Abstract
Surface-sensitive ambient pressure X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy combined with an electrocatalytic reactivity study, multilength-scale electron microscopy, and theoretical modeling provide insights into the gas-phase selective reduction of carbon dioxide to isopropanol on a nitrogen-doped carbon-supported iron oxyhydroxide electrocatalyst. Dissolved atomic carbon forms at relevant potentials for carbon dioxide reduction from the reduction of carbon monoxide chemisorbed on the surface of the ferrihydrite-like phase. Theoretical modeling reveals that the ferrihydrite structure allows vicinal chemisorbed carbon monoxide in the appropriate geometrical arrangement for coupling. Based on our observations, we suggest a mechanism of three-carbon-atom product formation, which involves the intermediate formation of atomic carbon that undergoes hydrogenation in the presence of hydrogen cations upon cathodic polarization. This mechanism is effective only in the case of thin ferrihydrite-like nanostructures coordinated at the edge planes of the graphitic support, where nitrogen edge sites stabilize these species and lower the overpotential for the reaction. Larger ferrihydrite-like nanoparticles are ineffective for electron transport.
Highlights
The electrocatalytic conversion of CO2 to chemicals and fuels is currently one of the challenging frontiers of research from both application and fundamental perspectives.[1]
Many contributions have focused on maximizing productivities toward C−C coupling products,[9] and numerous studies have analyzed the mechanism of multicarbon product formation in the CO2RR strategies for with the the aim selective of unravelling catalyst design reduction.[9−27] Still, contrasting opinions exist, mainly on the three following points: 1. Is nanostructured metallic Cu exclusively required for C2+ product formation or can these products form starting from nonmetallic nanoparticles of other transition metals? 2
By using C-supported Fe catalytic systems, we showed that a controlled surface chemical modification of the carbon support by O or N enables the tuning of the electrocatalytic performance and realizes high Faraday efficiencies and selectivities toward C2 and C2+ products both in the liquid phase[6] and in gas-phase approaches,[29] respectively
Summary
The electrocatalytic conversion of CO2 to chemicals and fuels is currently one of the challenging frontiers of research from both application and fundamental perspectives.[1]. A threeelectrode electrochemical flow cell designed for the APXPS end-station of the ISISS beamline at BESSY II/HZB was used for in situ spectroscopy (Figure 1) This technique allows the analysis of the electronic structure of the electrical double layer formed upon polarization at the electrode interfaces.[34−40] It is well-suited to characterize operando conditions that lead to multicarbon product formation during CO2 electrocatalytic reduction. The CE and the RE immersed into the electrolyte stream were separated from the evacuated XPS measurement chamber of the end station by a sandwiched membrane electrode assembly (MEA) based on a Nafion 117 PEM (Alfa Aeser), which previously was purified from organic contaminants and activated as described in ref 36 In this case, the PEM serves to prevent the liquid electrolyte from entering the measurement chamber and guarantees the leak-tightness of the in situ cell
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