The selective electroreduction of carbon dioxide to C2 compounds (ethylene and ethanol) on copper­(I) oxide films has been investigated at various electrochemical potentials. Aqueous 0.1 M KHCO3 was used as electrolyte. A remarkable finding is that the faradic yields of ethylene and ethanol can be systematically tuned by changing the thickness of the deposited overlayers. Films 1.7–3.6 μm thick exhibited the best selectivity for these C2 compounds at −0.99 V vs RHE, with faradic efficiencies (FE) of 34–39% for ethylene and 9–16% for ethanol. Less than 1% methane was formed. A high C2H4/CH4 products’ ratio of up to ∼100 could be achieved. Scanning electron microscopy, X-ray diffraction, and in situ Raman spectroscopy revealed that the Cu2O films reduced rapidly and remained as metallic Cu0 particles during the CO2 reduction. The selectivity trends exhibited by the catalysts during CO2 reduction in phosphate buffer, and KHCO3 electrolytes suggest that an increase in local pH at the surface of the electrode is not the only factor in enhancing the formation of C2 products. An optimized surface population of edges and steps on the catalyst is also necessary to facilitate the dissociation of CO2 and the dimerization of the pertinent CH x O intermediates to ethylene and ethanol.

Stable and selective electrochemical reduction of carbon dioxide to ethylene was achieved using copper mesocrystal catalysts in 0.1 M KHCO 3 . The Cu mesocrystal catalysts were facilely derived by the in situ reduction of a thin CuCl film during the first 200 seconds of the CO 2 electroreduction process.At −0.99 V vs. RHE, the Faradaic efficiency of ethylene formation using these Cu mesocrystals was 18× larger than that of methane and forms up to 81% of the total carbonaceous products. Control CO 2 reduction experiments show that this selectivity towards C 2 H 4 formation could not be replicated by using regular copper nanoparticles formed by pulse electrodeposition. High resolution transmission electron microscopy reveals the presence of both (100) Cu facets and atomic steps in the Cu mesocrystals which we assign as active sites in catalyzing the reduction of CO 2 to C 2 H 4 . CO adsorption measurements suggest that the remarkable C 2 H 4 selectivity could be attributed to the greater propensity of CO adsorption on Cu mesocrystals than on other types of Cu surfaces. The Cu mesocrystals remained active and selective towards C 2 H 4 formation for longer than six hours. This is an important and industrially relevant feature missing from many reported Cu-based CO 2 reduction catalysts.

Incorporating small organic molecules with redox-active sites into a suitable porous organic framework could enhance both ion diffusion rate and electronic conductivity while reducing its solubility in electrolytes. Principles for the construction of a redox-active porous organic framework should not sacrifice the theoretical capacity and should balance various important parameters such as specific capacity, cycling stability, rate capability, as well as scalability. Herein, we designed two new porous organic frameworks as cathode materials for lithium-ion batteries (LIBs) using hexaazatrinaphthalene (HATN) cores which show high theoretical capacities. The polymer materials were synthesized in a facile and scalable manner with different structural features ranging from a rigid conjugated framework (HATNPF1) to a flexible nonconjugated framework (HATNPF2). HATNPF polymers demonstrated a high specific capacity (309 mA h g–1), and excellent long-term cycling stability (92% capacity retention after 1200 cycles) and rate capability (65% capacity retention at 2 A g–1 as compared to capacity at 0.2 A g–1), which is an improvement over previously reported porous organic polymers and the HATN monomer. The structure–property relationships of these porous frameworks were also studied using computational modeling.

A method to facilitate the electrochemical reduction of carbon dioxide (CO2) to ethane (C2H6) was developed. The electrolyte used was aqueous 0.1 M KHCO3. Chronoamperometry, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, online gas chromatography, and nuclear magnetic resonance spectroscopy were used to characterize the electrochemical system and products formed. Carbon dioxide reduction using a Cu2O-derived copper working electrode gave ethylene (C2H4) and ethanol as main C2 products, with optimized faradic efficiencies (FE) of 32.1 and 16.4% at −1.0 V vs RHE. The active catalysts were ∼500 nm-sized crystalline Cu0 particles, which were formed via the reduction of the Cu2O precursor during the initial phase of the CO2 reduction reaction. When palladium­(II) chloride was added to the electrolyte, C2H6 formation could be achieved with a significant FE of 30.1% at the said potential. The production of C2H4 was, on the other hand, suppressed to a FE of 3.4%. The alternate use of Pd0, PdO, or Pd–Al2O3 dopants did not afford the same conversion efficiency. Extensive mechanistic studies demonstrate that C2H4 was first produced from CO2 reduction at the Cu0 sites, followed by hydrogenation to C2H6 with the assistance of adsorbed PdCl x . Interestingly, we discover that both Cu and PdCl x sites are necessary for the efficient reduction of C2H4 to C2H6. The PdCl2 was “consumed” during the reaction, and a hypothesis for how it contributes to the reduction of CO2 to ethane is proposed.