Herein, we introduce a permeable carbon nanotube hollow-fiber electrode incorporated with SnO 2 nanoparticles (SnO 2 −CHE) and propose a new type of gas-phase operational mode. Highly efficient electrochemical syngas production from CO 2 is made possible by switching the operating mode from liquid phase to gas phase. The operation of SnO 2 −CHE in the conventional liquid-phase mode yielded a H 2 /CO ratio higher than 4.59, and the maximum j CO was only 2.16 mA/cm 2 at −0.88 V (vs RHE) due to the low solubility and limited mass transfer of CO 2 in liquid electrolytes. On the other hand, SnO 2 −CHE operated under the newly designed gasphase mode achieved a H 2 /CO ratio ranging from 1.22 to 4.11 with a maximum j CO of 7.42 mA/cm 2 at −0.76 V (vs RHE), which is proper for direct post-conversion processes. Therefore, this work could offer a new avenue for electrochemical syngas production using a nonprecious metal-based hollow-fiber type electrode, which allows for a large electrode surface area and high CO 2 availability in gas-phase operation.

In this study, NaTi2(PO4)3 (NTP) nanoparticles were incorporated into a carbon nanotube hollow-fiber (CHF) electrode for the selective removal of Na+ during the capacitive deionization (CDI) of salty water. Due to the Na+-selective electro-sorption of NTP nanoparticles, NTP-CHF achieved 1.5 ~2 times higher Na+ adsorption capacity than that of CHF only electrodes at a range of 1.7 mM~17.1 mM (100 mg L−1~1000 mg L−1) NaCl solution. Moreover NTP-CHF sustained the Na+ adsorption capacity even at the presence of Ca2+ ions, whereas the dramatic decrease in Na+ removal was observed in CHF with an increase of Ca2+ concentration. As the result, NTP-CHF can retain 52% of the initial Na+ removal capacity after three times of capture and release cycles at the presence of Ca2+, while CHF showed <10% of the initial Na+ removal capacity due to the irreversible adsorption of Ca2+ ions onto the MWCNT surface. Thus, the incorporation of NTP into the conductive carbon nanomaterial network can greatly improve both the adsorption capacity and selectivity of Na+ compared to the conventional carbon-based electrode during the CDI of salty water containing multivalent cations such as Ca2+.

The production of biogas was promoted via direct interspecies electron transfer (DIET) by employing electro-conductive carbon-nanotube hollow-fiber media (CHM) in anaerobic digestion. Experimental results showed a positive effect of CHM presence on CH4 productivity with 34% higher CH4 production rate than that of in the presence of non-electroconductive polymeric hollow fiber media. An increased CH4 production rate was due to the shift in the microbiome with more abundant Pelobacter (10.0%), Geobacter (6.9%), and Methanosaeta (15.7%), which play key roles in promoting CH4 production via syntrophic metabolism associated with DIET. Microscopic morphology analysis, using confocal laser scanning microscopy and scanning electron microscopy, exhibited that several living cells were attached with electro-conductive pili on the CHM surface, thereby facilitated electron transport between microbial cells.

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