Selectivity Control of Cu Nanocrystals in a Gas-Fed Flow Cell through CO₂ Pulsed Electroreduction

Abstract

In this study, we have taken advantage of a pulsed CO 2 electroreduction reaction (CO 2 RR) approach to tune the product distribution at industrially relevant current densities in a gas-fed flow cell. We compared the CO 2 RR selectivity of Cu catalysts subjected to either potentiostatic conditions (fixed applied potential of −0.7 V RHE ) or pulsed electrolysis conditions (1 s pulses at oxidative potentials ranging from E an = 0.6 to 1.5 V RHE , followed by 1 s pulses at −0.7 V RHE ) and identified the main parameters responsible for the enhanced product selectivity observed in the latter case. Herein, two distinct regimes were observed: (i) for E an = 0.9 V RHE we obtained 10% enhanced C 2 product selectivity (FE C 2 H 4 = 43.6% and FE C 2 H 5 OH = 19.8%) in comparison to the potentiostatic CO 2 RR at −0.7 V RHE (FE C 2 H 4 = 40.9% and FE C 2 H 5 OH = 11%), (ii) while for E an = 1.2 V RHE , high CH 4 selectivity (FE CH 4 = 48.3% vs 0.1% at constant −0.7 V RHE ) 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 E an = 0.9 V RHE , including the presence of highly defective interfaces and grain boundaries, was found to play a key role in the enhancement of the C 2 product formation. In turn, pulsed electrolysis with E an = 1.2 V RHE caused the consumption of OH – species near the catalyst surface, leading to an OH-poor environment favorable for CH 4 production.

Tracking heterogeneous structural motifs and the redox behaviour of copper–zinc nanocatalysts for the electrocatalytic CO2 reduction using operando time resolved spectroscopy and machine learning

“…For the four different catalytic systems under investigation (derived from the pure and Zn-decorated Cu2O NCs with 4, 7 and 15% Zn in as-prepared state), we compared the product distribution after applying CO2RR conditions for 60 minutes at high current densities, namely -500 mA/cm² (Figure 2a) and -250 mA/cm² (Figure S3). In agreement with our previous study on Cu2O-derived catalysts, 8,10,25 the pure Cu2O-derived catalysts show excellent activity and selectivity for the conversion of CO2 to hydrocarbons and oxygenates, with a relatively low FE for the parasitic HER (FE = ca. 13-16%), Figure 2.…”

“…By using QXAFS in combination with LCA-XANES (Figure 8) and the NN-EXAFS method (Figures S25-S26), it is possible to directly correlate the current peaks in CV scans to the chemical evolution of Cu and Zn species. 8 In this case, the advantage of the LCA-XANES method is the higher achievable timeresolution, which is only limited by the QXAFS acquisition time (in our case -one second per spectrum). For the NN-EXAFS method, we averaged every 10 spectra to ensure sufficient signal to noise ratio in the EXAFS data, thus decreasing the timeresolution to 10s/spectrum.…”

“…26,27 Moreover, the application of the quick X-ray absorption fine structure (QXAFS) method, which allows the collection of XAS data with subsecond time-resolution, has recently gained significance as an invaluable tool for understanding the catalyst evolution with time, both under static and dynamic reaction conditions. 8,28 In particular, in depth analysis of time-resolved X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra 26 is key for the understanding of the dynamic changes that electrocatalytic materials undergo under working conditions.…”

Plasma-assisted oxidation of Cu(100) and Cu(111)

“…Recently our group investigated the role of Cu oxide species electrochemically re-generated on Cu 2 O nanocubes through potential pulses during CO 2 RR. 63 A pronounced selectivity shift from C2 to C1 products was observed, depending on the pulsing potential regime, with thin Cu 2 O/Cu interfaces being more selective for C 2 H 4 , while Cu 2 O/CuO interfaces and bulk-like Cu 2 O yielding CH 4 .…”

Customizing the microenvironment of CO2 electrocatalysis via three‐phase interface engineering

“…(B) The FEs for C 2+ products under potentiostatic and pulsed electrocatalysis. Reproduced with permission: Copyright 2016, American Chemical Society 96 . (C) Introduction of carbon support to suppress Cu nanoparticles growth derived from Cu 3 (HITP) 2 and tuning the CRR selectivity.…”