CrOx-Mediated Performance Enhancement of Ni/NiO-Mg:SrTiO3 in Photocatalytic Water Splitting
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ABSTRACT:
SUBMITTER: Han K
PROVIDER: S-EPMC8422963 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Transients in the composition of Ni@NiO x core-shell co-catalysts deposited on SrTiO3 are discussed on the basis of state-of-the-art continuous analysis of photocatalytic water splitting, and post-XPS and TEM analyses. The formation of excessive hydrogen (H2:O2 ≫ 2) in the initial stages of illumination demonstrates oxidation of Ni(OH)2 to NiOOH (nickel oxyhydroxide), with the latter catalyzing water oxidation. A disproportionation reaction of Ni and NiOOH, yielding Ni(OH)2 with residual embedded Ni, occurs when illumination is discontinued, which explains repetitive transients in (excess) hydrogen and oxygen formation when illumination is reinitiated.
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Project description:Large-scale growth of low-cost, efficient, and durable non-noble metal-based electrocatalysts for water splitting is crucial for future renewable energy systems. Atomic layer deposition (ALD) provides a promising route for depositing uniform thin coatings of electrocatalysts, which are useful in many technologies, including the splitting of water. In this communication, we report the growth of a NiO/Ni catalyst directly on carbon fiber paper by atomic layer deposition and report subsequent reduction and oxidation annealing treatments. The 10-20 nm NiO/Ni nanoparticle catalysts can reach a current density of 10 mA·cm-2 at an overpotential of 189 mV for hydrogen evolution reactions and 257 mV for oxygen evolution reactions with high stability. We further successfully achieved a water splitting current density of 10 mA·cm-2 at 1.78 V using a typical NiO/Ni coated carbon fiber paper two-electrode setup. The results suggest that nanoparticulate NiO/Ni is an active, stable, and noble-metal-free electrocatalyst, which facilitates a method for future water splitting applications.
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Project description:Sonophotocatalysis has garnered significant attention due to its potential to enhance advanced oxidation processes, particularly water splitting, by employing materials with combined sonocatalytic and photocatalytic properties. In this study, we synthesized and investigated core-shell BaTiO3@SrTiO3 nanowires (BST NWs) with varying Sr/Ba molar ratios (2.5:7.5, 5.0:5.0, 7.5:2.5 mM, denoted as BST-1, BST-2, and BST-3, respectively) as catalysts for hydrogen production through water splitting. The piezoelectric nanowires demonstrated hydrogen evolution via both sonocatalysis and photocatalysis. In the sonophotocatalysis process, the ultrasonic vibration induced mechanical forces on the BST nanowires, thereby establishing a built-in electric field. This built-in electric field facilitated the effective separation of photo-generated charge carriers and prolonged their lifetimes, leading to a synergistic enhancement of hydrogen evolution. The pristine BaTiO3 and SrTiO3 nanowires exhibited relatively low hydrogen evolution rates (HER) of 7.0 and 6.0 µmol·g-1min-1, respectively. In contrast, the core-shell nanowires exhibited a substantial improvement in the hydrogen evolution rate. The HER increased with the addition of Sr, and BST-1, BST-2, and BST-3 achieved HERs of 12.0, 13.5, and 18.0 µmol·g-1min-1, respectively. The superior performance of BST-3 nanowires can be attributed to their highest piezoelectric potential and largest surface area. Additionally, BST-3 nanowires demonstrated remarkable stability over multiple cycles, validating their practical applicability as efficient photocatalysts.
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Project description:Eco-friendly and cost-effective catalysts with multiple active sites, large surface area, high stability and catalytic activity are highly desired for efficient water splitting as a sustainable green energy source. Within this line, a facile synthetic approach based on solventless thermolysis was employed for the simple and tunable synthesis of Ni1-xMgxFe2O4 (0 ≤ x ≤ 1) nanosheets. The characterization of nanosheets (via p-XRD, EDX, SEM, TEM, HRTEM, and SAED) revealed that the pristine ferrites (NiFe2O4 and MgFe2O4), and their solid solutions maintain the same cubic symmetry throughout the composition regulation. Elucidation of the electrochemical performance of the nanoferrite solid solutions showed that by tuning the local chemical environment of Ni in NiFe2O4 via Mg substitution, the intrinsic catalytic activity was enhanced. Evidently, the optimized Ni0.4Mg0.6Fe2O4 catalyst showed drastically enhanced HER activity with a much lower overpotential of 121 mV compared to the pristine NiFe2O4 catalyst. Moreover, Ni0.2Mg0.8Fe2O4 catalyst exhibited the best OER performance with a low overpotential of 284 mV at 10 mA/cm2 in 1 M KOH. This enhanced electrocatalytic activity could be due to improved electronic conductivity caused by the partial substitution of Ni2+ by Mg2+ in the NiFe2O4 matrix as well as the synergistic effect in the Mg-substituted NiFe2O4. Our results suggest a feasible route for developing earth-abundant metal oxide-based electrocatalysts for future water electrolysis applications.
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Project description:Development of a robust photocathode using low-cost and high-performing materials, e.g., p-Si, to produce clean fuel hydrogen has remained challenging since the semiconductor substrate is easily susceptible to (photo)corrosion under photoelectrochemical (PEC) operational conditions. A protective layer over the substrate to simultaneously provide corrosion resistance and maintain efficient charge transfer across the device is therefore needed. To this end, in the present work, we utilized pulsed laser deposition (PLD) to prepare a high-quality SrTiO3 (STO) layer to passivate the p-Si substrate using a buffer layer of reduced graphene oxide (rGO). Specifically, a very thin (3.9 nm ∼10 unit cells) STO layer epitaxially overgrown on rGO-buffered Si showed the highest onset potential (0.326 V vs RHE) in comparison to the counterparts with thicker and/or nonepitaxial STO. The photovoltage, flat-band potential, and electrochemical impedance spectroscopy measurements revealed that the epitaxial photocathode was more beneficial for charge separation, charge transfer, and targeted redox reaction than the nonepitaxial one. The STO/rGO/Si with a smooth and highly epitaxial STO layer outperforming the directly contacted STO/Si with a textured and polycrystalline STO layer showed the importance of having a well-defined passivation layer. In addition, the numerous pinholes formed in the directly contacted STO/Si led to the rapid degradation of the photocathode during the PEC measurements. The stability tests demonstrated the soundness of the epitaxial STO layer in passivating Si against corrosion. This study provided a facile approach for preparing a robust protection layer over a photoelectrode substrate in realizing an efficient and, at the same time, durable PEC device.
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Project description:Carbon quantum dots were prepared by a simple chemical process using activated carbon as carbon source. The as-prepared carbon quantum dots are fine with a narrow size distribution and show excellent hydrophilicity. The carbon quantum dots were combined with SrTiO3 nanoparticles through a simple impregnation process to obtain a carbon quantum dots/SrTiO3 nanocomposite. The photocatalytic reaction rate of carbon quantum dots/SrTiO3 nanocomposite is about 5.5 times as large as that of pure SrTiO3 in the degradation of rhodamine B under sunlight irradiation. The enhanced performance in the degradation of rhodamine B may be attributed to the interfacial transfer of photogenerated electrons from SrTiO3 to carbon quantum dots, leading to effective charge separation in SrTiO3. Carbon quantum dots show potential applications in high-efficiency photocatalyst design.
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Project description:Earth-abundant and efficient bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are highly significant for renewable energy systems. However, the performance of existing electrocatalysts is usually restricted by the low electroic conductivity and the limited amount of exposed active sites. In this work, (Fe0.2Ni0.8)0.96S tubular spheres supported on Ni foam have been prepared by a sulfuration of FeNi layered double hydroxide spheres grown on Ni foam. Benefiting from the unique tubular sphere architecture, the rich inner defects and the enhanced electron interactions between Fe, Ni and S, this electrocatalyst shows low overpotential of 48 mV for HER at 10 mA cm-2 in 1.0 mol L-1 KOH solution, which is one of the lowest value of non-previous electrocatalyts for HER in alkaline electrolyte. Furthermore, assembled this versatile electrode as an alkaline electrolyzer for overall water splitting, a current density of 10 mA cm-2 is achieved at a low cell voltage of 1.56 V, and reach up to 30 mA cm-2 only at an operating cell voltage of 1.65 V.
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