Role of Cu <i>δ</i> + sites for a favorable electrocatalytic CO2 reduction on CuSiO3 surface

Copper metasilicate (CuSiO3) derived from mineral dioptase is a unique anisotropic compound with planar edge-sharing CuO4+2 “octahedra” interspaced by SiO4 tetrahedra running along [001] direction. Combined with multivalent Cu sites and Si, it provides a robust structure for electrocatalytic CO2 reduction (ECR) reactions. Unlike metallic Cu, widely studied for ECR initially, Cu-based materials have drawn more attention lately as they not only exhibit selective formation of products due to the presence of Cuδ+ (1 &amp;lt; δ &amp;lt; 2) sites, but also ensure structural stability. Herein, we study the electronic structure of the novel orthorhombic CuSiO3 in bulk, [100] and [020] surfaces. We then investigate stepwise ECR on the [100] surface of CuSiO3 due to its appropriate alignment of d-band center, suitable chemical structure, and active surface atoms. Furthermore, the spin-polarized studies show [100] planes of CuSiO3 are half-metallic and promising for ECR. The detailed analysis of various parallel reaction pathways of ECR and the calculated free energies shows that *CHO formation is the potential-determining step with an energy barrier of 0.58 eV. ECR investigation indicates that the most feasible CO2→CH3OH conversion occurs with the on-site magnetic moment (μB) ≈0.2 for Cu atoms, and the changes in Gibbs free energies are closely related to the variations of on-site μB of Cu atoms on CuSiO3 [100]. We studied how the Cu–O–Si interaction affects the reaction pathways, influencing formation of specific reaction intermediates, thereby leading to the most probable products. Due to the presence of abundant active surface sites with varying oxidation states, and higher conductivity, CuSiO3100 exhibits a reduced activation barrier and a favorable CO2 reduction to CH3OH.