Cu-Ag Tandem Catalysts for High-Rate CO2 Electrolysis toward Multicarbons

Abstract

Electrochemically upgrading CO2 to carbon-neutral multicarbons (C2+) is a promising technology for CO2 recycling and utilization. Since such transformations involve multiple elementary steps, a tandem strategy becomes attractive as catalysts can be optimized for specific reaction steps independently. Related strategies have been demonstrated under low working current densities; however, the applicability of a tandem strategy towards high-rate CO2 electrolysis to C2+ is unknown. Here, we demonstrate that a Cu-Ag tandem catalyst can enhance the multicarbon production rate in CO2RR by decoupling high-rate CO2 reduction to CO on Ag and subsequent CO coupling on Cu. With the addition of Ag, the partial current towards C2+ over a Cu surface increased from 37 mA/cm 2 to 160 mA/cm 2 at -0.70 V vs RHE in 1M KOH while no mutual interference between two metals was observed. Moreover, the normalized intrinsic activity of C2H4 and C2H5OH in the tandem platform under CO2 reduction conditions is significantly higher than Cu alone under either pure CO2 or CO atmosphere. Our results indicate that the CO-enriched local environment generated by Ag can enhance C2+ formation on Cu beyond CO2 or CO feeding, suggesting possible new mechanisms in a tandem three-phase environment. Manuscriptprove CO2RR catalytic performance. Thus, we conducted post-electrolysis characterization of the tandem Cu500Ag1000 catalyst to determine whether the structure is maintained. Previous works have shown structural and electronic differences owing to strong Ag interactions with Cu: for example, up to 0.8 o Cu(111) peak shift in XRD could be found for a Cu-Ag alloy system 14 whereas up to 0.3 eV Cu 2p3/2 peak shift in XPS was reported for a Cu-Ag dimer. 23 In contrast, no peak shift of Cu or Ag could be observed for the tandem Cu500Ag1000 catalyst in either XRD, XPS or Cu LMM Auger peak after electrolysis, indicating the structural maintenance of this tandem catalyst and absence of electronic interactions between Ag and Cu throughout electrolysis. This absence is likely due to the bulk-like nature of Ag and Cu used, in addition to the mild conditions in which the electrode is fabricated, resulting in thermodynamically favored separation 52 . Importantly, this does not preclude the Ag-Cu surface and interfacial alloying observed in other reports which use more energetic fabrication conditions.2.2 Enhanced CO2RR catalytic performances toward C2+ products over tandem Cu-Ag catalysts. The polarization response curve of Cu500Ag1000 in Fig. 2a shows higher geometric current density than Cu500 or Ag1000 alone under the same potentials. Interestingly, partial current densities toward C2+ products over different catalysts are also observed to be substantially higher for Cu500Ag1000, which cannot be explained simply through the individual contributions of Cu500 and Ag1000 (Fig. 2b). Explicitly, Ag1000 does not contribute to C-C coupling reactions in the potential range from -0.5 V to -0.8 V vs RHE. Thus, all partial current toward C2+ products should come from the C...

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Engineering Sn‐based Catalytic Materials for Efficient Electrochemical CO2 Reduction to Formate

“…To reduce the thermodynamically stable CO 2 , catalysts are needed to increase the kinetics of the electrochemical reduction reaction and achieve an appreciable yield. Most of the catalytic materials studied to date can be divided into 1) metallic such as Au, [4–5] Ag, [6–7] Pd, [8–9] Pt, [10] Zn, [11–12] Cu, [13–15] Ni, [16–17] Fe, [18] Sn, [19–20] In, [21–22] Bi, [23] and alloys which include a combination of 2 or more of these metals, [24–33] 2) non‐metallics such as MoS 2 , [34] carbon compounds and its derivatives such as N‐doped carbon and carbon nanofibers [35–37] and 3) molecular catalysts [38–39] …”

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