Tunable Thermal Conductance of Termination-Engineered MXenes through Intercalation

First discovered in 2011, selective etching of transition metal carbides and nitrides with general formula M_n+1AX_n in Hydrofluoric acid (HF) or HF-forming etchants results in a new class of layered two-dimensional (2D) materials called MXenes (M_n+1X_nT_z, where T is termination group, such as –O, -F, PH, -Cl). First principle thermal conductivity calculations of monolayer MXenes have demonstrated an order of magnitude change in thermal conductivity by changing surface termination from -F to -O due to increased phonon scattering rate and reduced phonon mean free path. While extensive research on unique electrical, electrochemical, and mechanical properties of MXenes has been reported, no experimental investigations exist characterizing thermal transport performance of a stack of MXene nanosheets or large area free-standing multi-layer MXene sheets. Here I will present our current research endeavors in advancing the application of MXenes in thermal management. Combining elemental analysis tools such as XRD with AFM for chemical and structural characterization and Time-Domain Thermoreflectance (TDTR) for thermal conductance measurements, we explore the correlation between surface functionalization and thermal transport. I will also describe our efforts beyond surface functionalization to further control the thermal transport through MXenes via electrochemical intercalation. Our findings lay the groundwork for advancing the engineering thermal transport through MXenes, both actively or passively, having wide reaching impact in energy harvesting, conformal/wearable electronics, electromagnetic interference shielding, and thermal management.