Recent Advances in 3D Printed Electrodes - Bridging the Nano to Mesoscale.

3D architected electrodes offer inherent physicochemical advantages for energy storage, conversion, and sensing. 3D printing methods such as stereolithography and two photon polymerization are uniquely capable of fabricating these architected electrodes with a high degree of geometric complexity impossible to achieve with other methods at the mesoscale (10 µm-1 mm). The material set for 3D printing traditionally is focused on structural materials rather than functional materials suitable for electronic and electrochemical applications. In this review the fundamental challenges are considered for transforming 3D printed materials into conductive, multifunctional electrodes suitable for electrical and electrochemical devices by printing nanocomposites, infusing molecular precursors and post-processing these structures via carbonization. To understand the design of 3D electrodes toward their use in both sensors and electrochemical devices such as catalysts, this review summarizes recent advances in hierarchical design of porous metastructures, the engineering of mass transport and electronic transport in 3D structures, and the application of high-throughput materials design by machine learning and artificial intelligence. These emerging approaches to 3D electrode design and architecture promise to expand the capabilities of additive manufacturing beyond structural materials and bring its advantages to bear on modern devices such as sensors, batteries, supercapacitors, and electrocatalysts.