）₂/Ccomposite electrode holds a sensitivity of1004.6A mM^-1cm^-2in thewide linear range of1×10^-6-1.5×10^-2M （R=0.9999）. These performancesshow that the Ni（OH）₂/C nanocomposite electrode in concentrated KOHis a promising platform as glucose sensor.