Structure Design And Performance Regulation Of Precious-Metal Based Electrocatalysts For Alkaline Hydrogen Oxidation Reaction

Anion exchange membrane fuel cells(AEMFCs)has stimulated an increasing interest due to the faster oxygen reduction reaction(ORR)kinetics and the employment of the non-precious metal catalyst.However,the sluggish kinetics of the anodic hydrogen oxidation reaction(HOR)in alkaline medium becomes a new“stumbling block”.Even for monometal Pt,the catalytic activity is still 2-3 orders of magnitude slower than that in acidic medium,and the mechanism is still unclear.Therefore,it is crucial to design efficient HOR catalyst and explore the reaction mechanism.Based on the above considerations,this paper intends to start with the catalyst design,gradually realizing the structure construction from ordered Pt-based intermetallics to low-Pt core-shell structure,finally achieving the non-Pt Ruthenium-based catalyst.Accomplishing the internal transformation from exploring the structure-activity relationship to analyzing the catalytic mechanism.The main contents are as follows,(1)A new class of ternary(Pt_0.9Pd_0.1)₃Fe intermetallic is developed,and the HOR performance of(Pt_0.9Pd_0.1)₃Fe/C is 2.7 times higher than that of Pt/C.In addition,it could work stably for 10,000 cycles accelerated stability test.The Pd substitution not only promote the formation of the L1₂ Pt-Fe ordered structure,but also regulate the electronic structure of the catalyst in the form of the interstitial alloying Pd H_x during the electrochemical cycle.Meanwhile,the surface Fe(OH)_x species enhance the oxophilicity of the catalyst.Therefore,the construction of an ordered structure with double active sites can improve both the catalytic activity and stability.(2)The Pd@Pt/C core-shell structure is constructed via a spontaneous displacement method.The hydrogen absorption into the lattice of Pd can be significantly regulated by the gradually increased heat-treatment temperature,and the activity of Pd@Pt/C will correspondingly improves with the increase of hydrogen absorption capacity into the lattice of Pd.Especially for Pd-500@Pt/C,the kinetic current density j_k@?=50 m V increases by?87.3 times compared with that of Pd/C-500,which further confirms the positive effect of surface Pt atoms on the release of the hydrogen atoms absorbed into the lattice of Pd.Therefore,increasing the capacity of the H adsorption into the lattice of Pd can significantly improve the catalytic activity of the Pd@Pt/C.The Ir Pd@Pt core-shell structure is constructed by imploying the strain effect of the Ir-core and the positive effect of Pd H_x on the improvement of the performance,aiming to further enhance the catalytic activity and the stability.The robust durability of the Ir₉Pd-core in alkaline medium greatly mitigate the corrosion of carbon support and detachment of the nanoparticle.Thus,the synthesized Ir₉Pd@Pt/C catalyst could work stably for 50,000 cycles at 0.5 V vertex potential and 20,000cycles at 1.0 V,both of which are far better than Pt/C.(3)The electronic structure and oxophilicity of the Pd₃M@Pt core-shell model is regulated by the introduction of the 3d transition metal,to verify the main descriptor affecting the activity of the alkaline HOR catalysts.The results confirm that the oxophilicity optimization by low-valence M(OH)_x species,rather than the hydrogen binding energy(HBE)optimization caused by strain engineering,influence the activity obviously.(4)A non-Pt catalyst of face centered cubic(fcc)structure Ru is further developed for alkaline HOR.With conventional hexagonal close packing(hcp)structure Ru as the counterpart,it indicates that the superior performance of fcc Ru origins from the higher proportion of the most active sites,and the stronger hydroxyl species(OH_ad)affinity leads to the higher activity on these sites.Thus,both hydrogen binding energy(HBE)and OH binding energy(OHBE)should be considered for subsequent alkaline HOR catalyst design.