Tunable Product Selectivity in Electrochemical CO₂ Reduction on Well-Mixed Ni–Cu Alloys

Abstract

Electrochemical reduction of CO 2 on copper-based catalysts has become a promising strategy to mitigate greenhouse gas emissions and gain valuable chemicals and fuels. Unfortunately, however, the generally low product selectivity of the process decreases the industrial competitiveness compared to the established large-scale chemical processes. Here, we present random solid solution Cu 1−x Ni x alloy catalysts that, due to their full miscibility, enable a systematic modulation of adsorption energies. In particular, we find that these catalysts lead to an increase of hydrogen evolution with the Ni content, which correlates with a significant increase of the selectivity for methane formation relative to C 2 products such as ethylene and ethanol. From experimental and theoretical insights, we find the increased hydrogen atom coverage to facilitate Langmuir−Hinshelwood-like hydrogenation of surface intermediates, giving an impressive almost 2 orders of magnitude increase in the CH 4 to C 2 H 4 + C 2 H 5 OH selectivity on Cu 0.87 Ni 0.13 at −300 mA cm −2 . This study provides important insights and design concepts for the tunability of product selectivity for electrochemical CO 2 reduction that will help to pave the way toward industrially competitive electrocatalyst materials.

The importance of a charge transfer descriptor for screening potential CO2 reduction electrocatalysts

“…2 , with the stronger binding CO metals showing increased HER activity. The high CO coverage, however, can to some degree suppress HER by poisoning active sites 66 . Therefore if means to suppress HER can be employed and improved, such electrocatalysts might become highly promising candidates 67 , 68 .…”

Structure–activity relationship of Cu-based catalysts for the highly efficient CO2 electrochemical reduction reaction

“…Based on the CDD and PDOS results, the mechanism of CO 2 activation can be summarized as follows: anti-bonding orbitals of CO 2 accept 3 d -electrons from the Cu-3 d and Ni -3d orbitals; meanwhile, the π electrons from the CO 2 bonding orbitals revert to empty Cu-3 d and Ni -3d orbitals. The activation strength of the C=O double bond of the adsorbed CO 2 molecule is quantitatively studied by calculating the ICOHP values, in which lower values indicate stronger bond strength ( Li et al, 2021 ; Song et al, 2021 ). As seen in Figures 3D–F , the C=O double bond anti-bonding states move down relative to the Fermi level after CO 2 adsorption.…”

Catalytic Performance and Near-Surface X-ray Characterization of Titanium Hydride Electrodes for the Electrochemical Nitrate Reduction Reaction

“…For a fixed applied potential, θ H may sharply decrease with increasing pH, which we indeed observed in the catholyte for all electrochemical experiments (as drastic as pH 1.70 to 11.85, Figure S41). We therefore hypothesize that transient θ H plays a role in steering the reaction selectivities seen in Figure a, such as by controlling hydrogenation of surface intermediates to form NO x * and NH y * species. , Our calculated potential of zero charge (negative of −1.0 V RHE for nearly all θ H , Table S5) leads to a positively charged surface, likely promoting anionic nitrate adsorption, which is often the rate-determining step of NO 3 RR. , The DFT calculations predict that, regardless of the initial θ H , nitrogen species are competitive for surface sites compared to H (Figure b). While molecular nitrate (NO 3 *) exhibits weak adsorption that gets weaker with increasing NO 3 RR overpotential, dissociative adsorption into nitrite (NO 2 *) and surface (hydr)­oxide, O­(H)*, is favorable.…”

“…We therefore hypothesize that transient θ H plays a role in steering the reaction selectivities seen in Figure 3a, such as by controlling hydrogenation of surface intermediates to form NO x * and NH y * species. 37,38 Our calculated potential of zero charge (negative of −1.0 V RHE for nearly all θ H , Table S5) leads to a positively charged surface, likely promoting anionic nitrate adsorption, which is often the rate-determining step of NO 3 RR. 7,39 The DFT calculations predict that, regardless of the initial θ H , nitrogen species are competitive for surface sites compared to H (Figure 4b).…”