A Comprehensive Study on Air-Cathode Limitations and Its Mitigation Strategies in Microbial Desalination Cell—A Review

Microbial desalination cells (MDCs) are promising bioelectrochemical systems for desalination using the bacteria-generated electricity from the biodegradation of organic wastes contained in the wastewater. Instead of being a sustainable and eco-friendly desalination technology, the large-scale application of MDC was limited due to the high installation cost of the metal-catalyst-coated cathode electrode and the poor performance of the cathode in long-term operation due to catalyst fouling. Such cathodic limitations have hindered its large-scale application. The cathodic limitation has arisen mainly because of three losses, such as (1) Ohmic loss, (2) mass transfer loss, and (3) activation loss. The catalyst-assisted cathodic reduction reaction is an electrochemical surface phenomenon; thereby, the cathode’s surface charge transfer and thermodynamic efficiency are crucial for reaction kinetics. This review article aims to provide an overview of the MDC process, performance indicators, and summarizes the limiting factors that could hinder the process performance. Then, the article represented a comprehensive summary of the air-cathodic limitations and the mechanisms applied to improve the air-cathodic limitations in MDC to enhance the cathodic reaction kinetics through cathode surface modification through catalysts. The study is significantly different from other review studies by the precise identification and illustration of the cathodic losses and their mitigation strategies through surface modification. The details about the role of photocatalysts in the minimization of the cathode losses and improvement of the performance of MDC were well presented.