# Strategies for Enhancing Extracellular Electron Transfer in Environmental Biotechnology: A Review
## 1 Introduction  
Microorganisms have devised specific processes to transmit electrons to minerals that are located near the surface of the cell, and this process is termed extracellular electron transfer (EET) [1]. The microbial EET process serves as a source of energy for the growth and maintenance of microorganisms. These microorganisms capable of conducting the EET process are referred to as electroactive microorganisms (EAMs) [2]. EAMs are now used for many applications in many environmental biotechnologies such as energy recovery and environmental remediation. For bioelectrochemical systems like microbial electrolysis cells (MECs) and microbial fuel cells (MFCs), the power production, fuel generation rates, and overall energy recovery from organic matter are all improved by increasing EET efficiency [3]. In addition to the generation of bioelectricity, the biotransformation of valuable chemicals, and the bioremediation of environmentally hazardous pollutants, EAMs are now useful for biosensing and even biocomputing [4]. EET enhancement is important in studying and harnessing microbe-metal interactions [5; 6; 7; 8; 9], but the complexity of electron transfer mechanisms, the wide range of microbes in question, the influence of environmental factors, and the scaling-up of EET processes are among the key challenges that researchers and engineers face in this field [9; 10]. Overcoming these challenges will pave the way for the development of innovative applications for harnessing the potential of EET. There are now several techniques used in environmental biotechnology to improve EET. To improve the EET capabilities of EAMs like _Shewanella_ or _Geobacter_ species, genetic engineering approaches can be used. This includes adding exogenous electron transfer mediators or overexpressing crucial EET genes or pathways [3]. Biofilm growth can also improve EET between microorganisms and electrodes. Optimizing growth conditions, surface modification, and biofilm engineering approaches are methods to improve the formation of biofilm [11; 12]. Another method of improving EET is to optimize the material of the electrode. EET can be enhanced by modifying the composition and surface features of the electrodes [13; 14; 15]. This includes enhancing the contact between microbes and electrodes by employing conductive materials, such as carbon nanotubes or conductive polymers [2]. Redox mediators like riboflavin, neutral red, or anthraquinone derivatives can improve EET by promoting electron transport between microorganisms and solid surfaces or electron acceptors [16; 17]. Electrochemical techniques are essential in studying the behavior of microorganisms for various purposes. One popular electrochemical method for examining the redox behavior of electroactive species in a system is cyclic voltammetry (CV). CV is used in bioelectrochemical systems to describe the electrochemical activity of redox-active mediators and microorganisms involved in EET. CV offers insights into the kinetics and thermodynamics of EET processes by assisting in determining the redox potentials of electron-donor and electron-acceptor compounds. Chronocoulometry (CC) is an additional electrochemical method utilized to quantify the overall electric charge that traversed an electrochemical cell within a designated time interval. This method can be performed by imparting a constant potential to the working electrode and measuring the resulting current as a function of time. The term \"chronocoulometry\" is derived from the words \"coulometry\", which quantifies the amount of electricity (charge) exchanged within a system, and \"chrono\", which denotes time. Pyocyanin (PYO) is an identified redox mediator molecule produced by _Pseudomonas aeruginosa_. The electrochemical technique utilizing CV and CC was employed in a recent study [18], to facilitate the analysis of the adsorption process of PYO onto carbon-based electrodes using glassy carbon. By utilizing these electrochemical methods in conjunction with FT-IR analysis, the authors deduced that _P.