The carbonation behavior of calcium-containing sorbents, CaO and Ca(OH)₂, was investigated under pressurized CO₂ at nominal room temperature. The carbonation reaction was mechanically driven via reactive ball milling. The carbonation rate was determined by monitoring the CO₂ pressure inside the sealed milling jar. Two different versions of CaO were fabricated as starting materials. The addition of citric acid in CaO synthesis resulted in a significant increase in sorbent surface area, bringing up the conversion of CO₂ from 18% to 41% after 3 h of reactive milling. The hydroxide formation from these two oxides closed the surface area gap. Nevertheless, we found that hydroxides had a higher initial carbonation rate and greater final CO₂ uptake than their oxide counterparts. However, the formation of byproduct water limited the further carbonation of Ca(OH)₂. When we added a controlled amount of water to the CaO-containing milling jar, the highest carbonation rate and most extensive CO₂ uptake were attained due to the in situ formation of reactive Ca(OH)₂ nanoparticles. We saw CaCO₃ X-ray diffraction peaks only when Ca(OH)₂ was involved in this low-temperature carbonation, indicating that the grain growth of CaCO₃ is easier on the Ca(OH)₂ surface than on the CaO surface. We used the Friedman isoconversional method to calculate the effective activation energy of decarbonation for the high surface area CaO sorbent milled with water. The average effective activation energy was found to be about 72 kJ mol⁻¹, and its magnitude started to decrease significantly from 50% sorbent regeneration. The drastic change of the effective activation energy during decarbonation suggests that CaCO₃, formed at nominal room temperature by reactive milling under pressurized CO₂, should undergo a more drastic morphology change than the typical thermally carbonated CaCO₃.

Discovery of new materials plays a critical role in developing advanced high-temperature thermoelectric (TE) applications. Transition metal oxides (TMOs) are one of the attractive candidates for high-temperature TE applications due to their thermal and chemical stability. However, the trade-off relationship between thermopower (S) and electrical conductivity (σ) limits the maximum attainable power factor (PF), thereby hindering improvements in TE conversion efficiency. To overcome this trade-off relationship, the emerging approach of the redox-driven metal exsolution in TMOs shows promise in improving both S and σ. However, the effect of metal exsolution with different particle sizes and densities on S and σ is still largely unexplored. This study demonstrates an unusually large enhancement in PF through the exsolution of Ni nanoparticles in epitaxial La_0.7Ca_0.2Ni_0.25Ti_0.75O₃ (LCNTO) thin films. Metal exsolution leads to a decrease in the carrier concentration while increasing the carrier mobility due to energy filtering effects. In addition, the exsolved metal particles introduce the high-mobility electron carriers into the low-mobility LCNTO matrix. Consequently, the exsolution of metal particles results in a significant enhancement in S along with a substantial increase in σ, compared to the pristine film. Overall, the TE power factor of LCNTO is dramatically enhanced by up to 8 orders of magnitude owing to the presence of exsolved metal particles. This enhancement is attributed to the selective filtering of carriers caused by energy band bending at the metal-oxide interfaces and the high-mobility carriers from the exsolved Ni particles with a high Ni⁰ fraction. This study unequivocally demonstrates the impact of metal exsolution on oxide TE properties and provides a novel route to tailor the interconnected physical and chemical properties of oxides, leading to enhanced thermoelectric power output.

This study explores how junction type (Ohmic vs. Schottky) and oxide resistivity impact metal/oxide catalyst performance in urea oxidation, emphasizing the superior activity and stability of Ohmic junctions.