MXene Iontronics for Neuromorphic Computers and Actuators

2D materials and in particular MXenes can not only form passive metallic or supercapacitive structures but can also become active structures in which their optoelectronic or structural properties change as a function of doping. We term these materials 2D mixed ionic electronic materials (MIEC) or iontronics. Here we highlight two specific MXene MIECs devices that we have developed:<br/><br/><b>1)</b> A component for in memory computers called <b>MXene </b><b>electrochemical random-access memories (ECRAMs</b><b>).</b> The MXene ECRAM components has a channel like a conventional transistor, where the channel comprises a multi-layered MXene film formed using a highly accurate layer-by-layer self-assembly method developed by us.^[1] In the ECRAM, however, an electrolyte between the channel and gate is used instead of the dielectric used in a solid-state field-effect transistors (FET). As a result, we can electrochemically switch the redox state of the MXene MIEC material using a gate electrode. Conducting polymer ECRAMs were until now the only shown ECRAMs but can not be integrated into silicon chips because organic materials burn at the high temperatures used in CMOS fabrication. The multilayers of titanium carbide MXene^[1] can form ECRAMs with promising metrics for in-memory computation (also termed neuromorphic computers)^[2] and can withstand high temperatures for integration. In recent studies we analyze these components and describe their characteristics using equation derived for organic electrochemical transistors.^[3]<br/>We think our work paves the way for ECRAM based computers and MXene electrochemical transistors.<br/><br/><b>2)</b> We recently developed an MXene based actuators that we call <b>Electrochemical Osmotic (ECO) actuators.</b>^[4] These actuators are formed from bulk composite electroactive hydrogels, fabricated from cellulose nanofibrils from trees, and 2D MXenes.^[5] These nanoparticles self-assemble into an anisotropic composite networks with an open mesoporous structure that can hold lots of water and be highly permeable to substances in their surroundings, while being mechanically very strong. The anisotropy of the network allows high expansion in one direction while maintaining very high strength and high electric conductivity in the other. The electrochemical charge/discharge of the MXene in the hydrogels controls the internal salt concentration and consequently their osmotic swelling. This allows direct electrically controlled actuation where around 700 water molecules expand/contract the structure for each ion/electron pair inserted/de-inserted at only ±1 volt, resulting in 300% electroosmotic expansion, with very high pressures reaching 1 MPa. This mode of electronic actuation has not been shown before, and has emergent properties not present in any previously known soft material. ECOs allow for monolithic integration of sensors and other functions into one composite, rendering a new form of smart soft material not achieveable with other materials systems.<br/><br/><b>References</b><br/>[1] W. Tian, A. VahidMohammadi, Z. Wang, L. Ouyang, M. Beidaghi, M. M. Hamedi, <i>Nat. Commun.</i> <b>2019</b>, 10:2558.<br/>[2] A. Melianas, M. Kang, A. Vahidmohammadi, W. Tian, Y. Gogotsi, A. Salleo, M. M. Hamedi, <i>Adv. Funct. Mater.</i> <b>2022</b>, <i>32</i>, 2109970.<br/>[3] M. Kang, J. Shakya, J. Li, A. Vahidmohammadi, W. Tian, E. Zeglio, M. M. Hamedi, <i>ArXiv</i> <b>2023</b>, <i>2303.10768</i>.<br/>[4] L. Li, W. Tian, A. VahidMohammadi, J. Rostami, B. Chen, K. Matthews, F. Ram, T. Pettersson, L. Wågberg, T. Benselfelt, Y. Gogotsi, L. A. Berglund, M. M. Hamedi, <i>Adv. Mater.</i> <b>2023</b>, <i>35</i>, 1.<br/>[5] W. Tian, A. Vahidmohammadi, M. S. Reid, Z. Wang, L. Ouyang, J. Erlandsson, T. Pettersson, L. Wågberg, M. Beidaghi, M. M. Hamedi, <i>Adv. Mater.</i> <b>2019</b>, <i>1902977</i>