Storing Solar Energy in Sodium Acetate-Based Hand Warmers Using Light-Absorbing Particles

We have fabricated an eco-friendly, affordable, and recyclable heat-releasing chemical bag (hence forth termed as hand warmers), which melts when exposed to solar radiation and can be suitable for warming the hands and feet of mountain dwellers, hikers, and motorbike/vehicle riders during winter. Our hand warmer uses sodium acetate trihydrate (CH3COONa center dot 3H(2)O, SAT)-based composites consisting of a suitable photothermal-responsive additive to shorten the melting time of the hand warmer for practical applications. Under simulated solar radiation, activated charcoal powder, graphite powder, graphene flakes, and copper nanoparticles (Cu-NPs) were tested as photothermalresponsive additives, which reduced the melting time of the hand warmer by a factor of 0.68, 0.65, 0.63, and 0.57 respectively, when compared to the sample without any additives. Moreover, the stability of the hand warmer was maintained for two-three months (at which point the samples were deliberately discharged) by incorporating 9 mL of extra water (8% wt) in the SAT composites, which demonstrates the long-term heat storage capacity of the hand warmer.