No abstract

Silicon microwire-arrays mitigate the effects of gas bubbles on the total overpotential of hydrogen-evolving cathodes oriented against gravity.

Experimental Details Materials: 100mm P-type Si <100> wafers with a thickness of 525 µm and resistivity of 10-20 Ω-cm were obtained from Addison Engineering. All chemicals were commercially available and used as received. Cobalt(II) chloride hexahydrate (CoCl 2 , >99.9%) was obtained from Alfa Aesar, whereas sodium hypophosphite monohydrate (NaPO 2 H 2), boric acid (H 3 BO 3 , >99.5%), concentrated ammonium hydroxide (NH 4 OH, ACS reagent 28%-30%) and potassium hydroxide (KOH, 99.99%) were obtained from Sigma-Aldrich. Buffered oxide etchant (6:1 (v/v) 40% NH 4 F to 49% HF) was obtained from Transene Inc. Sodium chloride (NaCl, 99%) and hydrogen peroxide (H 2 O 2 , ACS grade 30%) were obtained from Macron Chemicals. TraceMetal grade sulfuric acid (H 2 SO 4) was obtained from Fisher Scientific and diluted to 0.50 M with water with a resistivity of 18.2 MΩ•cm, obtained from a Millipore deionized (DI) water system. Preparation of Si Photocathodes: Si was structured into microwire arrays via deep reactive ion etching, RIE, of a wafer that was patterned with an array of >120 nm thick Al 2 O 3 masks with diameter 3 µm and a pitch of 7 µm. Shipley 1813 photoresist was spin coated onto a degreased wafer at 4000 RPM for 30 s and a pattern was defined using UV exposure through a chrome

Planar silicon and silicon microwire arrays oriented towards sunlight release layers of small gas bubbles that stir the electrolyte and do not impede photoelectrochemical water splitting.