The electrochemical CO₂ reduction reaction (CO₂RR) to value-added and readily collectable liquid products is promising. Among these products, formic acid/formate is a key intermediate renewable chemical feedstock and potential hydrogen storage material.

Bismuthene (Bi-ene), atomically thin layers of Bi atoms, has emerged as a superior candidate for electrocatalytic CO₂ reduction to formate. However, great efforts are still needed to meet the commercial requirements with current densities greater than 200 mA cm^-2 and long-term stability for industrial applications.

In a study published in Energy & Environmental Science, the research group led by Prof. ZHU Qilong from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences assembled a self-supported large-size 3D porous conductive network of bismuthene (Bi-ene-NW) as an efficient superstructure electrocatalytic membrane for CO₂RR, in which atomically thin Bi-ene nanosheets with rich edge-site-involved defects are interconnected.

The nanostructure of Bi-ene-NW was delicately engineered through a versatile electrochemical template strategy including the confinement growth of 3D Bi₂O₃ nanosheet network and in situ cathodically topotactic transformation. This superstructured electrocatalytic membrane can be utilized as an ascendant catalytic cathode, displaying an unprecedented CO₂RR performance with near-unity selectivity in a wide potential window and large current density for formate production.

The researchers revealed that the Bi-ene nanolayers are atomically thin with abundant defects in the roughened plane edges and in-plane pore edges. Besides, they found that Bi-ene-NW used as membranous catalyst features abundant accessible sites with high intrinsic activity, multiple interconnected channels and superior conductivity for mass/charge transport.

The unique spatial arrangement and high intrinsic activity of the Bi-ene make the Bi-ene-NW superstructure capable of delivering industry-compatible current densities up to 500 mA cm^-2 for formate production in a flow cell. Bi-ene-NW possess ultrahigh stability for electrocatalysis. It was ultrastable to continuously operate for over 500 h at a high current density without significant activity decay.

The operando ATR-IR and theoretical calculations demonstrated that the rich defects in the roughened plane edges and in-plane pore edges of Bi-ene are conducive to the *OCHO intermediate stabilization for formate production. 

This study may inspire the development of efficient electrocatalysts for electrochemical CO₂ reduction and other electrosynthesis with industrial prospects.

3D porous conductive network of atomically thin and defect-rich bismuthene nanolayers with an unparalleled catalytic performance for CO₂ electroreduction to formate. (Image by Prof. ZHU’s Group)