Silicon-Indium Tin Oxide Schottky Junction with Nickel Oxide Catalyst for Water Oxidation

The sunlight assisted water splitting using a photoelectrochemical (PEC) cell is an attractive approach to generate pure H₂ and O₂ without environmental pollution. The products by PEC solar fuel conversion can be separated, stored and transported, easily. To achieve high performance of PEC cell, the photoelectrode has several considerations such as efficient light absorption, catalysts and stability under aqueous solution. While hydrogen evolution reaction is simple electrochemical reaction and fast, oxygen evolution reaction (OER) is kinetically sluggish and includes multistep proton-coupled electron transfer.^1-3 Therefore, effective catalysts are vital to be high efficiency of photoanode with OER. Recently, nickel oxide (NiO) receives attention as alternative OER catalyst of RuO₂ or IrO₂, because of low cost and high activity. Silicon (Si) with 1.1eV band gap and wide light absorption of the solar specturm is promising materials for water splitting. However, in alkaline electrolyte, the long-term stability of Si without passivation layer is poor and there cannot be formed photovoltage between Si and electrolyte. For effective PEC water oxidation of Si, it is necessary to select suitable protection layer, effective catalyst and generate large photovoltage.⁴

In this research, schottky junction between n-Si and ultrathin indium tin oxide (ITO) with high work function was fabricated for water oxidation by sputtering of ITO and the NiO nanoparticles were deposited by spray deposition method at relative low temperature of 260^oC.  A photocurrent density of 27.4mA/cm² at 1.23V vs RHE, saturation current density of 37mA/cm², and photovoltage as high as 545mV were achieved under solar illumination with 100mW/cm²(Fig. 1). In the high pH (1M KOH) electrolyte, the long-term stability of PEC water oxidation at 1.23V vs REH was observed with degradation of 34.23% for 96 hrs (Fig. 2). This work suggests the great approach to generate high voltage without n-p junction using doping process of Si and improve the performance and stability of Si photoanodes.

Reference

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