| The electrolytic manganese dioxide(EMD)has been widely used as raw materials,with major applications in dry batteries and preparation of the lithium manganate electrode material used in Li batteries.China is the largest,batteries producer in the world and EMD is used as green energy storage material with an annual output value of 290,000 metric tons in China but it is a classic high-energy consuming.The by-product of EMD is hydrogen gas,which produces considerable quantities of acidic fog into the air.Our team obtained the new method of saving energy and green electrodeposition of manganese dioxide using high potential(E0= 1.229 V)gas diffusion electrode(GDE)instead of traditional hydrogen evolution cathode(E0=0 V).The theoretical cell voltage of the GDE is 1.23 V lower than traditional electrode and there is no hydrogen gas production.Therefore,it is a new method of saving energy and green electrodeposition of manganese dioxide.However,saving energy and lifetime of the previous Pt GDE in high temperature and strong acid electrolyte systems(120 g·dm-3 MnSO4·H2O+30 g·dm-3 H2SO4)need to be improved.Thus,this paper will continue energy-saving mechanism and longevity research of the Pt/C GDE,and three problems are discussed.(1)The energy saving mechanism of Pt/C gas diffusion electrode for saving energy and green electrodeposition of manganese dioxide and the effect laws of the factors on energy saving were studied.(2)The failure mechanism of Pt/C GDE using in strong acid electrolyte systems(120 g·dm-3 MnSO4·H2O+30 g·dm-3 H2SO4)and the effect laws of the factors on life time of Pt/C GDE are studied.(3)The component and performance requirement of the longevous GDE are studied to obtain high energy saving and long life.The energy saving mechanism and the effect factors of Pt/GDE have been clear.Electrolytic MnO2 experiments were assembled with a Ti-based Ti-Mn alloy as the anode,an electrolyte of 120 g·dm-3 MnSO4·H2O+30 g·dm-3 H2SO4(80 ?)and the Pt/C GDE as the cathode.The energy saving mechanism of Pt/C GDE has been obtained by studying the effect laws of the factors on cell voltage and the oxygen reduction reaction(ORR)of Pt/C GDE.The energy saving mechanism of Pt/C GDE is that first the ORR of GDE makes it have the high potential,and the oxygen reduction reaction of Pt/C GDE adopts a 4 electron transfer process as the main process as the main process in electrolyte and has low overpotential.The factors on cell voltage of electrodeposition of MnO2 in strong acid electrolyte systems were the structure of the cell,the temperature of electrolyte,current density,the activity of the nanocatalyst(the effect of the nanoparticle size)and mechanism of ORR.The optimum technological condition of EMD which has high saving energy has been obtained.The optimum technological condition is the cell with an air chambers and high liquid transfer efficiency structure,an electrolyte of 120 g·dm-3 MnSO4·H2O+30 g·dm-3 H2SO4(80 ?),100 A·m-2,the Pt particle sizes with ranging from 2-4 nm and the cell voltage can be reduced 1.0 V.The failure mechanism and the effect factors of Pt/C GDE using in strong acid electrolyte systems(120 g·dm-3 MnSO4·H2O+30 g·dm-3 H2SO4)are obtained by the lifetime and failure analysis of Pt/C GDE.The lifetime of the nickel foam which has poor corrosion resistance is the shortest in the electrolysis,the sponge titanium is easily blocked,however,the Pt/C GDE with high corrosion resistance and hydrophobic current collector(carbon paper)has longest life.The cell voltage can be reduced 1.0 V using Pt/C GDE as cathode instead of the traditional electrode(Cu,1.8 V),and the lifetime of Pt/C GDE with high corrosion resistance and hydrophobic current collector is 469 h.The corrosion of catalyst layer of Pt GDE with high corrosion resistance and hydrophobic current collector(carbon paper)playing a major role.The failure of Pt/C GDE is degradation and losses of carbon supports,the crack of catalyst layer,and losses and agglomeration of Pt nanoparticles.The GDEs of high saving energy and long lifetime have been developed with high activity and stability of catalyst at the core,and the Pt/CNx,Pt/TiO2-CNx and Pt/TiN-CNx nanowires have been synthesized and were prepared to Pt based GDE.The cell voltage can be reduced 1.1 V using Pt/CNx GDE,Pt/Ti02-CNx GDE and Pt/TiN-CNx GDE as cathode instead of the traditional electrode(Cu),and the electric energy consumption of electrolysis can save 60%.The lifetimes of the Pt/CNx GDE,Pt/Ti02-CNx GDE and Pt/TiN-CNx GDE are 1041 h,1511 h and 1612 h and the longest lifetime is 3.4 times as long as that of Pt/C GDE.EMD using Pt/TiN-CNx GDE as cathode instead of the traditional electrode is y-MnO2 and the discharge capacity is 1.9 times that of commercial battery grade manganese dioxide.The durability test shows that the corresponding shift for the Pt/TiN-CNx catalyst is only 15 mV after 10000 cycles in 0.5 M H2SO4.Thus the Pt/TiN-CNx catalyst has high stability.The failure analysis of Pt/CNx GDE,Pt/TiO2-CNx GDE and Pt/TiN-CNx GDE found that the corrosion of GDEs with high corrosion resistance and hydrophobic current collector(carbon paper)is supports degradation,the crack of catalyst layer,and losses and agglomeration of Pt nanoparticles.The Co3O4(30-100 nm),Co3O4/graphene,MnO2/graphene,graphene and Co3O4/C GDE have been synthesized to explore a low-cost and easily prepared Pt free catalyst.Low cell voltage of 0.9 V and high saving electric energy of-50%were exhibited by a cobalt oxide/graphene gas diffusion electrode compared with the traditional cathodes(copper and carbon)for electrodeposition of manganese dioxide in acid solution attributing to synergetic chemical coupling effects between cobalt oxide and graphene. |
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