Enhancing the Performance of Si-Based Photocathodes for Solar Hydrogen Production in Alkaline Solution by Facilely Intercalating a Sandwich N-Doped Carbon Nanolayer to the Interface of Si and TiO₂

Photoelectrochemical (PEC) water splitting is a promising but immensely challenging technology for sustainable production of hydrogen. To this end, highly active, durable, and inexpensive photocathodes that operate under conditions compatible with those for photoanodes are desired. Herein, Si-based composite photocathodes were constructed by coating the front surface of Si with an N-doped carbon nanolayer and then a TiO2 protective layer, followed by decorating the electrode surface with Ni and Ni–Mo catalysts. The carbon nanolayer, denoted as CPDA, was formed directly on the Si surface by in situ self-polymerization of dopamine, followed by carbonization of the polydopamine (PDA) coating. The performance of the as-fabricated Si photocathodes with and without the CPDA layer was comparatively studied for PEC hydrogen evolution reaction (HER) in alkaline electrolytes to evaluate the effect of the sandwich CPDA layer in between the Si substrate and the TiO2 layer on the photoelectrocatalytic behaviors of Si-based electrodes. The photocathodes containing the CPDA layer demonstrated lower electron transfer resistance, higher built-in photovoltage, and larger band bending relative to the analogous electrodes without the CPDA layer. Accordingly, the short-circuit photocurrents of the Ni and Ni–Mo-decorated photocathodes with the CPDA layer were enhanced by a factor of 2.8–3.3, and their open-circuit photovoltages were enlarged by 0.14–0.22 V, compared to those of the corresponding electrodes without the CPDA layer in 1 M KOH under simulated 1 sun illumination. Moreover, the photocathodes with the CPDA layer also exhibited an improved stability for PEC HER in alkaline solutions, with a faradaic efficiency of 90–97% in the initial hour.