Cuprous oxide-Shewanella mediated photolytic hydrogen evolution

Hydrogen could be an environmentally friendly option as an energy vector for the future. However, its green production process is expensive, involving water electrolysis, which requires a significant amount of energy. New technologies have been developed to decrease the cost associated with water electrolysis, such as using microbial electrolysis cells (MECs). The integration of power performance enhancing elements into bioelectric systems is of applied interest. As in this work the integration of a photocathode into the microbial electrolysis cell, the energy output increases in theory without needing more reactor space. The microbial electrolysis process requires an additional energy input to overcome the theoretical thermodynamic barrier if any and the involved overpotentials for reasonable rate of hydrogen production. In this work, a microbial electrolysis half-cell was combined with a photoelectrochemical half-cell, so called MPEC (microbial photoelectrochemical cell). The MPEC consisted of a Shewanella oneidensis MR-1 bioanode and a five-layered p-type Cu 2 O-based photocathode, using lactate as electron donor to produce H 2 without any external bias than light of 210 and 700 W m −2 . The novelty of the work can be summarized in the following points: The use of MPEC for H 2 production with a stable and efficient multilayer Cu 2 O photocathode. The quantification of the anodic, cathodic and global coulombic efficiencies considering the selectivity of lactate to acetate conversion. The electrochemical characterization (I–V curves) of the bioanode and photocathode for the determination of the electrode which limit the current in the process. Proposition of a model to explain the low anodic coulombic efficiencies (7 ± 2%). In this model lactate may be involved in either a surface reaction at the bioanode (the main reaction producing current) or a bulk aerobic or anaerobic reaction catalysed by planktonic cells (a side reaction that consumes lactate without producing current). This work is of interest of research that aims to integrate multiple processes into bioelectric systems and to use light energy in a direct manner to generate energy vectors such as hydrogen. • A Shewanella oneidensis anode and Cu 2 O-photocathode were employed in an MPEC. • Hydrogen was produced at varying light intensities without an external bias. • During MPEC processing, the coulombic efficiencies were determined. • A model explains two kind of lactate oxidation and eventual efficiency losses.