Abstracts Book - IMRC 2018

• SD1-O003
OVERCOMING SITE HETEROGENEITY IN SEARCH OF METAL
NANOCATALYSTS FOR OXYGEN REDUCTION
Hongliang Xin 1
1 Virginia Polytechnic Institute and State University, Chemical Engineering, United States.
Low temperature polymer electrolyte membrane (PEM) fuel cells have great
potential as a clean and efficient electric energy generation system. An
important obstacle to the commercialization of this technology is the significant
voltage loss in converting chemical energy of fuels, e.g., H 2 , to electricity, also
known as overpotential, mainly due to the sluggish electrochemical kinetics of
the oxygen reduction reaction (ORR) at the cathode, O 2 + 4(H + + e - ) → 2H 2 O (E 0 :
+1.23 V). The state-of-the-art elemental metal electrocatalyst, consisting of 2~5
nm Platinum (Pt) nanoparticles, sacrifices ~300 mV for appreciable current
densities. Therefore, there has been a great deal of interest in identifying
electrocatalysts that exhibit improved catalytic performance, possibly with a
reduced amount of precious metals.
Among many types of materials, multimetallic Pt monolayer electrocatalysts
have emerged as a promising alternative. It has been demonstrated that the
adsorption energies of oxygen-containing species (e.g., O, OH, and OOH) at an
active site are predictive ORR reactivity descriptors. The stability of those
intermediates can be tuned by controlling the lattice strain (the bond distance
of an active site with neighboring atoms) and the metal ligand (the nature of
atoms surrounding a catalytic center). Since a perturbation of a metal site by
alloying affects concurrently the ligand and strain, it is not known a priori which
metals can be introduced in what geometric arrangements to attain desired
catalytic properties. To accelerate catalyst discovery, it is of pivotal importance
to develop an approach that efficiently maps catalytic activity onto geometrybased
descriptors while considering the geometric strain and metal ligand of an
active site. We demonstrate that there exist linear correlations between
orbitalwise coordination numbers and free formation energies of oxygen
species (e.g., OH and OOH) at Pt sites. Kinetic analysis along with herein
developed structure-activity relationships accurately predicts the activity trend
of pure Pt nanoparticles (~1-7 nm) toward oxygen reduction. Application of the
approach to an extensive search of Pt nanocatalysts leads to several Pt
monolayer core-shell nanostructures with enhanced oxygen reduction activity
and reduced cost.