In situ-engineered interfaces in copper oxynitride (CuxOyNz) systems with synergistic properties for photocatalytic H2 production and N2 fixation applications

Abstract

In this study, an atypical copper oxynitride (Cu_xO_yN_z) system was synthesized with tunable Cu–O–N compositions. Structural analyses using X-ray diffraction, Rietveld refinement, micro-Raman, and high-resolution transmission electron microscopy confirmed the presence of Cu–O, Cu–N, and metallic Cu phases in the Cu_xO_yN_z system. Physicochemical investigations revealed the distinct properties of O_rich-, N_rich-, and Cu_rich–Cu_xO_yN_z systems. The O_rich–Cu_xO_yN_z system exhibited enhanced stability in photocatalytic reactions, while the N_rich–Cu_xO_yN_z system displayed a broader optical response due to a lower bandgap energy compared to pure-CuO. The Cu_rich–Cu_xO_yN_z system, with its meta-stable Cu–N lattice, formed a plasmonic ohmic junction, facilitating efficient charge transfer and leading to enhanced photocatalytic activities. The photocatalytic dye degradation (in %), H₂ evolution (in μmol g⁻¹ h⁻¹), and NH₃ formation (in μmol g⁻¹ h⁻¹) over the O_rich–Cu_xO_yN_z system (∼95/963.6/495.8) were found to be superior compared to those over the N_rich–Cu_xO_yN_z (∼73/741.8/435.4) and bare oxide (∼62/418.3/270.2) systems. Unlike conventional bare or N-doped copper oxide materials, the synthesized copper oxynitride systems demonstrated synergistic properties, showing organized interactions among oxide, nitride, and metallic components. This research paves the way for a better understanding of the formation mechanism of atypical unary metal oxynitride systems and highlights their unique features as an emerging class of materials for energy and environmental applications.