Large‐Area Vertically Aligned Bismuthene Nanosheet Arrays from Galvanic Replacement Reaction for Efficient Electrochemical CO₂ Conversion

There is a lack of straightforward methods to prepare high‐quality bismuthene nanosheets, or, even more challengingly, to grow their arrays due to the low melting point and high oxophilicity of bismuth. This synthetic obstacle has hindered their potential applications. In this work, it is demonstrated that the galvanic replacement reaction can do the trick. Under well‐controlled conditions, large‐area vertically aligned bismuthene nanosheet arrays are grown on Cu substrates of various shapes and sizes. The product features small nanosheet thickness of two to three atomic layers, large surface areas, and abundant porosity between nanosheets. Most remarkably, bismuthene nanosheet arrays grown on Cu foam can enable efficient CO 2 reduction to formate with high Faradaic efficiency of >90%, large current density of 50 mA cm −2 , and great stability.