DOE OSTI · 3030766
Structured electrolytes facilitate Grotthuss-type transport for enhanced proton-coupled electron transfer reactions
Abstract
Concentrated hydrogen-bonded electrolytes (CoHBEs) are structured, electrochemically stable, less-volatile alternatives to aqueous and dilute nonaqueous electrolytes, however, with high viscosities that limit molecular diffusion. This work provides an understanding of the proton conduction mechanism in CoHBEs based on mixtures of acids and azoles and establishes a link between the structurally dictated transport properties and the proton-coupled electron transfer (PCET) reaction rates that can be leveraged for enhancing electrochemical reactions. Diffusion and relaxation NMR studies suggest a breaking of the viscosity–conductivity tradeoff, where at high azole concentrations (>45 mol%), Grotthuss transport is more likely with lowered proton transfer energy barriers between the azole and the acid according to the machine learning (ML) accelerated ab initio path integral MD (AI-PIMD) simulations. Proton conduction pathways are found to be switchable between the hydrogen bonding networks of the acid and the azole, with imidazole chain forming structures better facilitating Grotthuss hopping. Supported by small-angle neutron scattering studies, the chains are found to have six member molecules on average with maximum of 3 to 4 imidazole/imidazoliums at 50 to 60 mol%. Despite their high viscosities, the measured PCET rates for quinones and phenazines measured in the protic CoHBEs present relatively high electron transfer rate constants (k 0 ~ 10 −4 cm/s), validated by rotating disc electrode and scanning electrochemical microscopy measurements. The results demonstrate that strategic tuning of hydrogen-bond donor–acceptor interactions enables the decoupling of proton transport and viscosity, thereby impacting PCET reactions.
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Muñoz, Miguel [Case Western Reserve Univ., Cleveland, OH (United States)], Chen, Michael S. [New York Univ. (NYU), NY (United States)], de Araujo Lima e Souza, Giselle [City Univ. of New York (CUNY), NY (United States)], Simunovic, Thomas [Univ. of Tennessee, Knoxville, TN (United States)], Khokhar, Vaishali [Case Western Reserve Univ., Cleveland, OH (United States)], Qian, Peisen [Univ. of Illinois at Urbana-Champaign, IL (United States)] (ORCID:0000000294421708), Wainright, Jesse [Case Western Reserve Univ., Cleveland, OH (United States)], Savinell, Robert [Case Western Reserve Univ., Cleveland, OH (United States)], Parnell, Andrew [Univ. of Sheffield (United Kingdom)] (ORCID:0000000186068644), Parnell, Steven [Science and Technology Facilities Council (STFC), Oxford (United Kingdom). Rutherford Appleton Lab., ISIS Neutron and Muon Source], Kilbride, Rachel C. [European Synchrotron Radiation Facility (ESRF), Grenoble (France). UK X-ray Materials Science Facility; Univ. of Warwick, Coventry (United Kingdom)], Zawodzinski, Thomas A. [Univ. of Tennessee, Knoxville, TN (United States)], Dadmun, Mark [Univ. of Tennessee, Knoxville, TN (United States)], Greenbaum, Steven G. [City Univ. of New York (CUNY), NY (United States)], Rodríguez-López, Joaquín [Univ. of Illinois at Urbana-Champaign, IL (United States)] (ORCID:0000000343464668), Tuckerman, Mark [New York Univ. (NYU), NY (United States)], Gurkan, Burcu [Case Western Reserve Univ., Cleveland, OH (United States)] (ORCID:0000000348863350). 2026-01-02. Structured electrolytes facilitate Grotthuss-type transport for enhanced proton-coupled electron transfer reactions. https://doi.org/10.1073/pnas.2530367122
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