Structural and defect chemistry guidelines for Sr(V,Nb)O3-based SOFC anode materials.
Structural and defect chemistry guidelines were used for Nb-substituted SrVO3-δ materials, designed to meet SOFC anode requirements, with emphasis on redox tolerance, thermochemical compatibility with other SOFC materials, electrical conductivity and adjustable changes in oxygen stoichiometry for their prospective impact on electrocatalytic performance. SrV1-xNbxO3-δ (x = 0-0.30) ceramics were prepared by solid-state synthesis and sintered at 1773 K in a reducing atmosphere. XRD and SEM/EDS showed that under these conditions a single-phase cubic perovskite structure appears up to x ≈ 0.25. Electrical conductivity is metallic-like and nearly p(O2)-independent. Although substitution by niobium decreases the conductivity, which still exceeds 100 S cm(-1) for x ≤ 0.20 at temperatures below 1273 K, it also expands the stability domain of the cubic perovskite phase and suppresses partly high thermochemical expansion characteristic of parent SrVO3-δ. The upper p(O2) limit of phase stability was found to shift from ∼2 × 10(-15) atm for the undoped material to ∼2 × 10(-12) atm for x = 0.30, whereas the average thermal expansion coefficient at 773-1223 K decreased from 22.7 × 10(-6) to 13.3 × 10(-6) K(-1). SrV1-xNbxO3-δ perovskites undergo oxidative decomposition in air, which causes dimensional and microstructural changes. However, sluggish kinetics of oxidation under inert gas conditions results in nearly reversible behavior in relatively short-term redox cycles between reducing and inert atmospheres. Subtle structural changes and a close correlation with point defect chemistry clarify these sluggish changes and provide guidelines to retain the metastability.
Nb-substituted PrBaCo 2 O 5+δ as a Cathode for Solid Oxide Fuel cells: A Systematic Study of Structural, Electrical, and Electrochemical Properties
Abstract Double perovskite oxides, such as PrBaCo2O5+δ (PBC), are among the most promising cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) thanks to their high catalytic activity and mixed ionic and electronic conductivity. Here, we investigate the impact of Nb substitution on the crystal structure, catalytic activity, and electrical conductivity of PBC. Several studies have outlined that doping high valence cations, such as Nb5+, effectively stabilizes the perovskite structure, decreases the thermochemical expansion coefficient of the material, and can benefit the peak power density of the fuel cell. The as-prepared PrBaCo2−xNbxO5+δ with x = 0, 0.25, 0.50, 0.75, and 1.00 (PBCN) exhibit structural change from P4/mmm (x = 0) to I4/mmm (x = 1), whereas both phases are present for intermediate compositions. The analysis of electrochemical impedance spectroscopy (EIS) data shows that PBCN is characterized by relatively low polarization resistance. Between 300 and 800 °C, the electrical conductivity of PBCN, with x = 0.25, 0.50, lies above 100 S cm−1. If x = 0.75 or 1.00, the conductivity drops below 100 S cm−1. Our work suggests that the Nb-doped PBC exhibits excellent chemical compatibility with typical electrolyte material and good electrochemical performance, making it a promising cathode material for applications in IT-SOFCs.
Arc flash hazard assessment in the mining industry
When it comes to electrical safety in the workplace, arc flash has become the most prominent topic over the past decade. The Occupational Safety and Health Administration (OSHA, including state chapters) is the only government body that recognizes NFPA-70E, Standard for Electrical Safety in the Workplace. However, OSHA does not have jurisdiction in mining operations. Electrical safety for the metal and nonmetal surface mining industry is covered by the Code of Federal Regulations (CFR) Title 30, Part 56, Subpart K (Electricity). The Mine Safety and Health Administration (MSHA) is responsible for enforcing electrical safety in mining operations. CFR Title 30 does not reference personal protective equipment (PPE) to protect electrical workers against arc flash hazards. This paper provides maintenance and safety personnel in surface Metal/Nonmetal mining operations with a step by step guide to implementing an electrical safety program that meets the requirements of MSHA, CFR Title 30 and NFPA-70E.