Mechanistic Insights on Permeation of Water over Iron Cations in Nanoporous Silicon Oxide Films for Selective H₂ and O₂ Evolution

Journal Article · 28 March 2023 · ACS Applied Materials and Interfaces

DOI: https://doi.org/10.1021/acsami.2c22865 · OSTI ID:2204954

Aydin, Fikret  ^[1]; Andrade, Marcos F. Calegari ^[1]; Stinson, Robert S. ^[2]; Zagalskaya, Alexandra ^[1]; Schwalbe-Koda, Daniel  ^[1]; Chen, Zejie ^[3]; Sharma, Shubham ^[1]; Maiti, Amitesh ^[1]; Esposito, Daniel V.  ^[2]; Ardo, Shane  ^[3]; Pham, Tuan Anh  ^[1]; Ogitsu, Tadashi ^[1]

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1. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
2. Columbia University, New York, NY (United States)
3. University of California, Irvine, CA (United States)

Electrocatalysts encapsulated by an ultrathin and semipermeable oxide layer offer a promising avenue for efficient, selective, and cost-effective production of hydrogen through photoelectrochemical water splitting. This architecture is especially attractive for Z-scheme water splitting, for which a nanoporous oxide film can be leveraged to mitigate undesired, yet kinetically facile, reactions involving redox shuttles, such as aqueous iron cations, by limiting transport of these species to catalytically active sites. In this work, molecular dynamics simulations were combined with electrochemical measurements to provide a mechanistic understanding of permeation of water and Fe(III)/Fe(II) redox shuttles through nanoporous SiO₂ films. It is shown that even for SiO₂ pores with a width as small as 0.8 nm, water does not experience any energy barrier for permeating into the pores due to a favorable interaction with hydrophilic silanol groups on the oxide surface. In contrast, permeation of Fe(III) and Fe(II) into microporous SiO₂ pores is limited due to high energy barriers, which stem from a combination of distortion and dehydration of the second and third ion solvation shells. Furthermore, our simulations and experimental results show that SiO₂ coatings can effectively mitigate undesired Fe(III)/Fe(II) redox reactions at underlying electrodes by attenuating permeation of iron cations, while allowing water to permeate and thus participate in water splitting reactions. In a broader context, our study demonstrates that selectivity of solvated cations can be manipulated by controlling the pore size and surface chemistry of oxide films.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Office of Sustainable Transportation. Hydrogen Fuel Cell Technologies Office (HFTO); National Science Foundation (NSF)
• Grant/Contract Number: AC52-07NA27344; EE0008838; DMR-2011967
• OSTI ID: 2204954
• Report Number(s): LLNL-JRNL-856107; 1085432
• Journal Information: ACS Applied Materials and Interfaces, Vol. 15, Issue 14; ISSN 1944-8244
• Publisher: American Chemical Society (ACS)Copyright Statement
• Country of Publication: United States
• Language: English