Copper-based metal–organic frameworks (MOFs) and their derivatives have been used for CO2 electroreduction; however, they still have obvious drawbacks like poor selectivity and durability. Here, Cu_btc (btc = benzene-1,3,5-tricarboxylate)-derived Cu2O/Cu anchored in a nitrogen-doped porous carbon framework (Cu2O/Cu@NC) was prepared for CO2 electroreduction. Cu2O/Cu@NC-800 (carbonizing Cu_btc at 800 °C) produced formate and ethanol concurrently with an overpotential as low as ∼380 mV. However, it exhibited higher selectivity toward formate against ethanol, with the maximum formate faradaic efficiencies of 70.5% at −0.68 V vs a reversible hydrogen electrode (RHE), which was 1.79 and 1.84 times higher than that of Cu2O/Cu@NC-700 and Cu2O/Cu@NC-900. This superior performance remained stable for over 30 h. The enhancement in activity and selectivity was attributed to (i) a higher Cu content and well-dispersed Cu2O/Cu nanoparticles inside the carbon frameworks, which provided abundant active reaction sites, and (ii) a higher content of N doped into the Cu2O/Cu lattice to possibly facilitate *OCHO generation. These findings provided a convenient strategy to enhance the activity and selectivity of catalysts for efficient CO2 electroreduction.

The photoelectrochemical cell (PEC) is a promising tool for the degradation of organic pollutants and simultaneous electricity recovery, however, current cathode catalysts suffer from high costs and short service lives. Herein, we present a novel biocathode coupled PEC (Bio-PEC) integrating the advantages of photocatalytic anode and biocathode. Electrochemical anodized TiO2 nanotube arrays fabricated on Ti substrate were used as Bio-PEC anodes. Field-emission scanning electron microscope images revealed that the well-aligned TiO2 nanotubes had inner diameters of 60-100 nm and wall-thicknesses of about 5 nm. Linear sweep voltammetry presented the pronounced photocurrent output (325 μA/cm(2)) under xenon illumination, compared with that under dark conditions. Comparing studies were carried out between the Bio-PEC and PECs with Pt/C cathodes. The results showed that the performance of Pt/C cathodes was closely related with the structure and Pt/C loading amounts of cathodes, while the Bio-PEC achieved similar methyl orange (MO) decoloration rate (0.0120 min(-1)) and maximum power density (211.32 mW/m(2)) to the brush cathode PEC with 50 mg Pt/C loading (Brush-PEC, 50 mg). The fill factors of Bio-PEC and Brush-PEC (50 mg) were 39.87% and 43.06%, respectively. The charge transfer resistance of biocathode was 13.10 Ω, larger than the brush cathode with 50 mg Pt/C (10.68 Ω), but smaller than the brush cathode with 35 mg Pt/C (18.35 Ω), indicating the comparable catalytic activity with Pt/C catalyst. The biocathode was more dependent on the nutrient diffusion, such as nitrogen and inorganic carbon, thus resulting in relatively higher diffusion resistance compared to the brush cathode with 50 mg Pt/C loading that yielded similar MO removal and power output. Considering the performance and cost of PEC system, the biocathode was a promising alternative for the Pt/C catalyst.

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