The synergy between metal alloy nanoparticles (NPs) and single atoms (SAs) should maximize the catalytic activity. However, there are no relevant reports on photocatalytic CO 2 reduction via utilizing the synergy between SAs and alloy NPs. Herein, we developed a facile photodeposition method to coload the Cu SAs and Au−Cu alloy NPs on TiO 2 for the photocatalytic synthesis of solar fuels with CO 2 and H 2 O. The optimized photocatalyst achieved record-high performance with formation rates of 3578.9 for CH 4 and 369.8 μmol g −1 h −1 for C 2 H 4 , making it significantly more realistic to implement sunlightdriven synthesis of value-added solar fuels. The combined in situ FT-IR spectra and DFT calculations revealed the molecular mechanisms of photocatalytic CO 2 reduction and C−C coupling to form C 2 H 4 . We proposed that the synergistic function of Cu SAs and Au−Cu alloy NPs could enhance the adsorption activation of CO 2 and H 2 O and lower the overall activation energy barrier (including the rate-determining step) for the CH 4 and C 2 H 4 formation. These factors all enable highly efficient and stable production of solar fuels of CH 4 and C 2 H 4 . The concept of synergistic SAs and metal alloys cocatalysts can be extended to other systems, thus contributing to the development of more effective cocatalysts.

Low extracellular electron transfer performance is often a bottleneck in developing high-performance bioelectrochemical systems. Herein, we show that the self-assembly of graphene oxide and Shewanella oneidensis MR-1 formed an electroactive, reduced-graphene-oxide-hybridized, three-dimensional macroporous biofilm, which enabled highly efficient bidirectional electron transfers between Shewanella and electrodes owing to high biomass incorporation and enhanced direct contact-based extracellular electron transfer. This 3D electroactive biofilm delivered a 25-fold increase in the outward current (oxidation current, electron flux from bacteria to electrodes) and 74-fold increase in the inward current (reduction current, electron flux from electrodes to bacteria) over that of the naturally occurring biofilms.

Electroactive biofilms play essential roles in determining the power output of microbial fuel cells (MFCs). To engineer the electroactive biofilm formation of Shewanella oneidensis MR-1, a model exoelectrogen, we herein heterologously overexpressed a c-di-GMP biosynthesis gene ydeH in S. oneidensis MR-1, constructing a mutant strain in which the expression of ydeH is under the control of IPTG-inducible promoter, and a strain in which ydeH is under the control of a constitutive promoter. Such engineered Shewanella strains had significantly enhanced biofilm formation and bioelectricity generation. The MFCs inoculated with these engineered strains accomplished a maximum power density of 167.6 ± 3.6 mW/m(2) , which was ∼ 2.8 times of that achieved by the wild-type MR-1 (61.0 ± 1.9 mW/m(2) ). In addition, the engineered strains in the bioelectrochemical system at poised potential of 0.2 V vs. saturated calomel electrode (SCE) generated a stable current density of 1100 mA/m(2) , ∼ 3.4 times of that by wild-type MR-1 (320 mA/m(2) ).

A novel bioelectrochemical membrane reactor (BEMR), which takes advantage of a membrane bioreactor (MBR) and microbial fuel cells (MFC), is developed for wastewater treatment and energy recovery. In this system, stainless steel mesh with biofilm formed on it serves as both the cathode and the filtration material. Oxygen reduction reactions are effectively catalyzed by the microorganisms attached on the mesh. The effluent turbidity from the BEMR system was low during most of the operation period, and the chemical oxygen demand and NH(4)(+)-N removal efficiencies averaged 92.4% and 95.6%, respectively. With an increase in hydraulic retention time and a decrease in loading rate, the system performance was enhanced. In this BEMR process, a maximum power density of 4.35 W/m(3) and a current density of 18.32 A/m(3) were obtained at a hydraulic retention time of 150 min and external resister of 100 Ω. The Coulombic efficiency was 8.2%. Though the power density and current density of the BEMR system were not very high, compared with other high-output MFC systems, electricity recovery could be further enhanced through optimizing the operation conditions and BEMR configurations. Results clearly indicate that this innovative system holds great promise for efficient treatment of wastewater and energy recovery.