Oxygen pumping characteristics of YBaCo₄O_7+δ for solar thermochemical cycles

A new medium-temperature oxygen sorbent material, YBaCo₄O_7+δ, was prepared and investigated for its potential applications as an oxygen pumping material to facilitate solar thermochemical fuel production using a two-step metal oxide redox cycle. The oxygen uptake and release attributes of YBaCo₄O_7+δ were studied by both thermogravimetric analysis and a small-scale vacuum test. The results reveal that the oxygen uptake capacity and kinetics of YBaCo₄O_7+δ depends on both the uptake temperature and partial pressure of oxygen (p_O2), and can also be affected by the particle size. In the vacuum test, YBaCo₄O_7+δ could bring down the p_O2 of a vacuum chamber from 21 kPa to 0.5 kPa, which accounted for over 97% of the oxygen in the system. It was also found that the major issue for applying YBaCo₄O_7+δ as pumping material came from the slow kinetics at the low p_O2 level. The current study has proved that the particle size has a significant effect on the pumping behavior of YBaCo₄O_7+δ, especially for the uptake kinetics. Further research would be required for material development to make this application economically practical.