Effective And Carbon Monoxide Tolerant Hydrogen Oxidation Electrocatalyst In The Alkaline Media

Anion exchange membrane fuel cells（AEMFCs）not only have the advantages of high efficiency,safety and environmental protection,but also compared with proton exchange membrane fuel cells（PEMFCs）,because of its low corrosion environment,AEMFCs can use non-precious metal catalysts to replace platinum,reduce the cost of AEMFCs,thus promoting the development of hydrogen fuel cells.However,the anodic HOR reaction of AEMFCs faces two serious challenges.On the one hand,AEMFCs are quite sensitive to CO and are prone to CO poisoning.On the other hand,HOR kinetics of Pt/C catalysts in alkaline electrolytes is two orders of magnitude slower than in acidic electrolytes.As a result,the anode catalytic layer of AEMFCs needs to increase the Pt load to balance the weakened HOR kinetics under alkaline environment.These two challenges increase the cost of AEMFCs and seriously restrict the practical application of AEMFCs.Therefore,there is an urgent need to study high efficiency,stable,cheap and anti-carbon monoxide poisoning low platinum or even platinum-free HOR catalysts for AEMFCs.In this paper,Pt,Ru and Ni systems are selected to systematically study these two challenges,providing a simple and feasible strategy for the design of simple,efficient and CO resistant low platinum or even no platinum catalysts.The main research progress is as follows:（1）Improving the CO-tolerant ability of Pt-based electrocatalysts is crucial for fuel cells fed with industrial byproduct hydrogen.Herein,we present a novel core-shell structured Pt@NC/C catalyst consisting of ultrafine Pt nanoparticles（1.63 nm）as the core and ultrathin nitrogen-doped carbon layers（0.36 nm）as the shell.The catalyst exhibits excellent alkaline hydrogen oxidation reaction（HOR）activity with a mass activity of 187 A g_Pt^-1 and a specific activity of 0.20 m A cm_Pt^-2,which are 1.3 and 2.2-folds to the counterpart Pt/C,respectively.More remarkably,it shows good anti CO-poisoning ability.In presence of H₂ with 100 ppm CO,the HOR current degraded by18.22%on 10%Pt/C versus only 4.81%on 10%Pt@NC/C-400.The combined X-ray photo-electron spectrum（XPS）analysis,CO_ad stripping,CO oxidation and Zeta potential measurements imply that hydroxyl adsorption is enhanced on the NC covered Pt in 10%Pt@NC/C-400 possibly due to electron modulation induced by the strong metal and support interaction,which accelerates HOR kinetics and improvs anti-CO ability.（2）In order to further reduce the catalyst cost,this chapter chooses Ru system to carry out research.In this work,a unique carbon molecular sieve（CMS）coating strategy is demonstrated for Ru nanoclusters,featuring strongly size sieving ultramicropores,which acts as a highly effcient and CO-tolerant hydrogen electrocatalyst in alkaline conditions.The CMS coating thickness and pore size could be regulated by low temperature carbonization of polydopamine which was beforehand in-situ polymerized over the Ru nanoclusters.It is demonstrated that dominant sub-4（?）ultramicropores in Ru@NC/C-400 is beneficial for H₂/CO separation.Taking advantage of such a physical sieving barrier,along with the electronic modulation of Ru by the carbon coating layer,the CO adsorption over Ru surface is suppressed and meanwhile the hydrogen/oxygen species adsorption energy are optimized.The Ru@NC/C-400 catalyst exhibits exceptional HOR activity with a specific activity of 0.30m A cm_Ru^-2 and a mass activity of 0.25 A mg_Ru^-1,which are 3-folds and 1.7-folds of the counterpart Pt/C catalyst,respectively.More importantly,the catalyst is highly tolerant to CO.In the presence of 100 ppm CO,the HOR current with the Ru@NC/C-400 catalyst lowers by just 9.5%,but the Pt/C catalyst drops by 33.3%in the chronoamperometry test.（3）In this chapter,we choose cheap nickel-based nanomaterials as the research system,aiming at the problem of poor electrochemical stability of nickel-based alkaline hydrooxidation catalysts.Herein,we report a nickel-gold nanodimer(Ni₁₀₀Au₁/C-P)synthesized via a galvanic replacement reaction,which via an electrochemical activation mostly transforms into highly dilute gold-in-nickel host nanoalloys(Ni₁₀₀Au₁/C-EA).The Ni₁₀₀Au₁/C-EA exhibits both a remarkable specific HOR activity of 47.3μA cm_Ni^-2,20%higher than Ni₁₀₀Au₁/C-P and 34%higher than Ni/C,and exceptional durability for 6000 cycles.Membrane electrode assembly tests further identify the practical application of Ni₁₀₀Au₁/C-EA,which delivers a power density of 192 m W cm^-2 and good durability.Theoretical studies suggest that the formation of Ni Au alloys is thermodynamically favored with the help of adsorbed hydrogen intermediates.The in situ-formed Ni Au nanoalloy,with lower d band center than Ni,is endowed with improved anti-oxidation ability and appropriate intermediate binding energy,leading to a robust and excellent HOR performance.