Hard Carbon Induced Ultrasmall TiO ₂ Nano‐Islands Grown on Ti ₃ C ₂ MXene for Robust Photocatalytic CO ₂ Reduction to CH ₄

A well‐constructed TiO 2 ‐based heterojunction, featuring high solar energy utilization, robust interfacial coupling, and strong affinity toward CO 2 and reaction intermediates, is critical for efficient photocatalytic CO 2 reduction to CH 4 . Herein, hard carbon (HC) was applied to induce the in situ growth of ultrasmall TiO 2 nano‐islands on Ti 3 C 2 MXene through one‐step calcination technique. The resulting HC/TiO 2 /Ti 3 C 2 (HTT) heterojunction realizes a nearly 100% CH 4 selectivity. The CH 4 production rate of the optimized HTT (H3TT‐400) reaches 1636.3 µmol·g −1 ·h −1 , a striking enhancement of 711‐ and 68‐fold over accordion‐like TiO 2 (AT) and TiO 2 /Ti 3 C 2 (TT). The incorporation of HC with abundant defects and active sites is of vital importance for the CH 4 photogeneration, which is ascribed to the improved light utilization, and the formation of ultrasmall TiO 2 nano‐islands and abundant oxygen vacancies (OVs). Especially, the multiple charge transfer channels in HTT are established at the tight interfaces of HC, TiO 2, and Ti 3 C 2 for achieving efficient separation and transfer of charge carriers. The experimental and theoretical results reveal that the reduced Schottky barrier height advances electron transfer across the heterojunction. This work pioneers the application of HC in photocatalysis, demonstrating preliminary potential in achieving highly selective CO 2 photoconversion to CH 4 .