Preparation Of Multimetallic Nanocatalysts And Their Applications In Fuel Cells And Electrolysis Of Water For Hydrogen Evolution

The direct alcohol fuel cell possesses the advantages of fast start-up,high efficiency,low working temperature which can be exploited as portable mobile power source or for new energy vehicles.The renewable fuels of methanol and ethanol are extensively conducted with high energy density and huge market prospect.The hydrogen energy is also considered as renewable energy and can be obtained by the electrolysis of water.The electrolytic water of industry for hydrogen evolution is generally adopted in alkaline solution due to the electrolytic cell and electrode materials will be seriously corroded by H⁺ions in strong acid.However,the energy consumption is always large on account of the slow kinetic reaction and high overpotential of hydrogen evolution.Therefore,it is of great significance to design and construct electrocatalyst with high activity and low overpotential for hydrogen evolution via alkali electrolytic water.Noble metal catalysts are widely applied in direct alcohol fuel cell and electrolysis of water hydrogen evolution reaction.As noble metals are scarce and expensive,the critical problem is to design electrocatalysts with low consumption of noble metals and high activity and stability.Due to the electrocatalytic reaction belongs to surface interface reaction,the interface design of catalyst is of great importance to develop the reaction activity.Herein,our topic mainly focuses on the development of the electrocatalytic performance as well as reducing the amount of noble metals usage.The multi-active electrocatalysts of Pt Pd/（Ni,Co）（OH）₂/C,Pt Ru/Ni（OH）₂/C and Pd Ru/Ni（OH）₂/C electrocatalysts were employed for alcohols electrocatalytic oxidation and hydrogen evolution under alkaline conditions.The catalyst of low cost and high efficiency towards fuel cell and hydrogen evolution were successful prepared by simple synthesis route.This paper mainly obtains the following research results:1.A method for the design and preparation of multi-active catalyst for the composite of noble metals and transition metal hydroxides was proposed.The PtPd/（Ni,Co）（OH）₂/C,PtRu/Ni（OH）₂/C and PdRu/Ni（OH）₂/C electrocatalysts of multi-active electrocatalysts were fabricated by hydrazine hydrate reduction method and metal replacement method.The electrocatalytic oxidation of methanol/ethanol（MOR/EOR）and HER under alkaline conditions were carried out.The structure of precious metal/transition metal hydroxide/carbon black were prepared via this method for the electrocatalytic oxidation of methanol and ethanol and electrolysis of water for hydrogen evolution is seldom reported.2.The interface structures of various noble metals anchored on transition metal hydroxides（including Pt single-atom,Pd clusters-on-（Ni,Co）（OH）₂,Pd,Ru clusters-on-Ni（OH）₂/C,Pt,Ru single-atom and Pt,Ru clusters-on-Ni（OH）₂/C）are revealed by the synchrotron radiation（XANES,EXAFS）and spherical aberration-corrected scanning transmission electron microscope（AC-STEM）.3.Different interface structure of noble metals and transition metal hydroxide showed high efficiency and stable electrochemical performance towards the oxidation of methanol/ethanol and hydrogen evolution.According to the above results of synchrotron radiation（XANES,EXAFS,AC-STEM）characterization techniques as well as electrochemical test,not only the interface coordination between the noble metals and transition metal hydroxide but also the synergistic effect between single atoms and clusters were puts forward to develop the reactivity of MOR/EOR and HER in ialkaline water.The possible reaction mechanism was described and the possible"structure-activity relationship"between the catalyst structure and its electrocatalytic performance was established.4.The interface structures of three different noble metals with transition metal hydroxides for MOR/EOR and HER in alkaline solution have been obtained.（1）The mass activity of Pt_1.5Pd_1.5/（Ni,Co）（OH）₂/C catalyst with the interface structure of Pt single atom,Pd cluster-on-（Ni,Co）（OH）₂ is 18.53 times and 33.35 times over that of commercial Pt/C,and the overpotential of HER in electrolytic water is 10 mV@10 mA cm^-2,51 mV@100 mA·cm^-2,while that of commercial Pt/C(23 mV@10 mA·cm^-2,129 mV@100 mA·cm^-2).（2）The mass activity of Pd₁₂Ru₃/Ni（OH）₂/C with Pd,Ru cluster-on-Ni（OH）₂/C interface towards EOR is 19.5 times over that of commercial Pd/C,and the overpotential of HER in alkaline solution is 16 mV@10 mA·cm^-2,97 mV@100 mA·cm^-2.（3）The PtRu/Ni（OH）₂/C interfaces with Pt,Ru single atom,Pt,Ru cluster-on-Ni（OH）₂/C show the highest reactivity for alkaline MOR.The mass activity of PtRu/Ni（OH）₂/C interfaces is 20.61times over that of commercial Pt/C.The HER overpotential of electrolytic water is 21 mV@10mA·cm^-2,87 mV@100 mA·cm^-2.5.Based on the excellent performance of these noble metals/transition metal hydroxide/carbon black structure,the amount of noble metal precursor was further modulation to explore the synergy strength between the transition metal hydroxide.The low cost and high efficiency catalyst for fuel cell and hydrogen evolution were prepared by simple synthesis route and low amount of noble metals.6.The noble metal/transition metal hydroxide/carbon black structure exhibited superior performance.For the further comparison,hydroxide was removed through high temperature hydrogen roasting and annealing to form multimetal alloy catalysts such as PtPdNiCo/C,PdRuNi/C and PtRuNi/C.The mass activity of Pt_1.5Pd_1.5Ni_8.5Co_8.5/C catalyst with alloy interface structure is about 1/23.41 of Pt_1.5Pd_1.5/（Ni,Co）（OH）₂/C catalyst,and Pd Ru Ni/C is about 1/5.93 of Pd₁₂Ru₃/Ni（OH）₂/C catalyst,Pt Ru Ni/C is about 1/4.55 of Pt Ru/Ni（OH）₂/C catalyst.The important role of interface coordination between metals and transition metal hydroxides is further confirmed.