Project description:Three dimensional (3D) porous carbon materials are highly desirable for electrochemical applications owing to their high surface area and porosity. Uniformly distributed porosity in the 3D architecture of carbon support materials allows reactant molecules to access more electrochemically active centres and simultaneously facilitate removal of the product formed during electrochemical reactions. Herein, we have prepared a nitrogen-doped entangled graphene framework (NEGF), decorated with NiFe-LDH nanostructures by an in situ solvothermal method followed by freeze-drying at high vacuum pressure and low temperature. The freeze-drying method helped to prevent the restacking of the graphene sheets and the formation of a high surface area nitrogen-doped entangled graphene framework (NEGF) supported NiFe-LDHs. The incorporation of the NEGF has significantly reduced the overpotential for the electrochemical oxygen evolution reaction (OER) in 1 M KOH solution. This corresponds to an overpotential reduction from 340 mV for NiFe-LDHs to 290 mV for NiFe-LDH/NEGF to reach the benchmark current density of 10 mA cm-2. The preparation of the catalyst is conceived through a low-temperature scalable process.
Project description:Layered double hydroxides (LDHs) are bimetallic hydroxides that currently attract considerable attention as co-catalysts in photoelectrochemical (PEC) systems in view of water splitting under solar light. A wide spectrum of LDHs can be easily prepared on demand by tuning their chemical composition and structural morphology. We describe here the electrochemical growth of NiFe-LDH overlayers on Cu2O electrodes and study their PEC behavior. By using the modified Cu2O/NiFe-LDH electrodes we observe a remarkable seven-fold increase of the photocurrent intensity under an applied voltage as low as -0.2 V vs Ag/AgCl. The origin of such a pronounced effect is the improved electron transfer towards the electrolyte brought by the NiFe-LDH overlayer due to an appropriate energy level alignment. Long-term photostability tests reveal that Cu2O/NiFe-LDH photocathodes show no photocurrent loss after 40 hours of operation under light at -0.2 V vs Ag/AgCl low bias condition. These improved performances make Cu2O/NiFe-LDH a suitable photocathode material for low voltage H2 production. Indeed, after 8 hours of H2 production under -0.2 V vs Ag/AgCl the PEC cell delivers a 78% faradaic efficiency. This unprecedented use of Cu2O/NiFe-LDH as an efficient photocathode opens new perspectives in view of low biasd or self-biased PEC water splitting under sunlight illumination.
Project description:Defect engineering has proven to be one of the most effective approaches for the design of high-performance electrocatalysts. Current methods to create defects typically follow a top-down strategy, cutting down the pristine materials into fragmented pieces with surface defects yet also heavily destroying the framework of materials that imposes restrictions on the further improvements in catalytic activity. Herein, we describe a bottom-up strategy to prepare free-standing NiFe layered double hydroxide (LDH) nanoplatelets with abundant internal defects by controlling their growth behavior in acidic conditions. Our best-performing nanoplatelets exhibited the lowest overpotential of 241 mV and the lowest Tafel slope of 43 mV/dec for the oxygen evolution reaction (OER) process, superior to the pristine LDHs and other reference cation-defective LDHs obtained by traditional etching methods. Using both material characterization and density functional theory (DFT) simulation has enabled us to develop relationships between the structure and electrochemical properties of these catalysts, suggesting that the enhanced electrocatalytic activity of nanoplatelets mainly results from their defect-abundant structure and stable layered framework with enhanced exposure of the (001) surface.
Project description:As an important two-dimensional material, layered double hydroxides (LDHs) show considerable potential in electrocatalytic reactions. However, the great thickness of the bulk LDH materials significantly limits their catalytic activity. In this work, we report ultrathin NiFe-LDH nanosheets with sulfate interlayer anions (Ni6Fe2(SO4)(OH)16·7H2O) (U-LDH(SO4 2-)), which can be synthesized in gram-scale by a simple solvothermal method. The U-LDH(SO4 2-) shows excellent stability and great electrocatalytic performance in OER with a current density of 10 mA cm-2 at a low overpotential of 212 mV and a small Tafel slope of 65.2 mV dec-1, exhibiting its great potential for a highly efficient OER electrocatalyst.
Project description:Electrochemical water splitting has been considered one of the most promising methods of hydrogen production, which does not cause environmental pollution or greenhouse gas emissions. Oxygen evolution reaction (OER) is a significant step for highly efficient water splitting because OER involves the four electron transfer, overcoming the associated energy barrier that demands a potential greater than that required by hydrogen evolution reaction. Therefore, an OER electrocatalyst with large surface area and high conductivity is needed to increase the OER activity. In this work, we demonstrated an effective strategy to produce a highly active three-dimensional (3D)-printed NiFe-layered double hydroxide (LDH) pyramid electrode for OER using a three-step method, which involves direct-ink-writing of a graphene pyramid array and electrodeposition of a copper conducive layer and NiFe-LDH electrocatalyst layer on printed pyramids. The 3D pyramid structures with NiFe-LDH electrocatalyst layers increased the surface area and the active sites of the electrode and improved the OER activity. The overpotential (η) and exchange current density (i0) of the NiFe-LDH pyramid electrode were further improved compared to that of the NiFe-LDH deposited Cu (NiFe-LDH/Cu) foil electrode with the same base area. The 3D-printed NiFe-LDH electrode also exhibited excellent durability without potential decay for 60 h. Our 3D printing strategy provides an effective approach for the fabrication of highly active, stable, and low-cost OER electrocatalyst electrodes.
Project description:To overcome the poor stability of natural lutein to environmental factors, layered double hydroxide was incorporated by a green mechanical grinding process. The influences of external factors (chemical reagents, heating and light) on the stability of lutein before and after being loaded were evaluated. The results confirmed that lutein was mainly adsorbed on the surface of layered double hydroxide (LDH) via the chemical interaction. Compared with pure lutein, the thermal decomposition of lutein/LDH was improved from 100 °C to 300 °C, and the retention ratio of lutein was increased by about 8.64% and 21.47% after 96 h of light exposure and accelerated degradation, respectively. It is expected that the stable lutein/LDH composites may constitutean additive in animal feed.
Project description:Layered double hydroxides (LDHs) have potential applications for pollutant removal. Enhancing their pollutant removal ability by fully utilizing the synergistic effects of physical adsorption and chemical catalysis has received widespread attention. In this study, a high methyl orange (MO) removal capacity was achieved by utilizing the synergistic effects of physical adsorption and chemical catalysis of NiFe-LDH. wNiFe-LDH showed a significant removal amount of MO, up to 506.30 mg/g due to its reserving of the active surface to the largest extent. Experiment and molecular simulation clarified the high removal capacity derived from surface adsorption and the degradation ability of the active surface. The presence of more -OH groups on the surface enhanced the removal of MO, and the vacancies in the surface were beneficial for the formation of •O2- and contributed to the degradation of MO. As K2S2O8 was introduced, the removal rate of MO improved to 100% from 60.67%. However, a deeper study showed that the degradation was incomplete, as K2S2O8 inhibited the formation of •O2-, and the active species in the system changed to holes. The degradation path of MO was also altered. Thus, this study gives new insight into the reactivity of the active surface of NiFe-LDH and affords a new path to preserve the active surface.
Project description:SignificanceSeawater is one of the most abundant resources on Earth. Direct electrolysis of seawater is a transformative technology for sustainable hydrogen production without causing freshwater scarcity. However, this technology is severely impeded by a lack of robust and active oxygen evolution reaction (OER) electrocatalysts. Here, we report a highly efficient OER electrocatalyst composed of multimetallic layered double hydroxides, which affords superior catalytic performance and long-term durability for high-performance seawater electrolysis. To the best of our knowledge, this catalyst is among the most active for OER and it advances the development of seawater electrolysis technology.
Project description:The inclusion of water oxidation active polyoxometalates (POMs) inside layered materials is a promising strategy to increase their catalytic efficiency while overcoming their fragility under homogeneous conditions. In this sense, intercalation of POMs in the interlaminar space of layered double hydroxides (LDHs), formed by positively charged brucite-type inorganic layers, is a very interesting strategy that is gaining attention in the field. Despite their huge potential, there is a lack of accurate characterization of the materials, especially after their use as water oxidation catalysts under pH conditions in which the POM counterpart has been demonstrated to be unstable (strong alkali media). For this reason and as a proof of concept, we have intercalated the well-known [Co4(H2O)2(PW9O34)2]10- POM (Co4-POM) in the lamellar space of the Mg2Al-LDH, to study its catalytic capabilities and stability. Remarkably, the nanocomposites show improved water oxidation efficiencies with excellent stability in close-to-neutral media compared with the water-insoluble cesium salt of Co4-POM or commercial Co3O4. However, thorough postcatalytic characterization of the nanocomposites demonstrates that the polyoxotungstate framework of the POM suffers from hydrolytic instability in strong alkali conditions, leading to the formation of a mixed-valence cobalt(II/III) oxide in the interlayer space of Mg2Al-LDH. This work highlights the importance of accurately assessing the fate of the catalytic POM after the catalytic reaction, especially when conditions are employed outside the pH stability window of the POM, which can lead to erroneous conclusions and mistaken catalytic activities.
Project description:Microwave-absorbing materials have attracted increased research interest in recent years because of their core roles in the fields of electromagnetic (EM) pollution precaution and information security. In this paper, microwave-absorbing material NiFe-layered double hydroxide (NiFe-LDH) was synthesized by a simple co-precipitation method and calcined for the fabrication of NiFe-mixed metal oxide (NiFe-MMO). The phase structure and micromorphology of the NiFe-LDH and NiFe-MMO were analyzed, and their microwave-absorbing properties were investigated with a vector network analyzer in 2-18 GHz. Both NiFe-LDH and NiFe-MMO possessed abundant interfaces and a low dielectric constant, which were beneficial to electromagnetic wave absorption, owing to the synergistic effect of multi-relaxation and impedance matching. The optimum reflection loss (RL) of NiFe-LDH and NiFe-MMO was -58.8 dB and -64.4 dB, respectively, with the thickness of 4.0 mm in the C band. This work demonstrates that LDH-based materials have a potential application in electromagnetic wave absorption.