Nanoporous silicon photocathodes with [Co] molecular catalyst for enhanced solar-driven hydrogen generation

Abstract

Silicon (Si) is a commercially available semiconductor used for photoelectrochemical (PEC) hydrogen production, which has various advantages of earth-abundant element, non-toxicity, broad absorption of the solar spectrum, high saturation current and industrial applicability. However, it suffers from surface light reflection, short carrier-transport distance, slow charge transfer at the electrode–electrolyte interface, and poor stability in aqueous electrolytes, resulting in decreased photocurrent density and elevated overpotential. In this work, a surface-modified nanoporous Si photocathode, called black Si (b-Si), was fabricated with a large electrochemical surface area for loading of Co(dmgH)₂(py)Cl catalyst. Under the illumination of simulated sunlight, the optimal b-Si/[Co] photocathode exhibited a high photocurrent density of −4.15 mA cm⁻² (0 V_RHE), a value 319 times that of the f-Si electrode under the same conditions. Moreover, the onset potential positively shifted to 0.31 V_RHE and the driving force required for H₂ production was significantly decreased. The enhanced water splitting was attributed to the rapid transfer of charge across the electrode–electrolyte interface and efficient HER reactivity via the [Co] molecular catalyst. The surface engineering of the nanoporous structure and the deposition of molecular catalyst on the Si electrode have provided insights into the construction of semiconductor/catalyst hybrid photoelectrodes, and were concluded to synchronously improve the charge transfer at the electrode/electrolyte interface, reduce the overpotential, and speed up the PEC water splitting.