Nagore Ortiz-Vitoriano

Rate-Dependent Nucleation and Growth of NaO2 in Na–O2 Batteries

Understanding the oxygen reduction reaction kinetics in the presence of Na ions and the formation mechanism of discharge product(s) is key to enhancing Na-O2 battery performance. Here we show NaO2 as the only discharge product from Na-O2 cells with carbon nanotubes in 1,2-dimethoxyethane from X-ray diffraction and Raman spectroscopy. Sodium peroxide dihydrate was not detected in the discharged electrode with up to 6000 ppm of H2O added to the electrolyte, but it was detected with ambient air exposure. In addition, we show that the sizes and distributions of NaO2 can be highly dependent on the discharge rate, and we discuss the formation mechanisms responsible for this rate dependence. Micron-sized (∼500 nm) and nanometer-scale (∼50 nm) cubes were found on the top and bottom of a carbon nanotube (CNT) carpet electrode and along CNT sidewalls at 10 mA/g, while only micron-scale cubes (∼2 μm) were found on the top and bottom of the CNT carpet at 1000 mA/g, respectively.

Sodium–Oxygen Battery: Steps Toward Reality

Rechargeable metal-oxygen batteries are receiving significant interest as a possible alternative to current state of the art lithium ion batteries due to their potential to provide higher gravimetric energies, giving significantly lighter or longer-lasting batteries. Recent advances suggest that the Na-O2 battery, in many ways analogous to Li-O2 yet based on the reversible formation of sodium superoxide (NaO2), has many advantages such as a low charge overpotential (∼100 mV) resulting in improved efficiency. In this Perspective, we discuss the current state of knowledge in Na-O2 battery technology, with an emphasis on the latest experimental studies, as well as theoretical models. We offer special focus on the principle outstanding challenges and issues and address the advantages/disadvantages of the technology when compared with Li-O2 batteries as well as other state-of-the-art battery technologies. We finish by detailing the direction required to make Na-O2 batteries both commercially and technologically viable.

A novel one step synthesized Co-free perovskite/brownmillerite nanocomposite for solid oxide fuel cells

Cobalt-free perovskite oxides Pr1−xCaxFe0.8Ni0.2O3 (PCFN) were investigated as novel cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). Ca and Ni substitution in the PrFeO3 material shows that a wide range of perovskites Pr1−xCaxFe0.8Ni0.2O3 (0 < x < 0.9) can be prepared by sintering in air at 600 °C. Perovskites with 0 < x < 0.4 exhibit orthorhombic single phases (Pnma space group), whereas 0.4 < x < 0.9 show a coexistence of the perovskite and the brownmillerite-type structure (Ca2Fe2O5). The structure of the polycrystalline powders was analyzed by X-ray powder diffraction, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The analysis on the synthesized powders shows the presence of clusters formed by 30–100 nm nanoparticles. High-Resolution TEM (HRTEM) studies were carried out to confirm the existence of Ca2Fe2O5. The dc four-probe measurement exhibits a total electrical conductivity, over 100 S cm−1 at T ≥ 600 °C when 0 < x < 0.6, pointing out that strontium can be substituted for calcium without modifying the electrochemical properties. The Pr0.4Ca0.6Fe0.8Ni0.2O3/Ca2Fe2O5 composite cathode presents the better performance in electrochemical measurements, showing an area specific resistance value of 0.09 ohm cm2 at 850 °C.

Effect of Electrolyte Contribution on the Electrochemical Behaviour of Pr0.8Sr0.2Fe0.8Ga0.2O3

Pr0.8Sr0.2Fe0.8Ga0.2O3 (PSFG) phase with perovskite-type structure was obtained by a glycine nitrate process. The product was characterized by X-ray diffraction and an orthorhombic structure (Pbnm) was found. The study of morphology indicates the existence of inhomogeneous particle size and agglomerates. The polarization resistance was studied using different electrolytes: Yttrium-stabilized zirconia (YSZ); Samarium-doped ceria (SDC); Praseodymium-doped ceria (CPO) and Gadolinium-doped ceria (CGO). No chemical reactivity between the PSFG and the electrolytes was observed. Electrochemical Impedance Spectroscopy measurements of PSFG/electrolyte/PSFG test cells were carried out. These electrochemical experiments were performed at equilibrium from 850oC to room temperature, under both zero dc current intensity and air. The obtained ASR values at 850oC for the cell tests were: 0.67 Ω·cm (YSZ); 0.55 Ω·cm (SDC); 0.26 Ω·cm (CPO) and 0.68 Ω·cm (CGO).

Designing Perovskite Oxides for Solid Oxide Fuel Cells

Perovskite-type oxides with the general formula ABO3 have been widely studied and are utilized in a large range of applications due to their tremendous versatility. In particular, the high stability of the perovskite structure compared to other crystal arrangements and its ability, given the correct selection of A and B cations, to maintain a large oxygen vacancy concentration makes it a good candidate as electrode in solid oxide fuel cell (SOFC) applications. Utilizing this novel structure allows the engineer‐ ing of advanced, effective electrolytes for such devices. This review details the development of current state-of-the-art perovskite-type oxides for solid oxide fuel cell (SOFC) applications.