Positive Effects of H₂O on the Hydrogen Oxidation Reaction on Sr₂Fe_1.5Mo_0.5O_6−δ-Based Perovskite Anodes for Solid Oxide Fuel Cells

Abstract

The steam is commonly supplied with H2 to the anodes of Ni-based solid oxide fuel cells (SOFCs). Humidified H2 is also widely used for emerging perovskite anodes of SOFCs, although the influences of H2O on the hydrogen oxidation reaction (HOR) on their surfaces have not been well understood yet. In this work, the effects of H2O on the HOR on Sr2Fe1.5Mo0.5O6−δ (SF1.5M), La0.5Sr1.5Fe1.5Mo0.5O6−δ (LSFM), and Pr0.5Sr1.5Fe1.5Mo0.5O6−δ (PSFM) were systematically investigated using the electrochemical impedance spectroscopy (EIS) and electrical conductivity relaxation (ECR) methods. The EIS spectra suggested the possible promotional effect of H2O on decreasing the polarization resistance of SF1.5M. The ECR results confirmed that the presence of H2O in H2 can significantly increase the oxygen exchange coefficients of SF1.5M, LSFM, and PSFM. To gain a mechanistic understanding of the role of H2O, the density functional theory-based calculations and thermodynamic modeling were performed to unravel the effect of H2O on the HOR on the SF1.5M (001) surfaces. Benefiting from the increment of the oxygen chemical potential and decrement of the free electron concentration upon increasing humidity, the plateau intermediate state in the HOR energy landscape, the step of H2O plus surface oxygen vacancy formation, is reduced on the SF1.5M (001) BO2 (B = Fe and Mo)-terminated surfaces, when decreasing the slab oxygen nonstoichiometry. Furthermore, by comparing the scenarios of the HOR on the dry and hydrated surfaces, the H2O plus surface oxygen vacancy formation energies are lower in the latter case. These two proposed factors, i.e., (i) change of electron chemical potential upon the change of near-surface δ and (ii) enhanced interaction of surface H species with the hydrated perovskite surfaces, contribute to the promoted HOR in the presence of H2O. This work provides important insights into the effects of H2O on the HOR for SOFCs.

Enhancing CO2 Catalytic Adsorption on an Fe Nanoparticle-Decorated LaSrFeO4 + δ Cathode for CO2 Electrolysis

“…The ECR method is a robust technology to evaluate the catalytic activity of electrode materials for CO 2 reduction and has received considerable interest in CO 2 or H 2 O electrolysis. ,,− The conversion of CO 2 to CO can be expressed by the following eq where Fe Fe ′ , Fe Fe x , V O .. , and O O x represent Fe 2+ , Fe 3+ , oxygen vacancies, and lattice oxygen in cathode oxides, respectively.…”

Deconvolution of Water-Splitting on the Triple-Conducting Ruddlesden–Popper-Phase Anode for Protonic Ceramic Electrolysis Cells

“…The obtained ECR curve was fitted with the MATLAB program. 46 ALD was conducted with a self-built ALD system. Sublimation methods was chosen with the barium bis(2,2,6,6-tetramethyl-3,5heptanedionate) hydrate (BaTMHD 2 ) precursor.…”

“…The total flow rate of the mixture gas was 300 sccm. The obtained ECR curve was fitted with the MATLAB program …”

Recent Advances in Electrocatalysts for Alkaline Hydrogen Oxidation Reaction

“…ii) Advanced tools for in situ analysis: H 2 O* plays an important role in the HOR process. [174] The adsorption of H 2 O* not only affects HBE but also regulates the exchange coefficients of other intermediates during the HOR process. [49,72] Thus, there is a challenge to understand and control the competition among different reaction mechanisms.…”