Study On Electrocatalytic Oxygen Evolution Performance Of Iridium Doped Cobalt-Based Catalyst In Lead Methylsulfonate

With the increasement of the usage of lead-acid batteries used in electric bicycles,the demand for lead is increasing.The recycling process of waste lead-acid batteries is also attracting attention.Melt-reduction method with high-temperature reduction consuming huge energythe pollutant treatment is expensive.Therefore,lead electrolysis-based hydrometallurgy technology has been at the forefront of the development of recovery technologies,providing efficient and sustainable processes.In acidic conditional electrolysis lead recovery processes,fluoroboric acid and hexafluorosilicic acid are currently used in conventional electrochemical processes of refining lead.But hydrogen fluoride released during electrolysis can cause environmental pollution.Methanesulfonic acid has low corrosiveness,less toxicity,low volatility and high ionic conductivity compared with HBF₄ and H₂Fi S₆.It is considered as an ideal electrolyte.In the process of electrodepositing lead in the lead methanesulfonate system,there is a competitive reaction between lead dioxide and oxygen in the anode.The formation of lead dioxide by-products will increase the energy consumption of electrolysis and reduce the amount of lead deposition.This paper studies the anodic oxygen evolution reaction catalyst under the condition of methyl sulfonic acid,and suppresses the generation of lead dioxide to reduce the energy consumption in the process of lead methyl sulfonate electrolysis.For the above target requirements,the precious metal iridium catalyst under acid conditions is used.The main research contents of the paper are as follows:（1）Using ZIF-67,a ZIF-based MOF material,to synthesize Co@Ir-NCs by adding iridium into Co-NCs.By adjusting the synthetic conditions and the iridium doping amount,the Co@Ir-15%-NCs showed good catalytic properties and stability.The overpotential in 0.5 M methylsulfonic acid is 262 m V(J=10m A cm^-2)and the Tafel slope is 83 m V dec^-1,and the voltage is stably maintained for 10 h at 10 m A cm^-2 current density,showing good stability.The Co@Ir-25%-NCs catalyst was applied in the electrolysis of lead methanesulfonate anode,and the lead content on the electrode surface was characterized by mapping and EDS.The mass fraction is only 19.45 wt%,which is much lower than the lead content（93.02 wt%）on the electrode surface without catalyst addition.The potential during the galvanostatic electrolysis of lead methanesulfonate was 2.25 V（vs.RHE）,which was lower than that without the addition of catalyst（2.73 V（vs.RHE））.It is shown that the Co@Ir-15%-NCs catalyst can effectively inhibit the formation of anode lead dioxide and reduce the energy consumption of electrolysis.（2）The CC-Ir catalyst was obtained by plating the metal iridium on a carbon cloth.The catalyst with good catalytic performance and stability is obtained by optimizing the current density,time and temperature.A uniform iridium coating with a current density of 2 m A cm^-2,plating time of 2 h and plating temperature of 85℃can be obtained.The mass fraction of Iridium can reach about 7.2%,and most of the iridium exists in the form of simple iridium.The CC-Ir catalyst showed excellent electrochemical properties,with a superpotential of 257 m V(J=10 m A cm^-2)in a 0.5 M methylsulfonic acid solution and a Tafel slope of 73.5 m V dec^-1,while the voltage was stably maintained for 10 m A cm^-2 current density for 10 h.Through mapping and EDS analysis of the electrode surface of the CC-Ir catalyst electrolysis process of lead methanesulfonate,the mass fraction of lead is only 1.42 wt%,which is much lower than that of the electrode surface electrolysis without catalyst（93.02 wt%）.The potential during the galvanostatic electrolysis of lead methanesulfonate was 2.18 V（vs.RHE）,which was lower than that without the addition of catalyst（2.73 V（vs.RHE））.It is concluded that CC-Ir can effectively inhibit the formation of anode lead dioxide during the electrolysis of lead methanesulfonate and reduce the energy consumption of electrolysis.（3）Iridium and cobalt were plated on carbon paper,after which the resulting CP-Ir+Co was calcined at a temperature of 300℃,400℃,and 500℃air,and the Co obtained from carbon paper plating at a temperature of 400℃was oxidized to Co₃O₄ and finally the CP-Ir+Co₃O₄ catalyst.The surface of the CP-Ir+Co₃O₄ catalyst is lamellar and uniformly distributed,and the mass fraction of Iridium is 15.6%,most of which exists in the form of iridium.The mass fraction of cobalt is 28.04%and exists in the form of Co₃O₄.The resulting CP-Ir+Co₃O₄ has good electrochemical properties,with a superpotential of 267m V(J=10 m A cm^-2)and a Tafel slope of 72 m V dec^-1 in 0.5 M methylsulfonic acid solution,and the voltage is stably maintained for 10 h at 10 m A cm^-2 current density.CP-Ir+Co₃O₄ catalyst was applied in the electrolytic process of lead methanesulfonate anode.The lead content on the electrode surface was tested by mapping,EDS and other characterizations,and the mass fraction of lead was only 1.3 wt%,which was much lower than the lead content on the electrode surface after electrolysis without catalyst addition（93.02 wt%）.The potential during the galvanostatic electrolysis of lead methanesulfonate was 2.19 V（vs.RHE）,which was lower than that without catalyst addition（2.73 V（vs.RHE））.It is indicated that it can effectively inhibit the formation of anode lead dioxide during the electrolysis process and reduce the energy consumption of electrolysis.