cs7b00687_si_001.pdf (1.9 MB)
Understanding Selectivity for the Electrochemical Reduction of Carbon Dioxide to Formic Acid and Carbon Monoxide on Metal Electrodes
journal contribution
posted on 2017-06-22, 19:35 authored by Jeremy
T. Feaster, Chuan Shi, Etosha R. Cave, Toru Hatsukade, David N. Abram, Kendra P. Kuhl, Christopher Hahn, Jens K. Nørskov, Thomas F. JaramilloIncreases in energy
demand and in chemical production, together
with the rise in CO2 levels in the atmosphere, motivate
the development of renewable energy sources. Electrochemical CO2 reduction to fuels and chemicals is an appealing alternative
to traditional pathways to fuels and chemicals due to its intrinsic
ability to couple to solar and wind energy sources. Formate (HCOO–) is a key chemical for many industries; however, greater
understanding is needed regarding the mechanism and key intermediates
for HCOO– production. This work reports a joint
experimental and theoretical investigation of the electrochemical
reduction of CO2 to HCOO– on polycrystalline
Sn surfaces, which have been identified as promising catalysts for
selectively producing HCOO–. Our results show that
Sn electrodes produce HCOO–, carbon monoxide (CO),
and hydrogen (H2) across a range of potentials and that
HCOO– production becomes favored at potentials more
negative than −0.8 V vs RHE, reaching a maximum Faradaic efficiency
of 70% at −0.9 V vs RHE. Scaling relations for Sn and other
transition metals are examined using experimental current densities
and density functional theory (DFT) binding energies. While *COOH
was determined to be the key intermediate for CO production on metal
surfaces, we suggest that it is unlikely to be the primary intermediate
for HCOO– production. Instead, *OCHO is suggested
to be the key intermediate for the CO2RR to HCOO– transformation, and Sn’s optimal *OCHO binding energy supports
its high selectivity for HCOO–. These results suggest
that oxygen-bound intermediates are critical to understand the mechanism
of CO2 reduction to HCOO– on metal surfaces.