Metal-doped zeolitic imidazolate framework-8 (ZIF-8)-derived carbon materials are attractive for the electrocatalytic reduction of CO2 into CO. In such carbon materials, due to the fusion and aggregation of ZIF-8 precursors during the high-temperature pyrolysis process, it is desirable yet still challenging to create a high specific surface area with more active sites available for reacting with reactants. Using SiO2 as a protective coating on the ZIF-8 surface, we synthesize Fe, N-co-doped porous carbon nanoparticles (Fe-CNPs) which possess a hierarchical pore structure with a specific surface area as high as 1156.6 m2 g–1, much higher than the counterparts without a SiO2 coating (360.1 m2 g–1). Over these highly porous Fe-CNPs, the total current densities are more than 3 times higher than those of the lowly porous ones for the electrochemical CO2 reduction. More importantly, the maximum CO Faradaic efficiency for Fe-CNPs increases from ca. 75.0 to 98.8% in a concentrated KHCO3 solution (1 mol L–1). The porosity-induced high selectivity for CO production is also revealed on Ni-doped and Co-doped ZIF-derived CNPs, suggesting a new pathway for designing high-performance carbon catalysts through engineering the porosity for the electrochemical CO2 reduction.

Capacitive deionization (CDI) has shown great promise in desalinating salt water; however, conventional CDI electrode materials suffer from low specific salt capacity and charge efficiency owing to the co-ion expulsion effect. Herein, using expanded MoS 2 nanosheets supported by reduced graphene oxide (MoS 2 /rGO) as the intercalation electrode, we develop a hybrid CDI system that shows a battery-like behavior and can reversibly store cations through the intercalation mechanism. The incorporation of rGO in the composite not only affords a conductive support and ensures fast electron transfer but also, more importantly, widens the MoS 2 interlayer spacing from 0.62 to 0.73 nm. The expanded MoS 2 interlayer facilitates the diffusion of cations and decreases the internal strain during the intercalation/de-intercalation process. Also, it endows MoS 2 /rGO with more accessible sites and space for cations in the electrolyte. Benefiting from the desirable structure features, the hybrid CDI system delivers a remarkable specific salt capacity of 34.20 mg g −1 and a charge efficiency as high as 97% in 300 mg L −1 sodium chloride aqueous solution. The MoS 2 /rGO involved in the CDI system for the adsorption of other metal ions is also verified, indicating its potential applications for the removal of various metal ions in brackish water and seawater.

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