Conformal Electrocatalytic Surface Nanoionics for Accelerating High-Temperature Electrochemical Reactions in Solid Oxide Fuel Cells.

Additive implantation of electrocatalysts onto the internal surface of porous cathodes holds great promise to accelerate the electrochemical reactions within solid oxide fuel cells (SOFCs). Here we utilize atomic layer deposition (ALD) to apply dual catalysts with (Mn0.8Co0.2)3O4 and a minute amount of Pt on the cathode consisting of lanthanum strontium manganite (LSM) and yttria-stabilized zirconia (YSZ). Coating this material with optimum ALD layer thickness resulted in a 53% reduction of polarization resistance and a 350% SOFC peak power density enhancement at 750 °C. During the electrochemical operations, the dual catalysts interact synergistically and evolve into superjacent conformal electrocatalytic (Mn0.8Co0.2)3O4 nanoionics with high-density grain boundaries and subjacent discrete nano Pt particles evenly distributed on both the LSM and YSZ. The configuration consequently extends the active electrochemical reaction sites to the entire internal surface of the cathode. For the first time in the field of SOFCs, the present work demonstrates the formation of the electrocatalytic surface nanoionics and its resultant accelerated mass and charge transfer to dramatically boost the cell performance.

Grain Boundary Phase Segregation for Dramatic Improvement of the Thermoelectric Performance of Oxide Ceramics.

This work presents a novel approach of dramatically increasing the energy conversion efficiency of thermoelectric CaMnO3-δ ceramics through the combination of lattice dopants substitution and secondary phase segregation at the grain boundaries. The oxide ceramic samples are with the nominal composition of Ca1- xBi xMnCu yO3-δ ( x = 0, 0.02, 0.03; y = 0.02, 0.04). When Cu is introduced into the Ca1- xBi xMnCu yO3-δ samples, the grain growth from Bi-doped CaMnO3-δ grains is accompanied by the limited solubility of Cu ions in the grain interior, whereas Cu mainly formed a CuO secondary phase at the grain boundaries. Cu nonstoichiometry addition subsequently resulted in the increase of the Seebeck coefficient and decrease of electrical resistivity simultaneously. The sample with designed chemistry of Ca2.97Bi0.03MnCu0.04O3-δ exhibits the power factor of 2.4 mW m-1 K-2 at 337 K and figure of merit ZT of 0.67 at 773 K. This ZT of 0.67 is by far the highest ZT reported for various perovskites oxide ceramics. Such enhancements in electrical power factor and the overall ZT are attributed to the synergistic effect of decreasing the carrier concentration to increase the Seebeck coefficient and simultaneously increasing the carrier mobility through the existence of CuO phase at the grain boundaries.