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

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 degrees 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 degrees C to -10.8 degrees 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 degrees C, achieving 70.9% of the capacitance at 25 degrees C. The energy density is improved by 81.1% at 140 mW cm-2 at -40 degrees C, reaching 59.3% of the capacitance at 25 degrees 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.

Automated summary

A new photothermal-assisted supercapacitor using commercially available TiN nanocrystals as an electrode material has been developed, showing high charge-storage capacity and operability at harsh low-temperature conditions. The device benefits from broad light absorption and high photothermal conversion efficiency of bifunctional TiN, and achieves considerable temperature rise even in open atmospheric environment. Furthermore, the as-fabricated device exhibits stable and reversible charge-storage capability, and the energy density is significantly improved at low temperatures.