Highly efficient hydrogen production using p-Si wire arrays and NiMoZn heterojunction photocathodes

Highly efficient photoelectrochemical (PEC) hydrogen production is achieved using p-Si wire arrays loaded with NiMoZn particles in aqueous sulfuric acid under simulated sunlight (AM 1.5 G; 100 mW cm⁻²). Vertically-aligned wire arrays are grown on planar Si wafers via a quick electroless etching process within 5 min, leading to short Si wires of ∼4 μm and diameters of ∼0.2 μm. Despite the short length of the wires, the reflectance of the arrays is < 5% over the wavelength range of 400–800 nm (the reflectance of planar Si is ∼40%) and the photocurrent density (I_ph) is enhanced by ∼ 30% relative to planar Si. To further improve the PEC performance, ∼ 100 nm NiMoZn particles are photoelectrochemically deposited onto the wires. The wire arrays with evenly distributed NiMoZn particles show a photocurrent onset potential (E_on) of ∼ + 0.27 V vs. RHE and produce an I_ph of ∼1.45 mA cm⁻² at 0 V vs. RHE with a Faradaic efficiency of ∼ 100% for H₂ evolution. This I_ph value is ∼10-fold greater than that with the planar Si/NiMoZn samples. The excellent performance of the wire arrays and NiMoZn heterojunction is attributed to enhanced light absorption (decreased reflectance), facilitated charge transfer (radial-directional electron transfer), and NiMoZn-catalyzed hydrogen production.