Quasi-hydrophilic black silicon photocathodes with inverted pyramid arrays for enhanced hydrogen generation.

Micro-/nanostructured silicon (Si) photoelectrodes are promising for efficient solar-driven water splitting. In this work, an elaborate study on textured Si photocathodes is reported. Compared to conventional textured Si photocathodes, the well-designed Si photocathode with randomly-distributed inverted pyramid arrays (SiIPs) generates a larger photovoltage of 440 mV for its higher effective minority carrier density, and produces a higher photocurrent density at a high reverse bias voltage due to its quasi-hydrophilicity. With the help of cobalt disulfide (CoS2) nanocrystals, sluggish charge kinetics of SiIP photocathodes can be further improved. The optimal SiIP/CoS2 photocathode yields an onset potential of 0.22 V vs. reversible hydrogen electrode (RHE) and a saturated photocurrent density of 10.4 mA cm-2 at -0.45 V (vs. RHE). Besides, this cathode produces a stable photocurrent density of ∼6.60 mA cm-2 at 0 V (vs. RHE) for 12 000 s in acidic media. Notably, our work presents a facile and inexpensive method to fabricate efficient Si photoelectrodes, which may promote the evolution of textured Si-based electrodes for potential photoelectrochemical and photocatalytic applications.