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Here, we report a new microbial electrolysis cell (MEC) system for hydrogen generation that was composed of a microbial fuel cell (MFC) and a bio-photoelectrochemical cell (BPEC). The BPEC consisted of a photocathode and a microbially-catalyzed anode. In the new MEC system, hydrogen was produced by the BPEC photocathode when it was illuminated with visible light, with the voltage for electrolysis supplied by the MFC. The electrons produced from the MFC anode were transferred to the BPEC photocathode through an external circuit and then photogenerated holes captured some of the electrons emitted by the MFC anode under visible light. This prevented the recombination of the photogenerated hole and electron pairs, leaving more photogenerated electrons available for hydrogen evolution reactions. This also allowed the remaining electrons from the MFC anode to participate in hydrogen evolution reactions. Under visible light, hydrogen was continuously produced from the new MEC system, with a maximum current density of 0.68 A m−2 and an average hydrogen-production rate of 1.35 ± 0.15 mL h−1.

To enhance the performance of activated carbon air cathodes for microbial fuel cells (MFCs), scattered and dense air-cathodes are fabricated by the rolling-press method with the gas diffusion layer or the catalyst layer (CL) invaded to stainless steel meshes (SSM). The maximum power density with scattered cathodes (2503 ± 61 mW m−2) is 29% higher than those of dense cathodes because of the decreased internal resistance and increased oxygen reduction reaction activity. The decrease in the electrode volume density and invasion of CL into SSM has been demonstrated to be an optimal structure, with the highest exchange current density up to 1.26 A m−2 and the lowest charge transfer resistance as low as 1.5 Ω. The increase in performance is believed to result from the enhanced mass transport through extra pores and the contact of activated carbon to the current collector. This novel structure of an air-cathode has a promising future as an application in MFCs.

Bioelectrochemical remediation is an emerging technology for in situ removal of petroleum hydrocarbons in soil. Here we demonstrated that the remediation can be extended to a larger range by adding multilayer anodes in contaminated soils. Using a three anodes system with activated carbon as the cathodic catalyst, 918 C of charge transferred during 180 days in aged saline soil. The degradation of both polycyclic aromatic hydrocarbons (PAHs) and n-alkanes were accelerated in each layer compared to the disconnected control. The net degradation rates of total petroleum hydrocarbons, 16 priority PAHs and total n-alkanes (C8–C40) were 18%, 36% and 29%, respectively. Popular exoelectrogens (such as Geobacteraceae sp.) and Escherichia were identified, which possibly played an important role in this bioelectrochemical process.