High temperature Mn2O3/Mn3O4 and Co3O4/CoO systems for thermo-chemical energy storage

A major action to reduce CO 2 emissions is replacing fossil fuels by renewable energy sources . Matching the energy supply and demand by the mostly intermittent renewable resources (wind, solar, wave) is hence a hot topic, and energy storage has become crucial. Thermo-chemical energy storage (TCES) has a higher energy density than sensible and latent heat storage , and allows energy to be stored in the reaction products for multiple reuse and even off-site application. Design parameters are the equilibrium temperature , the reaction heat and the reaction rate, as obtained from both thermodynamic and kinetic assessments. Equilibrium temperatures of the selected metal oxides , Mn 2 O 3 /Mn 3 O 4 and Co 3 O 4 /CoO are between 1115 K and 1179 K. The present research studies both redox reactions as examples. Commercial Mn 2 O 3 and Co 3 O 4 were previously investigated in detail, and suffer from incomplete reversibility . The present study investigates the use of self-made Mn 2 O 3 and Co 3 O 4 mesoporous particles, of micrometer or nanometer scale, respectively. The average particle size of self-made Mn 2 O 3 particles is < 5 μm, with a BET surface area of 239.7 m 2 /g, and T eq of 1177 K at ambient pressure . Self-made Co 3 O 4 was of nano size, with average size of about 100 nm, a BET surface area of 54.2 m 2 /g, and T eq of 1109 K at ambient pressure. The redox reactions of these ultrafine particles are fast and nearly fully reversible. The effect of adding inert Al 2 O 3 or Fe 2 O 3 was also studied, but proven to offer no kinetic benefit, while reducing the reaction heat due to their inert additive character. The findings were used in the design of a 10 kW TCES pilot plant that is currently being tested in a concentrated solar furnace .