Size‐Dependent Activity of Palladium Nanoparticles: Efficient Conversion of CO₂ into Formate at Low Overpotentials

Abstract

Remarkable size-dependent activity of palladium nanoparticles (PdNPs) towards formate production is evident at very low overpotentials (-0.1 to -0.5 V vs. RHE). Size-selective PdNPs, chemically synthesized at sizes of 3.8-10.7 nm, effected an electrochemical CO reduction reaction in aqueous 0.5 m NaHCO . The faradaic efficiency of formate production (FE ) on 3.8 nm PdNPs exceeded 86 % at E=-0.1 V versus RHE, whereas on 6.5 nm PdNPs an even higher FE of 98 % was observed. However, FE decreased for larger PdNPs. The superior efficiency towards formate production at low overpotentials is rationalized in terms of a changed catalytic pathway through PdH phases. The observed maximum in the formate efficiency for a mean particle size of about 6.5 nm is discussed in terms of counterbalancing the size-dependent effects of a competing CO reduction reaction and a parasitic hydrogen evolution reaction. Production rates of formate are also remarkably high at -0.3 V versus RHE with 539.9 and 452.3 ppm h mg for the 6.5 and 3.8 nm PdNPs, respectively.

Synthesis and Characterization of Degradation‐Resistant Cu@CuPd Nanowire Catalysts for the Efficient Production of Formate and CO from CO2

“…Herein, we introduce a new approach towards the wet chemical synthesis of Cu nanowires that become further functionalized by a bimetallic Pd x Cu y shell and Pd x Cu y alloy nanoparticles (NPs). This novel catalyst shows similar electrocatalytic characteristics as the pure Pd‐NPs in terms of formate and CO formation at low and medium overpotentials, respectively, whereas the electrocatalytic characteristics of Cu involving hydrocarbon and oxygenate formation remain entirely suppressed. Moreover, this novel Pd x Cu y catalyst demonstrates an excellent resistance against irreversible CO poisoning most probably due to a weakened CO‐catalyst interaction on the bimetallic Pd x Cu y alloy.…”

“…In case of Pd‐based materials, PdH is considered as the actually active catalyst that is capable of transfering hydrogen to the CO 2 (rate determining step). This initial hydrogenation leads to a particularily low activation barrier for formate production . This also explains why this exceptionally high CO 2 RR efficiency remains restricted to Pd nanomaterials where the PdH formation is fast due to short diffusion pathways of the H inside the spatially confined Pd matrix .…”

“…This initial hydrogenation leads to a particularily low activation barrier for formate production . This also explains why this exceptionally high CO 2 RR efficiency remains restricted to Pd nanomaterials where the PdH formation is fast due to short diffusion pathways of the H inside the spatially confined Pd matrix . In contrast, the atomic hydrogen formed under HER conditions on the respective bulk material tends to diffuse into its spatially extended volume (e. g., Pd foil) which prevents reaching a sufficiently high H concentration in the near‐surface regime required for this particular CO 2 hydrogenation pathway …”

“…It is well known that the PdH formation, related volume changes and the pronounced miscibility gap in the PdHx phase diagram lead to drastic embrittlement in case of bulk Pd phases and significant changes in the size distributions of the respective Pd nanomaterials . The latter effect is critical insofar as the Faradaic efficiencies of both the CO and the formate production have been demonstrated to be strongly dependent on the particular size distribution of the Pd‐NP catalysts …”

Porous Palladium Nanomeshes with Enhanced Electrochemical CO2‐into‐Syngas Conversion over a Wider Applied Potential

“…[1][2][3] Syngas, made up of CO and H 2 ,i savital feedstock for the production of synfuel and industrial chemicals through classicalp etroleum industry processes, [4] for example, the optimal CO/H 2 = 1:2f or methanolb yt he Fischer-Tropsch synthesis, and CO/H 2 = 1:1f or the hydroformylation process. [1][2][3] Syngas, made up of CO and H 2 ,i savital feedstock for the production of synfuel and industrial chemicals through classicalp etroleum industry processes, [4] for example, the optimal CO/H 2 = 1:2f or methanolb yt he Fischer-Tropsch synthesis, and CO/H 2 = 1:1f or the hydroformylation process.…”