Microstructuring Conductive Electrospun Mats for Enhanced Electro‑active Biofilm Growth and High‑Performance Bioelectrocatalysis

Electrospun materials have attracted considerable attention in microbial fuel cells(MFC)owing to their porous structures,which facilitate the growth of electro-active biofilms(EABs).However,the impact of fiber diameter-controlled porous architectures on EAB growth and MFC performance has not been extensively studied.Herein,a highly conductive polypyrrole-modified electrospun polyacrylonitrile(PAN)mat was prepared as an electrode material for Shewanella putrefaciens CN32-based MFCs.The dominant pore size of the corresponding mat increases from 1 to around 20μm as the fiber diameter increases from 720 to 3770 nm.This variation affects the adhesion and growth behaviors of electrochemically active bacteria on the mat-based electrodes.The electrodes with poresranging from 2 to 10μm allow bacterial penetration into the interior,leading to significant biofilm loading and effective bioelectrocatalysis.However,the tight lamination of the electrospun fibers restricts bacterial growth in the deep interior space.We developed a friction-induced triboelectric expanding approach to rendering the mats with layered structures to overcome this limitation.The inter-layer spaces of the expanded conductive mat can facilitate bacterial loading from both sides of each layer and serve as channels to accelerate the catalysis of organic substances.Therefore,the expanded conductive mat with appropriate pore sizes delivers superior bioelectrocatalytic performance in MFCs and dye degradation.Based on the findings,a mechanism for the porous structure-controlled EAB formation and bioelectrocatalytic performance was proposed.This work may provide helpful guidance and insights for designing microfiber-based electrodes for microbial fuel cells.

Direct detection of a single[4Fe-4S]cluster in a tungsten-containing enzyme:Electrochemical conversion of CO_(2) into formate by formate dehydrogenase

The conversion of CO_(2) into fuels and valuable chemicals is one of the central topics to combat climate change and meet the growing demand for renewable energy.Herein,we show that the formate dehydrogenase from Clostridium ljungdahlii(ClFDH)adsorbed on electrodes displays clear characteristic voltammetric signals that can be assigned to the reduction and oxidation potential of the[4Fe-4S]^(2+/+)cluster under nonturnover conditions.Upon adding substrates,the signals transform into a specific redox center that engages in catalytic electron transport.ClFDH catalyzes rapid and efficient reversible interconversion between CO_(2) and formate in the presence of substrates.The turnover frequency of electrochemical CO_(2) reduction is determined as 1210 s^(-1) at 25℃ and pH 7.0,which can be further enhanced up to 1786 s^(-1) at 50℃.The Faradaic efficiency at−0.6 V(vs.standard hydrogen electrode)is recorded as 99.3%in a 2-h reaction.Inhibition experiments and theoretical modeling disclose interesting pathways for CO_(2) entry,formate exit,and OCN−competition,suggesting an oxidation-state-dependent binding mechanism of catalysis.Our results provide a different perspective for understanding the catalytic mechanism of FDH and original insights into the design of synthetic catalysts.

Electrocatalytic NAD(P)H regeneration for biosynthesis

The highly efficient chemoselectivity,stereoselectivity,and regioselectivity render enzyme catalysis an ideal pathway for the synthesis of various chemicals in broad applications.While the cofactor of an enzyme is necessary but expensive,the conversed state of the cofactor is not beneficial for the positive direction of the reaction.Cofactor regeneration using electrochemical methods has the advantages of simple operation,low cost,easy process monitoring,and easy product separation,and the electrical energy is green and sustainable.Therefore,bioelectrocatalysis has great potential in synthesis by combining electrochemical cofactor regeneration with enzymatic catalysis.In this review,we detail the mechanism of cofactor regeneration and categorize the common electron mediators and enzymes used in cofactor regeneration.The reaction type and the recent progress are summarized in electrochemically coupled enzymatic catalysis.The main challenges of such electroenzymatic catalysis are pointed out and future developments in this field are foreseen.

Direct electron transfer of glucose oxidase on the carbon nanotube electrode

The direct electron transfer of glucose oxidase (GOx) immobilized onto the surface of the carbon nanotube (CNT)-modified glassy carbon (CNT/GC) electrode is reported. The direct electron transfer rate of GOx is greatly enhanced when it was immobilized onto the surface of CNT/GC electrode. Cyclic voltammetric results show a pair of well-defined and nearly symmetric redox peaks, which corresponds to the direct electron transfer of GOx, with the formal potential (E 0′), which is almost independent on the scan rates, of about ?0.456 V (vs. SCE) in the phosphate buffer solution (pH 6.9). The apparent heterogeneous electron transfer rate constant (ks) of GOx at the CNT/GC electrode surface is estimated to be (1.74 ± 0.42) s-1, which is much higher than that reported previously. The dependence of E 0′ on solution pH indicates that the direct electron transfer of GOx is a two-electron-transfer coupled with two-proton-transfer reaction process. The experimental results also demonstrate that the immobilized GOx retains its bioelectrocatalytic activity toward the oxidation of glucose. The method presented here can be easily extended to obtain the direct electrochemistry of other enzymes or proteins.

Direct Electrochemistry of Horseradish Peroxidase Immobilized in a Low Molecular Weight Gel

The ternary system of dodecylpyridinium bromide(DDPB)/acetone/H2O with appropriate composition can form a gel spontaneously and the gel is stable in hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophos-phate([Bmim]PF_(6)).Based on the gelation phenomenon we observed,the low molecular weight gelator(LMWG)was first tried to immobilize horseradish peroxidase(HRP)on glassy carbon electrode(GCE).The scanning elec-tron microscope(SEM)images,the UV-Vis spectra and the bioactivity measurement indicate that the gel is suitable for the immobilization of HRP.The direct electrochemistry of the HRP-gel modified GCE(HRP-gel/GCE)in[Bmim]PF_(6)shows a pair of well-defined and quasi-reversible redox peaks with the heterogeneous electron transfer rate constant(ks)being 14.4 s^(−1),indicating that the direct electron transfer between HRP and GCE is fast.The HRP-gel/GCE is stable and reproducible.Also the electrode exhibits good electrocatalytic effect on the reduction of trichloroacetic acid(TCA),showing good promise in bioelectrocatalysis.