The development of low-cost and high-efficiency photocatalysts is an important way to realize photocatalytic hydrogen production. In this work, polyvinylpyrrolidone (PVP) is used as a morphological modifier to prepare a three-dimensional (3D) sea-urchin-structure NiCo₂O₄. Mn_0.05Cd_0.95S and NiCo₂O₄ spontaneously assemble into a spatial structure of the NiCo₂O₄–Mn_0.05Cd_0.95S p–n heterojunction under the action of the Coulomb force. The 3D sea-urchin-structure NiCo₂O₄ provides support for the Mn_0.05Cd_0.95S particles in the space, which improves the dispersion of Mn_0.05Cd_0.95S and exposes more reaction sites. Furthermore, the NiCo₂O₄–Mn_0.05Cd_0.95S composite catalyst with a spatial structure has good light absorption capacity. Mn_0.05Cd_0.95S is tightly bound on the surface of NiCo₂O₄, forming a built-in electric field at the contact interface to induce the directional migration of photogenerated carriers and effectively inhibit the recombination of electrons and holes. Photoelectrochemical and fluorescence tests show that the appropriate conduction band and valence band positions of NiCo₂O₄ and Mn_0.05Cd_0.95S, and the built-in electric field of the p–n heterojunction are more conducive to thermodynamic charge transfer. Because the composite catalyst has a large number of reaction sites, and shows faster charge transfer speed and effective inhibition of the recombination of electrons and holes, the hydrogen production rate of 3%NiCo₂O₄–Mn_0.05Cd_0.95S is as high as 17 008 μmol g⁻¹ h⁻¹, which is 4.45 times that of pure MCS. This work will provide new ideas for the design of 3D metal oxides and trigger the synthesis of other p–n heterojunction catalysts with a spatial structure.

中文翻译：

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海胆结构的NiCo2O4修饰的Mn0.05Cd0.95S pn异质结增强了光催化氢的释放。

低成本，高效率的光催化剂的开发是实现光催化制氢的重要途径。在这项工作中，聚乙烯吡咯烷酮（PVP）被用作形态改性剂，以制备三维（3D）海胆结构NiCo ₂ O ₄。在库仑力的作用下，Mn _0.05 Cd _0.95 S和NiCo ₂ O ₄自发地组装成NiCo ₂ O ₄ –Mn _0.05 Cd _0.95 S p–n异质结的空间结构。3D海胆结构NiCo ₂ O ₄为Mn _0.05 Cd提供支持空间中存在_0.95 S的颗粒，从而改善了Mn _0.05 Cd _0.95 S的分散，并暴露了更多的反应位点。此外，具有空间结构的NiCo ₂ O ₄ -Mn _0.05 Cd _0.95 S复合催化剂具有良好的光吸收能力。Mn _0.05 Cd _0.95 S紧密结合在NiCo ₂ O ₄的表面上，在接触界面处形成一个内置电场，以诱导光生载流子的方向迁移，并有效抑制电子和空穴的复合。光电化学和荧光测试表明，适当的NiCo ₂ O ₄和Mn _0.05 Cd _0.95 S的导带和价带位置以及p–n异质结的内置电场更有利于热力学电荷转移。由于该复合催化剂具有大量的反应部位，并且显示出更快的电荷转移速度和对电子和空穴再结合的有效抑制，制氢率为3％NiCo ₂ O ₄ -Mn _0.05Cd _0.95 S高达17 008μmolg ^-1 h ^-1，是纯MCS的4.45倍。这项工作将为3D金属氧化物的设计提供新思路，并引发其他具有空间结构的p–n异质结催化剂的合成。