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

- Vertically aligned ca. 4 μm-long p-Si microwire arrays are fabricated via a quick etching process within 5 min.
- NiMoZn particles are photoelectrochemically deposited onto the Si wires for 5 min.
- The p-Si wire array/NiMoZn produces Iph of ∼1.45 mA cm−2 at 0 V vs. RHE with a ∼100% Faradaic efficiency for H2 evolution.
- This Iph value is ∼10-fold greater than that with the planar Si/NiMoZn samples.
- The excellent performance of the p-Si wire arrays/NiMoZn heterojunctions is discussed.

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 (Iph) 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 (Eon) of ∼ + 0.27 V vs. RHE and produce an Iph of ∼1.45 mA cm−2 at 0 V vs. RHE with a Faradaic efficiency of ∼ 100% for H2 evolution. This Iph 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.

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