Supplementary files for S-scheme NaxCoO2/g-C3N4 heterojunction photo-electrocatalysts for water splitting

Article abstract:<br>Enabling a highly efficient charge separation on hetero-structural photo-electrocatalyst is crucial to achieve a high efficiency of water splitting technology for sustainable green hydrogen production. Herein, novel S-scheme hetero-structural materials, Na_<em>x</em>CoO₂/<i>g</i>-C₃N₄ (<i>x</i> = 0.5, 0.6, and 0.74), have been employed as photo-electrocatalysts for water splitting reaction. Their corresponding overpotential values under irradiation condition with the current density of 10 mA cm⁻² were about 590 mV (<i>x</i> = 0.74), 555 mV (<i>x</i> = 0.6) and 710 mV (<i>x</i> = 0.5), respectively. Compared to the dark condition, Na_<em>x</em>CoO₂/<i>g</i>-C₃N₄ exhibited lower overpotentials. XPS and in-situ KPFM results further confirmed that an interfacial electric field was formed at the interface of Na_<em>x</em>CoO₂ and <i>g</i>-C₃N₄. Under the irradiation condition, the electrons from the conduction band of NCO flow toward to the valence band of CN to form S-scheme heterostructure, which could highly accelerate the reducing capability of CN, hence splitting water to produce hydrogen gas.