Facile CO₂ Electro-Reduction to Formate via Oxygen Bidentate Intermediate Stabilized by High-Index Planes of Bi Dendrite Catalyst

Abstract

Electrochemical CO 2 conversion to chemical products is a promising strategy for sustainable industrial development. However, the success of this approach requires an in-depth understanding of catalysis because it involves highly complex multistep reactions. Herein, we suggest a rational design of a hierarchical Bi dendrite catalyst for an efficient conversion of CO 2 to formate. A high selectivity (∼89% at −0.74 V RHE ) and, more importantly, a stable performance during long-term operation (∼12 h) were achieved with the Bi dendrite. Density functional theory (DFT) is used to investigate three possible reaction pathways in terms of surface intermediate, and the one via *OCOH surface intermediate is calculated to be the most energetically feasible. DFT calculations further elucidate the plane-dependent catalytic activity and conclude that the high-index planes developed on the Bi dendrite are responsible for the sustainable performance of Bi dendrite. We expect that our experimental and theoretical study will provide a fundamental guideline for the CO 2 -to-formate conversion pathway as well as design principles for enhancing the catalytic performance.

Nitrogen‐Doped Graphene Quantum Dots Enhance the Activity of Bi2O3 Nanosheets for Electrochemical Reduction of CO2 in a Wide Negative Potential Region

“…For instance,t he polyethylenimine-nitrogen-doped carbon nanotubes (PEI-NCNT) exhibited alargest formate FE of 87 %at À1.8 V( vs.S CE) and then quickly dropped to 58 %a t À2.0 V. [8b] Kohe tal. prepared aB id endrite catalyst and achieved ahighest formate FE of 89 %atanoverpotential of 0.71 V, which decreased to 55 %a ta no verpotential of 0.95 V. [10] Similar trends were observed on Bi nanoparticles and nanostructured Sn catalysts. [11] It is known that the total current density increases sharply in awide negative potential range.T herefore,m aintaining ah igh FE over ab road potential range (more negative potentials range than the optimum potential) is very significant for increasing the production rate of the target products.…”

“…Because of its highly catalytic activity and low cost, bismuth-based catalysts have drawn attention recently.M ost of the Bi-based catalysts for CO 2 reduction reported previously are the metallic bismuth (Bi 0 ), [10,12] whereas there are fewer reports of bismuth oxide for electrochemical reduction of CO 2 in aqueous solution. [13] On the other hand, carbon quantum dots are desirable for an important component of photo-and electro-catalysts owing to their large number of exposed edge sites and excellent electronic properties.…”

“…Bi 2 O 3 -NGQDs show an apparent smaller R ct (charge transfer resistance) of 18.7 W than that of Bi 2 O 3 (31.1 W)a nd NGQDs (42.9 W), demonstrating af astest charge transfer rate for Bi 2 O 3 -NGQDs in the CO 2 reduction process (Table S1). [10][11] This property is beneficial to increase the formate production rate for CO 2 reduction. Electrochemical reduction of CO 2 was investigated by the controlled potential electrolysis method in agas-tight H-cell, which was separated by aN afion N117 membrane.F ormate and H 2 together account for over 99.5 %o fa ll products for these three electrocatalysts.A sab enchmark, we also conducted the electrolysis experiments in aN 2 -saturated 0.5 m KHCO 3 electrolyte (CO 2 -free electrolyte).…”

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

“…For instance, Bi nanosheets catalyst that are generated from atomic‐thick Bi oxycarbonate nanosheets display a FE HCOO − of ≈100% at −0.9 V and this activity is partly attributed to the presence of Bi(101) and Bi(111) facets, which are demonstrated to lower free energy barrier for formation of *OCHO radical, facilitating CO 2 RR . Similar facet dependent DFT results with Sn, In and Bi catalysts were used as theoretical evidence to justify the catalytic activity of these catalysts for CO 2 RR . In addition, SnO 2 (110) is reported to play a positive role in dictating formate generation during CO 2 RR with a number of literatures with SnO 2 nanoparticle catalysts ascribing the importance of this facet …”

Looking Back and Looking Ahead in Electrochemical Reduction of CO2

“…Based on electrochemical measurements including Tafel slope and pH dependent activity analyses, either a two‐electron and one‐proton transfer reaction to adsorbed CO 2 or a chemical proton transfer reaction to the CO 2 − was proposed as the possible rate determining step. Koh and co‐workers developed a hierarchical Bi dendrite by two‐step synthesis including e‐beam evaporation of Bi source on a Cu foil and subsequent electrodeposition of Bi 3+ precursor in ethylene glycol solution . Using DFT calculation, it was explained that the superior catalytic performance is originated from the high‐index plane of Bi dendrite leading to stabilization of *OCOH intermediate.…”