Development of Various Metal Sulfide Photocatalysts Consisting of d⁰, d⁵, and d¹⁰ Metal Ions for Sacrificial H₂ Evolution under Visible Light Irradiation

Abstract

We have developed metal sulfide photocatalysts with various crystal structures and constituent metal cations with d 0 , d 5, and d 10 electron configurations. Cu 3 VS 4 , Cu 3 NbS 4 , and Cu 3 TaS 4 with a sulvanite structure, ZnGa x In 2¹x S 4 (x = 00.6), and MnGaInS 4 with layered structures, BaLaCuS 3 with a onedimensionally anisotropic structure along the b-axis, and a (ZnS) 0.9 -(CuCl) 0.1 solid solution with a zinc blende structure have arisen as new photocatalysts for H 2 evolution in the presence of sacrificial electron donors under visible light irradiation. Water splitting has been extensively studied as artificial photosynthesis to convert solar energy to chemical energy. 110Metal sulfide photocatalysts with relatively narrow band gaps are a promising material group for harvesting solar energy efficiently.1,2,7 For example, (ZnS)-(CuInS 2 )-(AgInS 2 ) 11 and (CuAgZnSnS 4 )- (ZnS) 12 solid solutions and CuGa 2 In 3 S 8 13 are efficient photocatalysts for H 2 evolution utilizing the light of up to 700 nm. However, sacrificial electron donors are indispensable for producing H 2 steadily from water because of suppressing photocorrosion. Photoelectrochemical cells and Zscheme photocatalysts are suitable systems to achieve solar water splitting using such photocorrosive metal sulfide photocatalysts. Recently, we have successfully demonstrated solar water splitting using photoelectrochemical systems composed of a metal sulfide photocathode and a BiVO 4 photoanode. 14,15Powdered Z-scheme systems for solar water splitting were also fabricated upon combining metal sulfides as a H 2 -evolving photocatalyst with metal oxides as an O 2 -evolving photocatalyst and an electron mediator such as Co complexes 16 as an ionic electron mediator and a reduced graphene oxide 17,18 as a solidstate electron mediator. Thus, exploring new metal sulfide photocatalysts for H 2 evolution is still an important research topic to expand a solar water splitting system.To expand the kinds of crystal structures and constituent elements of metal sulfide photocatalysts, we focused on d 0 metal sulfides for Cu 3 MS 4 (M = V, Nb, and Ta) 19 with a sulvanite structure consisting of edge-and corner-shared MS 4 and CuS 4 tetrahedra, and BaLaCuS 3 20 with a one-dimensionally anisotropic structure consisting of corner-shared CuS 4 tetrahedra and edge-shared LaS 6 octahedra chains along the b-axis. Formations of solid solutions and substitution of elements are useful strategies for improvement of photocatalysts.1,2 Photocatalytic activity is determined with the balance of factors, such as the amount of photon absorption and driving forces for reduction and oxidation, depending on the band structure. In line with this strategy, we also focused on a (ZnS) 0.9 -(CuCl) 0.1 solid solution and ZnGa x In 2¹x S 4 with a layered structure in which In sites in ZnIn 2 S 4 21 were partially substituted with Ga, as candidates of a new metal sulfide photocatalyst. MnGaInS 4 also possesses a similar crystal structure to ZnIn 2 S 4 and interestingly contains M...

Cu3MS4 (M=V, Nb, Ta) and its Solid Solutions with Sulvanite Structure for Photocatalytic and Photoelectrochemical H2 Evolution under Visible‐Light Irradiation

“…Table shows the photocatalytic properties of Cu 3 MS 4 (M=V, Nb, Ta) and their solid solutions. Ru‐loaded Cu 3 MS 4 (M=V, Nb, Ta) showed photocatalytic activity for sacrificial H 2 evolution under visible‐light irradiation, as previously reported . All Cu 3 Nb 1− x V x S 4 and Cu 3 Ta 1− x V x S 4 solid solutions with the Ru cocatalyst also showed photocatalytic activity for sacrificial H 2 evolution with volcano‐type dependence on the V content.…”

“…Such p‐type metal sulfides can be used as photocathodes in photoelectrochemical systems . From the point of view of the metal ions that mainly form conduction bands, metal ions with a d 10 electron configuration, such as Cd 2+ , Ga 3+ , Ge 4+ , In 3+ , Sn 4+ , and Zn 2+ , are widely used in metal sulfide photocatalysts . In contrast, metal ions with a d 0 electron configuration are widely used as the main constituent elements for metal oxide and metal (oxy)nitride photocatalysts .…”

“…Many metal sulfides have narrow band gaps, because their valence bands formed by S 3p orbitals are located at relatively shallow (negative) energy levels. Moreover, many metal sulfides produce H 2 from water in the presence of sacrificial reagents under visible‐light irradiation . Thus, metal sulfides are attractive materials for efficient utilization of sunlight.…”

“…We preliminary reported that Cu 3 MS 4 (M=V, Nb, Ta) materials with a sulvanite structure show photocatalytic activity for sacrificial H 2 evolution under visible‐light irradiation . The p‐type semiconductor character of Cu 3 MS 4 has also been reported .…”

Development of Mixed‐Anion Photocatalysts with Wide Visible‐Light Absorption Bands for Solar Water Splitting

“…Metal sulfides free from oxygen atoms respond to visible light due to the raised VB, mainly composed of S 3 p orbitals, with a lower electronegativity than that of oxygen atoms . Clear H 2 evolution will be observed over a majority of metal sulfide photocatalysts in the presence of a sacrificial reagent under visible‐light irradiation.…”