Bimetallic electrocatalysts offer
great flexibility to tailor the
activity and selectivity in electrochemical carbon dioxide (CO2) reduction. Here, we report on the electrocatalytic behavior
of Au–Sn bimetallic nanoparticles with different intermetallic
phases toward CO2 electroreduction. Two high-value products
formed with reasonable current density: formic acid in the liquid
phase and syngas (CO + H2) in the gas phase. Notably, the
phase composition of the catalysts had a massive influence on both
activity and product distribution. Selective isotopic labeling studies
emphasized the role of bicarbonate as the source of CO and formic
acid formation on the AuSn bimetallic phase. In situ Raman spectroelectrochemical
studies also demonstrated that the catalytic performance of the AuSn
phase was superior to that of its parent metal and other bimetallic
counterparts. The achieved control over the product distribution demonstrated
the promise of bimetallic nanostructures being employed as efficient
catalysts in the electroreduction of CO2.
The
electrochemical conversion of carbon dioxide (CO2) to high-value
chemicals is an attractive approach to create an
artificial carbon cycle. Tuning the activity and product selectivity
while maintaining long-term stability, however, remains a significant
challenge. Here, we study a series of Au–Pb bimetallic electrocatalysts
with different Au/Pb interfaces, generating carbon monoxide (CO),
formic acid (HCOOH), and methane (CH4) as CO2 reduction products. The formation of CH4 is significant
because it has only been observed on very few Cu-free electrodes.
The maximum CH4 formation rate of 0.33 mA cm–2 was achieved when the most Au/Pb interfaces were present. In situ
Raman spectroelectrochemical studies confirmed the stability of the
Pb native substoichiometric oxide under the reduction conditions on
the Au–Pb catalyst, which seems to be a major contributor to
CH4 formation. Density functional theory simulations showed
that without Au, the reaction would get stuck on the COOH intermediate,
and without O, the reaction would not evolve further than the CHOH
intermediate. In addition, they confirmed that the Au/Pb bimetallic
interface (together with the subsurface oxygen in the model) possesses
a moderate binding strength for the key intermediates, which is indeed
necessary for the CH4 pathway. Overall, this study demonstrates how bimetallic nanoparticles
can be employed to overcome scaling relations in the CO2 reduction reaction.
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