A study based on operando electrochemical scanning tunneling microscopy (EC-STM) has shown that a polycrystalline Cu electrode held at a fixed negative potential, -0.9 V (vs SHE), in the vicinity of CO2 reduction reactions (CO2RR) in 0.1 M KOH, undergoes stepwise surface reconstruction, first to Cu(111) within 30 min, and then to Cu(100) after another 30 min; no further surface transformations occurred after establishment of the Cu(100) surface. The results may help explain the Cu(100)-like behavior of Cu(pc) in terms of CO2RR product selectivity. They likewise suggest that products exclusive to Cu(100) single-crystal electrodes may be generated through the use of readily available inexpensive polycrystalline Cu electrodes. The study highlights the dynamic nature of heterogeneous electrocatalyst surfaces and also underscores the importance of operando interrogations when structure-composition-reactivity correlations are intended.
We report the electrocatalytic reduction of CO 2 to the highly reduced C 2 products, ethylene and ethane, as well as to the fully reduced C 1 product, methane, on three different phases of nickel−gallium (NiGa, Ni 3 Ga, and Ni 5 Ga 3 ) films prepared by drop-casting. In aqueous bicarbonate electrolytes at neutral pH, the onset potential for methane, ethylene, and ethane production on all three phases was found to be −0.48 V versus the reversible hydrogen electrode (RHE), among the lowest onset potentials reported to date for the production of C 2 products from CO 2 . Similar product distributions and onset potentials were observed for all three nickel− gallium stoichiometries tested. The onset potential for the reduction of CO 2 to C 2 products at low current densities catalyzed by nickel−gallium was >250 mV more positive than that of polycrystalline copper, and approximately equal to that of single crystals of copper, which have some of the lowest overpotentials to date for the reduction of CO 2 to C 2 products and methane. The nickel−gallium films also reduced CO to ethylene, ethane, and methane, consistent with a CO 2 reduction mechanism that first involves the reduction of CO 2 to CO. Isotopic labeling experiments with 13 CO 2 confirmed that the detected products were produced exclusively by the reduction of CO 2 .
Quasi-operando electrochemical scanning tunneling microscopy (ECSTM) recentlyshowed that a polycrystalline Cu electrode kept in 0.1 M KOH at -0.9 V (SHE), a potential very close to that for electrochemical CO reduction, underwent a two-step surface reconstruction, initially to Cu(111), or Cu(pc)-[Cu (111)
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