Preparation Of Platinum-based Alloy Catalyst Based On Sodium Alginate And Its Electrocatalytic Oxygen Reduction Performanc

In the era of resource scarcity and cumulatively acute environmental destruction,which was induced by the combustion of traditional fossil fuels,it is imperative to search for novel,high-efficiency as well no-pollution energy storage and conversion devices,including proton exchange membrane fuel cells（PEMFCs）together with zinc-air batteries（ZABs）.They have made crucial breakthroughs in economy,safety and energy conversion efficiency.The electrocatalytic oxygen reduction reaction（ORR）at the cathods is the core electrochemical procedure in ZABs and PEMFCs.Owing to the high overpotential and slow kinetics of ORR,it is instant to search for the catalysts with superior activity.Platinum-based（Pt-based）catalysts have the virtues of lower overpotential,remarkable oxygen reduction ability and ideal electrocatalytic surface,so are taken as the most efficient ORR electrocatalyst at present.Whereas,they still have a serious problem of insufficient durability,low catalytic performance as well as high commercial costs,so they are difficult to be diffusely employed in daily life.So far,for purpose of promoting the ORR performance together with stability of Pt-based catalysts,numerous research has been devoted to altering catalyst support or synthesizing metal alloy materials.On the basis of the above-mentioned core scientific problems and research status of the exsisting Pt-based catalysts,this paper takes the regulation of the electronic structure of Pt-based catalysts as the starting point and takes the reduction of Pt consumption,enhancement of catalytic activity together with stability as the core of research,using marine polysaccharide sodium alginate as precursor to fabricate two different binary Pt-based alloy nanoparticles/carbon aerogel catalysts.This is of great significance to deal with the problem of resource scarcity and environmental injury on a global scale.The dominating contents are as follows:（1）The fixation of metal Co²⁺ions and the introduction of[PtCl₄]^2-ions in sodium alginate were realized,by taking it as dispersant and then utilizing its property of crosslinking with polyvalent metal cations.Subsequently,after simple freeze-drying,Pt Co alloy nanoparticles/carbon aerogel catalysts were fabricated via low temperature reduction as well high temperature nitrogen doping treatment.Among them,the prepared sample Pt Co/N-r-GO（Pt₁Co₅）delivers the best ORR activity and stability in acidic as well as alkaline media,when the Pt/Co molar ratio is 1:5.To be specific,its half-wave potential in0.5 M H₂SO₄ and 0.1 M KOH electrolyte can reach 0.804 and 0.930 V vs.RHE,respectively,which is superior to commercial Pt/C.Additionally,the catalytic activity of Pt Co/N-r-GO（Pt₁Co₅）still maintained nearly 90%after 15 h durability test under acid condition.（2）PtFe/N-r-GO（Pt_xFe_y）carbon aerogel catalysts with different Pt/Fe ratios and low-platinum content were fabricated by utilizing sodium alginate and r-GO as raw materials,introducing Fe³⁺ions through an ion-exchange procedure and precisely regulating the ion ratios of[Pt Cl₄]^2-/Fe³⁺in the precursor solution at the same time.Among them,in 0.5 M H₂SO₄ and 0.1 M KOH electrolyte,the Pt Fe/N-r-GO（Pt₁Fe₅）presents the best ORR activity（0.807 and 0.867 V vs.RHE）.In addition,it also owns great potential in the application of znic-air batteries,exhibiting ultra-high specific capacicty(840 m Ah g^-1),peak power density(0.248 W cm^-2)together with remarkable stability,it is able to continuously operate robustly for at least 250 h under the condition that the newly prepared electrolyte and polished zinc sheets are refuelled periodically.