# On‐Surface Synthesis of Bismuth Monolayers through Ice‐Confined Redox Reactions

## TL;DR

A new ice-based method creates ultra-thin bismuth sheets that could improve electronic devices and CO2 conversion.

## Contribution

A novel ice-confined synthesis method enables scalable production of atomically thin 2D bismuth with controlled thickness and high catalytic performance.

## Key findings

- 2D bismuth sheets with 1–3 atomic layers and micrometer-scale dimensions are synthesized using ice-confined redox reactions.
- The produced 2D bismuth achieves a 95.6% formate Faraday efficiency in electrochemical CO2 reduction.
- The method is extendable to other metals like silver, copper, and tellurium for advanced applications.

## Abstract

2D bismuth possesses a unique combination of properties, such as cryogenic‐free quantum spin Hall effects and intrinsic single‐element ferroelectricity, making it highly promising for next‐generation electronic devices. However, the synthesis of 2D bismuth via exfoliation or direct growth is hindered by the low structural anisotropy of bulk bismuth crystals. To address this challenge, we demonstrate an unprecedented ice‐confined bottom‐up strategy for growing 2D bismuth. This approach involves kinetically controlled nucleation in liquid nitrogen (‐196 °C), followed by redox‐driven anisotropic growth within the confined space between ice and aluminum surfaces at −20 °C. The surfactant‐free process yields solution‐processable crystalline 2D bismuth with micrometer‐scale lateral dimensions and atomic‐level thickness, where 72% of the sheets are 1–3 layers thick. Thanks to its oxophilic surfaces, the as‐grown 2D bismuth effectively captures CO2 molecules and facilitates their conversion to *OCHO intermediates during electrochemical CO2 reduction, leading to an excellent formate Faraday efficiency of 95.6%. Moreover, this versatile synthetic route can be extended to other functional 2D metals, including silver, copper, and tellurium, thereby opening new avenues for the design of advanced catalysis, electronics, and related technologies.

We report an ice‐confined growth strategy for the synthesis of atomically thin 2D bismuth and related 2D metals. This approach involves rapid freezing of a BiCl3 aqueous solution on an aluminum foil using liquid nitrogen, which triggers interfacial redox reactions between the ice and the aluminum surface. Nucleation and growth are subsequently finely regulated under precisely controlled low‐temperature conditions. As a result, 2D bismuth with a pristine crystal structure, atomic‐level thickness (predominantly 1–3 layers), and lateral dimensions in the micrometer range is obtained. The straightforward procedure also enables gram‐scale production under standard laboratory settings. Owing to its oxophilic character, the as‐prepared 2D bismuth exhibits exceptional capability in anchoring CO2 and facilitating its conversion into *OCHO intermediates. This leads to a Faradaic efficiency for formate production of up to 95.6% in the electrocatalytic CO2 reduction reaction.