Highly-ordered silicon nanowire arrays for photoelectrochemical hydrogen evolution: an investigation on the effect of wire diameter, length and inter-wire spacing

Vertically-aligned, highly-ordered silicon nanowire (SiNW) array photocathodes are fabricated employing e-beam lithography followed by deep reactive ion etching (DRIE) of Si. The effect of structural parameters of SiNWs, including wire diameter, length and inter-wire spacing, on their photoelectrocatalytic hydrogen evolution performance has been systematically investigated. Within the range of dimensions under study, the SiNW photocathode with a wire diameter of 200 nm, a length of 1 μm and an inter-wire spacing of 175 nm shows the best performance exhibiting a maximal saturated photocurrent density of 52 mA cm−2 and an onset potential (@−1 mA cm−2) of −0.17 V versus reversible hydrogen electrode. These lithography-patterned SiNWs with homogeneous structural parameters can help establish an unobscured structure–activity relation and facilitate Si-based photoelectrode design.