Narrow Results

Water splitting by electrolysis is an environmentally friendly and promising method to gain hydrogen energy. Since both oxygen evolution reaction (OER) process and hydrogen evolution reaction process of electrolysis are kinetically sluggish and need to overcome a large potential barrier, it is imperative, especially for the poor kinetic OER, to explore available electrocatalytic materials. Here, this paper proposed a preparation of copper-doped nickel–iron-layered double hydroxide (NiFeCu LDH) with sheet-like nanostructure arranged perpendicularly to nickel foam matrix (NiFeCu LDH/NF) through a facile hydrothermal process. Benefitting from the combination with nickel foam and doping with copper, the poor conductivity of pure NiFe LDH is remedied and the quantity of exposed catalytic active sites on the electrocatalyst is increased. Hence, the as-prepared NiFeCu LDH/NF possesses outstanding OER catalytic capacity in 1.0M KOH, and when applying a mere overpotential of 183mV, it can convey a current density of 10mA cm${}^{-2}$. Furthermore, both at 10 and 80mA cm${}^{-2}$, this electrocatalyst could maintain long-term durability at least for 24h. In our preparation, a simple approach was applied to bolster the OER catalytic performance of electrocatalysts based on NiFe LDH.

Hydrogen is a promising alternative energy without greenhouse gas emissions. The transition metal carbides (TMCs) are considered a sustainable alternatives to noble metals in catalysis. Among the TMCs, Co${}_x$C ($x$ = 2, 3) nanoparticles (NPs) act as an excellent electrocatalyst for hydrogen evolution reaction (HER) by water splitting. In our report, Co${}_x$C nanocomposites were synthesized by wet chemistry method using cobalt (II) acetate, sodium hydroxide as precursors and triethylene glycol as solvent. In addition, Co₂C NPs were synthesized by similar wet chemistry method using cobalt (II) acetate as precursors and triethylene glycol, oleylamine as solvent. The cobalt carbide NPs exhibited high electrocatalytic activity. Co${}_x$C nanocomposites performed a −0.33 V onset potential and 91 mV/dec Tafel slope, while the Co₂C NPs exhibited a better performance of −0.27 V and 60 mV/dec, respectively.

In this work, voltammetric, spectroelectrochemical, and electrocatalytic properties of the metallophthalocyanines bearing four chloro and four biphenyl-malonic ester bulky groups were investigated. Voltammetric and spectroelectrochemical measurements of the metallophthalocyanines show that while cobalt phthalocyanine presents both metal-based and ring-based redox processes, all other complexes give only ring-based reduction and oxidation processes. The redox processes have generally diffusion-controlled, reversible and one-electron transferred mechanisms. Cobalt phthalocyanine electrocoated easily on the glassy carbon working electrode during the repeating cycles, a very useful feature for application in fabrication of thin films. Electrocatalytic activity of cobalt phthalocyanine to hydrogen evolution reaction was studied in solution titrated with perchloric acid and on glassy carbon electrode modified with cobalt phthalocyanine in aqueous solution. Electrocatalytic measurements show that cobalt phthalocyanine has significant catalytic activities towards hydrogen evolution reaction. Moreover, the catalytic activity of the complex enhanced significantly when the complex was incorporated into the cation exchange Nafion polymeric matrix.

Monte Carlo lattice gas simulations are performed to study sintering in a realistic dendritic platinum nanosheet. The morphological and topological transformations observed in the simulations are in good agreement with sintering experiments. Employing an intuitive method of quantifying surface area, the stability of the surface area of the dendritic nanosheets is analyzed. The surface area is found to have a double exponential decay, one decay corresponding to rapid coarsening of dendritic features into pores and the other decay corresponding to a slow disappearance of unstable pores. Long duration simulations indicate that the thickness of the dendritic nanosheet remains fairly stable. Stability simulations of a single model pore in a sheet establish that there exists a narrow range of sheet thickness and pore size combinations that produces stable holey sheets. Outside this parameter range pores either rapidly close or expand without bound. The thickness of the engineered dendritic platinum nanosheet and the size of the crevices between dendritic arms put the Pt sheet into this stable range, further corroborating the detailed simulations and explaining the persistence of pores observed in actual dendritic platinum nanosheets.

A clam-shaped molecule comprising a Zn(II)-porphyrin and a Zn(II)-cyclam is synthesized and characterized. Its electrochemical behavior and catalytic activity for homogeneous electrochemical reduction of carbon dioxide (CO${}_2)$ are investigated by cyclic voltammetry and compared with those of Zn(II)-meso-tetraphenylporphyrin and Zn(II)-cyclam. Under N₂-saturated conditions, cyclic voltammetry of the featured complex has characteristics of its two constituents, but under CO₂-saturated conditions, the target compound exhibits significant current enhancement. Iterative reduction under electrochemical conditions indicated the target compound has improved stability relative to Zn(II)-cyclam. Controlled potential electrolysis demonstrates that, without addition of water, methane (CH${}_4)$ is the only detectable product with 1% Faradaic efficiency (FE). The formation of CH₄ is not observed under the catalysis of the Zn(II)-porphyrin benchmark compound, indicating that the CO₂-capturing function of the Zn(II)-cyclam unit contributes to the catalysis. Upon addition of 3% v/v water, the electrochemical reduction of CO₂ in the presence of the target compound gives carbon monoxide (CO) with 28% FE. Dominance of CO formation under these conditions suggests enhancement of proton-coupled reduction. Integrated action of these Zn(II)-porphyrin and Zn(II)-cyclam units offers a notable example of a molecular catalytic system where the cyclam ring captures and brings CO₂ into the proximity of the porphyrin catalysis center.

A new meso-tetrakis(3,5-di-tert-butylphenyl) substituted porphycene and its cobalt complex were synthesized and characterized. Several meso-tetraarylporphycene cobalt complexes having different substituents showed catalytic activity for the hydrogen gas evolution reaction (HER) in the presence of trifluoroacetic acid (TFA) under electrochemical reductive conditions. The electrochemical potential of the HER was -1.50V vs. Ag/AgCl in THF. The active species of this reaction were determined to be the ligand reduced species of Co(II) porphycenes. The catalytic efficiencies of the cobalt complexes of meso-aryl substituted porphycenes and meso-tetraphenylporphyrin were compared and meso-tetraphenyl porphycene cobalt complex exhibited the best current efficiency of 72%. Based on these experimental results and theoretical calculations, we proposed a possible HER mechanism of this system.

PtRu nanoparticles (NPs) supported on acid treated multiwall carbon nanotubes (Pt₁Ru₁/MWCNTs) were prepared by a modified polyol method without adding any other surfactant or protective agent. The structural and compositional properties of the as-obtained samples were characterized by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and X-ray photoelectron (XPS) spectroscopy. The electrocatalytic performance of the catalyst was evaluated by cyclic voltammetry (CV), CO stripping voltammetry and chronoamperometry, indicating a high catalytic activity, excellent CO tolerance and stability for methanol oxidation. Interestingly, a series of accurate controllable experiments have been designed to explore the enhancement mechanism of Pt₁Ru₁/MWCNTs for methanol oxidation reaction. Most importantly, Pt₁Ru₁/MWCNTs composites were used as an anode catalyst in the direct methanol fuel cells (DMFCs) exhibiting outstanding power density (126.1 mW/cm${}^{\mathrm{\text{2}}})$ 1.7 times higher than that of the commercial catalyst of Pt₁Ru₁/C (74.1 mW/cm${}^{\mathrm{\text{2}}})$ (E-TEK).

H₂O₂ detection plays an important role in electrochemical sensing since H₂O₂ often acts as an intermediate product or regulator in various reactions. Nanoporous carbon (NPC) can be a potential candidate in electrochemical sensing because of its high specific surface area, various pore sizes and structures. In this work, we reported the preparation of N-doped NPC derived from the highly available, accessible and recyclable plant Typha orientalis. The products have high surface area (highest surface areas of 1439.0 m² g${}^{-1})$ and a number of nanopores. Highest content of nitrogen atom in the product is 3.66 at.%). Typical product exhibits high electrocatalytic activity for reduction of hydrogen peroxide. The product may have further use for glucose biosensing. We developed a low-cost, simple and readily scalable approach to prepare the excellent carbon electrocatalyst directly from crude biomass. In addition, because of high surface area and doping of nitrogen element, the product may find broad applications in the fields of supercapacitors, lithium-ion batteries, gas uptake and so on.

Development of efficient electrocatalysts for the oxygen reduction reaction (ORR) remains a key issue for the commercialization of metal-air batteries. In this study, the novel structured Co₃O₄ nanoparticles-modified $\alpha$-MnO₂ nanorods supported on reduced graphene oxide (Co₃O₄-MnO₂/rGO) were synthesized with varying amounts of $\alpha$-MnO₂ via a facile two-step hydrothermal method. The relationship between the physical properties and the electrochemical results was investigated using X-ray diffraction spectrum, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammograms, electrochemical impedance spectroscopy and rotating disk electrode. The as-prepared Co₃O₄–MnO₂ nanohybrid exhibits enhanced catalytic activity for ORR under alkaline condition compared with MnO₂/rGO and Co₃O₄/rGO. Furthermore, it mainly favors a direct 4e-reaction pathway for ORR, which is attributed to the well-designed structure, the synergistic effect between Co₃O₄ and $\alpha$-MnO₂, and the covalent coupling between the Co₃O₄-MnO₂ and reduced graphene oxide. The role of Co₃O₄ in Co₃O₄–MnO₂ hybrid for catalyzing ORR also has been illustrated by varying the mass ratio of Co₃O₄ and MnO₂, which reveals that the Co₃O₄–MnO₂ with the ratio of 1:1 has better catalytic activity.

In this study, amorphous Co₃O₄-decorated Pd (carbon supported, denoted as Pd-Co₃O₄/C) was synthesized with a three-step approach. The as-obtained Pd-Co₃O₄/C consists of amorphous Co₃O₄ and Pd. Amorphous Co₃O₄ nanoparticle acts as the “catalytic promoter” and ultra-low Pd is the active component. Compared to Pd/C, as-prepared Pd-Co₃O₄/C catalyst offers high mass activity and stability. This high catalytic performance arises from good synergetic effects between Pd and amorphous Co₃O₄, which makes the Pd-Co₃O₄/C promising for direct methanol fuel cells.

A drastic demand for green energy has stimulated the development of H₂ production from water electrolysis. So, the exploration of electrocatalysts for water splitting has become an intensive concerned issue. For decades, utilization of ionic liquids (ILs) in the research of electrocatalysts has gradually evolved to an important branch in the field of energy storage and conversion. The participation of ILs offers the catalyst with almost the highest catalytic activity for water splitting so far. In this review, we describe in detail the application of ILs as media and templates in the preparation of catalysts for hydrogen evolution reaction and oxygen evolution reaction. Different from ordinary organic solvents, ILs have the ability to control the growth direction of nanomaterials, adjust phases, morphologies, electronic structures, mass transfer process, etc. so they can enhance the performance of electrocatalysts. In summarizing the function of ILs in the preparation of nanomaterials, the relationship among reaction media, material structures and catalytic efficiencies of catalysts is paid intensive attention. We expect that this review will guide the readers to have a more systematic understanding on preparing electrocatalysts assisted by ILs, while stimulating new thoughts on the reasonable design and controllable preparation of IL-mediated catalysts for water electrolysis.

Hydrogen energy is considered as an ideal replacement for traditional fossil energy sources because of its high combustion energy, clean combustion products, and abundant raw material storage. Hydrogen production by electrolysis of water is a highly efficient and feasible method. Besides, the by-product oxygen also has a high economic value. However, the slow kinetics leads to a higher than the theoretical voltage for water decomposition and requires additional energy. To deal with this problem, there is an urgent need to develop electrocatalysts for low consumption, high efficiency, and stable electrolytic water reactions. In recent years, non-precious metal nickel-based phosphide electrocatalysts have attracted a lot of attention. In this paper, three aspects of nickel-based monometallic phosphides, bimetallic phosphides, and polymetallic phosphides are reviewed. Finally, the current status, problems, and future directions of research on nickel-based phosphide electrocatalysts that do not contain precious metals are discussed.

In order to develop non-noble metal-based electrocatalysts for glucose oxidation, the Ni-doped, urchin-like Bi₂S₃ particles were prepared by a solvothermal method using the solvent of ethylene glycol/H₂O. The obtained products were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The background signal from capacitance current is relatively low and the electrocatalytic oxidation current of glucose relatively high due to the urchin-like nanostructure of Bi₂S₃ particles and high surface area where the presence of Bi also improves the electrocatalytic performance of Ni${}^{II}$/Ni${}^{III}$ shift.

Rational design of efficient electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential to promote the performance of overall water-splitting. In this work, we demonstrate the high performance electrolyzer by using Fe–Co phosphide grown on Ni foam (FeCoP/NF) as HER electrode and self-supported FeCo₂O₄@FeCo₂S₄/NF heterostructure as OER electrode. Thanks to the more active sites and faster charge transfer capability, the FeCoP/NF electrode can deliver low HER overpotentials of 59.6 and 233.6 mV at 10 and 100 mA cm${}^{-2}$. Furthermore, the synergistic effect at interfaces also endows low overpotentials of FeCo₂O₄@FeCo₂S₄/NF at specific current densities. As a result, the designed FeCoP/NF——FeCo₂O₄@FeCo₂S₄/NF device just needs a voltage of 1.52 V to afford 10 mA cm${}^{-2}$, indicating greatly potential in practical application.

In this paper, we report a special ${\mathrm{\text{MoS}}}_2$ nanoflower synthesized by hydrothermal approach, in which a heterostructure petal of ${\mathrm{\text{MoS}}}_2/\mathrm{\text{MXene}}$${\mathrm{\text{Ti}}}_3{\mathrm{\text{C}}}_2$ is constructed by growing the ${\mathrm{\text{MoS}}}_2$ active layers onto the few-layered MXene ${\mathrm{\text{Ti}}}_3{\mathrm{\text{C}}}_2$ substrate. Compared with the pristine ${\mathrm{\text{MoS}}}_2$ nanoflowers, the heterostructure ${\mathrm{\text{MoS}}}_2$ nanoflowers exhibit a lower onset overpotential of 207 mV and a lower Tafel slope of 28 mV dec${}^{-1}$. This can be explained by the heterostructure ${\mathrm{\text{MoS}}}_2$ nanoflowers providing a great number of exposed surfaces of ${\mathrm{\text{MoS}}}_2$, and increasing more active sites, and strengthening the interlayer coupling between ${\mathrm{\text{MoS}}}_2$ and MXene ${\mathrm{\text{Ti}}}_3{\mathrm{\text{C}}}_2$ to accelerate the charge transfer. All the merits are beneficial to the performance enhancement for hydrogen evolution catalytic.

To reduce energy crises and environmental pollution, it is imperative to logically create affordable, stable, efficient, and environmentally friendly bifunctional electrocatalysts based on non-precious metals for total water splitting. In this study, we designed and synthesized sea urchin-like structured CoFe/CuCo₂O₄ bifunctional electrocatalysts on nickel foam. Benefiting from the high conductivity of nickel foam and the positive synergistic effect between different component materials, this catalyst exhibited high activity in both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Specifically, the CoFe/CuCo₂O₄/NF-5 material required only 257 mV of OER overpotential and 178 mV of HER overpotential at a current density of 50 mA cm${}^{-2}$. It is worth noting that the alkaline electrolyzer prepared using CoFe/CuCo₂O₄/NF-5 material achieves a low cell voltage of 1.544 V to achieve a current density of 10 mA cm${}^{-2}$ in overall water splitting and can operate stably for a prolonged period. This work also provides a feasible strategy for green and low-cost electrocatalyst synthesis.

A clam-shaped molecule comprising a Zn(II)-porphyrin and a Zn(II)-cyclam is synthesized and characterized. Its electrochemical behavior and catalytic activity for homogeneous electrochemical reduction of carbon dioxide (CO₂) are investigated by cyclic voltammetry and compared with those of Zn(II)-meso-tetraphenylporphyrin and Zn(II)-cyclam. Under N₂-saturated conditions, cyclic voltammetry of the featured complex has characteristics of its two constituents, but under CO₂-saturated conditions, the target compound exhibits significant current enhancement. Iterative reduction under electrochemical conditions indicated the target compound has improved stability relative to Zn(II)-cyclam. Controlled potential electrolysis demonstrates that, without addition of water, methane (CH₄) is the only detectable product with 1% Faradaic efficiency (FE). The formation of CH₄ is not observed under the catalysis of the Zn(II)-porphyrin benchmark compound, indicating that the CO₂-capturing function of the Zn(II)-cyclam unit contributes to the catalysis. Upon addition of 3% v/v water, the electrochemical reduction of CO₂ in the presence of the target compound gives carbon monoxide (CO) with 28% FE. Dominance of CO formation under these conditions suggests enhancement of proton-coupled reduction. Integrated action of these Zn(II)-porphyrin and Zn(II)-cyclam units offers a notable example of a molecular catalytic system where the cyclam ring captures and brings CO₂ into the proximity of the porphyrin catalysis center.