Redox properties of two-dimensional copper boride

Abstract: Two-dimensional boron-based materials, including boride layers and borophene, are of growing interest due to their unusual electronic structures and potential applications in catalysis and energy storage. Although large-scale boron films can be synthesized on Cu(111), their precise structure remains debated, and distinguishing copper boride from borophene or mixed phases is still challenging. Chemical instability, especially the rapid oxidation of borophene in air, further limits practical use. In this work, we investigate two-dimensional copper boride grown on Cu(111) by diffusion-mediated synthesis. Surface analysis confirms the formation of copper boride, which resists oxidation by molecular oxygen, is reduced by atomic hydrogen, and undergoes reversible redox cycling between molecular oxygen and carbon monoxide, which are gases commonly present in catalytic environments. We find that molecular hydrogen does not reduce copper boride, indicating stability toward simple hydrogen exposure. In contrast, atomic hydrogen readily oxidizes the material at room temperature, although the boride tolerates partial oxidation without complete degradation. Oxidized copper boride can be reversibly reduced by carbon monoxide, demonstrating its ability to participate in catalytically relevant redox processes. These results establish the stability and redox behavior of two-dimensional copper boride and define the environmental conditions under which it remains functional, supporting its potential use in low-oxygen catalytic applications.