Tuning the Electrocatalytic Oxygen Reduction Reaction Activity of PtCo Nanocrystals by Cobalt Concentration and Phase Transformation Methods

2018 Spring Symposium

Jen­nifer D. Lee, Ph.D. Can­di­date, Christo­pher B. Mur­ray Group, Depart­ment of Chem­istry, Uni­ver­si­ty of Penn­syl­va­nia

Abstract — The pro­ton exchange mem­brane fuel cell (PEMFC) is a crit­i­cal tech­nol­o­gy to enhance the clean, sus­tain­able pro­duc­tion and usage of ener­gy, but prac­ti­cal appli­ca­tion remains chal­leng­ing because of the high cost and low dura­bil­i­ty of the cath­ode cat­a­lysts that per­form oxy­gen reduc­tion reac­tion (ORR). Efforts have been placed on the study of intro­duc­ing first-row tran­si­tion met­als in Pt-M alloys to reduce the Pt load­ing and mod­u­late geo­met­ric, struc­tur­al and elec­tron­ic effects. To fur­ther improve the ORR reac­tion rate and cat­a­lysts sta­bil­i­ty, alloys that adopt an inter­metal­lic struc­ture, espe­cial­ly the tetrag­o­nal L10-PtM phase, has been one of the most promis­ing mate­ri­als. In this con­tri­bu­tion, monodis­perse PtCo nanocrys­tals (NCs) with well-defined size and Co com­po­si­tion are syn­the­sized via solvother­mal meth­ods. The trans­for­ma­tion from face-cen­tered cubic (fcc) to ordered face-cen­tered tetrag­o­nal (fct) struc­ture was achieved via ther­mal anneal­ing. Depend­ing on the selec­tion of trans­for­ma­tion meth­ods, dif­fer­ent degrees of order­ing were intro­duced and fur­ther cor­re­lat­ed with their ORR per­for­mance. A detailed study of the anneal­ing tem­per­a­ture and com­po­si­tion depen­dent degree of order­ing is also high­light­ed. This work pro­vides the insight of dis­cov­er­ing the opti­mal spa­tial dis­tri­b­u­tions of the ele­ments at the atom­ic lev­el to achieve enhanced ORR activ­i­ty and sta­bil­i­ty.