الفهرس 
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Abstract
Photoelectrochemical (PEC) water splitting is an ideal technology that can convert solar light irradiation into clean hydrogen (H2) fuel. Significant potentials have been dedicated to design novel catalyst materials and to fabricate advanced heterojunction constructions. The creation of chemically-stable, inexpensive and highly photo-active, photoelectrocatalysts still remains a great challenging issue. On the other hand, developing active, natural abundant and non-expensive electrocatalysts for large scale production and storage of H2 fuel is a prerequisite to drive stable electrochemical water splitting reaction.
Herein, the sensitization of TiO2 nanoparticles with rod-like Sb2S3 (Stibnite) bundles as a type-II band alignment on the surface of reduced graphene oxide (RGO) in the same heterostructure (TiO2/Sb2S3/RGO) was produced for the first time by a facile one-pot hydrothermal method. X-ray diffraction (XRD) patterns and Raman spectroscopy revealed the formation of Sb2S3 orthorhombic structure with rod-like morphology and tetragonal phase of anatase TiO2 nanoparticles. TEM, SEM and HRTEM analysis confirmed XRD results. EDX elemental mapping and XPS spectroscopy analysis confirmed the elemental composition and the valence states of the as-synthesized photoanodes. The greatest improvement in the photocurrent density was 39.65 μA/cm2 (measured vs. SCE) for the TiO2/Sb2S3/10%RGO photoanode in 0.1 M Na2SO4 aqueous solution electrolyte. This is a four times enhancement of the photocurrent density measured on bare TiO2 photoanode and two times that measured on TiO2/Sb2S3. Electrochemical impedance spectroscopy (EIS) measurements revealed enhanced charge separation and facile electron transfer. The positive slopes of the Mott-Schottky plots assured the n-type nature of the samples. These outstanding results offer a unique strategy towards the engineering of future chalcogenide-based catalysts with promising photoelectrochemical features.
To drive electrocatalysts with outstanding OER performances, atomic Cu species loaded on hierarchical flower-like CoFe layered double hydroxides (LDHs) superlattice (denoted as Cux/CoFe LDHs) were firstly fabricated by a facile co-precipitation method followed by a room temperature treatment to load the atomic Cu species from alkaline copper salt solution. The superlattice structure was proved by the high resolution transmission electron microscopy (HRTEM). Remarkably, benefiting from high level long ordering associated with vacant cation sites and defects, the unique superlattice structural features and the atomic Cu % loading onto the LDHs matrix, the obtained Cux/CoFe LDHs electrocatalyst exhibited superior activity and stability for oxygen evolution reaction (OER). The loaded atomic Cu species improves the electronic structure and provides more exposed active sites due to synergetic electron coupling between copper and the LDHs. These loaded atomic Cu species have outstanding potentials for achieving high selectivity and reactivity in electrocatalysis. Importantly, the efficient resulted Cu4.76/CoFe LDHs electrode in which the atomic Cu % loading ratio is 4.76 % showed the best electrocatalytic activity which only required the much lower overpotential of 253 mV to reach 10 mA/cm2 and a small Tafel slope of 63 mV/decade in 1 M KOH. The Cu4.76/CoFe LDHs electrocatalyst had undergone in-situ surface reconstruction and electrons were transferred from M (Co or Fe) to Cu via the M-O-Cu bonds, which could elucidate the outstanding OER activity and stability of the electrocatalyst. This work paves a facile and novel method for enhancing the catalytic activity of CoFe LDHs based electrocatalyst, which may be extended to the synthesis of future electrocatalysts having highly active OER performance.
Herein, low-cost chromium (Cr) dopants are incorporated into Co2Fe layered double hydroxides (Co2Fe1−xCrx LDHs) via a simple one-pot co-precipitation approach at room temperature. The oxygen evolution reaction (OER) performances of the (Co2Fe1−xCrx LDHs) electrocatalysts with various atomic Cr dopants % contents were systematically studied. Intriguingly, the Co2Fe0.50Cr0.50 LDHs electrocatalyst exhibited outstanding electrocatalytic activities towards OER with an ultralow overpotential of 236 mV at 10 mA/cm2 and a small Tafel slope of 68 mV/decade, manifesting a superior long-term durability in 1 M KOH aqueous electrolyte solution. The remarkable OER results revealed that the introduction of the Cr dopants as new active sites could efficiently regulate the position of the d-band center of the metal sites, improving the adsorption of oxygen species and promoting the reaction kinetics. In addition to the effect of the electronic structure regulation, the Cr doping also enhanced the electrondonation ability for the obtained Co2Fe1−xCrx LDHs electrocatalysts because of the lower electronegativity of Cr when compared with both Co and Fe. Our work can provide a promising strategy to develop efficient transition metal layered double hydroxides based-electrocatalysts in the future for energy-related applications.
Keywords: TiO2/Sb2S3/RGO hybrids; Sb2S3 rod-like bundles; Band alignment; Chalcogenide-based catalysts; PEC water oxidation, Single atom catalyst; Co-precipitation; Superlattice; Cux/CoFe LDHs; Co2Fe1−xCrx LDHs, Overpotentail, OER.