Accelerated H2 Evolution during Microbial Electrosynthesis with Sporomusa ovata

Pier-Luc Tremblay,Neda Faraghiparapari,Tian Zhang

doi:10.3390/catal9020166

Abstract

Microbial electrosynthesis (MES) is a process where bacteria acquire electrons from a cathode to convert CO2 into multicarbon compounds or methane. In MES with Sporomusa ovata as the microbial catalyst, cathode potential has often been used as a benchmark to determine whether electron uptake is hydrogen-dependent. In this study, H2 was detected by a microsensor in proximity to the cathode. With a sterile fresh medium, H2 was produced at a potential of −700 mV versus Ag/AgCl, whereas H2 was detected at −500 mV versus Ag/AgCl with cell-free spent medium from a S. ovata culture. Furthermore, H2 evolution rates were increased with potentials lower than −500 mV in the presence of cell-free spent medium in the cathode chamber. Nickel and cobalt were detected at the cathode surface after exposure to the spent medium, suggesting a possible participation of these catalytic metals in the observed faster hydrogen evolution. The results presented here show that S. ovata-induced alterations of the cathodic electrolytes of a MES reactor reduced the electrical energy required for hydrogen evolution. These observations also indicated that, even at higher cathode potentials, at least a part of the electrons coming from the electrode are transferred to S. ovata via H2 during MES.

Highlights

IntroductionReductive bioelectrochemical processes rely on the transfer of electrons from a cathode to a microbial catalyst for the reduction of a substrate with protons coming from an anodic reaction [1,2]
Reductive bioelectrochemical processes rely on the transfer of electrons from a cathode to a microbial catalyst for the reduction of a substrate with protons coming from an anodic reaction [1,2].The substrate can be inorganic carbon molecules like CO2 that will be reduced to multicarbon compounds or CH4 via microbial electrosynthesis (MES) [3,4,5,6,7,8,9,10]
H2 concentration was measured in close proximity to the cathode surface where microbial catalysts in operating MES reactor [3,38,41] are likely to oxidize large fraction of H2, if any is produced, before it can diffuse away in the medium and in the reactor gas phase

Summary

Introduction

Reductive bioelectrochemical processes rely on the transfer of electrons from a cathode to a microbial catalyst for the reduction of a substrate with protons coming from an anodic reaction [1,2]. The substrate can be inorganic carbon molecules like CO2 that will be reduced to multicarbon compounds or CH4 via microbial electrosynthesis (MES) [3,4,5,6,7,8,9,10]. In reductive bioelectrochemical systems (BES), the electrons are thought to be transferred directly via physical contact between the microbes and the cathode or indirectly via an electron shuttle such as H2 [14,15,16]. It has been proposed that when the cathode potential is set higher than

Methods

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Conclusion