Improving the electrochemical characteristics and performance of a neutral all-iron flow battery by using the iron reduction bacteria

At present, the all-iron redox flow batteries (RFBs) have greater application potential due to high accessibility of electrolytes compared to traditional RFBs. Meanwhile, although electroactive bacteria can accelerate the electrons transfer, their potential to improve the performance of RFBs has been overlooked. Previously, we had confirmed that ferrous-oxidizing bacteria (FeOB) could enhance the performance of an all-iron RFB, therefore we conducted several batch experiments and chronopotentiometry experiments by using the ferric-reducing bacteria (FeRB) or mixed culture (FeOB and FeRB) to demonstrate whether they have the same or stronger effects on Fe3+-DTPA/Na4[Fe(CN)6] RFB. The results showed that the experimental reactors could achieve higher charging current density and initial cathodic potential during constant voltage charging process. The electrochemical impedance spectroscopy data and cyclic voltammetry curves demonstrated that the polarization impedance increased slower and reduction peak potential of experimental groups also emerged a positive shift compared to CK. According to chronopotentiometry experiments results, the microbes could function at maximum 0.3 M, 12 mA/cm2, and also improved the charging specific capacity. Combined the SEM pictures and microbial composition analysis, the main functional electroactive FeRB were Alcaligenes, Corynebacterium and Bacillus, which indicated to have important potential in improving the performance of RFBs.

Bioelectrochemical approach for enhancing lignocellulose degradation and biofilm formation in Geobacillus strain WSUCF1

Investigations on microbial electrocatalysis as a strategy for enhancing the rates of substrate utilization leading to enhanced yield of biomass and enhanced biofilm formation are reported. A thermophilic Geobacillus sp. strain WSUCF1 (60 °C), a potential lignocellulose degrading microorganism was used as the electrocatalyst. Glucose, cellulose, and corn stover were used as the feedstocks. The results of this investigation showed that applying the oxidation potential of -0.383 mV (vs PRE) increased the glucose utilization and COD removal by 25.5% and 29.7% respectively. The bioelectrocatalysis strategy also increased the biomass yield by 81.2, 42.1, and 49.5% in the case of systems fed with glucose, cellulose, and corn stover, respectively, when compared with the systems without applied oxidation potential. This is the first work reporting the effects of applied oxidation potential on increasing the rates of degradation of lignocellulosic biomass and enhanced biofilm formation.

Microbial electrocatalysis: Redox mediators responsible for extracellular electron transfer

Redox mediator plays an important role in extracellular electron transfer (EET) in many environments wherein microbial electrocatalysis occurs actively. Because of the block of cell envelope and the low difference of redox potential between the intracellular and extracellular surroundings, the proceeding of EET depends mainly on the help of a variety of mediators that function as an electron carrier or bridge. In this Review, we will summarize a wide range of redox mediators and further discuss their functional mechanisms in EET that drives a series of microbial electrocatalytic reactions. Studying these mediators adds to our knowledge of how charge transport and electrochemical reactions occur at the microorganism-electrode interface. This understanding would promote the widespread applications of microbial electrocatalysis in microbial fuel cells, bioremediation, bioelectrosynthesis, biomining, nanomaterial productions, etc. These improved applications will greatly benefit the sustainable development of the environmental-friendly biochemical industries.

Type III Secretion Filaments as Templates for Metallic Nanostructure Synthesis

Nanostructured materials can be interfaced with living cells to enable unique chemical and biological outcomes. However, it is challenging to precisely control the shape and chemical composition of submillimeter sized, cell-associated materials. In this protocol, we describe how to genetically modify and isolate a self-assembling filament protein from Salmonella enterica, PrgI, to bind Au nanoparticles. Au-conjugated filaments can be chemically reduced in vitro to form contiguous wires and networks that are several micrometers in length. We also describe a strategy to assemble PrgI-based filaments on live cells, which can then be sheared or remain tethered to cells for gold conjugation. These methods form the basis of a strategy for interactions between inorganic and organic systems, and could be expanded to introduce interactions with other metal nanoparticles for which peptide binding partners are known.

The type of ion selective membrane determines stability and production levels of microbial electrosynthesis

Microbial electrosynthesis (MES) can enable electricity-driven bioproduction from CO₂. Several membrane types such as anion exchange, cation exchange, and bipolar membranes (AEM/CEM/BPM) can be used to separate the anodic oxidation from the biocathodic reduction. The impact of the membrane type on MES has not yet been studied. Therefore we compared the three membranes for MES of acetic acid. The reactor with AEM enabled in situ recovery of acetic acid. This extraction led to a 32% higher production rate and efficiency compared to the systems that did not include product recovery, as product inhibition was likely occurring. Besides H⁺/OH^-, mainly HCO₃^- contributed to charge balancing. Due to water displacement across the membrane, the product concentration in the AEM reactor (9g/L) did not exceed the concentration in the CEM reactor (10.5g/L). Overall this comparison shows that the membrane type in MES can be critical towards a stable and efficient process.

Pyrolytic carbon-coated stainless steel felt as a high-performance anode for bioelectrochemical systems

Scale up of bioelectrochemical systems (BESs) requires highly conductive, biocompatible and stable electrodes. Here we present pyrolytic carbon-coated stainless steel felt (C-SS felt) as a high-performance and scalable anode. The electrode is created by generating a carbon layer on stainless steel felt (SS felt) via a multi-step deposition process involving α-d-glucose impregnation, caramelization, and pyrolysis. Physicochemical characterizations of the surface elucidate that a thin (20±5μm) and homogenous layer of polycrystalline graphitic carbon was obtained on SS felt surface after modification. The carbon coating significantly increases the biocompatibility, enabling robust electroactive biofilm formation. The C-SS felt electrodes reach current densities (jmax) of 3.65±0.14mA/cm(2) within 7days of operation, which is 11 times higher than plain SS felt electrodes (0.30±0.04mA/cm(2)). The excellent biocompatibility, high specific surface area, high conductivity, good mechanical strength, and low cost make C-SS felt a promising electrode for BESs.