Constructing Flexible Film Electrode with Porous Layered Structure by MXene/SWCNTs/PANI Ternary Composite for Efficient Low‐Grade Thermal Energy Harvest

Thermal energy, constituting the majority of the energy lost through various inefficiencies, is abundant and ubiquitous. With thermogalvanic effect, thermocells (TECs) can directly convert thermal energy into electricity without producing vibration, noise or other waste emissions. This work presents a rational design of flexible film electrodes constructed on a ternary composite of Ti3C2Tx MXene (Tx represents surface terminations), polyaniline (PANI) and single‐wall carbon nanotubes for TECs, which exhibit notably enhanced thermoelectrochemical performance compared to the widely adopted noble platinum electrodes. The ternary composite electrodes form a porous layered structure with a large electrochemical‐active surface area. Experiment and simulation results reveal that synergistic effects of Ti3C2Tx and PANI are induced for promoting both mass and charge transport at the electrolyte‐electrode interface, resulting in a TEC with an output power of 13.15 µW cm−2 at the ΔT of 40 K. The TEC also shows a rapid response to the small temperature difference between the human body and the ambient, demonstrating high potential in harvesting low‐grade heat to power small electronics. A flexible film electrode with porous layered structure is rationally designed with Mxene/SWCNTs/PANI ternary composite. In‐depth investigations reveal the synergistic effects that facilitate ion diffusion, temperature‐dependent redox reactions, and interfacial mass transport and charge transfer, accounting for the notable enhancement of thermoelectrochemical performance. A thermocell is further demonstrated to power electronics by harvesting low‐grade heat from human body.