Influence of electrolyte ions on rechargeable supercapacitor for high value-added conversion of low-grade waste heat

Low-grade waste heat, which exhibits widely in industrial production and daily life, shows great promise for smart electronics and sensors, but we always ignore this energy. Recently, developing thermoelectric conversion devices becomes a popular subject. Unfortunately, the relatively low Seebeck coefficient of current devices limits their further applications. Thus, it should give priority to matching suitable electrolyte and constructing high-rate system. Here, we employ a series of common neutral electrolytes to optimize the energy storage behavior towards high capacitance and rate capability. As a result, the commercial carbon electrode displays a high specific capacitance of 220.8 F g(-1) at a current density of 1 A g(-1) and a good retention of 61.2% even at a high rate of 20 A g(-1) in 1.0 mol L-1 potassium nitrate electrolyte. Meanwhile, the assembled symmetric supercapacitor can output the maximum energy/power density of 13.1 Wh kg 1/15.7 kW kg(-1) based on the active material, together with an excellent durability (similar to 109% capacitance retention over 10,000 cycles at 5 A g(-1). Besides, a thermally chargeable supercapacitor exhibits a satisfying output potential of 1.21 mV K-1 under optimized cases. Significantly, the potential value is highly determined by temperature gradient.