The Role of MXenes and Porosity in Alginate-Based Triboelectric Nanogenerators

MXenes are highly versatile and conductive 2D materials that can significantly enhance the triboelectric properties of polymer nanocomposites.¹ Despite the growing interest in the tunable chemistry of MXenes for energy applications, the effect of their chemical composition on triboelectric power generation has yet to be thoroughly studied. For instance, changing the composition of the surface terminations (T_x) influences the Fermi level and local surface dipole moments, consequently altering the work function (WF) of MXenes. These deliberate modulations to the work function of triboelectric materials can boost the voltage output from triboelectric nanogenerators (TENG).² On the other hand, it has also been reported that porosity is playing a role in triboelectric energy generation from polymer materials.³ By increasing the surface area more charge can be accumulated on the external and internal contact areas compared to dense films, which enhances the electrical output of these TENGs.

In this communication, we present our investigation on the impact of the chemical composition of Ti₃CNT_x vs. Ti₃C₂T_x on their interactions with sodium alginate biopolymer and, ultimately, the performance of a TENG device. Additionally, we prepared ice-templated Ti₃C₂T_x-alginate composite foams and investigated the role of Ti₃C₂T_x in triboelectric energy production, thermal insulation and flame retardancy of these foams.
Our results show that adding 2 wt % of Ti₃CNTx to alginate films produces a synergistic effect that generates a higher triboelectric output than the Ti₃C₂Tx system.⁴ Spectroscopic analyses suggest that a higher oxygen and fluorine content on the surface of Ti₃CNT_x enhances hydrogen bonding with the alginate matrix, thereby increasing the surface charge density of the alginate oxygen atoms. This was further supported by Kelvin probe force microscopy, which revealed a more negative surface potential on Ti₃CNT_x-alginate, facilitating high charge transfer between the TENG electrodes. Additionally, we demonstrate that plasma oxidation of the MXene surface further enhances triboelectric performance. We further show that the addition of 5 wt% Ti₃C₂T_x to alginate foams enhances the triboelectric output of 6 mm thick panels by a 110 %, overcompensating the output decline of thick tribolayers according to the distance depending electric field model. Finally, we demonstrate that these composite foams are suitable for the construction of smart fire alarm systems using small changes in the electrical resistance induced by fire. Our findings provide evidence that MXenes are versatile fillers for biopolymer bringing about complementary functionalities that can be exploited in energy and safety applications.

References:
1. Wang et al. Adv. Mater. 2022, 34, 2108560.
2. Cai et al. Adv. Funct. Mater. 2023, 33, 2304456.
3. Rastegardoost et al. Nano Energy 2023, 111, 108365.
4. Wicklein et. al. ACS Appl. Mater. Interfaces 2024, 16, 23948.