Revealing important role of graphitic carbon nitride surface catalytic activity in photocatalytic hydrogen evolution by using different carbon co-catalysts

Abstract Previous researches on photocatalytic hydrogen evolution (PHE) activity of graphitic carbon nitride (g-C3N4) mainly focus on its charge separation while the role of its surface catalytic activity is ignored. In this work, we focus on studying the role of surface catalytic activity in PHE of g-C3N4 by synthesising composites of g-C3N4 with different carbon nanoparticle (CP) co-catalysts. All three kinds of composites of in-situ formed N and P co-doped CP (NPCP) in g-C3N4, g-C3N4 mixed with P doped CP (PCP), and g-C3N4 mixed with un-doped CP have been proved to have improved charge separation over pristine g-C3N4 via comparing their dye molecules degradation activity, photoluminance, photocurrent and ESR characters. However, g-C3N4/CP displays lower PHE activity than g-C3N4, while g-C3N4/NPCP and g-C3N4/PCP display higher PHE activity than g-C3N4. Electrochemical analysis reveals that the PHE activity of g-C3N4 based photocatalysts is limited by their surface catalytic activity: poor surface catalytic activity of g-C3N4 hinders residual charges that successfully migrate to the surface of g-C3N4 involving in hydrogen evolution reaction during PHE process.