Photoelectrochemical Characterisation on Surface-Inverted Black Silicon Photocathodes by Using Platinum/Palladium Co-catalysts for Solar-to-Hydrogen Conversion

Black silicon (bSi) has recently captured research attention in photoelectrochemical (PEC) solar-to-hydrogen (STH) conversion devices. Because nanostructuring of silicon retains the photovoltaic attributes of the material, it also provides a range of excellent physicochemical properties, such as a vast active-site-rich electrochemical interface, owing to a high aspect ratio, and important light-scattering attributes, which significantly improve photoconversion. One method to gain control over p-type bSi interface energetics is surface inversion of the p-type interface by phosphorus doping to introduce a shallow n⁺-emitter layer, which provides a thin p–n junction at the interface of the nanostructures. Although this concept has been suggested in the literature, it has not been demonstrated experimentally for a platinum/palladium co-catalysed bSi photocathode device for STH conversion. Herein, preliminary investigations and proof-of-concept studies are reported for the fabrication and PEC characterisation of surface-inverted p-type bSi photocathodes prepared by wet chemical etching. The PEC tests on p-bSi|n⁺ photocathodes show that, for both metal nanoparticles (Pt and Pd), the catalytic activity for proton conversion is increased; this is evident from an anodic shift in the onset potentials shifts to 0.24 and 0.29 V and an increase in photocurrent by 9 and 13.8 mA cm⁻², respectively, at 0 V versus a reversible hydrogen electrode, as a result of introducing the emitter layer.