Construction of Pt-M (M = Co, Ni, Fe)/g-C₃N₄ composites for highly efficient photocatalytic H₂ generation

• Main Authors: Wang, Liang, Zhu, Chenglu, Yin, Li-Sha, Huang, Wei
• Other Authors: School of Materials Science and Engineering
• Format: Article
• Language: English
• Published: 2021
• Subjects: Engineering::Materials; Photocatalytic H₂ Generation; Composite; Cocatalyst
• Online Access: https://hdl.handle.net/10356/149193
• Institution: Nanyang Technological University

Platinum (Pt) is recognized as an excellent cocatalyst which not only suppresses the charge carrier recombination of the photocatalyst but also reduces the overpotential for photocatalytic H2 generation. Albeit of its good performance, the high cost and low abundance restricted the utilization of Pt in large-scale photocatalytic H2 generation. Pt based transition metal alloys are demonstrated to reveal enhanced activities towards various catalytic reactions, suggesting the possibility to substitute Pt as the cocatalyst. In the present work, Pt was partially substituted with Co, Ni, and Fe and Pt-M (M = Co, Ni, and Fe)/g-C3N4 composites were constructed through co-reduction of H2PtCl6 and transition metal salts by the reductant of ethylene glycol. The crystal structure and valence states were measured by X-ray diffractometer (XRD) and X-ray photoelectron spectrometer (XPS), respectively. The higher degree of XRD peaks and larger binding energies for Pt 4f5/2 and Pt 4f7/2 after incorporating Co2+ ions indicated that Co was successfully introduced into the lattice of Pt and Pt-Co bimetallic alloys was attained through the solvothermal treatment. The morphology was subsequently observed by transmission electron microscope (TEM), which showed a good dispersion of Pt-Co nanoparticles on the surface of g-C3N4. Meanwhile, the shrinkage of lattice fringe after introducing cobalt salt further confirmed the presence of Pt-Co bimetallic alloys. The UV-Vis absorption spectra of g-C3N4 and Pt, Pt-Co deposited g-C3N4 were subsequently performed. It was found that the absorption edges were all consistent for all three samples as anticipated, implying that the band gap energy was maintained after hybridizing with Pt or Pt-Co alloys. Furthermore, the photocatalytic H2 generation was carried out over the as-prepared composites with triethanolamine (TEOA) as sacrificial reagent. Under visible-light illumination, the1% (w) Pt2.5M/g-C3N4 (M = Co, Fe, Ni) composites all exhibited higher or comparable activity towards photocatalytic H2 generation when compared to 1% (w) Pt loaded counterpart. In addition, the atomic ratios of Pt/Co and the loading amount of Pt-Co cocatalyst were modified to optimize the photocatalytic performance, among which, 1% (w) Pt2.5Co/g-C3N4 composite revealed the highest activity with a 1.6-time enhancement. Electrochemical impedance spectra (EIS) and photoluminescence (PL) spectra indicated that the enhancement might be attributed to improved charge transfer from g-C3N4 to Pt2.5Co cocatalyst and inhibited charge carrier recombination in the presence of Pt2.5Co cocatalyst. Therefore, the present study demonstrates the great potential to partially replace Pt with low-cost and abundant transition metals and to fabricate Pt based bimetallic alloys as promising cocatalysts for highly efficient photocatalytic H2 generation. 铂(Pt)是公认的优秀助催化剂：一方面，Pt能抑制光催化过程中光生载流子的复合；另一方面，Pt能降低光解水制 氢反应过电势。尽管如此，高昂的价格和极低的丰度限制了Pt在光解水制氢中的应用。Pt基过渡金属合金在多种催化反 应中呈现出卓越的催化性能，是潜在的助催化材料。在本工作中，我们利用Co、Ni、Fe等过渡金属部分取代贵金属Pt，并 以乙二醇为还原剂，通过原位还原H2PtCl6和过渡金属盐制备了Pt-M/g-C3N4 (M = Co, Ni, Fe)复合材料。在可见光照射 下，1% (w) Pt2.5M/g-C3N4 (M = Co, Ni, Fe)均表现出比同样条件下Pt负载的复合材料更高或者相当的光解水制氢性能。其 次，我们通过调节Pt/Co的原子比例以及Pt-Co合金的负载量进一步优化了光催化性能。结果显示：1% (w) Pt2.5Co/g-C3N4 复合材料表现出最高的光解水制氢性能，是同样条件下Pt负载的1.6倍。电化学阻抗谱(EIS)和光致发光光谱(PL)表明光 催化性能的提升得益于电子从g-C3N4向Pt2.5Co的有效传输以及光生载流子复合被有效抑制。这一工作显示Pt基过渡金属 合金在高效光解水制氢中具有潜在的应用前景，对于开发低成本、高效助催化剂具有一定的指导意义。