Preparation Of Carbon-supported Pt-Fe Catalyst And Its Electrochemical Performance Studies

Direct borohydride fuel cell（DBFC）is an energy conversion technology that directly converts the chemical energy stored in sodium borohydride and oxygen into electrical energy.This technology is gaining attention because of its high cleanliness,high theoretical open circuit voltage（1.64 V）,and high theoretical energy density（5.67 Wh/g）.However,DBFC still faces chanllenges such as high cost and poor stability.To promote the commercialization of DBFC,it is crucial to develop cathode catalyst materials that exhibit high catalytic activity,good stability and low cost.One promising approach is the use of single-atom catalysts（SAC_S）which have attracted widesperead attention due to their high atomic availability,unique catalytic activity and selectivity.However,SACs are prone to agglomeration during the preparation process due to their high surface activity.This results in three problems:low effective metal load,poor stability,and difficulty in industrial application.In order to solve these issues,Pt-Fe/C catalysts were prepared by an instantaneous carbon-thermal shock method from H₂Pt Cl₆·6H₂O,Fe Cl₃·6H₂O,anhydrous ethanol and carbon powder（BP2000）.By investigating the correlation between preparation technology,microstructure,and catalytic performance,the Pt-Fe/C SACs with high metal loading was prepared.The electrocatalytic performance and the power generation performance of the Pt-Fe/C SACs as DBFC cathode were investigated,and the preparation mechanism of Pt-Fe/C SACs was elucidated.Firstly,four kinds of Pt-Fe/C catalysts with varying metal contents（3 wt.%,6 wt.%,10 wt.%and 13 wt.%）on carbon cloth were prepared by instantaneous carbon-thermal shock method using the Keithley.As the metal content in the precursors decreased,the size of the metal particles in the Pt-Fe/C catalyst also decreased gradually.The metal particle sizes of the 13 wt.%Pt-Fe/C and 10 wt.%Pt-Fe/C were 1.50 nm and 6.00 nm,respectively.The 6 wt.%Pt-Fe/C consisted of single-atom cluster with a metal particle size of about 0.60 nm,while the 3 wt.%Pt-Fe/C was a single-atom catalyst.The electrochemical performance results showed that the mass activity and electrochemical active area of the Pt-Fe/C catalyst were inversely related to the size of metal particles.The 3 wt.%Pt-Fe/C SACs exhibited the highest mass activity(0.34 A mg^-1 Pt)and electrochemical active area（95.80 cm²）,outperforming the 10 wt.%Pt-Fe/C catalyst with a larger metal particle size(mass activity:0.15 A mg^-1 Pt,electrochemical active area:65.50 cm²).Furthermore,the onset potential,half-wave potential,and fuel cell performance were positively correlated with the metal content.The onset potential（0.87V）,half-wave potential（0.72 V）and fuel cell performance(86 m W cm^-2,60°C)of the 3 wt.%Pt-Fe/C SACs were lower than those of the 13 wt.%Pt-Fe/C nanocatalysts under the same test conditions(onset potential（0.95 V）,half-wave potential（0.83 V）and fuel cell performance(174 m W·cm^-2,60°C)).Secondly,the relationship between preparation temperature,metal mass fraction and product particls size of Pt-Fe/C catalysts（3 wt.%,6 wt.%,10 wt.%and 13 wt.%）was explored by adjusting the temperature of the instantaneous carbon-thermal reaction.Using Bayesian neural network calculations,the optimal synthesis conditions for high-load Pt-Fe/C single-atom catalysts was determined with a metal mass fraction of 15 wt.%at 260°C.The 15 wt.%Pt-Fe/C SACs were synthesized using an instantaneous carbon-thermal shock method,and their catalytic activity was compared with that of commercial Pt/C.The 15 wt.%Pt-Fe/C SACs exhibited superior ORR catalytic activity with high mass activity(0.31 A mg^-1 Pt),high electrochemical activity area（97.50 cm²）)and better electrochemical kinetic properties(low Tafel slope(73.66 m V·dec^-1))compared to commercial Pt/C.Morevoer,the half-wave potential difference after 10000 potential cycling was only 9 m V,indicating good catalytic stability.At 60°C,the maximum power density of DBFC using 15 wt.%Pt-Fe/C SACs was 214 m W·cm^-2,which was 1.37 times higher than that of commercial Pt/C(156.48m W·cm^-2),and 148%higher than that of 3 wt.%Pt-Fe/C SACs.Finally,the formation mechanism of Pt-Fe/C SACs was analyzed by first-principles calculation.This analysis indicated that the energy of Pt-Fe stable configuration（Hollow-Hollow,-672.075 e V）was significantly lower than that of Pt-Pt（Top-Top,-669.106 e V）,indicating a strong tendency for Pt atoms to bind with Fe atoms in the system.The addition of transition metal Fe effectively prevented Pt atoms aggregation and contributed to the dispersion of single Pt atoms.In summary,this study discusses the preparation of carbon-supported Pt-Fe single-atom catalyst with high metal concentration and the practical application as cathode catalyst for fuel cells.These findings provide an experimental basis for the development of fuel cell cathode catalyst with high efficiency and low cost in future.