Electrochemical surface reconstructed Ptx(x=2,3)Si/PtSi/p-Si photocathodes for achieving high efficiency in photoelectrochemical H2 generation

Abstract

Using Si-based photoelectrodes to generate H₂ through photoelectrochemical (PEC) water splitting has attracted extensive attention in recent years. To produce H₂ with a high efficiency, the key issues that need to be solved are the relatively low photovoltage of the Si-based photoelectrode and the sluggish kinetics of the H₂ generation reaction occurring on the surface of Si. In this study, we designed and fabricated the Pt_x(x=2,3)Si/PtSi/p-Si photocathode for high-efficiency H₂ generation via PEC. The theoretically lower PtSi/p-Si junction Schottky barrier height was elevated to a high value of 0.9 eV by dopant segregation, thereby obtaining a high photovoltage. Upon the electrochemical surface reconstruction of PtSi, a thin layer of Pt_x(x=2,3)Si with a high catalytic activity is in situ formed on the photocathode which significantly enhances the hydrogen evolution reaction (HER) kinetics. Accordingly, a favorable onset potential for HER of 0.54 V vs. RHE and a high saturated photocurrent density of 30 mA cm⁻² at 0 V vs. RHE are achieved from the Pt_x(x=2,3)Si/PtSi/p-Si photocathode. The applied-bias photo-to-current efficiency (ABPE) of the Pt_x(x=2,3)Si/PtSi/p-Si photocathode reaches a maximum at 5.8%, which is record-high for the Si-based single junction photocathodes without a buried p–n junction. Moreover, the Pt_x(x=2,3)Si/PtSi/p-Si photocathode exhibits an excellent stability in the long-term PEC H₂ generation test. This work provides a new perception onto the design and construction of Si-based photocathodes with improved catalytic activity, as well as the possibility of efficient and stable PEC H₂ generation.