Amine-linked covalent organic frameworks (COFs) were synthesized by the reduction of parent imine-linked COFs by crystal-to-crystal transformation. The excellent chemical stability of these COFs in combination with the presence of a large amount of amine functional groups led to a robust and molecularly defined interface at the silver metal surface as an electrode for the electrochemical reduction of CO 2. The concerted operation of COF and the metal surface resulted in high conversion efficiency and excellent selectivity against the reduction of water.

Electrochemical reduction of carbon dioxide (CO2RR) to liquid fuels and valued chemicals is a meaningful approach to decreasing CO2 emissions and alleviating the energy crisis. In particular, the conversion of CO2 into multicarbon products is of technological significance. Cu is the only transition metal that is able to catalyze the CO2RR to produce C2+ hydrocarbons, but the catalytic selectivity of pristine Cu is low. Herein we report a facile method to largely enhance the C2+ selectivity of polycrystalline Cu toward the CO2RR. By coating the Cu surface with a 50 nm thick film of polyaniline (PANI), the faradaic efficiency (FE) of C2+ hydrocarbons was increased from ca. 15% to 60% at −1.1 VRHE in KHCO3 solutions. When applying the PANI coating onto Cu nanoparticles, the FE of C2+ hydrocarbons can even reach 80%, with the FE of ethylene over 40%. Such performance remained stable in a test period of 20 h. The superiority of the Cu/PANI interface is not due to the change in the morphology or the electronic properties of the Cu substrate but instead is due to an improvement in the coverage and interaction of the CO intermediate, which facilitates the CO–CO coupling, as revealed by in situ infrared spectroscopy. This study opens an avenue to tuning the catalytic activity and selectivity of Cu toward the CO2RR, not through the structure of the catalyst but through the environment above the surface.

An approach to the industrial-scale conversion of CO2 through electrolysis is realized in this work. Such a device is fully based on alkaline polymer electrolytes, both as the membrane and the ionomer inside electrodes, and works only with pure water. Typical current density is 500 mA cm−2 @ 3V 60 °C, with the faradaic efficiency of CO production over 90%.

Powered by renewable electricity, the electrochemical conversion of CO2 to liquid fuels and valuable chemicals is a meaningful approach to enable carbon cycling and tackle environmental issues. An intrinsic challenge has been the low efficiency and selectivity, in particular for deep reduction products. Here, we report on an interface-enhanced strategy for transforming the catalytic selectivity toward the CO2 reduction reaction (CO2RR). Inspired by the enzyme catalysis in nature, where the catalytic center is surrounded by a chemically selective environment, we create a thin layer of nitrogen-doped carbon (N x C) over the Cu surface. The N x C environment does not modify the electronic property of Cu but selectively enriches and activates CO2 molecules through the specific N–CO2 interaction, as experimentally identified. Such a Cu/N x C interface has boosted the faradic efficiency (FE) of the CO2RR to be above 90%, with the C2 products (ethylene and ethanol) being the majority (80% in total FE). The N x C overlayer also protects well the Cu substrate from the morphological change, thus increasing the catalytic stability. Our findings manifest that the chemical environment over the metal surface indeed plays a crucial, but not well recognized, role in selectivity control, which can hardly be achieved by solely tuning the electronic structure of metal catalysts.

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