CO2 Electroreduction to Formate at a Partial Current Density up to 590 mA mg-1 via Micrometer-Scale Lateral Structuring of Bismuth Nanosheets

Regulating the Electronic Structure of Bismuth Nanosheets by Titanium Doping to Boost CO2 Electroreduction and Zn-CO2 Batteries

The electrochemical carbon dioxide reduction reaction (E-CO2 RR) to formate is a promising strategy for mitigating greenhouse gas emissions and addressing the global energy crisis. Developing low-cost and environmentally friendly electrocatalysts with high selectivity and industrial current densities for formate production is an ideal but challenging goal in the field of electrocatalysis. Herein, novel titanium-doped bismuth nanosheets (TiBi NSs) with enhanced E-CO2 RR performance are synthesized through one-step electrochemical reduction of bismuth titanate (Bi4 Ti3 O12 ). We comprehensively evaluated TiBi NSs using in situ Raman spectra, finite element method, and density functional theory. The results indicate that the ultrathin nanosheet structure of TiBi NSs can accelerate mass transfer, while the electron-rich properties can accelerate the production of *CO2 - and enhance the adsorption strength of *OCHO intermediate. The TiBi NSs deliver a high formate Faradaic efficiency (FEformate ) of 96.3% and a formate production rate of 4032 µmol h-1  cm-2 at -1.01 V versus RHE. An ultra-high current density of -338.3 mA cm-2 is achieved at -1.25 versus RHE, and simultaneously FEformate still reaches more than 90%. Furthermore, the rechargeable Zn-CO2 battery using TiBi NSs as a cathode catalyst achieves a maximum power density of 1.05 mW cm-2 and excellent charging/discharging stability of 27 h.

Boosting CO2 Electroreduction on Bismuth Nanoplates with a Three-Dimensional Nitrogen-Doped Graphene Aerogel Matrix

Electrochemical CO₂ reduction reaction (CO₂RR), which uses renewable electricity to produce high-value-added chemicals, offers an alternative clean path to the carbon cycle. However, bismuth-based catalysts show great potential for the conversion of CO₂ and water to formate, but their overall efficiency is still hampered by the weak CO₂ adsorption, low electrical conductivity, and slow mass transfer of CO₂ molecules. Herein, we report that a rationally modulated nitrogen-doped graphene aerogel matrix (NGA) can significantly enhance the CO₂RR performance of bismuth nanoplates (BiNPs) by both modulating the electronic structure of bismuth and regulating the interface for chemical reaction and mass transfer environments. In particular, the NGA prepared by reducing graphene oxide (GO) with hydrazine hydrate (denoted as NGA_hdrz) exhibits significantly enhanced strong metal-support interaction (SMSI), increased specific surface area, strengthened CO₂ adsorption, and modulated wettability. As a result, the Bi/NGA_hdrz exhibits significantly boosted CO₂RR properties, with a Faradaic efficiency (FE) of 96.4% at a current density of 51.4 mA cm^-2 for formate evolution at a potential of -1.0 V versus reversible hydrogen electrode (vs RHE) in aqueous solution under ambient conditions.

A tandem effect of atomically isolated copper-nitrogen sites and copper clusters enhances CO2 electroreduction to ethylene

Direct electrochemical conversion of CO₂ to C₂H₄ with high selectivity is highly desirable for lowering CO₂ emissions. However, limited by the slow *CO dimerization step at a single active site, it is difficult for current electrocatalysts to further improve the selectivity toward C₂H₄. Here we report a tandem catalyst PDI-Cu/Cu with Cu-N sites and Cu clusters, synthesized by uniformly dispersing Cu clusters on a coordination polymer PDI-Cu, which has atomically isolated Cu-N sites. This tandem catalyst, which has an optimal content of Cu clusters, shows more than 2 times the enhancement in C₂H₄ production compared with that of the non-tandem catalyst PDI/Cu. Density functional theory (DFT) calculations support the tandem reaction mechanism, where Cu-N sites first reduce CO₂ into highly concentrated CO and then the CO migrates to the surfaces of Cu clusters for further conversion into C₂H₄, decoupling the complex C₂H₄ generation pathway at single active sites into a two-step tandem reaction. This work offers a rational approach to design electrocatalysts for further boosting the selectivity of the CO₂RR to C₂₊ products via a tandem route.

Defect engineered SnO2 nanoparticles enable strong CO2 chemisorption toward efficient electroconversion to formate

Oxygen vacancy (O_v) engineering of SnO₂ electrocatalysts plays a crucial role in realizing efficient CO₂ electroreduction (CO₂RR) into formate. Herein, we demonstrate the rational synthesis of highly dispersed SnO₂ nanoparticle electrocatalysts with an ultrahigh O_v content of up to 25.1% by a thermally induced strategy. The high O_v content greatly improves the intrinsic conductivity and remarkably enhances the chemisorption capacity to CO₂, thus boosting the catalytic activity and reaction kinetics of CO₂ electroconversion into formate. These advantages make the O_v-engineered SnO₂ electrocatalysts exhibit both a high Faraday efficiency (FE) of nearly 90% and a superior cathodic energy efficiency of above 60% to produce formate in a wide current range from 100 to 400 mA cm^-2 in a flow cell. A commercially required current of 200 mA cm^-2 can be obtained at only 2.8 V in a full cell. The present O_v engineering strategy exhibits the possibility for the design and construction of high-activity oxide-based electrocatalysts.

Integrated 3D Open Network of Interconnected Bismuthene Arrays for Energy-Efficient and Electrosynthesis-Assisted Electrocatalytic CO2 Reduction

Electrocatalytic CO₂ reduction reaction (CO₂ RR) toward formate production can be operated under mild conditions with high energy conversion efficiency while migrating the greenhouse effect. Herein, an integrated 3D open network of interconnected bismuthene arrays (3D Bi-ene-A/CM) is fabricated via in situ electrochemically topotactic transformation from BiOCOOH nanosheet arrays supported on the copper mesh. The resulted 3D Bi-ene-A/CM consists of 2D atomically thin metallic bismuthene (Bi-ene) in the form of an integrated array superstructure with a 3D interconnected and open network, which harvests the multiple structural advantages of both metallenes and self-supported electrodes for electrocatalysis. Such distinctive superstructure affords the maximized quantity and availability of the active sites with high intrinsic activity and superior charge and mass transfer capability, endowing the catalyst with good CO₂ RR performance for stable formate production with high Faradaic efficiency (≈90%) and current density (>300 mA cm^-2 ). Theoretical calculation verifies the superior intermediate stabilization of the dominant Bi plane during CO₂ RR. Moreover, by further coupling anodic methanol oxidation reaction, an exotic electrolytic system enables highly energy-efficient and value-added pair-electrosynthesis for concurrent formate production at both electrodes, achieving substantially improved electrochemical and economic efficiency and revealing the feasibility for practical implementation.

Lattice-dislocated Bi nanosheets for electrocatalytic reduction of carbon dioxide to formate over a wide potential window

Electrochemical reduction of CO₂ to HCOOH (ERC-HCOOH) is one of the most feasible and economically valuable ways to achieve carbon neutrality. Unfortunately, achieving optimal activity and selectivity for ERC-HCOOH remains a challenge. Herein, ultrathin Bi nanosheets (NS) with lattice dislocations (LD-Bi) were prepared by the topological transformation of Bi₂O₂CO₃ NS under high current conditions. LD-Bi exhibited excellent activity and selectivity as well as stability in ERC-HCOOH. Electrochemical tests and DFT calculations revealed that the excellent performance of LD-Bi was attributed to lattice dislocations, which can induce the production of more active sites on the catalyst surface and improve the electronic transfer ability. In addition, LD-Bi was beneficial to enhance the adsorption of CO₂ and key reaction intermediates (OCHO*), thus improving the reaction kinetics. The result provides a unique perspective on the crucial role of lattice dislocations, which may have a significant impact on highly selective electrochemical conversion of CO₂.

Cation-Deficiency-Dependent CO2 Electroreduction over Copper-Based Ruddlesden-Popper Perovskite Oxides

We report an effective strategy to enhance CO₂ electroreduction (CER) properties of Cu-based Ruddlesden-Popper (RP) perovskite oxides by engineering their A-site cation deficiencies. With La_2-x CuO_4-δ (L_2-x C, x=0, 0.1, 0.2, and 0.3) as proof-of-concept catalysts, we demonstrate that their CER activity and selectivity (to C₂₊ or CH₄ ) show either a volcano-type or an inverted volcano-type dependence on the x values, with the extreme point at x=0.1. Among them, at -1.4 V, the L_1.9 C delivers the optimal activity (51.3 mA cm^-2 ) and selectivity (41.5 %) for C₂₊ , comparable to or better than those of most reported Cu-based oxides, while the L_1.7 C exhibits the best activity (25.1 mA cm^-2 ) and selectivity (22.1 %) for CH₄ . Such optimized CER properties could be ascribed to the favorable merits brought by the cation-deficiency-induced oxygen vacancies and/or CuO/RP hybrids, including the facilitated adsorption/activation of key reaction species and thus the manipulated reaction pathways.