We report the synthesis of two‐dimensional metal–organic frameworks (MOFs) on nickel foam (NF) by assembling nickel chloride hexahydrate and 1,1′‐ferrocenedicarboxylic acid (NiFc‐MOF/NF). The ...NiFc‐MOF/NF exhibits superior oxygen evolution reaction (OER) performance with an overpotential of 195 mV and 241 mV at 10 and 100 mA cm−2, respectively under alkaline conditions. Electrochemical results demonstrate that the superb OER performance originates from the ferrocene units that serve as efficient electron transfer intermediates. Density functional theory calculations reveal that the ferrocene units within the MOF crystalline structure enhance the overall electron transfer capacity, thereby leading to a theoretical overpotential of 0.52 eV, which is lower than that (0.81 eV) of the state‐of‐the‐art NiFe double hydroxides.
2D MOFs on nickel foam (NF) were assembled. NiFc‐MOF/NF exhibits superior OER performance (overpotential of 195 mV at 10 and 241 mV at 100 mA cm−2) under alkaline conditions. The ferrocene units within the MOF crystalline structure enhance the overall electron transfer capacity, thereby leading to a theoretical overpotential of 0.52 eV (lower than NiFe double hydroxides: 0.81 eV).
The overall water splitting efficiency is mainly restricted by the slow kinetics of oxygen evolution. Therefore, it is essential to develop active oxygen evolution catalysts. In this context, we ...designed and synthesized a tungsten oxide catalyst with oxygen vacancies for photocatalytic oxygen evolution, which exhibited a higher oxygen evolution rate of 683 μmol h−1 g−1 than that of pure WO3 (159 μmol h−1 g−1). Subsequent studies through transient absorption spectroscopy found that the oxygen vacancies can produce electron trapping states to inhibit the direct recombination of photogenerated carriers. Additionally, a Pt cocatalyst can promote electron trap states to participate in the reaction to improve the photocatalytic performance further. This work uses femtosecond transient absorption spectroscopy to explain the photocatalytic oxygen evolution mechanism of inorganic materials and provides new insights into the design of high‐efficiency water‐splitting catalysts.
In photocatalytic oxygen evolution, some excited electrons can be trapped more easily to form trapped state electrons due to the presence of oxygen vacancies in Ov‐WO3‐600. This process can partially inhibit direct recombination and prolong the lifetime of photogenerated charges. In addition, photodeposited Pt can serve as an active site to capture the trapped state electrons to react with electron sacrificial agents.
A central question important to understanding DNA repair is how certain proteins are able to search for, detect, and fix DNA damage on a biologically relevant time scale. A feature of many base ...excision repair proteins is that they contain 4Fe4S clusters that may aid their search for lesions. In this paper, we establish the importance of the oxidation state of the redox-active 4Fe4S cluster in the DNA damage detection process. We utilize DNA-modified electrodes to generate repair proteins with 4Fe4S clusters in the 2+ and 3+ states by bulk electrolysis under an O2-free atmosphere. Anaerobic microscale thermophoresis results indicate that proteins carrying 4Fe4S3+ clusters bind to DNA 550 times more tightly than those with 4Fe4S2+ clusters. The measured increase in DNA-binding affinity matches the calculated affinity change associated with the redox potential shift observed for 4Fe4S cluster proteins upon binding to DNA. We further devise an electrostatic model that shows this change in DNA-binding affinity of these proteins can be fully explained by the differences in electrostatic interactions between DNA and the 4Fe4S cluster in the reduced versus oxidized state. We then utilize atomic force microscopy (AFM) to demonstrate that the redox state of the 4Fe4S clusters regulates the ability of two DNA repair proteins, Endonuclease III and DinG, to bind preferentially to DNA duplexes containing a single site of DNA damage (here a base mismatch) which inhibits DNA charge transport. Together, these results show that the reduction and oxidation of 4Fe4S clusters through DNA-mediated charge transport facilitates long-range signaling between 4Fe4S repair proteins. The redox-modulated change in DNA-binding affinity regulates the ability of 4Fe4S repair proteins to collaborate in the lesion detection process.
The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction. Iron-based non-precious metal catalysts exhibit ...promising activity and stability, as an alternative to state-of-the-art platinum catalysts. However, the identity of the active species in non-precious metal catalysts remains elusive, impeding the development of new catalysts. Here we demonstrate the reversible deactivation and reactivation of an iron-based non-precious metal oxygen reduction catalyst achieved using high-temperature gas-phase chlorine and hydrogen treatments. In addition, we observe a decrease in catalyst heterogeneity following treatment with chlorine and hydrogen, using Mössbauer and X-ray absorption spectroscopy. Our study reveals that protected sites adjacent to iron nanoparticles are responsible for the observed activity and stability of the catalyst. These findings may allow for the design and synthesis of enhanced non-precious metal oxygen reduction catalysts with a higher density of active sites.
Nucleation and growth are two important and entwined processes in materials synthesis and engineering. While understanding of the fundamental mechanisms of the processes remain challenging, there is ...a growing demand for much improved control over and modification of nanostructures with precise geometrical and chemical features, well-tailored surface properties and functional attributes. To this end, we first examine the key concepts of the classical and non-classical theories and then emphasise mechanistic studies of nucleation and growth. Particularly, the state-of-the-art imaging, signal and/or data acquisition techniques are discussed, including in-situ liquid phase transmission electron microscopy, in-situ synchrotron X-ray diffraction, microfluidic platforms and machine learning. Both quantitative and qualitative experimental results with high temporal and spatial resolutions provide further insights into these nanofabrication processes for representative systems, such as Au nanoparticles and CaCO3, and subsequently guide the rational design and production of materials with desirable properties. Based on current knowledge, strategies of leveraging external fields to manipulate the nucleation and growth processes are presented. Several case studies in important technological scenarios are discussed to inspire further attempts for precisely engineered solutions. Finally, further understanding of the processes are highlighted along with potential applications and future perspectives of controlling solution-synthesized nanostructures.
Nitrate electroreduction (NO3RR) holds promise as an energy-efficient strategy for the removal of toxic nitrate to restore the natural nitrogen cycle and mitigate the adverse impacts caused by ...overfertilization from suboptimal agricultural practices. However, existing catalysts suffer from limited electrocatalytic activity, poor selectivity, inadequate durability, and low scalability. To address this quadrilemma, in this study, we developed a cost-effective layered double hydroxide (LDH) electrocatalyst with a lamellar structure that presents trimetallic CuCoAl active sites on the nanomaterial surface. This codoping design enabled electrochemical upcycling of nitrate into ammonia exclusively and efficiently with an onset potential at 0 V vs RHE, where the electrocatalytic process is less energy intensive and has a lower carbon footprint than conventional practices. The synergistic interaction among Cu, Co, and Al further afforded a 99.5% Faradic efficiency (FE) and a yield rate of 0.22 mol h–1 g–1 for nitrate-to-ammonia electroreduction, surpassing the performance of state-of-the-art nonprecious metal NO3RR electrocatalysts over an extended operation period. To gain insights into the origin of the catalytic performance observed on LDH, control materials were employed to elucidate the roles of Cu and Co. Cu was found to improve the NO3RR onset potential despite displaying limited FE for ammonia synthesis, while Co was discovered to suppress the formation of nitrite byproduct though requiring large overpotential. Simulated wastewater containing phosphate and sulfate, which are typically present in industrial effluents, was used to further investigate the effect of electrolytes on NO3RR. Intriguingly, the use of phosphate buffer resulted in a superior yield rate and FE for ammonia production while simultaneously inhibiting nitrite byproduct formation compared with the sulfate case. These experimental findings were supported by density functional theory (DFT) calculations, which explored the adsorption strength of nitrate adducts adjacent to coadsorbed electrolytes on the LDH surface. Additionally, the relative free energies of NO3RR species were also computed to examine the proton-coupled electron transfer (PCET) mechanism on CuCoAl LDH, shedding light on the potential-dependent step (PDS) and the exclusive selectivity for nitrate-to-ammonia conversion. The CuCoAl LDH developed here offers scalability by eliminating the need for precious metals, rendering this earth-abundant catalyst particularly appealing for sustainable nitrate electrovalorization technology.
The development of renewable energy schemes requires the scalable production of highly robust electrocatalysts using a sustainable synthesis process that does not generate toxic liquid wastes. Here, ...an industrial laser system is utilized to prepare electrocatalysts in a continuous fashion using a laser-induced-forward-transfer-assisted nanomaterial preparation (LANP) method without generating liquid wastes. This dry processing method at room temperature and under ambient pressure enables the production of well-dispersed Pt, Ru, and Ni nanoparticles (NPs) supported on a few-layer graphene carbon framework. This versatile LANP procedure allows for the efficient deposition of binder-free Pt, Ru, and Ni NPs onto flexible polyimide films and glass surfaces at a rate of 400 mm/s. The size and quantity of the spherical NPs present on the conductive carbon surface can be tuned by adjusting the LANP parameters such as the laser power, the scribing speed, and the source thickness. Upon increasing the laser power, the size of Pt NPs decreases and the amount of Pt in the laser-derived materials increases. A second laser treatment can further modulate the hydrophilicity and solvent accessibility of graphene-supported Pt NPs. Our results demonstrate that the binder-free Pt, Ru, and Ni NPs supported on a few-layer graphene generated using the LANP strategy can serve as practical, active, and robust electrocatalysts for water-splitting reactions in advanced electrolyzer technology.
Adipic acid (AA) is a crucial feedstock for nylon polymers, and is industrially produced by thermal oxidation of cyclohexanone/cyclohexanol mixture (KA oil). However, this process consumes large ...quantities of corrosive nitric acid as oxidants, while emits ozone‐depleting greenhouse gas N2O. Here, an electrocatalytic strategy for selective oxidation of KA oil to AA coupled with H2 evolution over a Co3O4/graphdiyne cooperative catalyst (Co3O4/GDY) is reported. The Co3O4/GDY displays high electrooxidation activity of KA oil to AA (100 mA cm−2 at ≈1.5 V vs RHE), outperforming all the reported findings. Detailed ex situ and in situ experimental studies, theoretical calculations, and molecular dynamic simulations reveal that GDY not only facilitates the enrichment of cyclohexanone on the catalyst surface in aqueous medium, but also upshifts the d‐band center of Co sites, strengthening the adsorption/activation of cyclohexanone. This study offers a green route for AA synthesis and proposes a GDY interface engineering strategy for efficient electrooxidation.
Highly efficient electrooxidation of cyclohexanone/cyclohexanol mixture (KA oil) into adipic acid coupled with H2 evolution is achieved over a Co3O4/graphdiyne cooperative catalyst (Co3O4/GDY). GDY, as an electron modifier, can upshift the d‐band center of Co3O4, which facilitates the enrichment, adsorption, and activation of cyclohexanone on the catalyst surface in aqueous solutions, resulting in top‐level activity (100 mA cm−2 at ≈1.5 V vs RHE) and high yield of AA (>82%).
Abstract
Electronic gaps play an important role in the electric and optical properties of materials. Although various experimental techniques, such as scanning tunnelling spectroscopy and optical or ...photoemission spectroscopy, are normally used to perform electronic band structure characterizations, it is still challenging to measure the electronic gap at the nanoscale under ambient conditions. Here we report a scanning probe microscopic technique to characterize the electronic gap with nanometre resolution at room temperature and ambient pressure. The technique probes the electronic gap by monitoring the changes of the local quantum capacitance via the Coulomb force at a mesoscopic scale. We showcase this technique by characterizing several 2D semiconductors and van der Waals heterostructures under ambient conditions.
Precise regulation of proton-coupled electron-transfer (PCET) rates holds the key to simultaneously optimizing the turnover frequency and product selectivity of redox reactions that are central to ...the realization of renewable energy schemes in a sustainable future. In this work, a self-assembled monolayer (SAM) of a Ru complex electrografted onto a glassy carbon (GC) electrode was prepared as a heterogeneous electrocatalytic interface to facilitate the hydrogen peroxide (H2O2) oxidation half-cell reaction of a direct hydrogen peroxide/hydrogen peroxide fuel cell. A functional lipid membrane embedded with catalytic amounts of proton carriers was appended on top of the Ru SAM to construct a hybrid bilayer membrane (HBM) platform that can modulate the thermodynamics and kinetics of proton- and electron-transfer steps independently. The performances of the as-prepared Ru SAMs and HBMs toward H2O2 oxidation were investigated using electrochemical means, kinetic isotope effect (KIE) studies, and Tafel analyses. Proton carriers featuring borate, phosphate, and nitrile headgroups were found to dictate the transmembrane proton removal rate, thereby controlling the H2O2 oxidation activity. The first significance of this work was the expansion of HBM platforms to GC substrates to overcome the limited redox potential window on gold thiol systems, thereby enabling electrochemical investigations of anodic reactions at the SAM–lipid interface. The second highlight of this work was demonstrating for the first time that deprotonation kinetics can be taken advantage of to enhance the electrocatalytic oxidation performance of a metal complex anchored at the SAM–lipid interface of a HBM platform. When the knowledge gaps regarding how PCET steps govern redox pathways are closed, the advances achieved using our unique bioinorganic platform are envisioned to accelerate the understanding and optimization of electrocatalytic processes involving proton- and electron- transfer steps that are fundamental to the development of high-performance energy devices.
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