Hydrochar-Supported NiFe₂O₄Nanosheets with a Tailored Microstructure for Enhanced CO₂Photoreduction to Syngas

Constructing high-efficiency composite photocatalysts with enhanced charge transfer and a rapid surface catalytic reaction has recently received significant attention. Herein, a hydrochar-mediated NiFe₂O₄ nanosheet (C/NFO) composite was rationally constructed by a simple hydrothermal method. Intimate interface contacts and chemical interactions between hydrochar and NFO were formed. The prepared C/NFO samples exhibited remarkable visible-light-driven catalytic CO₂ reduction properties under mild reaction conditions with Ru(bpy)₃²⁺ sensitization. As the optimized sample, 16%-C/NFO achieved a 4-fold enhancement of CO production (17.49 μmol/h) compared with that of pure NFO. The C/NFO samples demonstrated good activity and structural stability in the CO₂ photoreduction system. The carbon source of CO derived from CO₂ was verified through isotopic labeling experiments using ¹³CO₂. In situ photoluminescence and electrochemical characterizations confirmed the role of electron transfer intermediates of C/NFO. The synergistic effect of the nanosheet-like structure of NFO, combined with the surface functional groups of hydrochar, facilitated an exceptionally high rate of charge transfer and exposed abundant active adsorption sites for CO₂, thereby promoting the efficient separation of photogenerated charge carriers and enhancing photocatalytic activity for CO₂ reduction. This study presents a promising strategy for the rational design of hydrochar coupled with transition metal compound catalysts for efficient CO₂ photoreduction.