A Polymer Solution To Prevent Nanoclustering and Improve the Selectivity of Metal Nanoparticles for Electrocatalytic CO₂ Reduction

Abstract

The stability of metal nanocatalysts for electrocatalytic CO2 reduction is of key importance for practical application. We report the use of two polymeric N‐heterocyclic carbenes (NHC) (polydentate and monodentate) to stabilize metal nanocatalysts (Au and Pd) for efficient CO2 electroreduction. Compared with other conventional ligands including thiols and amines, metal–carbene bonds that are stable under reductive potentials prevent the nanoclustering of nanoparticles. Au nanocatalysts modified by polymeric NHC ligands show an activity retention of 86 % after CO2 reduction at −0.9 V for 11 h, while it is less than 10 % for unmodified Au. We demonstrate that the hydrophobicity of polymer ligands and the enriched surface electron density of metal NPs through σ‐donation of NHCs substantially improve the selectivity for CO2 reduction over proton.

Transition metal-based catalysts for the electrochemical CO2reduction: from atoms and molecules to nanostructured materials

“…To further confirm the beneficial role played by the NHC polymer on catalysis, an analogous effect was also observed for Pd NPs, which showed an increase in the CO selectivity and stability as compared to commercial Pd/C. 456 In addition to metal NPs, the functionalization of NHCs was recently reported to affect the catalytic properties of polycrystalline metal surfaces. In particular, Pd electrodes modified with tridentate NHC ligands displayed a 32-fold activity enhancement for CO 2 conversion to C 1 products as compared to an unmodified Pd foil, producing HCOO À in high faradaic yields.…”

“…Recently, the encapsulation of metal NPs into monodentate or polydentate polymeric NHC matrices was explored as an effective strategy to further improve at the same time catalyst selectivity and longterm durability, preventing nanoclustering. 456 The embedded Au NPs exhibited excellent FE CO with a ca. 86% activity retention over 11 h electrolysis under CO 2 atmosphere at À0.9 V vs. RHE, clearly outperforming the bare Au NPs which lost approximately 90% of their initial activity.…”

Synthesis and Electrocatalytic HER Studies of Carbene-Ligated Cu3–xP Nanocrystals

“…It has been demonstrated that NHC ligands have the ability to enhance nanocrystal catalyst stability and increase nanocrystal catalyst activity and/or selectivity. [9][10][11][12] NHC-stabilized nanocrystals have been shown to display catalytic activity toward, for example, hydrogenations and semihydrogenations, 9,[12][13][14] lactonization, 10 asymmetric arylations, 15 Buchwald-Hartwig aminations, 16 and cross-coupling reactions. 15 NHC-stabilized nanocrystals have also been shown to be competent electrocatalysts for CO2 reduction.…”

“…15 NHC-stabilized nanocrystals have also been shown to be competent electrocatalysts for CO2 reduction. 11,17 For example, Cao et al investigated the use of NHC-stabilized Au nanocrystals as electrocatalysts for the reduction of CO2 to CO. Interestingly, the Au nanocrystal catalyst with surface-bound carbene ligands exhibited a higher Faradaic efficiency for CO2 reduction to CO than did bare (or ligand-less) Au nanoparticles; it was further shown that the NHC affected the mechanistic pathway of catalysis. 17 Despite the proven benefits of applying NHC ligands to nanocrystal catalysts, they have thus far only been supported on metal nanocrystal catalysts (e.g., Ru, Au, Pt, Pd, Cu).…”

“…17 Despite the proven benefits of applying NHC ligands to nanocrystal catalysts, they have thus far only been supported on metal nanocrystal catalysts (e.g., Ru, Au, Pt, Pd, Cu). [9][10][11][12][13][14][15][16][17][18] Therefore, the potential utility of NHC ligands as supporting ligands for other types of nanocrystal catalysts is currently unknown. Certain metal phosphide nanocrystals have emerged as an important class of catalysts for reactions such as hydrodesulfurization, [19][20][21] hydrodeoxygenation, 22 and the hydrogen evolution reaction (HER).…”