Studies on the Design Synthesis of Pt-/Ru-Based Electrocatalysts and Their Performance Towards Methanol Oxidation and Hydrogen Evolution

Author:Wang Ya Jing

Supervisor:du chun yu song ying

Database:Doctor

Degree Year:2019

Download:59

Pages:144

Size:9786K

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Developing the next-generation eco-friendly and green energy system has gained great attention from all over the world.Electrochemical energy storage and coversion system,such as direct methanol fuel cells(DMFCs)and water splitting devices have been regarded as the most promising candidates to solve energy and environment-related issues.The involvement of electrochemical reactions with sluggish kinetics in these devices requires electrocatalyts to accelerate the reaction rate.So far,it has been demonstrated that the commercial Pt/C exhibited excellent electrocatalytic activity towards methanol oxidation reaction(MOR)in DMFCs and hydrogen evolution reaction(HER)in water splitting devices.However,the high cost,limited reserves and poor stability restrict the wide application of those devices.For methanol oxidation reaction the Pt-based electrocatalyst with high utilization efficiency,superior activtiy and stability,and enhanced CO tolerance is urgently needed,while for hydrogen evolution reaction,cost-effective HER electrocatalyst with high activity and stability is required.To solve the drawback of carbon corrosion under harsh electrochemical environment for commercial Pt/C,two dimensional FeP nanosheet with high conductivity,stability and large surface area was employed as support to anchor Pt nanoparticles.The as-synthesized Pt/FeP exhibited MOR current density of 0.994mA/cm2,2.74 times higher than that of commercial Pt/C,suggesting the excellent MOR performance of Pt/FeP.The research showed that the unique nanosheet structure and high conductivity of FeP could increase mass and charge transfers.In addition,FeP with special Feδ+and Pδ-active sites can be used as co-catalyst to promote water dissociation.The produced hydroxyl was adsorbed on FeP surface to remove CO-like species on neighbor Pt sites,making its activity higher than that of Pt/C.What’s more,the electronic structure of Pt was changed by FeP support,which was in favor of weakening the adsorption of CO on Pt sites and then enhancing CO tolerance.The HER experiment of Pt/FeP in 0.5 mol/L H2SO4 revealed that the overpotential(η)with 17 mV at-10 mA/cm2 was smaller than that of commercial Pt/C(20 mV).HER performance of Pt/FeP in 1.0 mol/L KOH solution(η=130 mV)was inferior to Pt/C(η=95 mV),but the stability in both acidic and basic media were superior to that of Pt/C.To further improve the performance and stability of Pt-based catalyst,Pt nanoparticles were successfully anchored on two dimensional layered Ti3C2 MXene with superior metallic conductivity and structural stability.Methanol oxidation experiment showed that Pt/Ti3C2 possessed higher electrocatalytic activity(1.137mA/cm2)than that of Pt/C(0.388 mA/cm2),as well as higher MOR stability.The HER performance and stability of Pt/Ti3C2 MXene in both acidic and basic media were superior to Pt/FeP and Pt/C.The analysis revealed that the superior activity and stability of Pt/Ti3C2 could be ascribed to the unique structure,robust structual stability and outstanding metallic conductivity.Although the MOR activity and stability of the above Pt-based electrocatalyst have been improved,the utilization efficiency of noble metal Pt was still low.To solve this problem,Ru@Pt core-shell nanostructure was constructed by two-step reduction and further combined with TiO2 nanoparticle.Finally,Ru@Pt/C-TiO2composite electrocatalyst was prepared.The methanol oxidation experiment revealed that the electrocatalytic activity,stability and CO tolerance of Ru@Pt/C-TiO2 were superior to that of Ru@Pt/C,Pt/C-TiO2 and Pt/C.Meantime,the electrochemically active surface area(ECSA,69.6 m2/g)of Ru@Pt/C-TiO2 was distinctly higher than that of Pt/FeP(30.0 m2/g)and Pt/Ti3C2 MXene(30.2 m2/g),indicating the highest utilization efficiency of Pt for Ru@Pt/C-TiO2 electrocatalyst.The core-shell nanostructure of Ru@Pt and introduction of TiO2 can enhance the MOR performance of Ru@Pt/C-TiO2 ascribed to bifunctional mechanism and strong electronic interaction.In addition,the HER performance and stability of Ru@Pt/C-TiO2 in both acidic and basic media outperformed Pt/FeP,Pt/Ti3C2MXene,Ru@Pt/C,Pt/C-TiO2 and Pt/C.Although the as-synthesized Pt-based electrocatalysts exhibited outstanding HER performance,the stability was still poor.Recently,Ru-based electrocatalysts were widely reported due to their excellent activity and stability towards hydrogen production.On account of this,HRu4O8 microrod was prepared by solid phase reaction-ion exchange process,and firstly utilized as electrocatalyst for HER.The influences of calcination temperature on structure,morphology and catalytic activity were studied in detail.The results unraveled that HRu4O8 calcined at 300℃(denoted as HRu4O8-300)exhibited outstanding HER activity with the overpotential of 31 mV to drive the current density of-10 mA/cm2 in 1.0 mol/L KOH,obviously lower than that of the benchmark Pt/C.The Tafel slope of HRu4O8-300(30.3mV/dec)was significantly lower than that of HRu4O8(117.2 mV/dec)and Pt/C(81.5mV/dec),indicating that the rate-determining step was changed from Volmer step to Tafel step after 300℃calcination and the prior water dissociation was greatly enhanced.The analysis showed that calcination at 300℃contributed to the phenomena that more active sites were exposed and most importantly the exposed H+could induce the destabilization of the HO-H bond in H2O,thus enhancing HER activity.The i-t curves displayed the stability of HRu4O8-300 was superior to the as-synthesized Pt-based electrocatalysts.In addition,the HER overpotential at-10mA/cm2 of HRu4O8-300 in 0.5 mol/L H2SO4 is only 39 mV,and the charge transfer rate is fast.HRu4O8-300 possess excellent catalytic activity and stability for HER,indicating potential alternative to precious metal Pt for water splitting reaction.