Thermochemical energy storage characteristics of hydrophilically modified activated carbon-SrBr2 composite materials

Abstract To enhance the thermochemical heat storage and release performance of SrBr 2 during its hydration reaction, activated carbon was employed as a matrix and subjected to hydrophilic modification using two organic acids, citric acid (CA) and phytic acid (PA), at gradient concentrations. The modified activated carbon-based SrBr 2 composite heat storage materials were successfully prepared via a solution impregnation method. The surface chemical properties and microstructural characteristics of the materials were systematically analyzed by scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. Characterization results indicated that both CA and PA modification increased the content of hydrophilic functional groups, such as carboxyl and hydroxyl groups, on the AC surface, while maintaining the integrity of its porous framework. The enhanced surface hydrophilicity led to a higher SrBr 2 loading capacity. Dynamic water vapor adsorption tests revealed that the modified composites exhibited markedly improved moisture uptake performance, with the maximum adsorption rates of CA- and PA-modified samples reaching 1.60 and 1.23 times that of the unmodified sample, respectively. Thermogravimetric-differential scanning calorimetry analysis further confirmed that the heat storage density of the modified composites was significantly increased, with CA-and PA-modified samples showing 18% and 15% improvements over the unmodified sample, respectively.