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

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 PC3, PO4 and PO3 via synthesis temperature controlled simple hydrothermal process. Specifically, PGQDs having PC3-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 & sdot;g � 1 & sdot;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 & sdot;cm � 2 as well as oxygen evolution reaction (OER) with 262 mV at 10 mA & sdot;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 & sdot;cm � 2 with excellent stability for 1000 h continuous operation, outperforming the commercial Pt/C and IrO2. This work demonstrates the role of PC3-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.