Redox‐Driven Cu─Pd Bond Formation to Enhance the Efficiency for Electroreduction of CO₂ to CO

Abstract

The redox reaction as the driving force induces the dynamic structure of the electrocatalyst, which enhances the performance of the catalysis. Yet, it lacks the understanding of the influence of redox driving force on the transforming process, inhibiting obtaining the actual factor that determines the catalytic performance. Resorting to the pulse and in situ methodology, herein, the effect of spontaneous reoxidation on the structural transformation of the Cu–Pd bimetallic catalyst for CO2 electroreduction is investigated. During the pulse program, applying the open‐circuit voltage and cathodic potential intermittently oxidizes and reduces the Cu–Pd bimetallic catalyst, which systematically reveals the catalyst redox reaction imparting the increase in CO2‐to‐CO selectivity. Through in situ X‐ray absorption spectroscopy (XAS), the dynamic structure induced by the spontaneous reoxidation is unveiled, suggesting the Cu─Pd bond formation for the bimetallic catalyst with a higher Pd content. Such a reoxidation‐induced Cu─Pd bond enhances the CO faradaic efficiency to 88% with the CO current density of −132 mA cm−2. By the methodologies, a new perspective is provided to understand the redox‐driven dynamic structure and the corresponding effect on the product selectivity, which is a vital concept to design the new catalysts in the future.

Dynamic (Sub)surface‐Oxygen Enables Highly Efficient Carbonyl‐Coupling for Electrochemical Carbon Dioxide Reduction

“…However, at each potential above −0.35 V, the Raman shift discerned the *CO-binding strength in Cu 2 O and Cu 2 O@Pd x catalysts: the apparent red shift of the top-bound-*CO peak from Cu 2 O to Cu 2 O@Pd 3.14 , deciphering the intensification of the top-bound-*CO binding strength because of the back-𝜋-donation effect. [21,57,58] This finding indicated that the presence of various (sub)surface oxygen varied *CO binding strength, and accordingly, tuned the energy barrier for the multi-carbon production reaction. [10,12,18] Nevertheless, one assumption should be considered: as Pd nanoparticle is the CO-favoring electrocatalyst, [66] the tandem effect driven by the addition of Pd is likely to increase the *CO coverage and enhance the multi-carbon production.…”

“…This phenomenon, as indicated in Figure 8c, evidently highlighted the important roles of kinetically-stabilized (sub)surface oxygen stemming from the dynamic oxygen diffusion in catalysts (solid) or the re-oxidation process, which considered the overall contribution of oxygen species in the electrolyte (liquid) such as hydroxide, water molecules, or the dissolved oxygen gas. [20,57,58] Accordingly, both oxygen species in electrolyte and dynamic (sub)surface-oxygen were going to stabilize the high-valent Cu 𝛿 + species, indicating that re-oxidation behavior greatly dominated the surface high-valent Cu 𝛿 + species and resulting product profile of CO 2 RR. By our methodology and discussion, the PdO x could serve as a surface probe for oxygen because of the (sub)surface oxygen bound to both Pd and Cu sites.…”

“…[56] Nevertheless, it should be considered that the diffusion of oxygen on the (sub)surface of catalysts kinetically stabilized the oxidized species during the CO 2 RR, in which the replenished oxygen on the (sub)surface could stem from the lattice oxygen and the oxygen in the electrolyte (i.e., OH − (aq) , H 2 O (l) , and O 2(aq) ). [20,57,58] As a result, based on the consideration from both thermodynamic and kinetic aspects, it was rational that the high-valent Cu species could exhibit in the 1 m KOH electrolyte under the cathodic potentials.…”

Atomic Ordering Engineering of Precious Metal Alloys in Liquid Phase Synthesis

“…In contrast, the Pd–M coordination numbers in fcc -PdCu/C are 5.3 and 7.5 at 2.637 and 2.709 Å, respectively. The coordination numbers of the first layer in bcc -PdCu/C and fcc -PdCu/C correspond to bcc and fcc structures, respectively. , Considering that the Pd–Cu bond is shorter than the Pd–Pd bond in the same crystal structure, the close coordination number of the two bond lengths in fcc -PdCu/C indicates the coexistence of Pd–Cu and Pd–Pd bonds. , Moreover, HRTEM images (Figure S6) indicated that lattice distances of 0.214 nm ( bcc -PdCu) and 0.217 nm ( fcc -PdCu) correspond to the {110} facet of bcc PdCu and the {111} facet of fcc PdCu, respectively.…”

“…29,34 Considering that the Pd− Cu bond is shorter than the Pd−Pd bond in the same crystal structure, the close coordination number of the two bond lengths in fcc-PdCu/C indicates the coexistence of Pd−Cu and Pd−Pd bonds. 29,35 Moreover, HRTEM images (Figure S6) indicated that lattice distances of 0.214 nm (bcc-PdCu) and 0.217 nm (fcc-PdCu) correspond to the {110} facet of bcc PdCu and the {111} facet of fcc PdCu, respectively. Moreover, the surface properties were studied by using X-ray photoelectron spectroscopy (XPS).…”