Dan Ren

Stable and selective electrochemical reduction of carbon dioxide to ethylene on copper mesocrystals

Stable and selective electrochemical reduction of carbon dioxide to ethylene was achieved using copper mesocrystal catalysts in 0.1 M KHCO3. The Cu mesocrystal catalysts were facilely derived by the in situ reduction of a thin CuCl film during the first 200 seconds of the CO2 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 CO2 reduction experiments show that this selectivity towards C2H4 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 CO2 to C2H4. CO adsorption measurements suggest that the remarkable C2H4 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 C2H4 formation for longer than six hours. This is an important and industrially relevant feature missing from many reported Cu-based CO2 reduction catalysts.

Mechanistic Insights into the Enhanced Activity and Stability of Agglomerated Cu Nanocrystals for the Electrochemical Reduction of Carbon Dioxide to n-Propanol

The reduction of carbon dioxide (CO2) to n-propanol (CH3CH2CH2OH) using renewable electricity is a potentially sustainable route to the production of this valuable engine fuel. In this study, we report that agglomerates of ∼15 nm sized copper nanocrystals exhibited unprecedented catalytic activity for this electrochemical reaction in aqueous 0.1 M KHCO3. The onset potential for the formation of n-propanol was 200-300 mV more positive than for an electropolished Cu surface or Cu(0) nanoparticles. At -0.95 V (vs RHE), n-propanol was formed on the Cu nanocrystals with a high current density (jn-propanol) of -1.74 mA/cm(2), which is ∼25× larger than that found on Cu(0) nanoparticles at the same applied potential. The Cu nanocrystals were also catalytically stable for at least 6 h, and only 14% deactivation was observed after 12 h of CO2 reduction. Mechanistic studies suggest that n-propanol could be formed through the C-C coupling of carbon monoxide and ethylene precursors. The enhanced activity of the Cu nanocrystals toward n-propanol formation was correlated to their surface population of defect sites.

Efficient and Stable Evolution of Oxygen Using Pulse-Electrodeposited Ir/Ni Oxide Catalyst in Fe-Spiked KOH Electrolyte

Metal oxides have been extensively explored as catalysts for the electrochemical oxygen evolution reaction (OER). Here, we present an excellent OER catalytic system consisting of pulse-electrodeposited Ir/Ni oxides in Fe(3+)-spiked 1 M KOH. In pure 1 M KOH electrolyte, the optimized catalyst, which had an Ir:Ni atom ratio of 1:1.49, could catalyze 10 mA/cm(2) of O2 production at a small overpotential (η) of 264 mV. Remarkably, we found that its OER performance could be significantly improved by adding 0.3 mM Fe(3+) into the electrolyte. At an η of just 343 ± 3 mV, a huge current of 500 mA/cm(2) was achieved. Furthermore, this catalytic system exhibited a small Tafel slope of 31 mV/dec and a large iridium mass-normalized current of 1260 mA/mgIr at η = 280 mV. We also discovered that the durability of the Ir/Ni oxide catalyst during OER (at 10 mA/cm(2) with η < 280 mV) could be maintained for more than 4.5 days by simply spiking Fe(3+), Ir(3+), and Ni(2+) into the KOH electrolyte. The figures-of-merit in this work, in terms of both activity and stability, compare favorably against values from several state-of-the-art catalysts. Hypotheses for the outstanding performance of the Ir/Ni catalyst are proposed and discussed.

Investigating the Role of Copper Oxide in Electrochemical CO2 Reduction in Real Time

Copper oxides have been of considerable interest as electrocatalysts for CO2 reduction (CO2R) in aqueous electrolytes. However, their role as an active catalyst in reducing the required overpotential and improving the selectivity of reaction compared with that of polycrystalline copper remains controversial. Here, we introduce the use of selected-ion flow tube mass spectrometry, in concert with chronopotentiometry, in situ Raman spectroscopy, and computational modeling, to investigate CO2R on Cu2O nanoneedles, Cu2O nanocrystals, and Cu2O nanoparticles. We show experimentally that the selective formation of gaseous C2 products (i.e., ethylene) in CO2R is preceded by the reduction of the copper oxide (Cu2OR) surface to metallic copper. On the basis of density functional theory modeling, CO2R products are not formed as long as Cu2O is present at the surface because Cu2OR is kinetically and energetically more favorable than CO2R.

Electrocatalysts for the Selective Reduction of Carbon Dioxide to Useful Products.

The electrochemical reduction of carbon dioxide (CO(2)) to hydrocarbons and alcohols holds great promise as a sustainable and green method to produce valuable carbon fuels. In this work, we review the catalysts used in the selective reduction of CO(2) to formate, carbon monoxide, methane and ethylene.

Practices for the collection and reporting of electrocatalytic performance and mechanistic information for the CO2 reduction reaction

The complexities of the physical and analytical chemistry surrounding the CO2 reduction reaction introduce significant challenges to how appropriate catalysts can be designed. This perspective describes the important factors to consider when analyzing the performance of catalysts and reaction mechanisms for the CO2 reduction reaction in aqueous electrolytes. It focuses on the practical aspects of experimental design and instrumentation that are required for the accurate study of these complex reactions. We discuss the common figures-of-merit and suggest appropriate methods for analyzing and reporting experimental data, such that comparisons between research reports can be more easily drawn. In addition, we highlight notable instances of applications of our suggested practices that already exist in the literature in order to emphasize the excellent work that is being performed in the field.