Emerging nanoporous anodized stainless steel for hydrogen production from solar water splitting. (20th November 2020)

• Record Type: Journal Article
• Authors: Farrag, Heba H.; Sayed, Sayed Youssef; Allam, Nageh K.; Mohammad, Ahmad M.
• Is Part Of: Journal of cleaner production. Volume 274(2020)
• Publication Date: 2020-11-20
• Subjects: H2 -- Stainless steel 316L -- Photoelectrochemical -- Anodization -- Water splitting -- Nanoporous; Factory and trade waste -- Management -- Periodicals; Manufactures -- Environmental aspects -- Periodicals; Déchets industriels -- Gestion -- Périodiques; Usines -- Aspect de l'environnement -- Périodiques; 628.5
• DOI: 10.1016/j.jclepro.2020.122826
• Languages: English
• ISSNs: 0959-6526

Abstract

Abstract: A nanoporous anodized stainless steel 316L (NASS316L) has emerged as a propitious photoanode for the visible-light-induced photoelectrocatalysis of hydrogen production from water splitting. The innovation of this work pertained exclusively in adapting the anodization conditions to convert stainless steel from a state of inertness (toward water splitting) to a highly efficient "low-band gap" semiconductor. Several key anodization's parameters were sought, and their corresponding influence on the NASS316L's morphology and activity toward water splitting was inspected. The anodization was finally optimized in ethylene glycol electrolyte containing ammonium fluoride, methanol, water, and sulfuric acid at 40 V for 5 min at room temperature. Surprisingly, the sulfuric acid content in the anodization recipe played a vital role to tune the morphology toward an enhanced photoelectrocatalysis of water splitting. Keeping the sulfuric acid content in the optimized recipe at 3.4 vol % could produce the thickest (2 μm) nanoporous array of NASS316L, which, in turn, realized a remarkable photocatalytic activity (∼4.1 mA cm −2 at 0.65 V vs. Silver/Silver chloride) with a long-term stability toward water splitting. The NASS316L photoanode owned, moreover, a narrow band gap (1.77 eV) with an indirect transition, entitling the absorption of solar radiation in the visible regime. It also retained a flat band potential of −0.78 V, which sustained the separation of the generated charge carriers effectively upon illumination. Highlights: A robust anodized stainless steel photoanode was proposed for H2 production from water splitting. The H2 SO4 content in the anodizing electrolyte influenced the morphology and activity of the photoanode. The photoanode owned a narrow band gap of 1.77 eV and a flat band potential of ‒ 0.78 V. Enhanced activity (∼4.1 mA cm −2 at 0.65 V vs. Ag/AgCl) toward water splitting was achieved. Effective separation of the generated charge carriers was attained.