Impact of carbon N-doping and pyridinic-N content on the fuel cell performance and durability of carbon-supported Pt nanoparticle catalysts [original]

Elisabeth Hornberger, Thomas Merzdorf, Henrike Schmies, Jessica

Hübner, Malte Klingenhof, Ulrich Gernert, Matthias Kroschel, Björn

Anke, Martin Lerch, Johannes Schmidt, Arne Thomas, Raphaël

Chattot, Isaac Martens, Jakub Drnec, Peter Strasser

Impact of carbon N-doping and pyridinic-N content

on the fuel cell performance and durability of

carbon-supported Pt nanoparticle catalysts

Open Access via institutional repository of Technische Universität Berlin

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Journal article | Accepted version

(i. e. final author-created version that incorporates referee comments and is the version accepted for

publication; also known as: Author’s Accepted Manuscript (AAM), Final Draft, Postprint)

This version is available at

https://doi.org/10.14279/depositonce-16165

Citation details

Hornberger, Elisabeth; Merzdorf, Thomas; Schmies, Henrike; Hübner, Jessica; Klingenhof, Malte; Gernert,

Ulrich; Kroschel, Matthias; Anke, Björn; Lerch, Martin; Schmidt, Johannes; Thomas, Arne; Chattot, Raphaël;

Martens, Isaac; Drnec, Jakub & Strasser, Peter (2022). Impact of carbon N-doping and pyridinic-N content on

the fuel cell performance and durability of carbon-supported Pt nanoparticle catalysts. ACS Applied Materials

Interfaces, 14(16), 18420–18430. https://doi.org/10.1021/acsami.2c00762.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS

editing by the publisher. To access the final edited and published work see

https://doi.org/10.1021/acsami.2c00762.

This work is protected by copyright and/or related rights. You are free to use this work in any way permitted by

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Impact of Carbon N-Doping and Pyridinic-N

Content on the Fuel Cell Performance and

Durability of Carbon Supported Pt Nanoparticle

Catalysts

Elisabeth Hornbergera,‡,*, Thomas Merzdorfa,‡, Henrike Schmiesa, Jessica Hübnera, Malte

Klingenhofa, Ulrich Gernerta, Matthias Kroschela, Björn Ankea, Martin Lercha, Johannes

Schmidta, Arne Thomasa, Raphaël Chattotb, Isaac Martensb, Jakub Drnecb and Peter

Strassera,*.

a Department of Chemistry, Technische Universität Berlin, 10623 Berlin, Germany

b ESRF, The European Synchrotron, 71 Avenue des Martyrs, CS40220, 38043 Grenoble

Cedex 9, France

KEYWORDS. Fuel cell, oxygen reduction reaction, electrocatalyst, N-doped carbon,

operando HE-XRD, MEA

ABSTRACT.

Cathode catalyst layers of proton exchange membrane fuel cells (PEMFC) typically

consist of carbon-supported platinum catalysts with varying weight ratios of proton-conducting

ionomer. N-doping of carbon support materials is proposed to enhance the performance and

durability of the cathode layer under operating conditions in a PEMFC. However, a detailed

understanding of the contributing N-moieties is missing. Here, we report the successful

synthesis and fuel cell implementation of Pt electrocatalysts supported on N-doped carbons,

with a focus on the analysis of the N-induced effect on catalyst performance and durability. A

customized fluidized bed reduction reactor was used to synthesize highly monodisperse Pt

nanoparticles deposited on N-doped carbons (N-C), the catalytic oxygen reduction reaction

(ORR) activity and stability of which matched those of state-of-art PEMFC catalysts. Operando

high energy X-ray diffraction (HE-XRD) experiments were conducted using a 4th Generation

storage ring, the light of extreme brilliance and coherence allow to investigate the impact of N-

doping on the degradation behavior of the Pt/N-C catalysts. Tests in liquid electrolyte were

compared by tests in membrane electrode assemblies (MEAs) in single cell PEMFCs. Our

analysis refines earlier views on the subject of N-doped carbon catalyst supports: it provides

evidence that the heteroatom-doping and thus the incorporation of defects into the carbon

backbone does not mitigate the carbon corrosion during high potential cycling (1–1.5 V),

however can promote the cell performance under usual PEMFC operating conditions (0.6–

0.9 V).

INTRODUCTION

Green hydrogen generated from water electrolysis using renewable energy power sources is

a clean and sustainable option to meet the fossil fuel free energy demands. The conversion from

the chemical energy stored in the hydrogen bond into usable electricity is realized most directly

in electrochemical device applications such as the low temperature proton exchange membrane

fuel cell (PEMFC), which is being utilized or planned to be used in passenger cars, heavy-duty

vehicles or stationary devices. The wider commercialization of such PEMFC devices is limited

by cost, power density and durability issues when compared to competing technologies such as

traditional combustion engines or battery systems.1, 2 Efforts have been made to reduce the

amount of Pt in the catalyst material while maintaining the performance and improving the

stability of the cathode catalytic layer.3, 4 The cathode side of the PEMFC, where the oxygen

reduction reaction (ORR) takes place, is one of the key concerns due to its sluggish kinetics of

the ORR that cause large overpotential losses. The catalytic activity and the power density are

strongly depending on the realization of the triple phase boundary: Pt catalyst, oxygen gas and

ionomer electrolyte interface. The ionomer in low temperature PEMFC, such as the commonly

used Nafion polymer, not only provides protons, but also free sulfonate groups that can adsorb

on the active Pt surface and attenuate the performance in the low current density region.5-7 Non-

homogeneously distributed ionomer, however, limits the oxygen transport towards the Pt

surface and reduces the performance in the high current density region.8-11 One solution for

improved ionomer-catalyst interaction was proposed to be N-doped carbon support materials.4,

12 Surface -NHx groups can be introduced to the carbon support, e.g. via ammonolysis, which

develop Coulombic interactions with the -SO3- groups of the ionomer beneficially influencing

the ionomer distribution towards an increased homogeneity.13 Orfanidi et al. applied this

concept to a solid Vulcan XC 72R (moderate surface area (SA), higher degree of graphitization)

and Ott et al. used a mesoporous Ketjenblack EC-300J (internal pores, high SA) as carbon

material for the ammonolysis.4, 12 Both studies showed an improved H2/air performance in

membrane electrode assembly (MEA) testing that was directly attributed to an improved

ionomer distribution and thus an enhanced oxygen mass transport at high current densities. The

latter study demonstrated an impressive performance that was further credited to highly

accessible pores. The concept of accessible pores refers to porous carbon materials with

preferred pore openings of 4–7 nm that can host Pt particles in the internal pores protected from

the ionomer poisoning but are still accessible by protons and oxygen.14 Such catalysts with

accessible pores can facilitate both high ORR activity and reactant transport properties without

adversely affecting each other.

The durability of Pt/C catalysts is a key issue in fuel cell application.3, 15, 16 Degradation

phenomena in relation to the Pt particles of the catalyst have been identified as a) particle

growth accompanied with decreased electrochemical active surface area (ECSA) due to

coalescence/Ostwald ripening and aggregation/agglomeration processes, b) Pt dissolution and

c) particle migration/detachment.17 The carbon support material is prone to degradation

phenomena due to carbon corrosion via electrochemical oxidation in the presence of water

following equation 1 at potentials above +0.207 V18:

C + H2O → CO2+ 4H++ 4e−

However, the kinetics of the carbon oxidation reaction are poor under typical fuel cell

operating conditions. Several studies reported that minor carbon corrosion develops for

potentials above 0.6 V, and becomes severe at potentials above 1.4 V in situations of start-

up/shutdown and/or local fuel starvation at the anode.19-22 Reiser et al.22 rationalized that at

these conditions when the anode is partially exposed to both, hydrogen and oxygen, the

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