Tuning the activity and selectivity of electroreduction of CO2 to synthesis gas using bimetallic catalysts

Abstract

The electrochemical carbon dioxide reduction reaction to syngas with controlled CO/H 2 ratios has been studied on Pd-based bimetallic hydrides using a combination of in situ characterization and density functional theory calculations. When compared with pure Pd hydride, the bimetallic Pd hydride formation occurs at more negative potentials for Pd-Ag, Pd-Cu, and Pd-Ni. Theoretical calculations show that the choice of the second metal has a more significant effect on the adsorption strength of *H than *HOCO, with the free energies between these two key intermediates (i.e., ΔG(*H)–ΔG(*HOCO)) correlating well with the carbon dioxide reduction reaction activity and selectivity observed in the experiments, and thus can be used as a descriptor to search for other bimetallic catalysts. The results also demonstrate the possibility of alloying Pd with non-precious transition metals to promote the electrochemical conversion of CO 2 to syngas.

Accelerating CO2 Electroreduction to CO Over Pd Single‐Atom Catalyst

“…The HER and CO 2 RR are competing reactions. Therefore, as demonstrated in previous DFT and experimental studies, [ 25 ] the CO 2 RR activity is determined by the relative effect of *H and *HOCO bindings that compete for the similar active sites and the difference in H and HOCO binding energies (i.e., BE(*H) – BE(*HOCO)) is a CO 2 RR activity descriptor. The DFT‐calculated BE(*H) – BE(*HOCO) values are 1.63, 1.84, and 2.20 eV on Pd(111), PdH(111), and PdN 4 , respectively (Figure 4d).…”

“…Gold (Au), silver (Ag), and palladium (Pd) based catalysts have been shown to be selective for CO production through electrochemical CO 2 RR. [ 22–26 ] Especially, Pd‐based catalysts were found to yield CO and H 2 simultaneously by transforming into palladium hydride (PdH) at the electrochemical potentials for CO 2 RR. [ 21 ] However, the scarce reserve of Pd might hinder its large‐scale CO 2 RR applciations.…”

“…In this regard, the approaches engaging metal‐carbide modification or bimetallic alloying formation turned out to be effective in reducing the Pd amount and enhancing the CO 2 RR activity. [ 25,27 ] In spite of these successful attempts, the commonly‐adopted Pd loading of ≈10 wt% offered limited progress from a cost‐effective viewpoint. Hence, it should be a significant step forward in advancing CO 2 RR research to identify effective catalysts with minimum Pd loading.…”

“…In‐situ XAFS analysis and electrochemical evaluation revealed that, owing to the isolated environment of Pd, PdNC produced CO without the formation of PdH that was essential for typical Pd‐based nanoparticle catalysts. [ 21,25,27 ] Furthermore, electrokinetic analysis on PdNC indicated this unique coordination nature of Pd helped stabilize and activate adsorbed CO 2 , thus enabling CO production at low overpotentials. DFT calculations identified the favorable desorption of *CO from the PdN 4 center.…”

In Situ Transmission Electron Microscopy on Energy‐Related Catalysis

“…Many studies and researches about NPs have been performed to elucidate the relationships between features of NPs (size, shape, composition, crystal structure, surface atomic arrangement, support, etc.) and catalytic properties because the fundamental understanding of these correlations is of crucial importance for rational designs of new catalysts . In order to make better catalysts, there is a substantial need to understand how catalysts work.…”