Recovering low-temperature heat Low-temperature heat sources are both abundant and largely dissipated into the environment. Yu et al. discovered a way to boost the concentration gradient in a liquid thermogalvanic cell that allows low-temperature heat to be recovered. The authors added a component that boosts the concentration gradient by forcing crystallization of the electrolyte at the cold end, and these crystals then melt at the hot end. This process boosts efficiency and is a potential method for recovering low-grade heat. Science , this issue p. 342