Abstract
The renewable-electricity-powered CO2 electroreduction reaction provides a promising means to store intermittent renewable energy in the form of valuable chemicals and dispatchable fuels. Renewable methane produced using CO2 electroreduction attracts interest due to the established global distribution network; however, present-day efficiencies and activities remain below those required for practical application. Here we exploit the fact that the suppression of *CO dimerization and hydrogen evolution promotes methane selectivity: we reason that the introduction of Au in Cu favors *CO protonation vs. C−C coupling under low *CO coverage and weakens the *H adsorption energy of the surface, leading to a reduction in hydrogen evolution. We construct experimentally a suite of Au-Cu catalysts and control *CO availability by regulating CO2 concentration and reaction rate. This strategy leads to a 1.6× improvement in the methane:H2 selectivity ratio compared to the best prior reports operating above 100 mA cm−2. We as a result achieve a CO2-to-methane Faradaic efficiency (FE) of (56 ± 2)% at a production rate of (112 ± 4) mA cm−2.
Highlights
The renewable-electricity-powered CO2 electroreduction reaction provides a promising means to store intermittent renewable energy in the form of valuable chemicals and dispatchable fuels
We found that lowering the *CO coverage on a Cu surface improved the selectivity to methane in CO2 electroreduction reaction (CO2RR) while still suffering from prominent hydrogen evolution reaction (HER)
We note that selecting an element that is on the same side of the hydrogen adsorption volcano curve as Cu avoids any synergistic effects that may optimize the *H binding energy leading to better HER, such as with Cu–Ni or Cu–Pt
Summary
The renewable-electricity-powered CO2 electroreduction reaction provides a promising means to store intermittent renewable energy in the form of valuable chemicals and dispatchable fuels. We construct experimentally a suite of Au-Cu catalysts and control *CO availability by regulating CO2 concentration and reaction rate This strategy leads to a 1.6× improvement in the methane:H2 selectivity ratio compared to the best prior reports operating above 100 mA cm−2. Prior CO2RR studies have reported the generation of C1 to C3 chemicals such as CO, methane, formate, ethylene, ethanol, and n-propanol[2,3,4,5,6,7,8,9,10]. Most advances in improving the selectivity to methane in CO2RR operate at current densities below 50 mA cm−2 The methane:H2 selectivity ratio is improved 1.6× compared with prior reports having a total current density above 100 mA cm−2 (Supplementary Table 1) The methane:H2 selectivity ratio is improved 1.6× compared with prior reports having a total current density above 100 mA cm−2 (Supplementary Table 1) (refs. 35–39)
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