Microtubular electrodes: An emerging electrode configuration for electrocatalysis, bioelectrochemical and water treatment applications

Electrochemical processes have attracted much attention as they can be empowered by renewable electricity for zero-emission processes under ambient conditions. Applications of electrochemistry in various areas such as electrocatalysis (e.g., water electrolysis, CO2 reduction), (waste)water treatment, fuel cells, and microbial processes have been recently emerging. Electrode design is a crucial feature in electrochemical systems. In some applications, porous electrodes are required to maximize the reaction sites and participate in reactants delivery, such as gas-diffusion electrodes (GDEs) for gas-phase electrolysis or membrane electrodes for water treatment. Planar shape porous electrodes are the conventional configuration with some drawbacks; for example, planar GDEs are made in multiple layers and are relatively complex to manufacture on large scales. Recently, microtubular (or hollow fiber) shape electrodes have been introduced as an alternative due to several advantages such as a higher active surface area to the volume ratio, small electrolyzer footprint, ease of processability, etc. This review presents a critical overview of the design and fabrication of microtubular electrodes and the structureperformance relationship. After that, the recent advances of microtubular electrodes in three main categories, including gas-phase electrocatalysis, (waste)water treatment, and bioelectrochemical systems, are discussed, with more focus on gas electrolysis wherein microtubular electrodes act as GDEs. GDEs for gas electrocatalysis are of great significance as they effectively boost reaction rate by continuously delivering reactant feeds to the reaction sites, resolving the issue of mass transport resistance, and microtubular GDEs can address several issues of planar GDEs. In the last section, future research opportunities are suggested to showcase the promises of microtubular electrodes as a versatile electrode configuration for electrochemical applications.

Automated summary

Electrochemical processes with applications in various areas are gaining attention, with microtubular electrodes showing advantages in gas-phase electrocatalysis, enhancing reaction rates and addressing issues of traditional planar electrodes.