Photothermal supercapacitors at −40 °C based on bifunctional TiN electrodes

Abstract Electrode materials are the key to electrochemical energy storage devices like supercapacitors. However, current materials can hardly meet the charge-storage capacity and/or operability requirements of practical scenarios in harsh low-temperature conditions. Here we report the advancement in photothermal-assisted supercapacitors operable at −40 °C using an electrochemically active and photothermal electrode material of commercially available TiN nanocrystals. Bifunctional TiN shows broad light absorption (>98%) in the whole solar spectrum and high photothermal conversion efficiency (62.5%). Even in an open atmospheric environment, the photochemical effect boosts the device with a considerable temperature rise from −36.6 °C to −10.8 °C under 1 solar illumination. Meanwhile, the as-fabricated device exhibits highly stable and reversible charge-storage capability. Its capacitance is enhanced by 38.0% at 5 mV s−1 at −40 °C, achieving 70.9% of the capacitance at 25 °C. The energy density is improved by 81.1% at 140 mW cm−2 at −40 °C, reaching 59.3% of the capacitance at 25 °C. The route for preparing TiN inks and fabricating screen-printed devices is simple and cheap, which is suitable for industrial mass production. The self-heating integration approach provides a promising strategy for designing new functionalized energy-storage devices with low temperature resistant features.