Built-In n<sup>+</sup>pp<sup>+</sup> Silicon Junction Photocathode with NiFe Layered Double Hydroxide for High-Performance Solar Hydrogen Production

This work demonstrates a highly efficient photocathode for water splitting in neutral electrolyte. It is based on a combination of the back-field p + doped Si junction, and the nanostructured NiFe layered double hydroxide as co-catalyst. This extraordinary photoelectrochemical performance is primarily attributed to the catalyst-induced dramatic increase in active surface sites, and the suppression of hole recombination. Following the deposition of Pt nanoparticles between the Si junction and NiFe layered double hydroxide, the platinized photocathode (n + pp + Si/Pt/NiFe LDH) exhibited an excellent photocurrent density of -4.98 mA/cm 2 at 0 V versus the standard reference (RHE) in 0.5 M Na 2 SO 4 electrolyte. The superior quality of our cathode is demonstrated by the magnitude of the photoinduced current density (after dark current correction), which approaches the theoretical maximum. This achievement is attributed to the successful construction of built-in electric fields.