Ultrafast Thermal Shock Synthesis and Porosity Engineering of 3D Hierarchical Cu–Bi Nanofoam Electrodes for Highly Selective Electrochemical CO₂ Reduction

Abstract

Massive production of practical metal or alloy based electrocatalysts for electrocatalytic CO2 reduction reaction is usually limited by energy-extensive consumption, poor reproducibility, and weak adhesion on electrode substrates. Herein, we report the ultrafast thermal shock synthesis and porosity engineering of free-standing Cu–Bi bimetallic nanofoam electrocatalysts with 3D hierarchical porous structure and easily adjustable compositions. During the thermal shock process, the rapid heating and cooling steps in several seconds result in strong interaction between metal nanopowders to form multiphase nanocrystallines with abundant grain boundaries and metastable CuBi intermetallic phase. The subsequent porosity engineering process via acid etching and electroreduction creates highly porous Cu–Bi structures that can increase electrochemically active surface area and facilitate mass/charge transfer. Among the Cu–Bi nanofoam electrodes with different Cu/Bi ratios, the Cu4Bi nanofoam exhibited the highest formate selectivity with a Faradaic efficiency of 92.4% at −0.9 V (vs reversible hydrogen electrode) and demonstrated excellent operation stability.

Recent research progresses of Sn/Bi/In‐based electrocatalysts for electroreduction CO2 to formate

“…Attributed to the highly porous and proper proportion, the Cu 4 Bi nanofoam exhibited a high formate selectivity of 92.4 % at À 0.9 V(vs RHE). [40] As previously reported, the Bi-based catalyst can provide a high FE of formate/formic acid (> 90 %). However, the properties of the active site for Bi-based materials during CO 2 !formic reaction is still controversial.…”

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

“…More specifically, bimetallic Zn–In and Zn–Sn catalysts have been extensively studied for the formate production . Bismuth (Bi) has also gained attention due to its higher stability, low toxicity, and cost effectiveness. − Bi-based catalysts that have been previously reported were mainly bimetallic CuBi catalysts , or Bi nanoparticles deposited on different carbon supports. , Yang et al synthesized Cu–Bi nanofoam catalysts with a three-dimensional porous structure by the thermal shock method and porosity engineering, showing that the mass transfer kinetics was enhanced and the overpotential for CO 2 RR to formate was decreased . Zhang et al showed that mass transport could also be facilitated by the nanoconfinement effect using bismuth nanorods filled in nitrogen-doped carbon nanotubes .…”

A Cu hollow fiber with coaxially grown Bi nanosheet arrays as an integrated gas-penetrable electrode enables high current density and durable formate electrosynthesis

“…15,16 However, the limited mass transfer of CO 2 in aqueous electrolytes due to its low solubility (∼34 mM) and diffusion coefficient (∼1 × 10 −5 cm 2 s −1 ) significantly suppresses the activity of the aqueous-phase CO 2 RR with the current density being restricted in the range of tens of mA cm −2 . 17–19 Moreover, the competitive hydrogen evolution reaction (HER) in aqueous solutions further decreases the selectivity of the CO 2 RR. 20–22…”