posted on 2021-05-06, 19:47authored byHyo Sang Jeon, Janis Timoshenko, Clara Rettenmaier, Antonia Herzog, Aram Yoon, See Wee Chee, Sebastian Oener, Uta Hejral, Felix T. Haase, Beatriz Roldan Cuenya
In this study, we
have taken advantage of a pulsed CO2 electroreduction reaction
(CO2RR) approach to tune the
product distribution at industrially relevant current densities in
a gas-fed flow cell. We compared the CO2RR selectivity
of Cu catalysts subjected to either potentiostatic conditions (fixed
applied potential of −0.7 VRHE) or pulsed electrolysis
conditions (1 s pulses at oxidative potentials ranging from Ean = 0.6 to 1.5 VRHE, followed by
1 s pulses at −0.7 VRHE) and identified the main
parameters responsible for the enhanced product selectivity observed
in the latter case. Herein, two distinct regimes were observed: (i)
for Ean = 0.9 VRHE we obtained
10% enhanced C2 product selectivity (FEC2H4 = 43.6% and FEC2H5OH = 19.8%) in comparison to the potentiostatic CO2RR at −0.7 VRHE (FEC2H4 = 40.9% and FEC2H5OH = 11%),
(ii) while for Ean = 1.2 VRHE, high CH4 selectivity (FECH4 =
48.3% vs 0.1% at constant −0.7 VRHE) was observed. Operando spectroscopy (XAS, SERS) and ex situ microscopy (SEM and TEM) measurements revealed that these differences
in catalyst selectivity can be ascribed to structural modifications
and local pH effects. The morphological reconstruction of the catalyst
observed after pulsed electrolysis with Ean = 0.9 VRHE, including the presence of highly defective
interfaces and grain boundaries, was found to play a key role in the
enhancement of the C2 product formation. In turn, pulsed
electrolysis with Ean = 1.2 VRHE caused the consumption
of OH– species near the catalyst surface, leading
to an OH-poor environment favorable for CH4 production.