Construction of Graphene-Wrapped Pd/TiO₂ Hollow Spheres with Enhanced Anti-CO Poisoning Capability toward Photoassisted Methanol Oxidation Reaction

Abstract

The development of high activity and durable Pd-based electrocatalysts is highly desired for methanol oxidation reaction (MOR). Herein, the unique graphene-encapsulated Pd/TiO 2 hollow sphere (PHTG) heterostructure is fabricated through a self-assembly strategy. The as-fabricated hierarchical PHTG exhibits the highest forward current for MOR of 2657 mA• mg −1 and excellent mass activity of 3687 mA•mg −1 with the aid of visible light irradiation, which is higher than all the reported TiO 2 -based photoassisted electrocatalysts. Impressively, the PHTG shows the highest long-time stability within 10,000 s (retained current density up to 1627 mA•mg −1 , which is 51% of the initial activity), compared to that of the state-of-art MOR catalysts. The detailed analyses (XPS, zeta potential, and CO-stripping) reveal that the superior performance of PHTG can be ascribed to the unique architectures of PHTG and the synergetic effect from the mutual interfaces of Pd NPs, hollow TiO 2 sphere (HTS), and conductive graphene shell. Notably, the introduction of the HTS provides abundant oxygen species to the Pd surface, fast mass and electron transportation, and strong CO oxidation ability for oxidative removal of the poisonous carbonaceous materials.

One-Step Hydrothermal Synthesis of Precious Metal-Doped Titanium Dioxide–Graphene Oxide Composites for Photocatalytic Conversion of CO2 to Ethanol

“…The Pd 3d band of Pd–TiO 2 /GO was studied via a narrow scan to indicate the Pd 3d 3/2 (337.4 eV) and Pd 3d 1/2 (335.1 eV). 45 Oxidative states of Pd were determined by analyzing four subpeaks in the main peaks ( Figure 7 f), 46 in which the local bands at 337.2 and 334.9 eV can be attributed to metallic Pd and the bands at 337.9 and 335.5 eV were of palladium oxides. Figure 7 g shows a wide scan of the Cu–TiO 2 /GO composite, locating binding energy bands for Cu 2p, O 1s, Ti 2p, and C 1s at 933.1, 531.8, 457.7, and 284.8 eV, respectively.…”

“…A C 1s narrow scan of the of Pd–TiO 2 /GO (Figure e) exhibits peaks, which are designated as O–CO (288.7 eV), CO (286.8 eV), C–C/CC/C–H (284.5 eV), and C–Ti (282.5 eV), respectively. The Pd 3d band of Pd–TiO 2 /GO was studied via a narrow scan to indicate the Pd 3d 3/2 (337.4 eV) and Pd 3d 1/2 (335.1 eV) . Oxidative states of Pd were determined by analyzing four subpeaks in the main peaks (Figure f), in which the local bands at 337.2 and 334.9 eV can be attributed to metallic Pd and the bands at 337.9 and 335.5 eV were of palladium oxides.…”

“…For Ag−TiO 2 /GO (Figure 7a), a wide scan reveals binding energies at 532.3, 458.6, 368.2, and 284.8 eV, corresponding to O 1s, Ti 2p, Ag 3d, and C 1s components. A C 1s narrow scan (Figure 7b) shows binding energy peaks at 288.5, 286.4, 284.6, and 282.6 eV that can be 45 Oxidative states of Pd were determined by analyzing four subpeaks in the main peaks (Figure 7f), 46 in which the local bands at 337.2 and 334.9 eV can be attributed to metallic Pd and the bands at 337.9 and 335.5 eV were of palladium oxides. Figure 7g shows The Cu 2p band peaks at 952.5 and 933.7 eV (Figure 7i) are attributed to Cu 2p 1/2 and Cu 2p 3/2 .…”

Critical Review on Synthetic Routes and Catalytic Applications of Hollow Nanomaterials

“…[86] Mercapto propyl trimethoxysilane (HS(CH 2 ) 3 −Si(OCH 3 ) 3 )in toluene used to functionalize silica surface. [87] Palladium acetylacetonate (Pd(acac) 2 ) (precursor) absorbed on the surface. Metallic palladium obtained after heating the sample for 3 h at 250 °C.…”

Plasmon-Enhanced Photocatalysis Coupling Electrocatalysis Steering Methanol Oxidation toward a CO-Free Dominant Pathway

“…Inspired by the progresses on photo-electrocatalysis of water splitting, − solar energy has been recently coupled with energy conversion devices, such as fuel cells and batteries to promote the chemical energyelectricity conversion efficiency. − To maximize solar energy utilization, a semiconductor with a narrow band gap (metal oxides, sulfides, and so forth) is usually adopted, − and it often couples an electrocatalyst to activate reactants. Under irradiation, as the photon energy ( h ν) is higher than the band gap energy of semiconductors, electrons in the valence band (VB) would be excited to the conduction band (CB), which are subsequently transferred to catalyst surface driven by the build-in electric fields and strengthened by the applied bias potentials.…”