High-Temperature Energy Storage: Kinetic Investigations of the CuO/Cu₂O Reaction Cycle

Abstract

Thermochemical energy storage (TCES) is considered a possibility to enhance the energy utilization efficiency of various processes. One promising field is the application of thermochemical redox systems in combination with concentrated solar power (CSP). There, reactions of metal oxides are in the focus of research, because they allow for an increase in the process temperature. The reaction system CuO/Cu2O has been reported as a suitable candidate for TCES. For proper development and modeling of combined CSP–TCES processes, reliable kinetic data are necessary. This work studies the reduction of CuO and the oxidation of Cu2O under isothermal and isokinetic conditions. The reactions are analyzed using a simultaneous thermal analysis (STA) and a lab-scale fixed-bed reactor. The reaction behavior shows significant differences between both analyses. To develop kinetic models, the non-parametric kinetic (NPK) approach is used. This model-free approach is expanded by the Arrhenius correlation to increase the applicable temperature range of the models. The resulting models are evaluated and compared. Furthermore, the cycle stability of the system over 20 cycles is assessed for a small sample mass in the STA and a large sample mass in the fixed-bed reactor.

First-principles study of a new structure and oxidation mechanism of Pt3Zr

“…are important parts of solid oxide fuel cells. [32][33][34][35] To estimate the catalytic activity of Pt 3 Zr, we compare the oxygen doped formation energy between Pt 3 Zr and many metals. As shown in Fig.…”

Impact of Partial Pressure, Conversion, and Temperature on the Oxidation Reaction Kinetics of Cu2O to CuO in Thermochemical Energy Storage

“…Unusual Arrhenius trends at high temperatures were observed and reported by Kyaw et al [64] in their study "Carbonation of CaO for High Temperature Thermal Energy Storage" and by Schaube et al [65] for the CaO/Ca(OH) 2 system at high H 2 O partial pressures. Deutsch et al found a negative activation energy for the CuO/Cu 2 O system in STA experiments [33].…”

“…Implementation of the those kinetics investigations in thermochemical energy storage would not be possible due to the impact of support materials on the kinetics of Cu2O/CuO, which should be studied separately. In thermochemical energy storage, the kinetics of the reduction of CuO to Cu2O was reported by Deutsch et al [33] in simultaneous thermal analysis (STA) and in a fixed-bed reactor. They indicated cycle stability of Cu2O/CuO system up to 20 cycles at 950 °C and at an oxygen partial pressure of 0.21 bar for the oxidation reactions, reduction was carried out in a nitrogen atmosphere.…”

“…The sample was spun with back loading zero background sample holders and 2θ = 5-90 • at 25 • C. The diffractograms were evaluated with the PANalytical program suite HighScorePlus, version 3.0d. A Background correction and a Kα 2 strip were performed" [33].…”

“…The metal redox oxides Co 3 O 4 /CoO and Cu 2 O/CuO have been investigated in recent research, because they possess the highest energy density, 844 and 810 kJ/kg, respectively. However, Cu 2 O/CuO have several unresolved challenges regarding application in TCES for this redox system, such as grain growth after thermal cycling, the close reduction temperature of CuO to the Cu 2 O melting point of 1235 • C, and a decrease in the conversion rate with O 2 after the very low number of redox cycles reported by various authors [22,23,[31][32][33]. However, the economic aspect and non-toxicity compared to Co 3 O 4 /CoO make the redox system Cu 2 O/CuO interesting for utilization as a thermochemical energy storage material [6,33].…”