Localized surface plasmon resonance-induced bidirectional electron transfer of formic acid adsorption for boosting photocatalytic hydrogen production on Ni/TiO2

Photocatalytic hydrogen production from formic acid (FA) is a daunting challenge, yet an essential task for the development of hydrogen energy. In this study, a p-NiO/n-TiO2 heterojunction incorporating 7-nm metallic Ni was fabricated, which demonstrated a remarkable localized surface plasmon resonance (LSPR) effect. Notably, 5 wt% Ni/TiO2 exhibited 1271-fold higher photocatalytic activity (2416 μmol⋅g−1⋅h−1) than TiO2 alone under light radiation at room temperature. The experimental investigations revealed the excitation of distinct components via irradiation by different light sources. Visible light-driven hydrogen production was predominantly influenced by the LSPR-induced hot electrons and holes effects of Ni. Further, FA molecules simultaneously lost and accepted electrons at the Ni0–Ti3+ and Ni0–O2− sites, respectively, generating a bidirectional electron transfer behavior with "valley-shaped" gas-sensitive responses, which was crucial to boost the activity. Moreover, the photocatalytic activity was mainly attributed to the heterojunction and defects structure under UV light irradiation, and Ti3+, VOs, and O2− as adsorption sites for FA. Thus, the synergistic interplay among different light sources could effectively boost the photocatalytic hydrogen production performance. Significantly, this research reveals that the LSPR effect of metallic Ni can effectively regulate electron transfer behavior and enhance visible light-driven photocatalytic activity.