A n-Si/CoOx/Ni:CoOOH photoanode producing 600 mV photovoltage for efficient photoelectrochemical water splitting

Abstract

n-Si, believed as a promising photoanode candidate, has suffered from sluggish oxygen evolution reaction (OER) kinetics and poor chemical stability when exposed to aqueous electrolyte. Herein, CoOx/Ni:CoOOH bilayers were successfully deposited on n-Si substrate by atomic layer-deposition (ALD) and photoassisted electrochemical deposition (PED) for stabilizing and catalyzing photoelectrochemical (PEC) water oxidation. In comparison to the n-Si/CoOx photoanode as reference, the prepared n-Si/CoOx/Ni:CoOOH photoanode upon the optimized PED process presents a much improved PEC performance for water splitting, with the onset potential cathodically shifted to ∼1.03 V vs. reversible hydrogen electrode (RHE) and the photocurrent density much increased to 20 mA cm−2 at 1.23 V vs. RHE. It is revealed that the introduction of Ni dopants increases the work functions of the deposited Ni:CoOOH overlayers, which gives rise to the upward band bending weakened at the n-Si/CoOx/Ni:CoOOH cascading interface while strengthened at the Ni:CoOOH/electrolyte interface (with the band bending shifted from downward to upward), contributing to the decreased and the increased driving forces for charge transfer at the interfaces, respectively. Then, the balanced driving forces at the interfaces would endow the n-Si/CoOx/Ni:CoOOH photoanode with the best PEC performance. Moreover, PED has been evidenced superior to ED to dope Ni into CoOOH with the formed overlayer effectively catalyzing and stabilizing PEC water splitting.