Improved performance and stability of photoelectrochemical water-splitting Si system using a bifacial design to decouple light harvesting and electrocatalysis

Photoelectrochemical (PEC) splitting of water into hydrogen and oxygen is a promising way for the production of clean, and storable form of fuel but the PEC efficiency has remained low. Herein, we demonstrate enhanced light harvesting, charge carrier separation/transfer, and catalyst management with bifacial design for the Si-based photocathodes to achieve best-in-class hydrogen generation with excellent electrochemical stability. Decoupling the light harvesting side from the electrocatalytic surface nullifies parasitic light absorption and enables Si photocathodes that exhibit a photocurrent density of 39.01 mA/cm² and stability over 370 h in 1 M H₂SO₄(aq) electrolyte due to fully covered a 15 nm Pt without any intentional protective layer. Furthermore, the bifacial Si photocathode system with semi-transparent Pt layer of 5 nm developed herein are capable of collecting sunlight not only on the light harvesting side but also on the back side of the device, resulting in a photocurrent density of 61.20 mA/cm² under bifacial two-sun illumination, which yields 56.88% of excess hydrogen when compared to the monofacial PEC system. Combining the bifacial design with surface texturing and antireflection coating enables excellent omnidirectional light harvesting capability with a record hydrogen (photocurrent) generation, which provides a promising way to realize practical PEC water splitting applications.