Multifunctional Ti₃C₂T_<i>x</i>-alginate foams for energy harvesting and fire warning

Foams that combine seemingly opposite properties, such as high thermal insulation and electrical conductivity, are highly sought after for modern-day advanced applications. However, achieving a balance of these properties necessitates careful tuning of material compositions. Here, we prepared ice-templated Ti₃C₂T_<i>x</i>-alginate composite foams and investigated the role of Ti₃C₂T_<i>x</i> MXene in triboelectric energy production, thermal insulation, and flame retardancy. Our results show that adding 5 wt% Ti₃C₂T_<i>x</i> enhances the triboelectric output of 6 mm thick foams (380 V, 7.7 μA, 43 mW m^-2) by 110%. Despite incorporating electrically conducting Ti₃C₂T_<i>x</i>, these macroporous composite foams have a thermal conductivity of only 62 mW m^-1 K^-1, while they also show flame-retardant properties, exhibiting self-extinguishing behavior. Finally, we demonstrate these composite foams for constructing smart fire alarm systems as they respond to small changes in electrical resistance induced by fire. Our findings prove that Ti₃C₂T_<i>x</i> is a versatile filler for biopolymer foams, introducing complementary functionalities that can be exploited in energy and safety applications.