Nanostructured Catalysts Research Articles

Alloy Nanostructured Catalysts for Cathodic Reactions in Energy Conversion and Fuel Generation

The increasing energy demand, especially from fossil fuels, leads to pollution and consequent extreme climate changes, which drives us to face the challenges of exploring sustainable energy for the...

γ-NiOOH electrocatalyst derived from a nickel dithiooxamide chelate polymer for oxygen evolution reaction in alkaline solutions

The oxygen evolution reaction (OER) is a key process in number of electrochemical energy conversion technologies that demands the design of efficient electrocatalysts. In this work, catalytically active gamma-nickel oxyhydroxide (γ-NiOOH) was obtained from a two-dimensional (2D) nickel(II) dithiooxamide Ni(dto) chelate polymer via in situ electrochemical transformation in an acetylene black matrix. The transformation was carried out on the surface of a glassy carbon electrode in 1 M KOH solution, in which the nickel(II) centers of the chelate polymer were transformed into nano-sized γ-NiOOH crystallites dispersed in the carbon matrix. The resultant nanostructured catalyst exhibits OER overpotential of 390 mV (at 12 mA/cm2) and a Tafel slope of 328 mV/dec in 1 M KOH solution. The OER overpotential of the catalyst is lower than that of IrO2/C electrode, with the same material loading. The oxygen evolution is initiated by adsorption of hydroxide ions at the Ni metal sites of the layered γ-NiOOH, with a subsequent release of oxygen molecules. This study unfolds the potential of in situ electrochemical transformation of 3d transition metal 2D chelate polymers to fabricate active electrocatalysts.

Synthesis of Cu2O Nanostructures with Tunable Crystal Facets for Electrochemical CO2 Reduction to Alcohols.

Electrochemical CO2 reduction enables the conversion of intermittent renewable energy to value-added chemicals and fuel, presenting a promising strategy to relieve CO2 emission and achieve clean energy storage. In this work, we developed nanosized Cu2O catalysts using the hydrothermal method for electrochemical CO2 reduction to alcohols. Cu2O nanoparticles (NPs) of various morphologies that were enclosed with different crystal facets, named as Cu2O-c (cubic structure with (100) facets), Cu2O-o (octahedron structure with (111) facets), Cu2O-t (truncated octahedron structure with both (100) and (111) facets), and Cu2O-u (urchin-like structure with (100), (220), and (222) facets), were prepared by regulating the content of a polyvinyl pyrrolidone (PVP) template. The electrochemical CO2 reduction performance of the different Cu2O NPs was evaluated in the CO2-saturated 0.5 M KHCO3 electrolyte. The as-synthesized Cu2O nanostructures were capable of reducing CO2 to produce alcohols including methanol, ethanol, and isopropanol. The alcohol selectivity of the different Cu2O NPs followed the order of Cu2O-t < Cu2O-u < Cu2O-c < Cu2O-o (with the total Faradaic efficiencies of alcohol products of 10.7, 25.0, 26.2, and 35.4%). The facet-dependent effects were associated with the varied concentrations of oxygen-vacancy defects, different energy barriers of CO2 reduction, and distinct Cu-O bond lengths over the different crystal facets. The desired Cu2O-o catalyst exhibited good reduction activity with the highest partial current density of 0.51 mA/cm2 for alcohols. The Faradaic efficiencies of alcohol products were 4.9% for methanol, 17.9% for ethanol, and 12.6% for isopropanol. The good electrochemical CO2 reduction performance was also associated with the surface reconstruction of Cu2O, which endowed the catalyst with abundant Cu0 and Cu+ sites for promoted CO2 activation and stabilized CO* adsorption for enhanced C-C coupling. This work will provide a new route for enhancing the alcohol selectivity of nanostructured Cu2O catalysts by crystal facet engineering.

Magnetocatalysis: The Interplay between the Magnetic Field and Electrocatalysis

Magnetocatalysis: The Interplay between the Magnetic Field and Electrocatalysis

Unveiling microbiologically influenced corrosion engineering to transfigure damages into benefits: A textile sensor for H2O2 detection in clinical cancer tissues

With the ongoing increasing research interests in economical electrocatalysts, transforming damages into benefits to prepare useful electrode materials is an ideal strategy to achieve the goals. Corrosion engineering converts harmful corrosion processes into high performance catalyst nanostructures. In this work, we develop an inexpensive, scaled-up corrosion engineering strategy for value-added transformation of low-cost iron substrates into highly efficient Cu-Fe(OH)2-FeS deposited on polyester cloth fabric (PCF) flexible electrode by a process of electroless plating combined with microbes assisted corrosion product. The anaerobic sulfate reducing bacteria (SRB) converting sulfate to sulfide play vital role to carry out the construction of Cu-Fe(OH)2-FeS/PCF electrode which reveals high electrochemical sensing performance for H2O2 with broad linear range and low detection limit of 0.2 nM (S/N = 3). The enhanced activity arises from densely deposited nanosheets of transition metals oxides/hydroxides, plethora of surface active sites and synergistic effect between Cu-Fe(OH)2 and FeS species. More importantly, the S2− ions serving as co-catalyst have been found to continuously fuel electrons during the reduction of Fe(III) and Cu(II) which accelerate the redox cycles of Fe(III)/Fe(II) and Cu(II)/Cu(I) further enhancing electrocatalytic H2O2 reduction. With high sensitivity achieved, the Cu-Fe(OH)2-FeS/PCF electrode has also been practically applied in real-time in vitro tracking of H2O2 excreted from different normal and human brain cancer cell lines as well as in situ sensitive detection of H2O2 released from human brain tumor tissues. This work presents a good way to bridge up the gap between annoying traditional corrosion engineering and emerging electrochemical technologies.

Solar-driven conversion of carbon dioxide over nanostructured metal-based catalysts in alternative approaches: Fundamental mechanisms and recent progress

Solar-driven carbon dioxide (CO2) conversion has gained tremendous attention as a prominent strategy to simultaneously reduce the atmospheric CO2 concentration and convert solar energy into solar fuels in the form of chemical bonds. Numerous efforts have been devoted to diverse photo-driven processes for CO2 conversion, which utilized a multidisciplinary strategy. Among them, the architecture of nanostructured metal-based catalysts is emerging as an eminent solution for the design of catalysts of this field. In this work, we first provide fundamental mechanisms of photochemical, photoelectrochemical, photothermal, and photobio(electro)chemical CO2 reduction processes to achieve an in-deep understanding of vital aspects. Importantly, the recent progress in the catalyst design for each reaction system is discussed and highlighted. Based on these analyses, an overview of photo-driven CO2 reduction on metal-based catalysts for solar fuel production is also spotlighted. Finally, we analyze challenges and prospects for the strategic direction of developments in the field.

Multiple ADF-STEM Towards the Optimization of Electron Tomography Reconstructions of Pt/C fuel cell catalyst nanostructures

Multiple ADF-STEM Towards the Optimization of Electron Tomography Reconstructions of Pt/C fuel cell catalyst nanostructures

Development of Fast Infiltration Technique for Metal Supported Solid Oxide Fuel Cells and Electrolyzers

Our recently developed fast infiltration technique enables loading of nanostructured catalyst into porous metal-supported solid oxide fuel cells in 30 minutes per cycle compared to a few hours in the standard slow infiltration process. This technique maintains the advantages of metal supported solid oxide fuel cells (MS-SOFC) such as rapid thermal cycling, mechanical ruggedness, and redox tolerance while developing more efficient and stable fuel cells and electrolyzers. The impact of process parameters such as heating rate, number of infiltration cycle, and firing temperature on the cell performance and stability will be discussed. The crystallite sizes of the catalysts fired at a temperature range of 400 to 900°C were calculated from X-ray diffraction patterns using the Scherrer equation, and compared to the particle size of the catalysts obtained from scanning electron microscopy images. The electrochemical performance of as-fabricated cells tested in hydrogen, reformate, and ethanol fuels under identical test conditions will be presented and related to the infiltration process conditions and resulting catalyst structure. For the Pr-oxide cathode and Ni (40)-SDC (60) anode catalysts, firing at low temperature (400 to 600°C) yields high initial performance but degrades quickly due to coarsening of the small nanoparticle catalysts. Optimal firing temperature and infiltration numbers, and pretest and posttest characterization of the MS-SOFC architecture and interfaces will be discussed. Phenomena of mass transportation, phase change, catalyst coarsening, and Cr poisoning on the catalysts will be diagnosed by real-time electrochemical impedance spectra, thermal gravimetric analysis, and scanning electron microscopy.

Multicomponent Pt-based catalyst for highly efficient chemoselective hydrogenation of 4-carboxybenzaldehyde

The design of efficient nanostructured catalysts is highly desirable for promoting the hydrogenation of 4-carboxybenzaldehyde (4-CBA), which are the key process of hydrorefining of crude terephthalic acid (CTA) to pure terephthalic acid (PTA). Herein, the Pt-FeNi@C, Pt-Fe@C and Pt-Ni@C catalysts were developed and proved to be active for the selective hydrogenation of 4-CBA. As a result, the excellent 4-hydroxymethylbenzoic acid (4-HMBA) selectivity (85%) and benzoic acid (BA) selectivity (88%) were achieved on Pt-FeNi@C and Pt/C, respectively. In comparison with the commercial Pd/C catalyst, the Pt-FeNi@C catalyst exhibits excellent activity (97%) and reduces the occurrence of decarbonylation. Moreover, the Pt-FeNi@C catalyst exhibits excellent recyclability: the catalytic activity did not decrease significantly after four reaction cycles. In combination with detailed characterization, the Pt-FeNi@C catalyst has porous graphene core-shell architecture and remarkable electron transfer capacity. This work may provide some inspirations for the exploration of new PTA hydrofining catalysts.

Imaging Heterogeneous Electrocatalyst Stability and Decoupling Degradation Mechanisms in Operating Hydrogen Fuel Cells

The proliferation of hydrogen fuel cell systems is hindered by a degradation of the platinum catalyst. Here, we provide a device-level assessment of the catalyst degradation phenomena and its coupling to nanoscale hydration gradients, using advanced operando X-ray scattering tomography tailored for device-scale imaging. Gradients formed inside the fuel cell produce a heterogeneous degradation of the catalyst nanostructure, which can be linked to the flow field design and water distribution in the cell. Striking differences in catalyst degradation are observed between operating fuel cell devices and the liquid cell routinely used for catalyst stability studies, highlighting the crucial impact of the complex operating environment on the catalyst degradation phenomena. This degradation knowledge gap accentuates the necessity of multimodal, in situ characterization of real devices when assessing the performance and durability of electrocatalysts and, more generally, electrochemically active phases used in energy conversion and storage technologies.

Interfacial engineering of 2D/2D MXene heterostructures: face-to-face contact for augmented photodegradation of amoxicillin

Antimicrobial resistance caused by the abuse of antibiotics constitutes a global burden that will jeopardize the ecosystem and public health. Herein, we reported an efficient and eco-friendly way based on photocatalysis for the degradation of amoxicillin, the most widely used antibiotic. A unique 2D/2D Bi2WO6/Ti3C2 MXene heterostructure with facet-to-face contact was elaborately constructed that allowed complete removal of amoxicillin in less than 40 min, superior to the respective constituents. It was demonstrated that the photocatalytic mechanism of the composite photocatalyst lied in the enhanced light adsorption capability, rapid charge carrier transfer and photothermal conversion property, which, in essence, fostered the generation of reactive oxygen species, mainly holes (h+) and superoxide anion radicals (O2−). This work involving the design of nanostructured catalysts and the advances of photocatalysis technology may provide fresh ideas for the wastewater treatment, degradation of organic pollutants, etc, for the environmental remediation.

Electronic coupling regulation in yolk-shell nanostructured nickel-cobalt diselenides with octahedral coordination for boosted oxygen evolution reaction

It is fairly desired but remains challenging to synthesize metal selenides with nanosized building blocks via simplified approaches which make more active sites exposed to electrolytes for achieving high-efficient electrocatalysts for oxygen evolution reaction (OER). Herein, on the basis of the Kirkendall effect, we developed a simple synthesis of yolk-shell nanostructured nickel-cobalt diselenides (NiCoSe2) with nanosized wide annular aisles via one-step electrodeposition. Expressly, the electronic coupling between Ni and Co cations was well regulated via the optimization of Ni/Co atomic ratios to regulate eg filling of Ni for optimized OER. The elaborate yolk-shell nanostructured NiCoSe2 catalyst exhibits remarkable OER performance, delivering a low overpotential of 249 mV at a geometric current density of 10 mA cm−2 in alkaline media, a small Tafel slope of 43 mV dec−1 and a decent durability with a tiny decay of 23 mV over 20 h electrolysis. The Kirkendall effect-induced formation route of the yolk-shell nanostructure will provide helpful guidance for the rational design of hollow structured catalyst in the field of energy catalysis and other extended applications.

MOF-derived CoP-nitrogen-doped carbon@NiFeP nanoflakes as an efficient and durable electrocatalyst with multiple catalytically active sites for OER, HER, ORR and rechargeable zinc-air batteries

Highly active, long-lasting, and low-cost nanostructured catalysts with efficient oxygen evolution and oxygen reduction reactions (OER and ORR) are critical for achieving high-performance zinc-air batteries. Herein, we developed CoP-nitrogen-doped carbon@NiFeP nanoflakes (CoP-NC@NFP), derived from MOF enriched with multiple active sites, for multifunctional water splitting and zinc-air battery applications. The experimental results revealed that the multiple active catalytic sites of CoP-NC@NFP were responsible for the excellent charge-transfer kinetics and electrocatalytic performance with respect to water splitting. This performance is comparable to that of precious metal catalysts in alkaline electrolytes (OER: overpotential of 270 mV; HER: overpotential of 162 mV; ORR: Tafel slope of 46 mV dec−1; overall water splitting device: cell voltage of 1.57 V at 10 mA cm−2) with excellent electrochemical durability. Additionally, the structural stability of the OER and the HER durability of the CoP-NC@NFP electrocatalyst were confirmed by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) studies. Most impressively, zinc-air batteries (ZABs) assembled with CoP-NC@NFP as the air–cathode exhibit exceptionally high power density of 93 mW cm−2 and prolonged operational stability over 200 h compared with a ZAB equipped with a benchmark air–cathode. The outcome of this study opens a practical possibility for the preparation of efficient multifunctional catalysts free of noble metals for clean energy production and storage.

Synthetic multiscale design of nanostructured Ni single atom catalyst for superior CO2 electroreduction

Rational design of nanoscale structures can greatly strengthen heterogeneous catalysis with the maximal utilization of active sites. Single atom catalysts (SACs) are recently emerging but a systematic design of nanostructured SAC has rarely been demonstrated yet. Here, distinct architectural structure-dependence of electrochemical CO2 reduction (CO2RR) on Ni-based SACs is presented. Starting from Ni-imidazolate coordination polymers (Ni-Im) and their supported counterparts with a carbon nanotube (CNT) and a zeolite imidazolate framework (ZIF-8), the respective derivatives, i.e. Ni-SAC, Ni-SAC-CNT, and Ni-SAC-ZIF8, are obtained after pyrolysis. The presence of substrates ultimately results in large surface porous N-doped carbon nanostructures, which facilitate the diffusion of etchants to remove undesired Ni nanoparticles effectively. The dense Ni single atomic sites contained within the nanostructure are easily accessible to CO2 reactants during CO2RR, thus promoting high utilization of active sites even at large current densities. Electro-conductive CNT substrates mediate fluent charge transfer and stimulates the intrinsic activity of catalytic sites. Consequently, operating at 400 mA cm−2, Ni-SAC-CNT attains a high faradaic efficiency of 99% toward CO at a low overpotential of 0.24 V, equivalent to a record cathodic energetic efficiency and turnover frequency of 83.4% and 439,000 h−1, respectively.

Design of Plasmonic Catalysts Utilizing Nanostructures

This review describes the design of nanostructured plasmonic catalysts, such as nanoparticles and nanosheet morphologies, that strongly absorb visible light over a wide range of the solar spectrum due to localized surface plasmon resonance (LSPR) and application to enhanced hydrogen evolution. A new method for the synthesis of Ag nanoparticles, with color dependent on the particle size and morphology, combined microwave heating and the use of mesoporous silica materials. Further combination with Pd nanoparticles significantly enhanced the catalytic activities for hydrogen production from ammonia borane (NH3BH3) compared with the inherent Ag catalysts under both dark and visible-light irradiation conditions. We also describe the synergistic catalysis activities of plasmonic Au(core)–Pd(shell) nanoparticles supported on amine-functionalized metal-organic frameworks (MOFs) for boosting room-temperature hydrogen production from formic acid (HCOOH) under visible light irradiation. Our search for plasmonic materials based on earth abundant elements found that reduced molybdenum oxide (HxMoO3−y) nanosheet with oxygen defects and doped hydrogen displayed intense absorption in a wide range from the visible to the near-infrared region. This unique plasmonic HxMoO3−y nanosheet can enhance dehydrogenation from ammonia borane under visible light irradiation.

Hydrogen oxidation and oxygen reduction reactions on palladium nano-electrocatalyst supported on nickel-deficient MOF-derived carbons

Pd/Ni-based catalysts consisting of Ni-rich MOF-derived carbon (Pd/Ni-r/MOFDC) and Ni-deficient counterpart (Pd/Ni-d/MOFDC) have been demonstrated as efficient nanostructured catalysts for alkaline hydrogen oxidation (HOR) and oxygen reduction reactions (ORR). Physico-chemical analysis of the catalysts unravels the significance of controlled chemical etching of the Ni-based MOFDC prior to deposition of Pd catalyst, thereby controlling the level of Ni(OH)2 interface and defects or oxygen vacancies. The Pd/Ni-d/MOFDC exhibits excellent performance towards HOR compared to the Pd/Ni-r/MOFDC in respects of decreased onset potential (Eonset), but increased exchange current density (jo.s), heterogeneous rate constant (k0), kinetic current (jK), diffusion coefficient (D) and mass activity (jo.m). The more facile HOR performance on Pd/Ni-d/MOFDC corroborates its reduced activation energy (EA) by a factor of 1/3. The alkaline HOR follows the Heyrovsky-Volmer and Tafel-Volmer processes on Pd/Ni-r/MOFDC and Pd/Ni-d/MOFDC, accordingly, evident by their Tafel slope (ba) values. The Pd/Ni-d/MOFDC equally shows improved ORR activity compared to the Pd/Ni-r/MOFDC. Density functional theory (DFT) calculations agree with the experimental data, especially the contributory effects of the chemically etched composite support. Pd/Ni-d/MOFDC promises to be a viable electrocatalyst for the development of alkaline membrane fuel cells (AMFCs).

Phase transformation and structural evolution in iron oxide nanostructures

Nanostructured iron oxide (Fe2O3) have attracted considerable attention due to their unique physical properties, which are size and shape-dependent. In this article, hydrothermal & sol-gel methods have been opted for the growth of different nanostructures. Based on the choice of synthesis route, rhombohedral (α-phase) and cubic (γ-phase) shape of Fe2O3 are originated as confirmed from XRD and Raman measurements. HRTEM revealed the formation of different nanostructure of Fe2O3. Due to structural similarities with Fe3O4, cubic phase and smallest size (~ 12.3 nm) among all the samples, sol–gel derived γ-Fe2O3 nanocubes display maximum magnetization along with superparamagnetic behavior. Further, photocatalytic activity of prepared samples was screened for degradation of RB dye under UV light. The higher efficiency of nanoflowers compared to other structures may be ascribed to defects present in the nanostructure of catalyst. The present research indicates that nanostructures of Fe2O3 are highly efficient catalysts for the cleanup of environmental pollution.

In situ atomic-scale studies of thermal stability and surface reconstruction of ZnO nanowires based Pd nanocatalysts

As innovative nanostructured catalysts, palladium nanoparticles supported on carbon-coated zinc oxide nanowires (PdNPs/C&ZnO-NWs) are widely applied in industrial thermal catalysis, and therefore the real-time insights into their thermal stability and microstructural reconstruction at thermal reaction conditions will greatly extend our knowledge of their physicochemical properties and provide valuable guidance for the applications and designs of future nanocatalysts. The in-situ transmission electron microscopy (TEM) studies revealed the high-temperature resistance to PdNPs aggregations with aids of carbon-coated low-dimensional nanostructures C&ZnO-NWs and elucidated ripening dynamics of PdNPs and the surface reconstruction of C&ZnO-NWs. The operando analysis of PdNPs/C&ZnO-NWs was executed in real-time under working-temperature situations. The aggregations of PdNPs were not observed until reaching a high working temperature of 300 °C and carbon-coated layers could functionally prevent PdNPs from sintering even when ZnO-NWs experienced melting at 500 °C. The time-lapsed TEM investigation proved that the ripening dynamics and time-dependent revolution of PdNPs size are in accordance with the Ostwald ripening process. The subsequent atomic-scale observation revealed the surface reconstruction of ZnO-NWs in the form of ZnO encapsulation over PdNPs and carbon-coated layers during the thermal process, which showed the microscopic evidence of potential deactivation of ZnO-NW-based nanocatalysts in thermal reactions.

Effect of the Nanostructured Zn/Cu Electrocatalyst Morphology on the Electrochemical Reduction of CO2 to Value-Added Chemicals.

Zn/Cu electrocatalysts were synthesized by the electrodeposition method with various bath compositions and deposition times. X-ray diffraction results confirmed the presence of (101) and (002) lattice structures for all the deposited Zn nanoparticles. However, a bulky (hexagonal) structure with particle size in the range of 1–10 μm was obtained from a high-Zn-concentration bath, whereas a fern-like dendritic structure was produced using a low Zn concentration. A larger particle size of Zn dendrites could also be obtained when Cu2+ ions were added to the high-Zn-concentration bath. The catalysts were tested in the electrochemical reduction of CO2 (CO2RR) using an H-cell type reactor under ambient conditions. Despite the different sizes/shapes, the CO2RR products obtained on the nanostructured Zn catalysts depended largely on their morphologies. All the dendritic structures led to high CO production rates, while the bulky Zn structure produced formate as the major product, with limited amounts of gaseous CO and H2. The highest CO/H2 production rate ratio of 4.7 and a stable CO production rate of 3.55 μmol/min were obtained over the dendritic structure of the Zn/Cu–Na200 catalyst at −1.6 V vs. Ag/AgCl during 4 h CO2RR. The dissolution and re-deposition of Zn nanoparticles occurred but did not affect the activity and selectivity in the CO2RR of the electrodeposited Zn catalysts. The present results show the possibilities to enhance the activity and to control the selectivity of CO2RR products on nanostructured Zn catalysts.

Ambient Hydrogenation and Deuteration of Alkenes Using a Nanostructured Ni‐Core–Shell Catalyst

AbstractA general protocol for the selective hydrogenation and deuteration of a variety of alkenes is presented. Key to success for these reactions is the use of a specific nickel‐graphitic shell‐based core–shell‐structured catalyst, which is conveniently prepared by impregnation and subsequent calcination of nickel nitrate on carbon at 450 °C under argon. Applying this nanostructured catalyst, both terminal and internal alkenes, which are of industrial and commercial importance, were selectively hydrogenated and deuterated at ambient conditions (room temperature, using 1 bar hydrogen or 1 bar deuterium), giving access to the corresponding alkanes and deuterium‐labeled alkanes in good to excellent yields. The synthetic utility and practicability of this Ni‐based hydrogenation protocol is demonstrated by gram‐scale reactions as well as efficient catalyst recycling experiments.