Abstract
Providing adequate supply of clean fresh water and energy as the world's population increases is one of the grand challenges facing society in the current century.1 One possible solution to address both challenges is to recover clean water for reuse and energy from wastewater by integrating micro‐ or ultrafiltration membrane cathodes with microbial electrochemical system in what is referred to as an electrochemical membrane bioreactor (EMBR).2 The porous flat cathodes used in EMBR studies served the dual function as the cathode for the oxygen reduction reaction (ORR) and the membrane for the filtration of treated water. A disadvantage of using porous flat cathodes is their low surface‐area‐to‐volume ratio. Hollow fibers with small radial dimensions provide a high surface‐area‐to‐volume ratio, combining compactness, simple and modular reactor design, and high performance.3 Porous inorganic hollow fibers composed of nickel and copper have been used recently as cathodes in aqueous electrolytes for proton or carbon dioxide (CO2) reduction.4, 5 Porous polymer‐based hollow fibers are flexible, cheaper, and easier to manufacture, as well as easier to integrate into modules.6 However, most polymers are electric insulators and there are only a few examples of conducting polymers such as polypyrrole and polyaniline.7 Processibility in solution is a problem, particularly for polypyrrole.8 Combining high electrical conductivity and catalytic activity with processibility in a hollow fiber is a challenge.In this work, we propose the use of polymeric hollow fibers as electrodes, prepared from regular non‐conductive polymers and coated with a thin electron‐conductive layer of metal catalyst. However, it is challenging to apply a uniform coating of catalysts on these 3D thin porous polymeric hollow fibers using traditional deposition techniques such as electrodeposition or chemical or physical vapor deposition.9, 10 The technique that best meets the requirements for uniform coating and precise catalyst loading on 3D hollow fibers, is atomic‐layer deposition (ALD). ALD is one of the most flexible and powerful deposition techniques currently available due to its exceptional conformality and ability to tune crystallinity, atomic composition, and film thickness down to the single‐atom level.11 Because of these advantages, ALD has been applied in various applications including microelectronics, photovoltaics, solid oxide fuel cells, and solar‐to‐fuel applications, just to name a few.9-13 To date there have been no reports on the application of ALD on porous polymeric hollow fibers, especially for enabling them to act as electrodes for current collection and catalysis.