期刊
ACS CATALYSIS
卷 8, 期 9, 页码 8357-8368出版社
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.8b01738
关键词
CO2 reduction; Ag nanofoam; nano-needle; hydrocarbons; methane formation
资金
- CTI Swiss Competence Center for Energy Research (SCCER Heat and Electricity Storage)
- Swiss National Science Foundation (SNSF) [200020_172507]
- interfaculty Microscopy Imaging Centre (MIC) of the University of Bern
Ag-foam catalysts have been developed for the electrochemical CO2 reduction reaction (ec-CO2RR) based on a concerted additive- and template-assisted metal-deposition process. In aqueous media (CO2-saturated 0.5 M KHCO3 electrolyte), these Ag foams show high activity and selectivity toward CO production at low and moderate over-Potentials. Faradaic efficiencies for CO (FECO) never fell below 90% within an extremely broad potential window of similar to 900 mV, starting at -0.3 V and reaching up to -1.2 V versus a reversible hydrogen electrode (RHE). An increased adsorption energy of CO on the Ag foam is discussed as the origin of the efficient suppression of the competing hydrogen-evolution reaction (HER) in this potential range. At potentials of <-1.1 V versus RHE, the FEH2 values significantly increase at the expense of FECO. Superimposed on this anti-correlated change in the CO and H-2 efficiencies is the rise in the CH4 efficiency to the maximum of FECH4 = 51% at -1.5 V versus RHE. As a minor byproduct, even C-C-coupled ethylene could be detected reaching a maximum Faradaic efficiency of FEC2H4 = 8.6% at -1.5 V versus RHE. Extended ec-CO2RR reveals the extremely high long-term stability of the Ag foam catalysts, with CO efficiencies never falling below 90% for more than 70 h of electrolysis at -0.8 V versus RHE (potential regime of predominant CO production). However, a more-rapid degradation is observed for extended ec-CO2RR at -1.5 V versus RHE (potential regime of predominant CH4 production), in which the FECH4 values drop to 32% within 5 h of electrolysis. The degradation behavior of the Ag-foam catalyst is correlated to time resolved identical-location scanning electron microscopy investigations that show severe morphological changes, particularly at higher applied over-potentials (current densities) at -1.5 V versus RHE. This study reports on the first ec-CO2RR catalyst beyond copper that demonstrates a remarkably high selectivity toward hydrocarbon formation, reaching a maximum of similar to 60% at -1.5 V versus RHE. The experimental observations presented herein strongly suggest that this newly designed Ag-foam catalyst shares, in part, mechanistic features with common Cu catalysts in terms of ec-CO2RR product selectivity and catalyst degradation behavior.
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