N-doped carbon dots coupled NiFe-LDH hybrids for robust electrocatalytic alkaline water and seawater oxidation

Electrolysis of seawater offers a highly promising and sustainable route to attain carbon-neutral hydrogen energy without demanding on high-purity water resource. However, it is severely limited by the undesirable chlorine oxidation reaction (ClOR) on the anode and the releasing toxic chlorine species, inducing anode corrosion and multiple pollutions to reduce the efficiency and sustainability of this technology. The effective way is to limit the overpotential of oxygen evolution reaction (OER) below 480 mV and thus suppress the ClOR. Herein, we demonstrate that nitrogen-doped carbon dots strongly coupled NiFe layered double hydroxide nanosheet arrays on Ni foam (N-CDs/NiFe-LDH/NF) can efficiently facilitate OER with an ultralow overpotential of 260 mV to deliver the geometric current density of 100 mA·cm−2 and a Tafel slope of as low as 43.4 mV·dec−1 in 1.0 M KOH. More importantly, the N-CDs/NiFe-LDH/NF electrode at 100 mA·cm−2 shows overpotentials of 285 and 273 mV, respectively, by utilizing 1.0 M KOH with 0.5 M NaCl and 1.0 M KOH with 1.0 M NaCl as the simulated seawater, well avoid triggering ClOR. Notably, despite the complex environment of real seawater, N-CDs/NiFe-LDH/NF still effectively promotes alkaline seawater (1.0 M KOH + seawater) electrolysis with a lifetime longer than 50 and 20 h, respectively, in 1.0 M KOH and alkaline seawater electrolytes. The investigation result reveals that M-N-C bonding generated between N-CDs and NiFe-LDH intrinsically optimizes the charge transfer efficiency, further promoting the OER kinetics.