Modulating the electrocatalytic CO2 reduction performances of bismuth nanoparticles with carbon substrates with controlled degrees of oxidation

Growth and Electrochemical Study of Bismuth Nanodendrites as an Efficient Catalyst for CO2 Reduction

There is a growing interest in creating cost-effective catalysts for efficient electrochemical CO2 reduction to address pressing environmental issues and produce valuable products. A bimetallic ZnBi catalyst that enhances catalytic activity and stability toward the electrochemical reduction of CO2 is designed. It is based on bismuth nanodendrites grown using a facile, scalable, and low-cost method. The results have shown that the incorporation of bismuth can decrease the charge transfer resistance and facilitate CO2 reduction toward the formation of CO and formate. It was revealed that the ZnBi catalyst exhibited higher catalytic activity compared with that of the pure Zn catalyst for CO2 reduction, with a lower onset potential [-0.75 V vs a reversible hydrogen electrode (RHE) compared with -0.85 V vs RHE for Zn]. In situ electrochemical attenuated total internal reflection Fourier transform infrared spectroscopy was employed to study the reaction mechanism, showing the formation of CO and formate through the adsorbed *COO- intermediates. This study has demonstrated a new approach for the feasible synthesis of high-performance catalysts for large-scale electrochemical CO2 reduction.

Rare-earth Element-based Electrocatalysts Designed for CO2 Electro-reduction

Electrochemical CO2 reduction presents a promising approach for synthesizing fuels and chemical feedstocks using renewable energy sources. Although significant advancements have been made in the design of catalysts for CO2 reduction reaction (CO2RR) in recent years, the linear scaling relationship of key intermediates, selectivity, stability, and economical efficiency are still required to be improved. Rare earth (RE) elements, recognized as pivotal components in various industrial applications, have been widely used in catalysis due to their unique properties such as redox characteristics, orbital structure, oxygen affinity, large ion radius, and electronic configuration. Furthermore, RE elements could effectively modulate the adsorption strength of intermediates and provide abundant metal active sites for CO2RR. Despite their potential, there is still a shortage of comprehensive and systematic analysis of RE elements employed in the design of electrocatalysts of CO2RR. Therefore, the current approaches for the design of RE element-based electrocatalysts and their applications in CO2RR are thoroughly summarized in this review. The review starts by outlining the characteristics of CO2RR and RE elements, followed by a summary of design strategies and synthetic methods for RE element-based electrocatalysts. Finally, an overview of current limitations in research and an outline of the prospects for future investigations are proposed.

Revealing the Intrinsic Restructuring of Bi2O3 Nanoparticles into Bi Nanosheets during Electrochemical CO2 Reduction

Bismuth is a catalyst material that selectively produces formate during the electrochemical reduction of CO2. While different synthesis strategies have been employed to create electrocatalysts with better performance, the restructuring of bismuth precatalysts during the reaction has also been previously reported. The mechanism behind the change has, however, remained unclear. Here, we show that Bi2O3 nanoparticles supported on Vulcan carbon intrinsically transform into stellated nanosheet aggregates upon exposure to an electrolyte. Liquid cell transmission electron microscopy observations first revealed the gradual restructuring of the nanoparticles into nanosheets in the presence of 0.1 M KHCO3 without an applied potential. Our experiments also associated the restructuring with solubility of bismuth in the electrolyte. While the consequent agglomerates were stable under moderate negative potentials (-0.3 VRHE), they dissolved over time at larger negative potentials (-0.4 and -0.5 VRHE). Operando Raman spectra collected during the reaction showed that under an applied potential, the oxide particles reduced to metallic bismuth, thereby confirming the metal as the working phase for producing formate. These results inform us about the working morphology of these electrocatalysts and their formation and degradation mechanisms.

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.