Abstract
Ultrathin metal layers can be highly active carbon dioxide electroreduction catalysts, but may also be prone to oxidation. Here we construct a model of graphene confined ultrathin layers of highly reactive metals, taking the synthetic highly reactive tin quantum sheets confined in graphene as an example. The higher electrochemical active area ensures 9 times larger carbon dioxide adsorption capacity relative to bulk tin, while the highly-conductive graphene favours rate-determining electron transfer from carbon dioxide to its radical anion. The lowered tin–tin coordination numbers, revealed by X-ray absorption fine structure spectroscopy, enable tin quantum sheets confined in graphene to efficiently stabilize the carbon dioxide radical anion, verified by 0.13 volts lowered potential of hydroxyl ion adsorption compared with bulk tin. Hence, the tin quantum sheets confined in graphene show enhanced electrocatalytic activity and stability. This work may provide a promising lead for designing efficient and robust catalysts for electrolytic fuel synthesis.
Highlights
Ultrathin metal layers can be highly active carbon dioxide electroreduction catalysts, but may be prone to oxidation
After subsequent temperature-programmed calcination for the carbon-coated ultrathin SnO2 layers, the amorphous carbon turned into graphene, while the ultrathin SnO2 layers simultaneously reduced into monodispersed Sn quantum sheets in the confined space of graphene, benefiting from the short calcination time and rapid subsequent cooling in an inert atmosphere of Ar gas
With regard to the notable enhancement of catalytic activity for the Sn quantum sheets confined in graphene, the increase in electrochemical active surface area (ECSA) may be one of the main contributors since larger ECSA could afford more catalytically active sites[2]
Summary
Ultrathin metal layers can be highly active carbon dioxide electroreduction catalysts, but may be prone to oxidation. The excessive utilization of fossil fuels provoked the increasing energy crisis and the worsening global climate, which triggered tremendous attention at CO2 capture, storage and utilization[1,2,3] To address these issues, electrocatalytic reduction of CO2 into hydrocarbon fuels is considered as a promising strategy[1,2,3], among which metal electrodes, benefiting from high electronic conductivity, show considerable catalytic activities toward CO2 electroreduction[4,5,6]. The metal ultrathin layers could serve as a ‘spacer’ to favour electrolyte diffusion into the matrix of graphene[9], and afford abundant surface atoms to act as the active sites for efficient CO2 adsorption[10,11], providing the prerequisite to involve the following reduction reactions. The intimate contact between ultrathin metal layers and graphene in a sandwich-like fashion could ensure excellent long-term stability
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