The transport of oxygen in a porous perovskite solid oxide fuel cell cathode with a relatively high oxygen ion conductivity is modeled by taking into account exchange kinetics at the gas/electrode interface, bulk diffusion of oxygen vacancies, surface diffusion of adsorbed oxygen atoms, and electrochemical kinetics at the cathode/electrolyte interface. The electrochemical mechanism is assumed to be controlled by direct exchange of oxygen vacancies between the cathode and electrolyte phases. Simulated polarization curves typically exhibit Tafel-like behavior in the cathodic direction, which, however, is caused by concentration rather than activation polarization. In the anodic direction, a limiting current behavior is predicted, due to occupation of oxygen lattice sites on the cathode side of the interface. The effective polarization resistance either decreases or remains constant upon reduction of the oxygen partial pressures depending on prevailing kinetic and material parameters. Analytical expressions valid for the asymptotic case of a fast oxygen adsorption process at the gas/electrode interface are derived for the apparent Tafel slope, apparent exchange current density, anodic limiting current, and the effective polarization resistance. The theoretical results are consistent with experimental data in the literature for dense perovskite electrodes and for porous electrode materials with high oxygen nonstoichiometries. An overall assessment of the two parts of this study indicates that the catalytic properties of the perovskite surface, which enhances adsorption and surface diffusion of oxygen, is more significant than processes involving the bulk material, such as fast oxygen exchange with the bulk and vacancy diffusion, in determining cathode performance. IntroductianRecent development of solid oxide fuel cell (SOFC) cath-* Electrochemical Society Active Member.

The transport of oxygen in a porous perovskite solid oxide fuel cell cathode is modeled by use of the principles of porous electrode modeling, by taking into account exchange kinetics at the gas/electrode interface, bulk diffusion of oxygen vacancies, surface diffusion of adsorbed oxygen atoms, and electrochemical kinetics at the cathode/electrolyte interface. The mechanism for the latter is based on the assumption that intermediately adsorbed oxygen atoms are reduced at the cathode/electrolyte interface in favor of direct exchange of oxygen vacancies. The significance of concentration polarization is demonstrated even at very low overpotentials, especially if the adsorption process is slow. Under such conditions, the empirical correlation Rnormalpnormaleff∝pO2−normalm claimed to exist between the measured potential resistance and the partial pressure of oxygen cannot be justified on fundamental grounds. A limiting current is obtained at high cathodic overpotentials due to the depletion of intermediately adsorbed species at the cathode/electrolyte interface. The existence of a correlation inormallim∝pO2n is predicted, where the exponent n is determined by the kinetic and transport properties of the cathode for oxygen exchange and transport.

Here, we are the first to report a spinel type Mn3O4 as cathode material for Mg-ion battery (MIB) with graphite foil (Gif) as current collector. High coulombic efficiency and good cyclic stability of Mn3O4 are demonstrated, and the process is enhanced by using Mn3O4 nanoparticles with a sponge-like morphology. The powder exhibits a network of interconnected mesopores with well-dispersed nanoparticles (~10 nm) and large specific surface area (102 m 2 g -1 ). This structural configuration provides easy access for electrolyte penetration which markedly enhances the utilization of electroactive material, generates high ion flux across the electrode-electrolyte interface and provides more active sites for electrochemical reactions to occur. This study can possibly open the way for exploring other similar compounds with a spinel type structure for MIB.

Various genetic loci harboring oncogenes, tumor suppressor genes, and genes for calcium receptors have been implicated in the development of parathyroid tumors. We have carried out loss of heterozygosity (LOH) studies in chromosomes 1p, 1q, 3q, 6q, 11q, 13q, 15q, and X in a total of 89 benign parathyroid tumors. Of these, 28 were sporadic parathyroid adenomas from patients with no family history of the disease, 41 were secondary parathyroid tumors, 5 were from patients with a history of previous irradiation to the neck, 12 were from patients with a family history of hyperparathyroidism, and 3 were parathyroid tumors related to multiple endocrine neoplasia type 1 (MEN1). In addition, we determined the chromosomal localization of a second putative calcium-sensing receptor, CaS, for inclusion in the LOH studies. Based on analysis of somatic cell hybrids and fluorescent in situ hybridization to metaphase chromsomes, the gene for CaS was mapped to chromosomal region 2q21-q22. The following results were obtained from the LOH studies: (1) out of the 24 tumors that showed LOH, only 4 had more than one chromosomal region involved, (2) in the tumors from uremic patients, LOH of chromosome 3q was detected in a subset of the tumors, (3) LOH of the MEN1 region at 11q13 was the most common abnormality found in both MEN1-related and sporadic parathyroid tumours but was not a feature of the other forms of parathyroid tumors, (4) LOH in 1p and 6q was not as frequent as previously reported, and (5) tumor suppressor genes in 1q and X might have played a role, particularly on the X chromosome, in the case of familial parathyroid adenomas. We therefore conclude that the tumorigenesis of familial, sporadic, and uremic hyperparathyroidism involves different genetic triggers in a non-progressive pattern.