Chemical and Biological Engineering ETDs

Publication Date

Fall 11-14-2018

Abstract

With the increasing demand on renewable energy, the fuel cell has attracted more and more interests because of its large power density and controllable size. However, the insufficiency of element abundance and unstable expensive price of conventional platinum-based electrocatalysts used in anode and cathode makes it essential to find their substitutes. As one of the most promising candidates to be used in cathode for oxygen reduction reaction (ORR), iron-nitrogen-carbon (Fe-N-C) catalysts have been widely investigated and get commercialized recently, but still lacks comprehensive understanding on the kinetic mechanism.

This dissertation has been divided into three parts with a discussion on rate-determining step (RDS) and selective active sites inhibition of Fe-N-C ORR electrocatalyst. This first part utilizes kinetic isotope effect (KIE) to figure out that RDS is the first charge transfer and has different proton dependency in the kinetic-controlled region and mass transport-controlled region. The atomically dispersed Fe-N-C catalyst can achieve KIE around 1 in the kinetic-controlled region, implying that Fe-N-C could compete with Pt-based catalysts by optimizing synthesis and structures, while KIE keeps around 2 but slightly decreases with potential dropping in the mass transport-controlled region, indicating that nitrogen active sites have strong proton dependence on kinetics.

In the second and third parts, nitrogen-contained tris(hydroxymethyl)aminomethane (Tris) and nitrogen-free 1-hydroxyethane 1,1-diphosphonic acid (HEDP) have been used as molecular probes to inhibit Fe-N-C catalysts. It is found that Tris has irreversible inhibition on iron active sites but reversible inhibition on nitrogen active sites, in addition that Tris could protonate pyridinic nitrogen active sites to enhance the 2-electron pathway, resulting in more reduction of oxygen to peroxide. It is also found that HEDP has no performance inhibition of iron active sites but obvious inhibition on pyrrolic/hydrogenated nitrogen active sites, leading to higher selectivity towards 4-electron pathway of oxygen reduction to water in ORR. These selective inhibitors reveal more research possibility on the mechanism study of Fe-N-C catalysts.

Keywords

fuel cell, oxygen reduction reaction, platinum-group-metal free, kinetic isotope effect, catalyst inhibition, catalyst active sites probing

Document Type

Dissertation

Language

English

Degree Name

Chemical Engineering

Level of Degree

Doctoral

Department Name

Chemical and Biological Engineering

First Committee Member (Chair)

Plamen Atanassov

Second Committee Member

Fernando Garzon

Third Committee Member

Iryna Zenyuk

Fourth Committee Member

Ivana Matanovic

Fifth Committee Member

Kateryna Artyushkova

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