A dual-electrolyte system for photoelectrochemical hydrogen generation using CuInS₂-In₂O₃-TiO₂ nanotube array thin film

The utilization of Na₂S/Na₂SO₃ mixture as the electrolyte solution to stabilize sulfide anode in a photoelectrochemical cell for hydrogen evolution generally compromises the current-to-hydrogen efficiency (η-_current) of the system. Here, the employment of a dual-electrolyte system, that is, Na₂S/Na₂SO₃ mixture and pH-neutral Na₂SO₄ as the respective electrolyte solutions in the anode and cathode chambers of a water splitting cell is demonstrated to suppress the photocorrosion of CuInS₂-In₂O₃-TiO₂ nanotube (CIS-In₂O₃-TNT) heterostructure, while simultaneously boosts the η-_current. Although n-type CIS and In₂O₃ nanoparticles can be easily formed on TNT array via facile pulse-assisted electrodeposition method, conformal deposition of the nanoparticles homogeneously on the nanotubes wall with preservation of the TNT hollow structure is shown to be essential for achieving efficient charge generation and separation within the heterostructure. In comparison to Na₂S/Na₂SO₃ solution as the sole electrolyte in both the anode and cathode chambers, introduction of dual electrolyte is shown to not only enhance the photostability of the CIS-In₂O₃-TNT anode, but also lead to near-unity η-_current as opposed to the merely 20% η-_current of the single-electrolyte system.