Silver Nanoparticles with Surface-Bonded Oxygen for Highly Selective CO₂ Reduction

Abstract

The surface electronic structures of catalysts need to be carefully engineered in CO 2 reduction reaction (CO 2 RR), where the hydrogen evolution side reaction usually takes over under a significant overpotential, and thus dramatically lowers the reaction selectivity. Surface oxides can play a critical role in tuning the surface oxidation state of metal catalysts for a proper binding with CO 2 RR reaction intermediates, which may significantly improve the catalytic activity and selectivity. Here, we demonstrate the importance of surface-bonded oxygen on silver nanoparticles in altering the reaction pathways and improving the CO 2 RR performances. A comparative investigation on air-annealed Ag (Air-Ag) catalyst with or without the post-treatment of H 2 thermal annealing (H 2 -Ag) was performed. In Air-Ag, the subsurface chemically bonded O species (O− Ag δ+ ) was identified by angle resolved X-ray photoelectron spectroscopy and X-ray absorption spectroscopy techniques, and contributed to the improved CO selectivity rather than H 2 in CO 2 RR electrolysis. As a result, though the maximal CO Faradaic efficiency of H 2 -Ag is at ∼30%, the Air-Ag catalyst presented a high CO selectivity of more than 90% under a current density of ∼21 mA/cm 2 .

Rational Design of Ag‐Based Catalysts for the Electrochemical CO2 Reduction to CO: A Review

“…It was also reported that structure, morphology, size, and composition of the catalyst can lead to adsorption and decoupling site preferences of different adsorbates of C bound on the surface and further result in the breaking of the linear scaling relationships and tuning of the adsorption strength, eventually exerting a dramatic influence on the ECR performance . Indeed, in addition to polycrystalline and single‐crystalline Ag, some new A types have been developed and characterized recently, such as nanostructured Ag with different sizes, supported Ag catalysts with different substrates including C, TiO 2 , Al 2 O 3 , dopant‐aided Ag, oxide‐derived Ag, and surface‐modified Ag …”

“…In another study, Jiang et al. compared the catalytic activity of Ag NPs pretreated in air (air‐Ag) and H 2 (H 2 ‐Ag) for the selective ECR to CO . As shown in Figure , air‐Ag exhibited a significantly higher CO FE and lower H 2 FE than H 2 –Ag in CO 2 ‐saturated 0.1 m KHCO 3 solution within a potential range of −0.3 to −1.0 V vs. RHE.…”

A Disquisition on the Active Sites of Heterogeneous Catalysts for Electrochemical Reduction of CO2 to Value‐Added Chemicals and Fuel

“…Typically in literature, the catalysts prepared through such intentional reduction of oxide layers to generate interfaces are commonly known as oxide‐derived (OD) catalysts. This section looks in depth of the various interface/OD catalysts reported in literature …”

“…Electrocatalytic data from refs. Abbreviations: NW, nanowires; NN, nanoneedles, NPs, nanoparticles; EOD, electrodeposited oxide derived; Air‐LC, low concentration; meso, mesoporous. The detailed catalytic activity of these catalysts is presented in Table S2 (Supporting Information).…”

“…While part of this improved activity can be attributed to the increase in surface area, EXAFS results have indicated that the variation in FE CO can also be correlated with the presence of O species. Similarly, an air annealed Ag catalyst (air‐Ag) was found to contain chemically bonded O‐Ag δ+ species using angle‐resolved X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption spectroscopy (XAS) techniques and the presence of O species was attributed to the capability of the air‐Ag catalyst to exhibit a high FE CO of 90% with a j of −21 mA cm −2 . In addition to exhibiting high selectivity and improved reaction kinetics (indicated by lower Tafel slopes), the OD‐Ag catalysts are also reported to demonstrate an outstanding mass activity of 465.04 A g −1 .…”