(581e) The Role of the Sacrificial Metal Center in Promoting Electrocatalytic Activity in MOF-Based Catalysts

Non-Precious Group Metal
Oxygen Reduction Electrocatalysts of Single-Atom Clusters from Atomically
Dispersed Precursors

Talha Al-Zoubi¹, Yu Zhou¹,
Wei Gao¹, Charles E. Schulz² and Hong Yang¹*

¹University of Illinois Urbana Champaign, Urbana, IL 61801
(USA)

²Knox College, Galesburg, IL 61401 (USA)

*hy66@illinois.edu

Introduction

Polymer-exchange
membrane fuel cells (PEMFCs) are devices used in the conversion of chemical
energy into electricity. Their environmentally-friendly emissions and high
efficiency make them model alternatives to combustion engines in transportation
applications.¹ However, a major hurdle in their commercialization is
the cost associated with the use of platinum as the catalyst to enhance the
sluggish kinetics of the cathodic oxygen reduction reaction. To address this,
research in the area of non-precious group metal (non-PGM) catalysts has grown.²

Non-PGM catalysts comprise some form of iron,
nitrogen and carbon synthesized through high-temperatures pyrolysis to generate
the necessary active centers to catalyze the reaction. However, these high
temperatures cause a high-level of heterogeneity within the catalyst which
leads to ambiguity around the nature of the active centers responsible for
catalyzing the reaction. To counter these problems, metal-organic frameworks
(MOFs), specifically ZIF-8, have been explored as structural precursors in the
synthesis of non-PGM catalysts.³ These MOFs rely on zinc as a
sacrificial metal center (SMC) which also serves as a dispersing agent to
scatter the active metal and generate pores during pyrolysis. However, due to zinc’s
relatively high boiling point, pyrolysis temperatures must exceed 850 °C to
generate an active catalyst. This tends to lead to a highly heterogeneous
catalyst with many different moieties from single-atomic iron sites to iron
nanoparticles.

In this
study, we propose a novel synthetic strategy in the synthesis of non-PGM
catalysts. By taking advantage of the highly tunable structure of MOF precursors
we can better develop an understanding of structure-property relationship
between catalysts synthesized under differing conditions and their performance
towards the electrocatalytic reduction of oxygen. The aim
is to develop a correlation between the structures formed and the activity
observed to further guide future research.

References

[1]
Debe, M. K., Electrocatalyst approaches and challenges for automotive fuel
cells. Nature 2012, 486, 43.

[2]
Osmieri, L.; Monteverde Videla,
A. H. A.; Specchia, S., Optimization of a Fe–N–C
electrocatalyst supported on mesoporous carbon functionalized with polypyrrole for oxygen reduction reaction under both
alkaline and acidic conditions. International Journal of Hydrogen Energy 2016,
41 (43), 19610-19628

[3]
Zhang H., Hwang S., Wang M., Feng Z., Karakalos S.,
Luo L., Qiao Z., Xie∥ X., Wang C., Su
D., Shao Y., and Wu G., J. Am. Chem. Soc. 2017, 139, 40, 14143-14149