Effect Of Tungsten Element On Electrocatalytic Performance Of Platinum-based Alloys

Fuel cell has been considered as the ultimate solution to terminate the environmental concern on automobile emission.Enhancing the activity and stability of the catalyst is a major challenge in developing high performance membrane electrode assemblies for fuel cells.The community has reached a consensus that Pt-based alloy electrocatalysts are the next-generation cathode active materials for MEA.However,the activity and stability of the Pt alloys remains as the biggest obstacle to their practical application,which may mainly stem from the dissolution of transition metal atoms induced by the oxidation at high electrochemical potentials.Possible strategies,such as surface engineering,constructing core–shell catalysts,doping/alloying with other highly stable noble metal elements,or designing new nanoparticle–support composite have been considered as effective approaches to address this issue.In this paper,the high-melting-point metal?such as tungsten?is alloyed with Pt-based alloy nanocrystals to explore the changes of electrocatalytic properties.The specific research contents are as follows:1)Pt Cu Ni NPs with different alloy compositions and sizes are obtained by controlling the ratio of metal precursors in the synthesis process.The oxidized acid treatment can effectively remove organic covering molecules and etch surface atoms to form high-performance porous Pt Cu Ni ternary alloy catalyst.On the basis of this,the catalytic activity and stability can be further changed by surface doping of W atoms towards oxygen reduction reaction?ORR?.After doping W,MA and SA of 111-Pt Cu Ni-W/C are enhanced by 17.7 and 11.2 times compared with commercial Pt/C,respectively.After 20,000 CV cycles of ADT in the oxygen-saturated electrolyte,the MA and SA only decrease by 34.1%and 37.7%,which is significantly better than the undoped 111-Pt Cu Ni/C catalyst,indicating that the W doping can simultaneously enhance the catalytic activity and stability of the Pt Cu Ni/C catalyst.It is found that during the surface W doping process,the Ni atoms on the surface are further etched due to the strong coordination of the carbonyl group and the presence of some high-valent W ions,which not only enhances the catalytic activity of a single site,but also induces the recombination of Pt and Cu atoms on a part of the surface,increasing the specific surface area and playing a more significant role in improving the mass specific activity.2).Pt₂Cu W_0.25 NPs with uniform size and similar morphology are synthesized in one step by strong reduction of W?CO?₆.Its MA and SA reach 0.75 A/mg _Pt and 1.43 m A/cm²_Pt,respectively.After 30k potential cycling,the MA and SA values of Pt₂Cu W_0.25/C only decrease by 4.1%and 10.5%compared with the initial values,exhibiting high ORR electrocatalytic stability.It is found by DFT calculation that the effect of the W atom is similar to that of the"glue",which can strongly maintain the atom and enhance the metals bonding,thereby improving the stability of the alloy.3).Through the exploration of synthetic solvents,structure directing agents and reducing agents,Necklace ultrafine Pt_2.2Ni W_0.11 NWs with ultra-high MOR properties are obtained.Its MA and SA reach 1101.95 m A/mg _Pt and 2.21 m A/cm²_Pt,which are 7.5times and 10.1 times than JM Pt/C.Pt_2.2Ni W_0.11 NWs/C also has better electrochemical stability.It is found that there are a large number of high-index crystal planes on the NWs surface,and there are a large number of defects inside the structure by HRTEM,which will change the adsorption energy of the surface active sites to methanol molecules,promote electron transfer,and rapidly oxidize methanol molecules into carbon dioxide.Resulting in the high MOR activity for Pt_2.2Ni W_0.11 NWs/C.