3D printing of electrodes and functional components for microbial electrolysis cells: materials, fabrication, and electrochemical performance

Abstract

Microbial electrolysis cells (MECs) have attracted increasing attention as sustainable bioelectrochemical systems capable of simultaneously converting organic waste into hydrogen while treating wastewater. Despite significant progress, their widespread implementation remains hindered by limited electrode performance, inefficient reactor components, poor long-term durability, and manufacturing constraints associated with conventional fabrication techniques. Three-dimensional (3D) printing has emerged as a transformative manufacturing strategy that enables precise control over electrode architecture, porosity, surface morphology, and multifunctional reactor components, thereby providing new opportunities to enhance bioelectrochemical performance and reactor integration. This review critically examines recent advances in the 3D printing of electrodes and functional components for MECs, covering printable materials, additive manufacturing technologies, post-processing approaches, and structure–property–performance relationships governing extracellular electron transfer (EET) and hydrogen evolution. Particular emphasis is placed on carbon-based materials, metals, conductive polymers, nanocomposites, and metal oxide-functionalized architectures, together with emerging multi-material and hybrid printing strategies for bioanodes, cathodes, membranes, current collectors, flow distributors, and complete reactor assemblies. The influence of printed geometries, surface chemistry, conductivity, mechanical integrity, and catalyst incorporation on biofilm development, charge transfer, hydrogen production, Coulombic efficiency, and reactor stability is comprehensively evaluated. Current challenges related to printable conductive materials, electrochemical durability, catalyst loading, fouling, manufacturing repeatability, scalability, and economic feasibility are critically discussed. Finally, future research directions, including multifunctional materials, embedded sensing, four-dimensional printing, and fully integrated printed bioelectrochemical systems, are proposed to accelerate the development of high-performance, scalable MEC technologies for sustainable hydrogen production and circular wastewater resource recovery.