Copper Silicophosphides: New Ternary Nanocrystals as Electrocatalysts for Carbon Monoxide Reduction

Incorporating <i>p</i>-block elements into transition metals offers a mean to fine-tune their electrocatalytic properties through localized structural distortion, charge transfer, and hybridization ^[1]. Beyond simply doping, the design of compounds with specific compositions and crystal structures can significantly expand the range of accessible properties. Notably, copper phosphides and silicides have been explored for their efficiency as catalysts or pre-catalysts in electrochemical water splitting ^[2] and as anodes in Li-ion batteries ^[3,4]. However, the properties of ternary copper silicophosphides, which possess unique structures distinct from binary phases, have been little investigated. Currently, only three ternary copper phases are known (CuSi₂P₃, CuSi₄P₃, Cu₄SiP₈) ^[5,6], and have remained at the status of scientific oddities.<br/><br/>To boost catalytic activity and selectivity for the generation of high-value added products containing C-C bonds in the electrocatalysis of the CO₂ reduction reaction (CO₂RR) and of the CO reduction reaction (CORR), one approach is to create single metal active sites, which can deeply modify catalytic cycles compared to metal clusters or nanoparticles ^[7,8]_. However, maintaining these single atom sites in an isolated state during electrocatalysis poses a significant challenge. Our strategy focuses on stabilizing these sites within crystallographic structures by seeking additional stabilization through the promotion of covalent bonding to establish a rigid crystal structure. It is also imperative to design nanostructures with a high surface-to-volume ratio, thereby amplifying catalytic activity. Copper silicophosphides present an ideal candidate for this purpose.<br/><br/>Here, we present the first synthesis of copper silicophosphide (CuSi₂P₃ and CuSi₄P₃) nanocrystals using molten salts as reaction media, promoting the nucleation of nanoparticles while limiting their growth ^[9]. <i>In situ</i> X-ray diffraction measurements conducted at the ESRF ID11 synchrotron beamline during the synthesis reveal the crystallization mechanism from the initial metal salts to the ternary phases. Following a comprehensive characterization of the nanomaterials, including their structure, composition, and morphology (TEM, HRTEM, STEM-EDX, EDS mapping, XPS), we will delve into the promising electrocatalytic properties of CuSi₂P₃ for CORR, studied via <i>in situ</i> X-ray absorption spectroscopy at the SOLEIL SAMBA synchrotron beamline.<br/><br/>[1] Chen, T. et <i>al</i>. <i>J. Am. Chem. Soc. </i><b>2019</b><br/>[2] Kong, L. et <i>al</i>. <i>RSC Adv.</i> <b>2016</b><br/>[3] Liu, Z. ; Yang, S. et <i>al. </i><i>Angew.Chem. Int.Ed</i>. <b>2020</b><br/>[4] Zeng, X. C. et <i>al</i>. <i>Nanoscale</i>. <b>2018</b><br/>[5] Wang P. et <i>al</i>. <i>Dalton Transaction</i>. <b>2009</b><br/>[6] Kaiser, P. and Jeitschko, W. <i>Z. anorg. allg. Chem</i>. <b>1995</b><br/>[7] Karapinar et al. <i>Angew. Chem. Int. Ed.</i> <b>2019</b><br/>[8] Karapinar et al. <i>ChemSusChem. </i><b>2020</b><br/>[9] Portehault, D. et <i>al. </i><i>Chem. Soc. Rev</i>. <b>2022</b>