A Critical View of Microbial Fuel Cells: What Is the Next Stage?

Abstract

Am icrobialf uel cell (MFC)i saheterogeneousr eactor in which redox reactions take place at the interfacesb etween electron conductors (electrodes) and ion conductors (electrolyte). The oxidation occurs on the anode surface, whereas the reduction takes place on the cathode. Thee lectrolyte allows the transport of ions in each half-cell, from the anode to the cathode and vice versa. The electric current flows from the anode to the cathode through an external circuit, because of the potential differencep roduced betweenb oth electrodes (E). This cell voltage is relatedt ot he Gibbs' free energy in Equation (1), in which n is the number of exchanged electrons and F is the Faraday constant. DG ¼ ÀnFE ð1ÞIf G is lower than 0( DG < 0), the processp roceeds spontaneously andt he cell transforms the energy produced by as pontaneous chemical reactioni nto electrical energy.T he most im-portant cellsa re those developed for transforming energy as batteries( discontinuouse lectrochemical cells),r edox flow batteries andr echargeableb atteries (semicontinuouse lectrochemicalcells), andfuelcells (continuouselectrochemicalcells).Despite the great variety of applications of batteries nowadays, the development of fuel cells is more interesting from a researchp erspective because there are many weaknesses that have yet to be solved, in particular those related with the catalysts used to transform the fuel into electricity.Because of that, during the last few decades, the use of bacteria as catalysts has gained special attention in this field, and this has led to the concept of MFCs. The uniqueness of biocatalysts is that the catalytic efficiency dependso nt he microbial interactions in the community among them and with the electrodeso fafuel cell. These types of bacteria are called exoelectrogens. [1] The positive point is that these types of microorganisms (also called bioelectrogenic microorganisms) are not limited to the use of the same simplef uels as inorganic catalysts, as they can also face the oxidation of more complexf uels. [2] One of the cheapest fuels is wastewater.For this reason, microbial fuel cells are frequently related to the treatment of wastewater, [3] but this is not their only application.To understand how aM FC works, the scheme for at ypical MFC is showninFigure 1. The MFC shown consists of two electrodic chambers (anodic and cathodic) and as emipermeable membrane betweent he electrodes. Bacteria oxidize the substrate in the anodic chamber to generate protons and other metabolic products, generallyC O 2 .T he electrons are collected in the anode and travel to the cathode through an external electricalc ircuit, whereas protons pass from the anode to the cathode through the membrane. [2] Oncee lectrons and protons Microbial fuel cells (MFCs) have garnered interestf rom the scientific community since the beginning of this century and this has caused ac onsiderable increase in the scientific production of MFCs. However,t he ability of MFCs to generate power has not increased considerably within this timeframe....

Feasibility of quaternary ammonium and 1,4-diazabicyclo[2.2.2]octane-functionalized anion-exchange membranes for biohydrogen production in microbial electrolysis cells

“…The fair reproducibility of each experiment under the influence of the same substrate loadings is reflected in the current density profiles(Fig. 2)[31], which seemed to be somewhat dependent on the membrane.In total, an acclimation period of 40 days was ensured for the anodic biofilm formation to take place as follows. A week after inoculation, the MECs for all three membranes (AMI-7001, AF49R27, PSEBS CM DBC), which were fed repeatedly with 1 gCOD L -1 using acetate as a substrate, began producing current and by the 21 st day, more or less similar current densities and hydrogen production capacities were observed.…”

A robust correlation based on dimensional analysis to characterize microbial fuel cells

“…Best way to assess the maximum improvement in power density in all the different scenarios (with different combinations of the system variables to identify the optimum gain) is through experimental studies. However testing each scenario through experiments is expensive, both in terms of time as well as resources 11,12 . An alternative is computational modeling.…”

Reproducibility and robustness of microbial fuel cells technology

“…MFC technology is stagnated due to scale-up limitations [3] The average, the median and the fashion indicate the central values. The values of these parameters are very similar in all the cases, especially for the OCV and the maximum power.…”

“…Microbial Fuel Cells (MFCs) are a promising green technology for a planet seriously affected by main problems related to traditional energy sources [1,2]. This interest is reflected by the Web of Science database which index more than 7000 publications related to the keyword microbial fuel cell up to the end of 2018 [3]. However, MFCs are yet to be accepted by the market, being compulsory to demonstrate its robustness and reproducibility.…”