Mn_0.4In_1.6S₃ Nanoflower Solid Solutions for Visible-Light Photocatalytic Hydrogen Evolution

A series of Mn2xIn2(1–x)S3 (x < 0.5) nanoflower solid solutions (NSS) were synthesized by a simple one-step hydrothermal method using l-cysteine as S source and chelating reagent. The Mn2xIn2(1–x)S3 NSS exhibit excellent hydrogen evolution performance compared with pure In2S3. In particular, the Mn0.4In1.6S3 nanoflower solid solution exhibits the best photocatalytic activity with a hydrogen evolution rate of up to 3570 μmol/(g h) under visible-light irradiation even without any noble metal or cocatalysts, which is about 22 times as high as the pure In2S3 dose, and it shows a favorable stability in catalytic and antiphotocorrosion properties. The apparent quantum efficiency of Mn0.4In1.6S3 NSS was 12.9% at 420 nm. The excellent photoactivity of Mn0. 4In1.6S3 NSS is mainly related to faster separation of photogenerated electron–hole pairs and the band-gap structures. Additionally, the Mn0.4In1.6S3 NSS possesses another active site of Mn for hydrogen evolution compared with pure In2S3, and density functional theory (DFT) simulations for the H binding free energy on active site (ΔGH*) are performed to gain the fundamental insight into the role of Mn in Mn0. 4In1.6S3 NSS. Furthermore, because of the Mn active site, the Mn0.4In1.6S3 NSS has a very appealing ΔGH* of 0.74 eV, which is closer to zero than In as active sites in both Mn0.4In1.6S3 NSS (−3.83 eV) and pure In2S3 (−4.29 eV). The DFT-based first-principles calculations clearly shows that hydrogen adsorbed at different reaction sites with Mn and In have distinctly different free energies which further impact on hydrogen evolution performance. The research lights a new insight for photocatalytic hydrogen evolution, thus broadening routes for designing photocatalytic materials with multiple reaction sites for enhanced photocatalysis.