Title: In Situ X-Ray Absorption Spectroscopy Disentangles the Roles of Copper and Silver in a Bimetallic Catalyst for the Oxygen Reduction Reaction

Abstract

Silver-based bimetallic catalysts for the oxygen reduction reaction (ORR) are promising for a wide variety of renewable energy technologies, including alkaline fuel cells and metal-air batteries. The activity of bimetallic catalysts can sometimes surpass that of either constituent element, but the origin of the enhanced performance is still debated. At a given active site, two complementary mechanisms are proposed to explain the performance improvements: the binding energy of intermediate adsorbates can be tuned by direct electronic contributions from the alloying element or by changes in the bond lengths from lattice distortion. To distinguish between these effects and elucidate the respective roles of each element in the bimetallic, it is critical to study catalysts at the molecular scale under reaction conditions. In this work, we use in situ X-ray absorption spectroscopy (XAS) alongside density functional theory (DFT) to show that direct electronic rather than geometric effects are the primary cause of improved ORR activity in a bimetallic CuAg catalyst. Our results indicate that the local bonding as well as the electronic structure of Ag are virtually unchanged by the presence of Cu, whereas the electronic states of Cu in CuAg are significantly altered. DFT calculations support these experimental findings. We showmore » strong evidence that the activity of the bimetallic CuAg catalyst exceeds the sum of the activities of Cu and Ag, not by incremental improvement of the active Ag sites, but by creating highly active Cu-centered catalytic sites. The insight that the main role of Ag in bimetallic catalysts may be to promote its fellow element through local electronic interactions provides a new design principle for engineering the next generation of bimetallic catalysts for the ORR and beyond.« less

Authors:

Gibbons, Brenna M. ^[1]; Wette, Melissa  ^[1];

• Search DOE PAGES for author "Wette, Melissa"
• Search DOE PAGES for ORCID "0000-0002-7127-1751"

Stevens, Michaela Burke  ^[1];

• Search DOE PAGES for author "Stevens, Michaela Burke"
• Search DOE PAGES for ORCID "0000-0003-3584-0600"

Davis, Ryan C. ^[2]; Siahrostami, Samira  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-1192-4634"

Kreider, Melissa  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-1750-6860"

Mehta, Apurva  ^[2];

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• Search DOE PAGES for ORCID "0000-0003-0870-6932"

Higgins, Drew C.  ^[4];

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• Search DOE PAGES for ORCID "0000-0002-0585-2670"

Clemens, Bruce M. ^[1]; Jaramillo, Thomas F.  ^[1]

• Search DOE PAGES for author "Jaramillo, Thomas F."
• Search DOE PAGES for ORCID "0000-0001-9900-0622"

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+ Show Author Affiliations

1. Stanford Univ., CA (United States)
2. SLAC National Accelerator Lab., Menlo Park, CA (United States)
3. Department of Chemistry, University of Calgary, Calgary, Alberta T2N 1N4, Canada
4. Stanford Univ., CA (United States); McMaster Univ., Hamilton, ON (Canada)

Publication Date:

Thu Feb 27 00:00:00 EST 2020

Research Org.:

SLAC National Accelerator Lab., Menlo Park, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1608321

Grant/Contract Number:  

AC02-76SF00515; ECCS-1542152

Resource Type:

Accepted Manuscript

Journal Name:

Chemistry of Materials

Additional Journal Information:

Journal Volume: 32; Journal Issue: 5; Journal ID: ISSN 0897-4756

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; X-ray absorption near edge spectroscopy; Redox reactions; Electrodes; Catalysts; Bimetals