Nitrogen/Carbon-Coated Zero-Valent Copper as Highly Efficient Co-catalysts for TiO₂ Applied in Photocatalytic and Photoelectrocatalytic Hydrogen Production

Zero-valent copper (Cu⁰) is a promising co-catalyst in semiconductor-based photocatalysis as it is inexpensive and exhibits electronic properties similar to those of Ag and Au. However, its practical application in photocatalytic hydrogen production is limited by its susceptibility to oxidation, forming less active Cu species. Herein, we have carried out in situ encapsulation of Cu⁰ nanoparticles with N-graphitic carbon layers (14.4% N) to stabilize Cu⁰ nanoparticles (N/C-coated Cu) and improve the electronic communication with a TiO₂ photocatalyst. A facile solvothermal procedure is used to coat the Cu⁰ nanoparticles at 200 °C, while graphitization is achieved by calcination at 550 °C under an inert atmosphere. The resultant N/C-coated Cu/TiO₂ composites outperform the uncoated Cu counterparts, exhibiting a 27-fold enhancement of the hydrogen evolution rate compared to TiO₂ and achieving a rate of 19.03 mmol g^–1 h^–1 under UV–vis irradiation. Likewise, the N/C-coated Cu co-catalyst exhibits a less negative onset potential of −0.05 V toward hydrogen evolution compared to uncoated Cu (ca. −0.30 V). This superior activity is attributed to coating Cu⁰ with N/C, which enhances the stability, electronic communication with TiO₂, conductivity, and interfacial charge transfer processes. The reported synthetic approach is simple and scalable, yielding an efficient and affordable Cu⁰ co-catalyst for TiO₂.