Generally, C3 N4 was widely used in the field of photocatalytic hydrogen production, but only few studies focused on electrocatalytic hydrogen production field in Ni/Co based systems. Herein, to investigate the enhanced HER property of C3 N4 , NiCo2 O4 @C3 N4 were fabricated successfully via a simple mixture method. With the introduction of C3 N4 , NiCo2 O4 @C3 N4 showed better HER property with small overpotential (89 mV, η10 mA cm-2 ), low Tafel slope (146 mV dec-1 ) and superior long-term stability, thereby indicating the excellent synergistic effect between NiCo2 O4 and C3 N4 . Besides, compared with NiCo2 O4 , the large electrochemically active surface areas of NiCo2 O4 @C3 N4 (ca. 126 cm2 ) indicated the abundant active sites, directly proofing the HER enhancement of C3 N4 . According to Density Functional Theory (DFT) calculation results, when NiCo2 O4 combined with C3 N4 , the EH2O* of NiCo2 O4 @C3 N4 decreased from 3.80 to 2.76 eV and, accordingly, the heterostructure possessed an appropriate ΔGH* (0.19 eV, close to Pt), suggesting the unique synergistic effect between NiCo2 O4 and C3 N4 . Meanwhile, H2 O interacted with the d orbital of the Co atom and induced more electrons to transfer from NiCo2 O4 to C3 N4 and H2 O sequentially, thereby accumulating plenty of electrons on H2 O molecule and further activating H2 O molecule. Accordingly, the H-O-H bond angle of H2 O was narrowed from 104.3° to 103.2°, meanwhile, the O-H bond length was extended from 0.975 to 0.989 Å, demonstrating the HER enhancement of C3 N4 .
Keywords: C3N4; HER; NiCo2O4; synergistic effect.
© 2022 Wiley-VCH GmbH.