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High frequency cycling of salt caverns is becoming common practice to meet the needs of energy markets and to foster underground energy storage. In the case of rapid cooling, tensile stresses and thermally-induced fractures can appear in the surrounding rock, with potential detrimental consequences to the integrity of the storage project. To further investigate the effects of rapid cycles on the integrity of rock salt, a thermo-mechanical test was performed in a salt mine. It consisted in cooling rapidly several times a salt surface of 10 m2 (ΔT=−20 °C in about 8 h). Extensive monitoring allowed tracking the thermo-mechanical response of the rock, including possible fracture creation and propagation. Although more research is needed, the test demonstrated that tensile fracturing due to rapid cooling is possible. Thermo-mechanical modeling allowed reproducing fairly well the location, orientation and timing of the first fracture; indeed, fractures should be avoided to ensure cavern integrity, and therefore knowledge about the critical zones where fractures could appear is sufficient at the design stage.

High frequency cycling of salt caverns is becoming common practice to meet the needs of energy markets and to foster underground energy storage. In the case of rapid cooling, tensile stresses and thermally-induced fractures can appear in the surrounding rock, with potential detrimental consequences to the integrity of the storage project. To further investigate the effects of rapid cycles on the integrity of rock salt, a thermo-mechanical test was performed in a salt mine. It consisted in cooling rapidly several times a salt surface of 10 m2 (ΔT=−20 °C in about 8 h). Extensive monitoring allowed tracking the thermo-mechanical response of the rock, including possible fracture creation and propagation. Although more research is needed, the test demonstrated that tensile fracturing due to rapid cooling is possible. Thermo-mechanical modeling allowed reproducing fairly well the location, orientation and timing of the first fracture; indeed, fractures should be avoided to ensure cavern integrity, and therefore knowledge about the critical zones where fractures could appear is sufficient at the design stage.

Summary: With regard to the hydrogen economy, setting the criteria for the durability evaluation of renewable energy‐powered proton exchange membrane water electrolysis (PEMWE) systems is an important milestone. In this study, accelerated stress test (AST) protocols that simulate the fluctuating power supply of renewable energy were explored. The average load was varied by changing the low voltage limit (LVL = 1.4, 1.5, 1.7, and 1.9 V) with fixation of a high voltage limit of 2.2 V. AST protocols can accurately reflect the real solar profile with various loads and high ramp rates. Protocols with the LVL = 1.4 V and LVL = 1.5 V demonstrated opposite trends even with minimal difference in LVL, resulting in positive and negative degradation slopes, respectively. The positive degradation slope (meaning performance decrease) for LVL 1.4 V is attributed to the reversal current, resulting in degradation of the cathode catalyst, which is characteristic of the fuel cell operating mode. On the contrary, a slight performance increase was observed for LVL 1.5 V, presumably caused by the thinning of the membrane and the creation of a rougher surface in the anode/membrane interface. Meanwhile, protocols with higher LVL (LVL 1.7 V and LVL 1.9 V) showed significant mass transport loss observed at voltages larger than 1.8 V. This may be attributed to severe delamination of the catalyst/membrane and/or diffuse layer/catalyst interface, presumably due to the changes in bubble nucleation and the resulting stress. The findings suggest a rational guideline for establishing a unified AST protocol applicable to renewable energy‐powered PEMWE systems, and subsequent material development strategies to minimize degradation processes. [ABSTRACT FROM AUTHOR]