Materials with high volumetric energy storage capacities are targeted for high-performance thermochemical energy storage systems. The reaction of transition metal salts with ammonia, forming reversibly the corresponding ammonia-coordination compounds, is still an under-investigated area for energy storage purposes, although, from a theoretical perspective this should be a good fit for application in medium-temperature storage solutions between 25 °C and 350 °C.

In the present study, the potential of reversible ammoniation of a series of transition metal chlorides and sulphates with gaseous ammonia for suitability as thermochemical energy storage system was investigated. Among the investigated metal chlorides and sulphates, candidates combining high energy storage densities and cycle stabilities were found. For metal chlorides, during the charging / discharging cycles in the presence of ammonia slow degradation and evaporation of the materials was observed. This issue was circumvented by reducing the operating temperature and cycling between different degrees of ammoniation, e.g. in the case of NiCl₂ by cycling between [Ni(NH₃)₂]Cl₂ and [Ni(NH₃)₆]Cl₂. In contrast, sulphates are perfectly stable under all investigated conditions. The combination of CuSO₄ and NH₃ provided the most promising result directing towards applicability, as the high energy storage density of 6.38 GJ m⁻³ is combined with full reversibility of the storage reaction and no material degradation over cycling. The results of this comparative systematic material evaluation encourage for a future consideration of the so far underrepresented transition metal ammoniates as versatile thermochemical energy storage materials.

具有高体积储能能力的材料是针对高性能热化学储能系统的。过渡金属盐与氨的反应可逆地形成相应的氨配位化合物，但在储能方面仍处于研究不足的领域，尽管从理论上讲，这应该非常适合中温储藏解决方案在25°C至350°C之间。

在本研究中，研究了一系列过渡金属氯化物和硫酸盐与气态氨的可逆氨化潜力，以适合用作热化学能量存储系统。在所研究的金属氯化物和硫酸盐中，发现了兼具高能量存储密度和循环稳定性的候选材料。对于金属氯化物，在存在氨的充电/放电循环中，观察到材料的缓慢降解和蒸发。通过降低操作温度和不同氨化程度之间的循环来解决此问题，例如在NiCl ₂的情况下，通过在[Ni（NH ₃）₂ ] Cl ₂和[Ni（NH ₃）₆ ] Cl ₂。相反，硫酸盐在所有研究条件下都非常稳定。CuSO ₄和NH ₃的组合提供了最有前途的应用前景，因为6.38 GJ m ^-3的高能量存储密度与存储反应的完全可逆性结合在一起，并且在循环过程中没有材料降解。这项比较系统的材料评估结果鼓励人们进一步考虑将目前代表性不足的过渡金属氨化物用作通用的热化学储能材料。