空心NiCo2S4纳米球助催化剂担载ZnIn2S4纳米片用于可见光催化制氢

纳米片与空心球上之间的合理界面调控是开发高效太阳能制氢光催化剂的潜在策略。在各类光催化材料中，金属硫化物由于具有相对较窄的带隙和优越的可见光响应能力而被广泛研究。ZnIn₂S₄是一种层状的三元过渡金属半导体光催化剂，其带隙可控(约2.4 eV)。在众多金属硫化物光催化剂中，ZnIn₂S₄引起了广泛兴趣。然而，单纯的ZnIn₂S₄光催化活性仍然相对较差，主要是因为光生载流子的复合率较高、迁移速率较慢。在半导体光催化剂上负载助催化剂是提升光催化剂性能的一种有效方法，因为它不仅可以加速光生电子和空穴的分离，而且还可以降低质子还原反应的活化能。作为一种三元过渡金属硫化物，NiCo₂S₄表现出较高的导电性、较低的电负性、丰富的氧化还原特性以及优越的电催化活性。这些特性表明，NiCo₂S₄可以作为光催化制氢的助催化剂，以加速电荷分离和转移。此外，NiCo₂S₄和ZnIn₂S₄都属于三元尖晶石的晶体结构，这可能有助于构建具有紧密界面接触的NiCo₂S₄/ZnIn₂S₄复合物，从而提高光催化性能。本文中，将超薄ZnIn₂S₄纳米片原位生长到非贵金属助催化剂NiCo₂S₄空心球上，形成具有强耦合界面和可见光吸收的NiCo₂S₄@ZnIn₂S₄分级空心异质结构光催化剂。最优NiCo₂S₄@ZnIn₂S₄复合样品(NiCo₂S₄含量：ca. 3.1%)的析氢速率高达78 μmol·h^-1，约是纳米片组装ZnIn₂S₄光催化剂析氢速率的9倍、约是1% (w, 质量分数)Pt/ZnIn₂S₄样品析氢速率的3倍。此外，该复合光催化剂在反应中表现出良好的稳定性。荧光和电化学测试结果表明，NiCo₂S₄空心球是一种有效的助催化剂，可促进光生载流子的分离和传输，并降低析氢反应的活化能。最后，提出了NiCo₂S₄@ZnIn₂S₄光催化析氢的可能反应机理。在NiCo₂S₄@ZnIn₂S₄复合光催化剂中，具有高导电性的NiCo₂S₄助催化剂可快速接受ZnIn₂S₄上的光生电子，用以还原质子生成氢气，而电子牺牲剂TEOA捕获光生空穴，进而完成光催化氧化还原循环。该研究有望为基于纳米片为次级结构的分级空心异质结光催化剂的设计合成及其光催化制氢研究提供一定的指导。

Hollow NiCo2S4 Nanospheres as a Cocatalyst to Support ZnIn2S4 Nanosheets for Visible-Light-Driven Hydrogen Production

The rational interface tailoring of nanosheets on hollow spheres is a promising strategy to develop efficient photocatalysts for hydrogen production with solar energy. Among the various photocatalyst materials, metal sulfides have been extensively researched because of their relatively narrow band gap and superior visible-light response. ZnIn₂S₄ is a layered ternary chalcogenide semiconductor photocatalyst with a tunable band gap energy (approximately 2.4 eV). Among various metal sulfide photocatalysts, ZnIn₂S₄ has gained considerable attention. However, intrinsic ZnIn₂S₄ only exhibits a relatively moderate photocatalytic activity, which is mainly owing to the high recombination and low migration rate of photocarriers. Loading cocatalysts onto semiconductor photocatalysts is an effective way to improve the performance of photocatalysts, because it can not only facilitate the separation of electron-hole pairs, but also reduce the activation energy for proton reduction. As a ternary transition metal sulfide, NiCo₂S₄ features a high electrical conductivity, low electronegativity, excellent redox properties, and outstanding electrocatalytic activity. Such favorable characteristics suggest that NiCo₂S₄ can expedite charge separation and transfer, thereby promoting photocatalytic H₂ production by serving as a cocatalyst. Moreover, both NiCo₂S₄ and ZnIn₂S₄ possess the ternary spinel crystal structure, which may facilitate the construction of NiCo₂S₄/ZnIn₂S₄ hybrids with tight interfacial contact for an enhanced photocatalytic performance. Herein, ultrathin ZnIn₂S₄ nanosheets were grown in situ on a non-noble-metal cocatalyst, namely NiCo₂S₄ hollow spheres, to form hierarchical NiCo₂S₄@ZnIn₂S₄ hollow heterostructured photocatalysts with an intimately coupled interface and strong visible light absorption extending to ca. 583 nm. The optimized NiCo₂S₄@ZnIn₂S₄ hybrid with a NiCo₂S₄ content of ca. 3.1% exhibited a high hydrogen evolution rate of 78 μmol·h^-1, which was approximately 9 times higher than that of bare ZnIn₂S₄ and 3 times higher than that of 1% (w, mass fraction) Pt/ZnIn₂S₄. Additionally, the hybrid photocatalysts displayed good stability in the reaction. Photoluminescence and electrochemical analysis results indicated that NiCo₂S₄ hollow spheres served as an efficient cocatalyst for facilitating the separation and transport of light-induced charge carriers as well as reducing the hydrogen evolution reaction barrier. Finally, a possible reaction mechanism for the photocatalytic hydrogen evolution was proposed. In the NiCo₂S₄@ZnIn₂S₄ composite photocatalyst, the NiCo₂S₄ cocatalyst with high electrical conductivity favorably accepts the photoinduced electrons transferred from ZnIn₂S₄ and then employs the electrons to reduce protons for H₂ production on the reactive sites. Concurrently, the photogenerated holes are trapped by TEOA that acts as a hole scavenger to accomplish the photoredox cycle. This study provides guidance for the fabrication of hierarchical hollow heterostructures based on nanosheet semiconductor subunits as remarkable photocatalysts for hydrogen production.