Bypassing Formation of Oxide Intermediate via Chemical Vapor Deposition for the Synthesis of an Mn-N-C Catalyst with Improved ORR Activity

Thomas Stracensky, Li Jiao, Qiang Sun, Ershuai Liu, Fan Yang, Sichen Zhong, David A. Cullen, Deborah J. Myers, A. Jeremy Kropf, Qingying Jia, Sanjeev Mukerjee, Hui Xu

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

A significant barrier to the commercialization of proton exchange membrane fuel cells (PEMFCs) is the high cost of the platinum-based oxygen reduction reaction (ORR) cathode electrocatalysts. One viable solution is to replace platinum with a platinum-group metal (PGM) free catalyst with comparable activity and durability. However, PGM-free catalyst development is burdened by a lack of understanding of the active site formation mechanism during the requisite high-temperature synthesis step, thus making rational catalyst design challenging. Herein we demonstrate in-temperature X-ray absorption spectroscopy (XAS) to unravel the mechanism of site evolution during pyrolysis for a manganese-based catalyst. We show the transformation from an initial state of manganese oxides (MnOx) at room temperature, to the emergence of manganese-nitrogen (MnN4) site beginning at 750 °C, with its continued evolution up to the maximum temperature of 1000 °C. The competition between the MnOx and MnN4 is identified as the primary factor governing the formation of MnN4 sites during pyrolysis. This knowledge led us to use a chemical vapor deposition (CVD) method to produce MnN4 sites to bypass the evolution route involving the MnOx intermediates. The Mn-N-C catalyst synthesized via CVD shows improved ORR activity over the Mn-N-C synthesized via traditional synthesis by the pyrolysis of a mixture of Mn, N, and C precursors.

Original languageEnglish
Pages (from-to)14782-14791
Number of pages10
JournalACS Catalysis
Volume13
Issue number22
DOIs
StatePublished - Nov 17 2023

Funding

This work was financially supported by the US Department of Energy’s Office of EERE under award number DE-EE0008075. This work was authored in part by Argonne National Laboratory, a Department of Energy (DOE), Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357 by UChicago, Argonne, LLC. The in-temperature XAS experiments were performed at beamline 10-ID at the Advanced Photon Source (APS) at Argonne National Laboratory, which is operated by the Materials Research Collaborative Access Team (MRCAT). MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. The APS is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. The ex situ XAS data were collected at the 8-ID (ISS) beamline of the National Synchrotron Light Source II, a DOE Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory. AC-STEM was conducted at the Center for Nanophase Materials Sciences located at Oak Ridge National Laboratory, which is a DOE Office of Science User Facility.

Keywords

  • PGM-free catalysts
  • electrocatalysis
  • in situ X-ray absorption spectroscopy
  • oxygen reduction reaction
  • proton exchange membrane fuel cells

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