## 1 Introduction
#### Stand-Alone Bioelectrochemical Systems and Their Limitations  
Organic compounds such as acetate and glucose are oxidized anaerobically in an MFC, resulting in the liberation of protons, electrons, and CO\({}_{2}\). The liberated protonsand electrons pass through a medium, which is an electrical circuit for electrons and a membrane for protons, to enter the cathode. The cathode is where water is generated by the reduction of protons and electrons using oxygen supplied from outside. The formation of water in the MFC is depicted by the equation below:  
\[\text{CH}_{3}\text{COO}^{-}+4\text{H}_{2}\text{O}\to 2\text{ HCO}_{3}^{-}+9\text{H}^{+}+8\text{e}^{-}\] \[2\text{O}_{2}+8\text{H}^{+}+8\text{e}^{-}\to 4\text{H}_{2}\text{O}\]  
In MFC, the anode undergoes oxidation, while the cathode undergoes reduction. This oxidation and reduction create the potential difference between the electrodes, resulting in the generation of bioelectricity (Figure 1). Considering the significance of electrodes in MFCs, selecting the right electrode material is an important part of the system's design. An effective cathode must have high conductivity and a high surface-area-to-volume (S/V) ratio, be noncorrosive, and have the least fouling. Cathode efficacy is critical in the generation of power in MFCs. The ORR is the most prevalent cathode reaction. One of the most limiting aspects of MFC operation is the steady reduction of oxygen on the interface of carbon or graphite electrodes, which results in a significant overpotential reduction. Hence, selecting the appropriate cathode material is important. The chemical oxygen demand (COD) varies between 60-220 mg/L during the continuous flow system and 23-164 mg/L during the fed-batch system. The COD is also influenced due to wastewater COD concentrations, system alignments, and hydraulic retention time (HRT) [13]. [PERSON] and [PERSON] [14] constructed a 26 L cheap air cathode MFC employing clayware as a divider, claiming that the efficiency was steady for 14 months. With a CE of 5.1%, the MFC had a maximum power of 17.85 mW and removed 78% of the COD. [PERSON] et al. [15] created a stacked large-scale horizontally constructed MFC (SHMFC) with such an overall capacity of 250 L that employs carbon brush electrodes to extract 116 mW of current (0.435 A) while also treating sewage. These SHMFC components may be used independently to process sewage and generate electricity without interfering with other SHMFC modules. Biofilm-based MFCs are unproductive in the elimination of minute entities and, therefore, lead to such high COD of the effluent [16]. Theoretically, the influents include constituents such as azo dyes, which are lethal to microorganisms and thus hamper the biofilm formation and electron transfer, thereby reducing the MFC's potential substantially [17]. Quite a few methods and approaches were employed and examined  
Figure 1: A typical stand-alone microbial fuel cell. to improve the energy generation of MFCs [18]. These methods comprise multifaceted enhancement and adaptation techniques [19], improvement of electrode biocompatibility by surface modification, and assembly of three-dimensional electrodes [20]. Even after all these signs of progress, the usage of cost-effective carbon electrodes deprived of the usage of catalysis was established to cause overpotential of the cathode and restricted oxygen transformation competence [21]. The enhancements performed were quite inferior from the contaminated water upscaling viewpoint. These matters have been a massive hindrance in the industrial employment of an MFC as an impartial contaminated water management podium. The productivity and consistency of the MFC have improved extraordinarily after long research and development. However, despite all these advancements, there are plenty of issues that need to be addressed and improved before this technique can be elevated and employed on a commercial scale. One of the most significant obstacles to the development of microbial fuel cells is the high cost of electrode and membrane components.