FeNi intermetallic compound nanoparticles wrapped with N-doped graphitized carbon: a novel cocatalyst for boosting photocatalytic hydrogen evolution

The loading of noble-metal cocatalysts on photocatalysts can significantly increase the energy conversion efficiency from light to hydrogen (H-2). However, the high cost of noble metals limits their practical application. Therefore, it is of great significance to explore alternative catalysts based on noble-metal-free materials. Herein, FeNi intermetallic compound nanoparticles wrapped with N-doped graphitized carbon (FeNi@NGC) are prepared by a facile pyrolysis approach. The FeNi@NGC is used as a novel cocatalyst of host photocatalysts, such as g-C3N4, to boost their photogenerated charge separation. In an aqueous solution containing triethanolamine and under visible-light irradiation, the optimized FeNi@NGC/g-C3N4 (FNC15) composite photocatalyst exhibits significantly increased PC activity with a H-2 production rate of 2.696 mmol g(-1) h(-1), which is over 283 times that of primary g-C3N4 and even higher than that of 1.0 wt% Pt/g-C3N4. Furthermore, the FNC15 showed excellent stability and reusability. The apparent quantum yield (AQY) of the FNC15 composite photocatalyst reaches 24.78% and 7.28% at 400 nm and 420 nm, respectively. Notably, the FNC15 can promote photocatalytic overall water splitting with an H-2 evolution rate of about 0.167 mmol g(-1) h(-1). Experimental analysis and DFT calculations are performed to investigate the mechanism of excellent PC H-2 evolution. It appears that the FeNi@NGC loading on the surface of host photocatalysts can (i) boost the charge carrier separation and transfer because of the secondary charge transfer in the FeNi intermetallic compound and (ii) ameliorate the kinetics of H-2 evolution on the surface of the photocatalyst and achieve obviously enhanced H-2 generation. This work provides a new strategy for preparing efficient noble-metal-free cocatalysts for boosting photocatalytic H-2 evolution.