Design,Synthesis And Mechanism Investigation Of Self-supported Noble-metal-based Trimetallic Nanocatalysts For Oxygen Reduction Reaction And Oxygen Evolution Reaction

With the rapid development of economy,the extensive use of fossil fuel has caused great pollution to the environment,resulting in negative consequences such as global warming.As the demand for clean energy is increasing,researchers have committed to developing alternative energy conversion and storage systems with high efficiency,low cost and environment friendliness,such as metal-air batteries,fuel cells,water electrolysis technology,and so on.At present,the bottleneck of the development of metal-air batteries,fuel cells and water electrolysis technology is mainly the slow oxygen reaction kinetics,super high overpotential in catalysis and extensive use of precious metal catalysts.Therefore,the development of low / non-noble metal catalysts with high electrocatalytic activity and good stability for oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)is of great significance.In this work,self-supported Au-Cu binary hybrid was taken as the basis.By adding "third elements" Pt,Pd,Ni,Co and optimizing the structure,we committed to the design and synthesis of ternary self-supported hybrid or alloy catalyst,the activity towards ORR and OER was studied and the catalytic mechanism was investigated.This work sheds new lights on the development of active sites and the tuning of intrinsic activity of electrocatalysts.The main contents are as follows:1.With octadecylamine as reducing agent,H2 Pt Cl6,HAu Cl4,Cu Cl2 as the precursors of Pt,Au and Cu was reduced to self-supported Pt Au Cu@Cu2O/Pt hybrid catalyst by soft template method under hydrothermal conditions.By the selection of precursors and optimizing the experimental conditions,we found that Au-Cu binary system played an important role in the formation of self-supported nanostructure,and the selection of "third elements" also had a great influence on the formation of branched structure.As an ORR catalyst,Pt Au Cu@Cu2O/Pt had a good activity and stability.In the 2200-cycle stability testing,Pt Au Cu@Cu2O/Pt had no attenuation in kinetic precious mass activity at 0.85 V,and the kinetic precious mass activity of Pt Au Cu@Cu2O/Pt-200 th and Pt Au Cu@Cu2O/Pt-2200 th were 316 and 331 m A.mg-1,respectively,under the same conditions.The kinetic precious mass activity at 0.85 V commercial Pt/C(20 wt%)activity dropped from 174 m A.mg-1 to 107 m A.mg-1.This illustrates that the Pt Au Cu@Cu2O/Pt catalyst has excellent catalytic activity and stability.2.On the basis of Au-Cu binary system,by adding H2 Pd Cl4 as Pd precursor,Pd Au Cu hybrid was formed via hydrothermal reduction.Through the high potential treatment(High potential treatment,HPT)method,ORR activity of Pd Au Cu hybrid was improved greatly,as the result of "self-repair".Before the 1500 cycle,the activity of Pd Au Cu catalyst was equivalent to that of commercial Pt/C(20 wt%).After 1500 cycles,the activity of Pd Au Cu catalyst was significantly higher than that of commercial Pt/C(20 wt%).When HPT was applied to the catalyst,the activity of Pd Au Cu-1500 th increased from 158 m A.mg-1 to 756 m A.mg-1,while Pd Au Cu-2000 th activity increased from 245 m A.mg-1 to 989 m A.mg-1,which was 5.65 times higher than that of commercial catalyst,and this was highly active in non-platinum catalysts.By combining different CV processing of 0.03-1.40 V and 0.96-1.96 V,both the number and intrinsic activity of the active sites of Pd Au Cu catalyst was significantly improved,so the catalytic activity was greatly improved compared with those of commercial Pt/C(20 wt%)and Pd/C(10 wt%).3.Based on the Au-Cu binary system,Ni Cl2 as the Ni precursor was added,and the Au Ni-Cu2 O hybrid catalyst was formed after the hydrothermal reaction.At the beginning,the ORR half potential of catalyst(E1/2)was 0.82 V,which was same to commercial Pt/C(20 wt%,0.82 V),and OER onset potential(Eonset)was 1.591 V,when the current at 1.965 V was 24.3 m A.cm-2,which was close to the activity of Ir O2/C(50 wt%,Eonset = 1.516 V,I = 27.5 m A.cm-2 @ 1.965 V).After the OER process,the Cu2 O was leached out and Au Ni surface was formed.Due to the interaction between Au and Ni,the ORR activity was higher than that of Pt/C(20 wt%),and OER activity was similar to that of Ir O2/C(50 wt%).In addition,Au Ni-Cu2 O hybrid catalyst's stability was obviously better than that of commercial Pt/C(20 wt%)and Ir O2/C(50 wt%).For ORR,after 36000 s' chronoamperometry(CA)test,the catalyst still had 87 % of the activity,and the commercial Pt/C(20 wt%)decreased by 33 %;for OER,after the 25000 s' CA test,the catalyst still had 95 % activity,while Ir O2/C(50 wt%)declined 56 %.4.On the basis of the Au-Cu binary system,Co Cl2,as the Co precursor,was added,and self-supported Au Cu Co alloy catalyst was formed after the hydrothermal reaction.The self-supported structure of Au Cu Co had a large number of twin structures,which greatly improved the number of active sites.The E1/2 of ORR of the catalyst was 0.824 V,which was higher than that of commercial Pt/C(20 wt%,0.817 V),while Eonset of OER was 1.573 V,the current was 21 m A.cm-2 at 1.965 V,and its activity was slightly lower than that of the Ir O2/C(50 wt%,Eonset= 1.481 V,I = 27.0 m A.cm-2 @ 1.965 V).In addition,the stability of Au Cu Co catalyst was obviously better than that of commercial Pt/C(20 wt%)and Ir O2/C(50 wt%).For ORR,after 36000 s' CA test,the catalyst still had 79.7% of the activity,and the commercial Pt/C(20 wt%)decreased by 33 %;for OER,after the CA test of 14400 s,the catalyst still had 80 % activity,while Ir O2/C(50 wt%)declined 30 %.