Fan Cai

Enhancing CO2 Electroreduction with the Metal–Oxide Interface

The electrochemical CO2 reduction reaction (CO2RR) typically uses transition metals as the catalysts. To improve the efficiency, tremendous efforts have been dedicated to tuning the morphology, size, and structure of metal catalysts and employing electrolytes that enhance the adsorption of CO2. We report here a strategy to enhance CO2RR by constructing the metal-oxide interface. We demonstrate that Au-CeOx shows much higher activity and Faradaic efficiency than Au or CeOx alone for CO2RR. In situ scanning tunneling microscopy and synchrotron-radiation photoemission spectroscopy show that the Au-CeOx interface is dominant in enhancing CO2 adsorption and activation, which can be further promoted by the presence of hydroxyl groups. Density functional theory calculations indicate that the Au-CeOx interface is the active site for CO2 activation and the reduction to CO, where the synergy between Au and CeOx promotes the stability of key carboxyl intermediate (*COOH) and thus facilitates CO2RR. Similar interface-enhanced CO2RR is further observed on Ag-CeOx, demonstrating the generality of the strategy for enhancing CO2RR.

Switchable CO2 electroreduction via engineering active phases of Pd nanoparticles

Active-phase engineering is regularly utilized to tune the selectivity of metal nanoparticles (NPs) in heterogeneous catalysis. However, the lack of understanding of the active phase in electrocatalysis has hampered the development of efficient catalysts for CO2 electroreduction. Herein, we report the systematic engineering of active phases of Pd NPs, which are exploited to select reaction pathways for CO2 electroreduction. In situ X-ray absorption spectroscopy, in situ attenuated total reflection-infrared spectroscopy, and density functional theory calculations suggest that the formation of a hydrogen-adsorbed Pd surface on a mixture of the α- and β-phases of a palladium-hydride core (α+β PdHx@PdHx) above −0.2 V (vs. a reversible hydrogen electrode) facilitates formate production via the HCOO* intermediate, whereas the formation of a metallic Pd surface on the β-phase Pd hydride core (β PdHx@Pd) below −0.5 V promotes CO production via the COOH* intermediate. The main product, which is either formate or CO, can be selectively produced with high Faradaic efficiencies (>90%) and mass activities in the potential window of 0.05 to −0.9 V with scalable application demonstration.

Gas-phase electrocatalytic reduction of carbon dioxide using electrolytic cell based on phosphoric acid-doped polybenzimidazole membrane

Abstract Carbon dioxide transformation to fuels or chemicals provides an attractive approach for its utilization as feedstock and its emission reduction. Herein, we report a gas-phase electrocatalytic reduction of CO 2 in an electrolytic cell, constructed using phosphoric acid-doped polybenzimidazole (PBI) membrane, which allowed operation at 170 °C. Pt/C and PtMo/C with variable ratio of Pt/Mo were studied as the cathode catalysts. The results showed that PtMo/C catalysts significantly enhanced CO formation and inhibited CH 4 formation compared with Pt/C catalyst. Characterization by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy revealed that most Mo species existed as MoO 3 in PtMo/C catalysts and the interaction between Pt and MoO x was likely responsible for the enhanced CO formation rate although these bicomponent catalysts in general had a larger particle size than Pt/C catalyst.

Coordinatively unsaturated nickel–nitrogen sites towards selective and high-rate CO2 electroreduction

High Faradaic efficiency and appreciable current density are essential for future applications of the electrochemical CO2 reduction reaction (CO2RR). However, these goals are difficult to achieve simultaneously due to the severe side reaction – the hydrogen evolution reaction (HER). Herein, we successfully synthesized coordinatively unsaturated nickel–nitrogen (Ni–N) sites doped within porous carbon with a nickel loading as high as 5.44 wt% by pyrolysis of Zn/Ni bimetallic zeolitic imidazolate framework-8. Over the Ni–N composite catalysts, the CO current density increases with the overpotential and reaches 71.5 ± 2.9 mA cm−2 at −1.03 V (vs. a reversible hydrogen electrode, RHE), while maintaining a high CO Faradaic efficiency of 92.0–98.0% over a wide potential range of −0.53 to −1.03 V (vs. the RHE). Density functional theory calculations suggest that the CO2RR occurs more easily than the HER over the coordinatively unsaturated Ni–N site. Therefore, highly doped and coordinatively unsaturated Ni–N sites achieve high current density and Faradaic efficiency of the CO2RR simultaneously, breaking current limits in metal–nitrogen composite catalysts.