Investigation on YSZ- and SiO2-Doped Mn-Fe Oxide Granules Based on Drop Technique for Thermochemical Energy Storage

TL;DR

This study explores how doping Mn-Fe oxide granules with YSZ and SiO2 improves their performance for thermal energy storage, focusing on reoxidation rates and mechanical stability.

Contribution

The paper introduces a scalable drop technique to fabricate Mn-Fe oxide granules doped with YSZ and SiO2 for enhanced thermochemical energy storage.

Findings

YSZ and SiO2 doping improved reoxidation rates but reduced reduction rates and energy storage density.

Doping enhanced stable reaction rates during cyclic tests, with Si-doped granules showing better long-term performance.

1 wt% Si and 2 wt% Si doping resulted in the best synthetic performance due to milder sintering effects.

Abstract

The Mn-Fe oxide material possesses the advantages of abundant availability, low cost, and non-toxicity as an energy storage material, particularly addressing the limitation of sluggish reoxidation kinetics observed in pure manganese oxide. However, scaling up the thermal energy storage (TCES) system poses challenges to the stability of the reactivities and mechanical strength of materials over long-term cycles, necessitating their resolution. In this study, Mn-Fe granules were fabricated with a diameter of approximately 2 mm using the feasible and scalable drop technique, and the effects of Y2O3-stabilized ZrO2 (YSZ) and SiO2 doping, at various doping ratios ranging from 1–20 wt%, were investigated on both the anti-sintering behavior and mechanical strength. In a thermal gravimetric analyzer, the redox reaction tests showed that both the dopants led to an enhancement in the reoxidation rates when the doping ratios were in an appropriate range, while they also brought about a decrease in the reduction rate and energy storage density. In a packed-bed reactor, the results of five consecutive redox tests showed a similar pattern to that in a thermal gravimetric analyzer. Additionally, the doping led to the stable reduction/oxidation reaction rates during the cyclic tests. In the subsequent 120 cyclic tests, the Si-doped granules exhibited volume expansion with a decreased crushing strength, whereas the YSZ-doped granules experienced drastic shrinkage with an increase in the crushing strength. The 1 wt% Si and 2 wt% Si presented the best synthetic performance, which resulted from the milder sintering effects during the long-term cyclic tests.

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