| Due to the complicated and severe environmental problems,new demands have been made in industrial cleaner production and wastewater discharge.The electrocatalytic technology meets the requirements of green chemical industry,and the chlorine evolution reaction(CER)is extensively used in the fields of chlor-alkali industry and wastewater treatment.The dimensionally stable anodes(DSA)commonly used for CER are based on Ir or Ru，and the high cost limits their industrial application at large scale.Therefore,the fabrication of CER electrocatalysts with high mass activity is of great significance to reduce the cost of chlor-alkali industry.Meanwhile,active chlorine(Cl2,ClO-,etc)with strong oxidation can be formed by CER to degrade ammonia nitrogen wastewater.However,the composition is complex and the Cl-concentration is low in industrial wastewater.Thus,the current efficiency of DSA is low and the degradation of ammonia nitrogen is not desirable.So improving the CER selectivity of DSA under low chlorine condition is the key to enhance the degradation performance of ammonia nitrogen.To solve these problems,this paper tuned the electronic structure of active coatings by doping metal elements and forming solid solutions.It could expose more active sites and accelerate the reaction kinetics on the electrode surface to promote the CER.As a result,it enhanced the mass activity under high chlorine condition and improved the CER selectivity under low chlorine condition.The main works are as follows:(1)In order to enhance the mass activity of DSA and decrease the usage of Ir under high chlorine condition,this paper determined HCl pretreatment and sol-gel method as the DSA preparation process,and fabricated Nd-doped Ti/IrO2 electrodes.The doping of Nd tuned the electronic structure and decreased the loss of Gibbs free energy for the rate-determining step(desorption of chlorine),which exposed more active sites and enhanced the intrinsic activity of active sites.Ti/Ir0.8Nd0.2Ox electrode exhibited optimal CER performance with a low potential of 1.520 V vs RHE at 100 mA cm-2,a high Faraday efficiency of 91.0%,and a great stability of over 200 h at 1 A cm-2 in 0.5 M H2SO4 solution and at 100 mA cm-2 in 5 M NaCl solution.Notably,the mass activity of Ti/Ir0.8Nd0.2Ox(96.5 A glr-1)at 1.5 V vs RHE was 2.05 times as high as that of Ti/IrO2,which was the highest among noble metal electrodes reported.(2)In order to improve the CER selectivity of DSA and enhance the degradation performance of ammonia nitrogen under low chlorine condition,this paper fabricated a series of bimetallic oxide titanium electrodes by using the sol-gel method.Benefiting from the solid solution between IrO2 and Sb2O4,and the mixed valence of Sb element,it strengthened the synergetic interactions of metal oxides and accelerated the transfer of interface electrons to promote the CER.Therefore,Ti/IrSbOx electrode displayed optimal CER performance with a high Faraday efficiency of 76.8%in 0.05 M NaCl solution and a great stability of over 180 h at 1 A cm-2 in 0.5 M H2SO4 solution.And the mass activity of Ti/IrSbOx electrode at 2 V vs RHE was 7.43 times higher than that of commercial Ir-based DSA.Simultaneously,Ti/IrSbOx electrode exhibited excellent degradation performance of ammonia nitrogen with a removal rate of 99.4%at 40 mA cm-2 after 120 min of electrolysis,an original current efficiency of 70.3%and an energy consumption of 0.042 kWh gN-1,which was only 60%of that of commercial Ir-based DSA.On the basis of laboratory research,we designed the Ti/IrSbOx ‖ Ti pilot-scale electrolyzer with a removal rate of 98.4%at the current of 15 A after 5.5 h of electrolysis and an original current efficiency of 72.9%.We successfully completed the pilot test of Ti/IrSbOx electrode for industrial wastewater treatment. |
