Carbon nanotubes modified reticulated vitreous carbon materials enhancing extracellular electron transfer of Shewanella loihica PV-4

Abstract

Increasing current output of bioelectrochemical devices is crucial for their real-world application. Electrodes modified with conductive nanoparticles increase the contact area between anodic microorganisms and solid electron acceptors, thus resulting in higher cells concentration and current output. Electron transfer mechanisms in Shewanella loihica PV-4 viable biofilms formed at carbon nanotubes (CNTs)-coated RVC electrode is investigated in potentiostat-controlled electrochemical cells set at oxidative potentials. Chronoamperometry showed a stable biofilm growth with final current output above 150 µA·cm−2 within two weeks, which was 3 times higher than unmodified RVC systems. The current output showed biphasic growth, which could be attributed to outer layer and inner layer biofilm growth, respectively, where aerobic and anaerobic growth occurred, respectively. Cyclic voltammetry and differential pulse voltammetry analysis indicated a contribution from both direct electron transfer (DET) and mediated electron transfer (MET) mechanisms. In the early stage, DET was dominant and contributed to biofilm formation. In the late stage, the contribution from MET to the overall extracellular electron transfer (EET) eventually became dominant. The mediators could be confined into the biofilm matrix and produce continuous current output. Scanning electron microscopy (SEM) showed that the bacteria distributed uniformly on the electrode surface, which enhanced the EET rate. The high surface of the RVC-CNTs electrode was accessible to biofilms in short-term batch experiments, and RVC-CNTs could be a potential anodic material for bioelectrochemical devices.