Engineering phosphorous doped graphene quantum dots decorated on graphene hydrogel as effective photocatalyst and high-current density electrocatalyst for seawater splitting.

[Display omitted] • P-doped graphene quantum dots were synthesized with different P-C bond configurations via simple hydrothermal process. • The PGQD3/GH composite demonstrated excellent photocatalytic hydrogen production of 20.47 mmol·g−1·h−1 in seawater splitting. • The PGQD3/GH composite performs superior bifunctional electrochemical activities of HER and OER. • The seawater electrolysis cell using PGQD3/GH composite delivers small overall voltage with excellent stability. Designing metal-free catalyst with outstanding activity for both photocatalytic and electrocatalytic seawater splitting is highly demand and still remained challenge. This work demonstrates the synthesis of P-doped graphene quantum dots (PGQDs) containing different P-configuration bonding of PC 3 , PO 4 and PO 3 via synthesis temperature controlled simple hydrothermal process. Specifically, PGQDs having PC 3 -bonds (PGQD3) shows effectively tunable electronic structure, significant enhancing visible light absorption, then their hybrid composite with graphene hydrogel (PGQD3/GH) is prepared. The PGQD3/GH composite possesses excellent photocatalytic hydrogen production with yield of 20.47 mmol·g−1·h−1 in seawater splitting. Furthermore, the PGQD3/GH composite performs superior electrochemical activities of hydrogen evolution reaction (HER) toward seawater with an overpontetial of 41 mV at 10 mA·cm−2 as well as oxygen evolution reaction (OER) with 262 mV at 10 mA·cm−2. In seawater electrolysis cell, the PGQD3/GH composite delivers small overall voltage of 1.62 V to obtain high current density of 500 mA·cm−2 with excellent stability for 1000 h continuous operation, outperforming the commercial Pt/C and IrO 2. This work demonstrates the role of PC 3 -bond in modulating the band gap and active site for photocatalytic and electrocatalytic seawater splitting reaction that may provide new idea for developing porous non-metal all-carbon catalyst for seawater splitting by both photocatalysis and electrocatalysis. [ABSTRACT FROM AUTHOR]