Stabilization of Catalytically Active Surface Defects on Ga-doped La–Sr–Mn Perovskites for Improved Solar Thermochemical Generation of Hydrogen

Journal Article · 08 April 2024 · Topics in Catalysis

DOI: https://doi.org/10.1007/s11244-024-01940-w · OSTI ID:2522089

Fernandes Cauduro, Andre L. ^[1]; Gager, Elizabeth ^[2]; King, Keith A. ^[3]; McCord, Dylan ^[2]; McDaniel, Anthony H. ^[3]; Scheffe, Jonathan ^[2]; Nino, Juan Claudio ^[2]; El Gabaly, Farid  ^[3]

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1. Sandia National Laboratories (SNL-CA), Livermore, CA (United States); University of Florida
2. University of Florida, Gainesville, FL (United States)
3. Sandia National Laboratories (SNL-CA), Livermore, CA (United States)

Solar thermochemical hydrogen (STCH) production from water splitting typically requires performing redox cycles at temperatures above 1200 °C to reduce and re-oxidize the bulk of a reversible material. Bulk processes such as oxygen vacancy formation and oxygen diffusion energies dictate the viability of a material for STCH. The surface plays an important role in the formation and destruction of vacancies and interacts with gas phase water and surface adsorbed species. These surface processes can lead to surface reconfigurations and even the formation of surface phases with stoichiometry and oxygen content very different from the bulk composition. Understanding in-situ the surface chemical state and its evolution under water splitting is important to design nonstoichiometric oxides capable of longer-lasting STCH generation at lower temperatures. In this work, we describe the water splitting active defect sites in LSM ((La_0.65Sr_0.35)_0.95MnO_3–δ) and Ga-doped LSM ((La_0.6Sr_0.4)_0.95(Mn_0.8Ga_0.2)O_3–δ) perovskites during Operando thermochemical water splitting conditions using ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) experiments at 800 °C under steam. We show that sub-stoichiometric La⁺³ in the oxygen-vacancy rich surface at operating conditions can be used to correlate surface water splitting activity and the creation of surface hydroxide intermediates. The addition of Ga in LSM is shown to drastically stabilize the surface chemical composition by preventing Sr segregation and stabilizing catalytically active surface defects that promote the binding of adsorbed hydroxides. Here, we use Operando AP-XPS quantification of metastable surface hydroxide intermediates (La(OH)₃) to determine the amount of catalytically active surface sites in LSM (2.9%) and in LSMG (7.8–8.1%, depending on the bulk oxidation state).

• Research Organization: University of Florida, Gainesville, FL (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)
• Grant/Contract Number: EE0008840; NA0003525
• OSTI ID: 2522089
• Journal Information: Topics in Catalysis, Journal Name: Topics in Catalysis Journal Issue: 13-14 Vol. 67; ISSN 1022-5528
• Publisher: SpringerCopyright Statement
• Country of Publication: United States
• Language: English