Integrated Microfluidic Flow-Through Microbial Fuel Cells

Sustainable circular biorefinery approach for novel building blocks and bioenergy production from algae using microbial fuel cell

The imminent need for transition to a circular biorefinery using microbial fuel cells (MFC), based on the valorization of renewable resources, will ameliorate the carbon footprint induced by industrialization. MFC catalyzed by bioelectrochemical process drew significant attention initially for its exceptional potential for integrated production of biochemicals and bioenergy. Nonetheless, the associated costly bioproduct production and slow microbial kinetics have constrained its commercialization. This review encompasses the potential and development of macroalgal biomass as a substrate in the MFC system for L-lactic acid (L-LA) and bioelectricity generation. Besides, an insight into the state-of-the-art technological advancement in the MFC system is also deliberated in detail. Investigations in recent years have shown that MFC developed with different anolyte enhances power density from several µW/m² up to 8160 mW/m². Further, this review provides a plausible picture of macroalgal-based L-LA and bioelectricity circular biorefinery in the MFC system for future research directions.

Microbial Fuel Cell-Based Biosensors and Applications

The sustainable development of human society in today's high-tech world depends on some form of eco-friendly energy source because existing technologies cannot keep up with the rapid population expansion and the vast amounts of wastewater that result from human activity. A green technology called a microbial fuel cell (MFC) focuses on using biodegradable trash as a substrate to harness the power of bacteria to produce bioenergy. Production of bioenergy and wastewater treatment are the two main uses of MFC. MFCs have also been used in biosensors, water desalination, polluted soil remediation, and the manufacture of chemicals like methane and formate. MFC-based biosensors have gained a lot of attention in the last few decades due to their straightforward operating principle and long-term viability, with a wide range of applications including bioenergy production, treatment of industrial and domestic wastewater, biological oxygen demand, toxicity detection, microbial activity detection, and air quality monitoring, etc. This review focuses on several MFC types and their functions, including the detection of microbial activity.

The Effect of Different Pretreatment of Chicken Manure for Electricity Generation in Membrane-Less Microbial Fuel Cell

The need for energy resources is growing all the time, which means that more fossil fuels are needed to provide them. People prefer to consume chicken as a source of protein, and this creates an abundance of waste. Thus, microbial fuel cells represent a new technological approach with the potential to generate electricity through the action of electrogenic bacteria toward chicken manure, while reducing the abundance of chicken manure. This study investigated the effect of different pretreatment (thermal, alkaline, and sonication pretreatment) of chicken manure to improve the performance of a membrane-less microbial fuel cell (ML-MFC). Statistical response surface methodology (RSM) through a central composite design (CCD) under a quadratic model was conducted for optimization of the ML-MFC performance focusing on the COD removal efficiency (R2 = 0.8917), biomass (R2 = 0.9101), and power density response (R2 = 0.8794). The study demonstrated that the highest COD removal (80.68%), biomass (7.8539 mg/L), and power density (220 mW/m2) were obtained when the pretreatment conditions were 140 °C, 20 kHz, and pH 10. The polarization curve of the best condition of ML-MFC was plotted to classify the behavior of the ML-MFC. The kinetic growth of Bacillus subtillis (BS) showed that, in treated chicken manure, the specific growth rate µ = 0.20 h−1 and doubling time Td = 3.43 h, whereas, in untreated chicken manure, µ = 0.11 h−1 and Td = 6.08.

Microfluidics for Electrochemical Energy Conversion

Electrochemical energy conversion is an important supplement for storage and on-demand use of renewable energy. In this regard, microfluidics offers prospects to raise the efficiency and rate of electrochemical energy conversion through enhanced mass transport, flexible cell design, and ability to eliminate the physical ion-exchange membrane, an essential yet costly element in conventional electrochemical cells. Since the 2002 invention of the microfluidic fuel cell, the research field of microfluidics for electrochemical energy conversion has expanded into a great variety of cell designs, fabrication techniques, and device functions with a wide range of utility and applications. The present review aims to comprehensively synthesize the best practices in this field over the past 20 years. The underlying fundamentals and research methods are first summarized, followed by a complete assessment of all research contributions wherein microfluidics was proactively utilized to facilitate energy conversion in conjunction with electrochemical cells, such as fuel cells, flow batteries, electrolysis cells, hybrid cells, and photoelectrochemical cells. Moreover, emerging technologies and analytical tools enabled by microfluidics are also discussed. Lastly, opportunities for future research directions and technology advances are proposed.

Monodispersed Ruthenium Nanoparticles on Nitrogen-Doped Reduced Graphene Oxide for an Efficient Lithium-Oxygen Battery

Lithium-oxygen batteries with ultrahigh energy densities have drawn considerable attention as next-generation energy storage devices. However, their practical applications are challenged by sluggish reaction kinetics aimed at the formation/decomposition of discharge products on battery cathodes. Developing effective catalysts and understanding the fundamental catalytic mechanism are vital to improve the electrochemical performance of lithium-oxygen batteries. Here, uniformly dispersed ruthenium nanoparticles anchored on nitrogen-doped reduced graphene oxide are prepared by using an in situ pyrolysis procedure as a bifunctional catalyst for lithium-oxygen batteries. The abundance of ruthenium active sites and strong ruthenium-support interaction enable a feasible discharge product formation/decomposition route by modulating the surface adsorption of lithium superoxide intermediates and the nucleation and growth of lithium peroxide species. Benefiting from these merits, the electrode provides a drastically increased discharge capacity (17,074 mA h g^-1), a decreased charge overpotential (0.51 V), and a long-term cyclability (100 cycles at 100 mA g^-1). Our observations reveal the significance of the dispersion and coordination of metal catalysts, shedding light on the rational design of efficient catalysts for future lithium-oxygen batteries.

Optimal Geometric Parameters for 3D Electrodes in Bioelectrochemical Systems: A Systematic Approach

In this study, the performance of electroactive bacteria (EAB), cultivated inside tubular electrode ducts, is systematically investigated to derive predictions on the behavior of EAB under conditions limited by electrochemical losses. A modeling approach is applied to assess the influence of the electrochemical losses on the electrochemical performance and scaling characteristics of complex 3D structures, such as sponges and foams. A modular flow reactor is designed that provides laminar and reproducible flow conditions as a platform for the systematic electrochemical and bioelectrochemical characterization of 3D electrodes in bioelectrochemical systems (BES). The bioelectrochemical experiments are carried out in a set of reactors incorporating cylindrical electrodes exhibiting ducts of 1 cm length and different diameters ranging from 0.1 cm up to 1 cm. Single duct calculations are extrapolated to three dimensions through geometrical considerations; trends in 3D bioanode performance are demonstrated using the resulting simplified 3D structure. The combined experimental and modeling approach constitutes a framework for future studies on systematic electrode design.

Enhancement of the Start-Up Time for Microliter-Scale Microbial Fuel Cells (µMFCs) via the Surface Modification of Gold Electrodes

Microbial Fuel Cells (MFCs) are biological fuel cells based on the oxidation of fuels by electrogenic bacteria to generate an electric current in electrochemical cells. There are several methods that can be employed to improve their performance. In this study, the effects of gold surface modification with different thiol molecules were investigated for their implementation as anode electrodes in micro-scale MFCs (µMFCs). Several double-chamber µMFCs with 10.4 µL anode and cathode chambers were fabricated using silicon-microelectromechanical systems (MEMS) fabrication technology. µMFC systems assembled with modified gold anodes were operated under anaerobic conditions with the continuous feeding of anolyte and catholyte to compare the effect of different thiol molecules on the biofilm formation of Shewanella oneidensis MR-1. Performances were evaluated using polarization curves, Electrochemical Impedance Spectroscopy (EIS), and Scanning Electron Microcopy (SEM). The results showed that µMFCs modified with thiol self-assembled monolayers (SAMs) (cysteamine and 11-MUA) resulted in more than a 50% reduction in start-up times due to better bacterial attachment on the anode surface. Both 11-MUA and cysteamine modifications resulted in dense biofilms, as observed in SEM images. The power output was found to be similar in cysteamine-modified and bare gold µMFCs. The power and current densities obtained in this study were comparable to those reported in similar studies in the literature.

Electricity generation of a laminar-flow microbial fuel cell without any additional power supply

Laminar-flow microbial fuel cells (LFMFCs) utilize the co-laminar flow feature in the microchannel as a virtual barrier to separate the anolyte and catholyte. However, for LFMFCs reported before, syringe pumps were always used to drive the fluid and form the co-laminar flow of anolyte and catholyte in the microchannel, reducing the net power output and the efficiency of the whole system. In this study, a laminar-flow microbial fuel cell (LFMFC) without any additional power supply is proposed. The LFMFC is successfully started-up after inoculation for 90 h. The anode biofilm distribution becomes sparser along the flow direction due to the thicker boundary layer and unfavorable crossover from the catholyte downstream. Moreover, the LFMFC delivers a maximum volumetric power density of 3200 W m⁻³, which is higher than that of previous LFMFCs without membranes. Considering the practical application of LFMFC as a power source, the cell voltage responses to different conditions are further investigated. When the external resistance is switched between 1000 Ω and 4000 Ω, it takes the LFMFC 10 minutes to reach a stable voltage output. However, the voltage response to the intermittent supply takes 1 h to reach a stable value. Additionally, short-term cold storage has little effect on bacterial metabolic activity and cell voltage.

A novel laminar-flow microbial fuel cell without any additional power supply is proposed.

A Controllable and Integrated Pump-enabled Microfluidic Chip and Its Application in Droplets Generating

A microfluidic chip with a controllable and integrated piezoelectric pump was proposed and demonstrated, where the pump was designed as a micro-actuator based on polyvinylidene fluoride (PVDF) organic piezoelectric film. In this case, the pump should integrate with the microfluidics device very well into one chip. The flow rate can be precisely controlled in the range of 0–300 µl/min for water by tuning the V_pp and frequency of Alternating Current (AC) voltage applied on the diaphragm. To analyze the relationship between the flow rate and the deflection of diaphragm, the deformations of diaphragm at different voltages were researched. The displacement of diaphragm was defined as 17.2 µm at the voltages of 3.5 kV, 5 Hz when the pump chamber was full of water. We have used the integrated microfluidic chip with two pumps for droplet generation to demonstrate its great potential for application in droplet-based microfluidic chip.