Globally seawater desalination depends on expensive and energy-intensive processes with high GHG emissions. Recently microbial desalination cell (MDC) has been explored as a promising desalination technique that uses bioenergy to operate as a low emission method while requiring little to no energy. MDC is fundamentally a bio electrochemical system (BES) that extracts bio-energy from the biological oxidation of pollutants to carry out desalination using beneficial bacteria. In a typical MDC, the anodic and cathodic processes govern the success of the desalination performance. However, the desalination in MDC is mainly restricted by cathodic limitations. The limitation in cathode accounts for more than 80% of the total over potential, which is the sum of the resistances contributed by the cathode, electron acceptors, and side reactions. Hence a thorough understanding of cathodic limitations from the resistance standpoint is required to guide the cathodic improvement for efficient MDC operation. Therefore this doctoral thesis comprehensively reviewed the literatures to identify the engineering and operational challenges in MDC and their possible solution from a cathodic limitation standpoint. Promising catalysts were reviewed and proposed for cathodic improvement. In order to understand the cathodic limitation, this research aimed (i) to understand the external and internal resistance as cathodic limiting factors in two separate three chamber microbial desalination cell (MDC) configurations, i.e., (a) Air pumped catholyte MDC and (b) Air cathode MDC, (ii) to investigate the effect of external and internal resistance, and substrate on improving desalination in a circular air cathode MDC using real leachate mixed municipal wastewater as anodic electrolyte. To mitigate the cathodic limitations, this research (iii) synthesized and applied the reduced graphene oxide (rGO) and polymerized aniline (PANI) composite as a promising electro-catalyst on stainless steel mesh for cathodic improvements in MDC and (iv) synthesized and applied the bismuth oxychloride (BiOCl) and graphitic carbon nitride (gCN) composite as electro-catalyst on stainless steel mesh for cathodic improvements in MDC. The first study investigated the impact of external resistance (Rext) on MDC performances having two different internal resistances (Rint) by changing the MDC cathode configurations. The results showed that the effect of Rext on the desalination rate (2.52 mg/h) was quite low when Rint of MDC was high (200Ω). However, operating MDC with low Rint (67Ω) significantly improved the desalination rate (9.85 mg/h) and current generation. When MDC was operated with low Rint the effect of variable Rext on desalination and current generation was noticeable. The MDC with low Rint was investigated to find the optimal range of Rext for efficient MDC performance. The optimal range was found as Rext << Rint, Rext < Rint, Rext ≈ Rint (ranging from 1-69 Ω) to achieve the highest desalination rates (10.41-8.59 mg/h). The findings suggested that in order to achieve the best desalination rate, MDC should be first manufactured with minimum internal resistance. Additionally, MDC with low internal resistance are only able to display an optimal range of external resistances that can significantly affect performance within that range. The first study used synthetic wastewater for investigation. It was important to know the impact of resistances (external and internal) in real wastewater context. The second investigation of cathodic limitation used real leachate mixed municipal wastewater in a circular air cathode MDC to do pre-treatment while investigating the effect of external and internal resistance, and substrate on improving desalination and power generation. This circular air cathode MDC had very low internal resistance. The measured bio electrochemical performances for MDC-1 (operated with 1 Ω Rext) showed a higher desalination rate (DR) (35.71 mg/h) and NH3-N removal (36%) with low removal of COD (28%) than MDC-100 (operated with 100 Ω Rext). While MDC-100 showed lower DR (17.98 mg/h) and NH3-N removal (10%) with higher removal of COD (78.26%). The results revealed that Rext could regulate the pollutants (organics, NH3-N) removal and desalination efficiency. Hence, adjustment of the external resistance at the outer circuit can significantly influence the electrochemical performance which was corroborated bt the first study. The lack of soluble organics could also result in significant discrepancies in bio-electrochemical performance. MDC-100 showed four times higher energy output (5.63 W·m-3 ) compared to MDC-1 (1.39 W·m-3 ), while MDC-1 showed five times higher columbic efficiency (29.3%) compared to MDC-100 (5.52%). After the cathodic limitation study, the thesis concentrated on investigations to improve cathodic limitation using new type of cathode catalysts. The third research studied the cathodic improvement by PANI-rGO electro-catalyst composite. The study synthesized the composite at four different concentrations of rGO and fixed concentration of PANI electro-deposited layer by layer on stainless steel mesh (SSM). Microstructure and morphology analysis showed good composite between PANI and rGO with layered nano-fibrous structure. The electron transfer was improved by increasing concentration of rGO layer. The best performing composite (PANI-rGO1.0-SSM) was applied in MDC cathodic improvement with variable loading of rGO1.0 by changing deposition cycles. The result showed promising improvement by PANI-rGO1.0 electro-catalyst with 30 cycles of rGO1.0 deposition. The desalination rate was improved by 40.5% compared to control plain SSM. The internal resistance was also significantly reduced to 96% than plain SSM. This study showed the rGO-PANI composite with high performing loading rate improved the MDC performance by decreasing the internal resistance and high electro-catalytic activity. Cost analysis showed layer by layer electro-deposition of PANI-rGO1.0 on SSM cathode is an advantageous and low cost binder free coating method compared to Platinum coated cathode. The last research of the thesis synthesized the BiOCl/g-CN electro-catalyst composite and investigated as cathode catalyst for MDC desalination improvement. Five differnet composites werer prepared by mutually increasing ratio of both the materials. The XRD and FT-IR result showed an efficient composite formation between BiOCl and g-CN. The ratio of BiOCl and g-CN has proportionally increased or decreased the characteristic peaks. All the composites showed improved redox performance compared to plain SSM in CV characterization. The two best-performing ratios and loading rates were C3 (50mg/cm2 ): BiOCl/g-CN (50:50) and C1(20 mg/cm2 ): BiOCl/g-CN (100:0) which were coated to use as cathode in MDC. C3 (50 loading) showed 49% and C1 (20 loading) showed 42% improvement in desalination rate compared to control. C3(50 loading) and C1(20 loading) effectively reduced the internal resistance of MDC by 50% and 13% respectively. Cost analysis showed low preparation expense (14%) for this catalyst coated cathode from this earth-abundant Bi-based catalyst and promising g-CN using brush coating. This study concluded that these green BiOCl and g-CN can be composited effectively to use as a sustainable electro-catalyst for stainless steel mesh cathode and to improve the desalination and current generation performance in MDC. This thesis concluded that fabricating an MDC with low internal resistance was critical prior to adjusting the external resistance. Low Rint MDC can effectively control treatment, desalination and energy production while using the real wastewater like leachate mixed with municipal wastewater as anolyte. Both PANI-rGO1.0 and BiOCl/g CN cathode electro-catalysts were effective to improve desalination performance and could be used as a alternative to expensive electrocatalysts like platinum. Future research should focus on thin layer electro-deposition composite preparation to optimize the loading rates of rGO to get improved reaction kinetics in MDC cathode. For BiOCl/g CN, the thickness and distribution of catalyst loading needs optimization. Both the composites should be investigated for air-cathode preparation to effectively use air available oxygen in the electrolyte for better oxygen reduction reaction.