How Strain Alters CO₂ Electroreduction on Model Cu(001) Surfaces

Abstract

Carbon dioxide electrolysis powered by renewable energy is a potentially attractive approach to close the carbon cycle and produce key chemical feedstocks. Here, we demonstrate the substantial influence of tensile strain on the selectivity of CO2 reduction toward higher value-added, multicarbon products by modulating the residual mismatch strain of Cu(001) thin film catalysts grown epitaxially on single-crystal Si substrates. By decreasing film thickness from 100 to 20 nm, up to 0.22% tensile strain is introduced in-plane, shifting the measured Cu d-band center at the surface upward, in good agreement with theory. CO2 electrolysis at moderate overpotential (−0.9 V vs reversible hydrogen electrode (RHE)) in 0.1 M KHCO3 electrolyte reveals that the shift in d-band center results in the suppression of single-carbon products, while activity for multicarbon products is maintained. Examination of the ratio of partial current densities for multicarbon products relative to CO and CH4 suggests increased CO insertion and hydrogenation on the tensile-strained Cu(001) surface, driven by a change in the adsorbate bonding because of an increased interaction with the upshifted d-band. This work provides direct experimental evidence on model thin film CO2 catalysts that strain can be systematically manipulated as a valuable tool, independent of catalyst composition, for the design of efficient CO2 electrocatalysts toward energy-dense products.

Structural evolution and strain generation of derived-Cu catalysts during CO2 electroreduction

“…Although the promoting effect of tensile strain on C-C coupling and suppression on the competing HER have been demonstrated theoretically, [51][52] a controversy exists in the literature on how the tensile strain in Cu affects the C 1 products during the CO 2 RR. For instance, a recent study reported that tensile strain in Cu is unfavorable for the formation of C 1 products, 22 which is inconsistent with our observations and the conclusions of other studies. 24,52 Another study concluded that tensile strain has different effects on the production of CH 4 , depending on the thickness of the Cu layer.…”

“…Density functional theory (DFT) calculations suggest that, according to the d-band theory, lattice strain can trigger a shift of the d-band center of the metal and tailor its catalytic activity. 19,[22][23]47 Taking Cu derived from Cu 2 (OH) 2 CO 3 as an example, four slab models were built, including strain-free Cu(111) and Cu(100), Cu(111) with 0.55% tensile strain (denoted as Cu(111)-strain), and Cu(100) with 0.72% tensile strain (denoted as Cu(100)-strain). By analyzing their projected density of states (PDOS) of d-band, the (111) and (100) surfaces with tensile strain have higher d-band centers than their strain-free counterparts (-1.999 vs. -2.021 eV, and -2.120 vs. -2.158 eV, respectively; Figs.…”

“…6a and 6b), which is consistent with previous reports. 19,[22][23] We then investigated the Gibbs free energy of formation (ΔG formation ) for *COH/*CHO and *CO*COH, which are key intermediates to generate CH 4 and C 2+ products (e.g., C 2 H 4 , C 2 H 5 OH, and n-C 3 H 7 OH), respectively, 48-50 on the four models to evaluate the strain effect on the reaction pathways on the Cu surface (Fig. 6c).…”

“…Lattice strain can modulate the activity and selectivity of electrocatalysts by breaking the linear scaling relationship. 19 Various approaches have been employed to induce strain in Cu catalysts, including the formation of bimetallic nanoparticles, [20][21] epitaxial growth of thin lms, [22][23] and crystal morphology engineering. 24 However, few studies have investigated strain effects in derived Cu catalysts for CO 2 RR.…”

Ag@Pd bimetallic structures for enhanced electrocatalytic CO2 conversion to CO: an interplay between the strain effect and ligand effect

“…Among the many optimization strategies, bimetallic structures and strain engineering have recently emerged as effective strategies to enhance catalytic performance by altering the electronic structures of catalysts. [7][8][9][10] Bimetallic nanoparticles often create strains due to lattice mismatch between the two components. 11 Nørskov et al proposed that strain can change the overlapping of orbitals in transition metal atoms and thus change the width of their d-band.…”