Tuning Surface Electronics State of P-Doped In_2.77S₄/In(OH)₃ toward Efficient Photoelectrochemical Water Oxidation

Indium sulfide with a two-dimensional layered structure offers a platform for catalyzing water oxidation by a photoelectrochemical process. However, the limited hole holders hinder the weak intrinsic catalytic activity. Here, the nonmetallic phosphorus atom is coordinated to In_2.77S₄/In(OH)₃ through a bridge-bonded sulfur atom. By substituting the S position by the P dopant, the work function (surface potential) is regulated from 445 to 210 mV, and the lower surface potential is shown to be beneficial for holding the photogenerated holes. In_2.77S₄/In(OH)₃/P introduces a built-in electric field under the difference of Fermi energy, and the direction is from the bulk to the surface. This band structure results in upward band bending at the interface of In_2.77S₄/In(OH)₃ and P-doped sites, which is identified by density functional theory calculations (∼0.8 eV work function difference). In_2.77S₄/In(OH)₃/P stands out with the highest oxidation efficiency (η_oxi = 70%) and charge separation efficiency (η_sep = 69%). Importantly, it delivers a remarkable water oxidation photocurrent density of 2.51 mA cm^-2 under one sun of illumination.