Utilization of geopolymer cements as supercapacitors: influence of the hardeners on their properties

The main target of this work was to investigate the influence of the hardeners on the properties of the prepared supercapacitors named geopolymer cements. The supercapacitors were obtained by mixing an aluminosilicate source (metakaolin) and hardeners (sodium waterglass or phosphoric acid solution). The obtained supercapacitors were characterized by measuring the compressive strengths, infrared spectroscopy and scanning electron microscope. The electrochemical properties of the prepared supercapacitors were carried out by cyclic voltammetry and electrochemical impedance spectroscopy. The obtained results show that the compressive strengths of geopolymer cements from sodium waterglass and phosphoric acid solution are 43.50 and 66.12 MPa, respectively. The micrograph images indicate that both supercapacitors are compact, homogeneous and denser matrix. It appears that the supercapacitors from acidic medium have a lower internal resistance (45 kΩ), i.e. higher ionic conductivity, whereas, the one from alkaline medium indicates the higher value of the internal resistance (450 kΩ). It was typically found that the geopolymer cements from acidic medium have a higher electrical conductivity making it a potential electrode material for structural supercapacitor compared to the one obtained in alkaline medium.