cs9b05272_si_001.pdf (770.17 kB)
Kinetic Analysis on the Role of Bicarbonate in Carbon Dioxide Electroreduction at Immobilized Cobalt Phthalocyanine
journal contribution
posted on 2020-03-23, 11:40 authored by Joy S. Zeng, Nathan Corbin, Kindle Williams, Karthish ManthiramThe mechanism for
carbon dioxide reduction (CO2RR) to
carbon monoxide (CO) at immobilized cobalt phthalocyanine (CoPc) in
aqueous electrolytes has been widely debated. In this work, we investigated
the mechanism of CO2RR to CO on CoPc via experimental reaction
kinetics coupled with model fitting. Unexpectedly, reactant order
dependences and Tafel slopes deviate from commonly expected values
and change depending on the testing conditions. For example, (1) the
effect of bicarbonate deviates from power law kinetics and transitions
from inhibitory to promotional with increasingly reductive potential,
and (2) the CO2 order dependence deviates from unity at
more-reductive potentials. We propose a kinetic model, chosen from
more than 15 candidate models, that is able to quantitatively fit
all of the experimental data. The model invokes (1) catalyst poisoning
via bicarbonate electrosorption, (2) mixed control between concerted
proton–electron transfer (CPET) and sequential electron transfer-proton
transfer (ET-PT), and (3) both water and bicarbonate as kinetically
relevant proton donors. The proposed model also predicts that the
relative importance of the above factors changes depending on the
reaction conditions, highlighting the potential downfalls of broadly
applying reaction mechanisms that were inferred from kinetic data
collected in a narrow range of testing conditions. This study emphasizes
the importance of cohesively using kinetic data collected over a wide
range of operating conditions to test and formulate kinetic models
of electrocatalytic reactions.