Local Electric Field Effects on Water Dissociation in Bipolar Membranes Studied Using Core-Shell Catalysts

Prasad V. Sarma, Boris V. Kramar, Lihaokun Chen, Sayantan Sasmal, Nicholas P. Weingartz, Jiawei Huang, James B. Mitchell, Minkyoung Kwak, Lin X. Chen, Shannon W. Boettcher*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The local electric field strength is thought to affect the rate of water dissociation (WD) in bipolar membranes (BPMs) at the catalyst-nanoparticle surfaces. Here, we study core-shell nanoparticles, where the core is metallic, semiconducting, or insulating, to understand this effect. The nanoparticle cores were coated with a WD catalyst layer (TiO2 or HfO2) via atomic layer deposition (ALD), and the morphology was imaged with transmission electron microscopy. Irrespective of the core material, these core-shell catalysts displayed comparable WD overpotentials at optimal mass loading, despite the hypothesized differences in the electric field strength across the catalyst particle suggested by continuum electrostatic simulations. Substantial atomic interdiffusion between the core and shell was ruled out by X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and diffuse reflectance optical measurements. However, the optimal mass loading of catalyst was roughly 1 order of magnitude higher for the conductive and high dielectric core materials than for the low dielectric insulating cores. These findings are consistent with the hypothesis that electric field screening within the core material focuses the electric field drop between particles such that larger film thicknesses can be tolerated. Collectively, these data support the idea that it is the local electric field at the molecular level that controls proton-transfer rates and that the metal core/dielectric-shell constructs introduced here modulate that field. Further materials and synthetic design may enable optimization of the electric field strength across the proton-transfer trajectory at the material surface.

Original languageEnglish (US)
Pages (from-to)11863-11872
Number of pages10
JournalChemistry of Materials
Volume36
Issue number24
DOIs
StatePublished - Dec 24 2024

Funding

This work was initially supported by the U.S. Office of Naval Research, Office of Naval Research grant N00014-20-1-2517, and finished under the U.S. Department of Energy, Office of Science Energy Earthshot Initiative, as part of the Bipolar Membrane Science Foundations for the Energy Earthshot under contact #DE-SC0024713. PVS acknowledges the Fulbright-Nehru postdoctoral fellowship supported by the United States\u2013India Educational Foundation (USIEF). The work made use of shared instrumentation in the Center for Advanced Materials Characterization in Oregon (CAMCOR) and the Phil and Penny Knight Campus for Accelerating Scientific Impact. The authors also acknowledge Dr. Josh Razink for collecting the TEM images. Use of the Advanced Photon Source (Beamline 12-BM), an Office of Science user facility, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract DE-AC02-06CH11357.

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering
  • Materials Chemistry

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