C60-Decorated nickel-cobalt phosphide as an efficient and robust electrocatalyst for hydrogen evolution reaction

Pressure and temperature diagram of C60 from atomistic simulations

Although widely studied experimentally in the 1990s, the structure and properties of low-dimensional or high-pressure phases of fullerenes have recently been re-examined. Remarkably, recent experiments have shown that transparent, nearly pure amorphous sp3-bonded carbon phases can be obtained by heating a C60 molecular crystal at a high pressure. With the additional aim of testing the ability of three classical carbon potentials reactive empirical bond order, environment-dependent interatomic potential, and reactive force-field to reproduce these results, we investigate the details of the structural transformations undergone by fullerene crystals over a wide range of pressures and temperatures. All the potentials tested show that the initial polymerization of fullerenes is accompanied by negative thermal expansion, albeit in slightly different ranges. However, more significant differences in structural and mechanical properties are observed in the amorphous phases, in particular the sp3 carbon fraction and the existence of layered amorphous carbon. Overall, these results indicate to which extent classical reactive potentials can be used to explore phase transitions over a wide range of pressures and temperatures.

An electron-hole rich dual-site nickel catalyst for efficient photocatalytic overall water splitting

Photocatalysis offers an attractive strategy to upgrade H₂O to renewable fuel H₂. However, current photocatalytic hydrogen production technology often relies on additional sacrificial agents and noble metal cocatalysts, and there are limited photocatalysts possessing overall water splitting performance on their own. Here, we successfully construct an efficient catalytic system to realize overall water splitting, where hole-rich nickel phosphides (Ni₂P) with polymeric carbon-oxygen semiconductor (PCOS) is the site for oxygen generation and electron-rich Ni₂P with nickel sulfide (NiS) serves as the other site for producing H₂. The electron-hole rich Ni₂P based photocatalyst exhibits fast kinetics and a low thermodynamic energy barrier for overall water splitting with stoichiometric 2:1 hydrogen to oxygen ratio (150.7 μmol h^-1 H₂ and 70.2 μmol h^-1 O₂ produced per 100 mg photocatalyst) in a neutral solution. Density functional theory calculations show that the co-loading in Ni₂P and its hybridization with PCOS or NiS can effectively regulate the electronic structures of the surface active sites, alter the reaction pathway, reduce the reaction energy barrier, boost the overall water splitting activity. In comparison with reported literatures, such photocatalyst represents the excellent performance among all reported transition-metal oxides and/or transition-metal sulfides and is even superior to noble metal catalyst.

Rational Design of a Low-Dimensional and Metal-free Heterostructure for Efficient Water Oxidation: DFT and Experimental Studies

A nitrogen-doped fullerene dimer is synthesized and compounded with multi-walled carbon nanotubes (MWCNTs) to construct a low-dimensional and metal-free 0D-1D heterostructure for electrocatalytic water oxidation. The (C₅₉N)₂/MWCNTs heterostructure exhibits a highly efficient performance, as verified by both first-principles density functional theory and experimental studies. The *O → *OOH process is confirmed as the rate-determining step of water oxidation. The negatively charged N-doping leads to electronic redistribution and intermolecular charge transfer and thus reduces the uphill free energies of intermediates on the (C₅₉N)₂/MWCNTs interface. Therefore, the (C₅₉N)₂/MWCNTs heterostructure has great potential to emit light and heat in metal-free-based electrocatalytic water oxidation.

Size-dependent melting of onion-like fullerenic carbons: a molecular dynamics and machine learning study

The melting thermodynamic characteristics of 2- to 20-layered onion-like fullerenes (OLF_n) (C₆₀@C₂₄₀to C₆₀@···@C₆₀₀₀···@C₂₄₀₀₀) are comprehensively explored using first-principles-based ReaxFF atomistic simulations and random forest machine learning (RF ML). It is revealed that OLF_nshows lower thermal stability than the counterparts of single-walled fullerenes (SWF_n). The melting point of SWF_nincreases monotonically with increasing size, whereas for OLF_n, an unusual size-dependent melting point is observed; OLF_nwith intermediate size shows the highest melting point. For small OLF_n, the melting occurs from the inner to the outer, whereas for large OLF_n, it nucleates from the inner to the outer and to intermediate fullerenes. The melting and erosion behaviors of both SWF_nand OLF_nare mainly characterized by the nucleation of non-hexagons, nanovoids, carbon chains and emission of C₂. RF ML model is developed to predict the melting points of both SWF_nand OLF_n. Moreover, the analysis of the feature importance reveals that the Stone-Wales transformation is a critical pathway in the melting of SWF_nand OLF_n. This study provides new insights and perspectives into the thermodynamics and pyrolysis chemistry of fullerenic carbons, and also may shed some lights onto the understanding of thermally-induced erosion of carbon-based resources and spacecraft materials.

Electrocatalytic activity for proton reduction by a covalent non-metal graphene-fullerene hybrid

A non-metal covalent hybrid of fullerene and graphene was synthesized in one step via fluorographene chemistry. Its electrocatalytic performance for the hydrogen evolution reaction and durability was ascribed to intrahybrid charge-transfer phenomena, exploiting the electron-accepting properties of C60 and the high conductivity and large surface area of graphene.

Computational Analysis of Strain-Induced Effects on the Dynamic Properties of C60 in Fullerite

A hybrid discrete-continuous physical and mathematical model is used to study what deformation characteristics cause the rolling effect of C60 fullerene in a fullerite crystal. The interaction of fullerene atoms with surrounding molecules is described using a centrally symmetric interaction potential, in which the surrounding molecules are considered as a spherical surface of uniformly distributed carbon atoms. The rotational motion of fullerene is described by the Euler dynamic equations. The results of a numerical study of the influence of the rate, magnitude, and direction of strain on the dynamic characteristics of the rotational and translational motion of C60 fullerene in a crystalline fragment are presented.

Noble Metal (Pt, Rh, Pd, Ir) Doped Ru/CNT Ultra-Small Alloy for Acidic Hydrogen Evolution at High Current Density

There are still great challenges to prepare high-efficiency Ru-based catalysts that are superior to Pt/C under acidic conditions, especially under high current conditions. In this work, a series of surfactant-free noble metal doped Ru/CNT (M-Ru/CNT, M = Pt, Rh, Pd, Ir, CNT stands for carbon nanotube) are prepared by microwave reduction method in 1 minute with ≈3-3.5 nm in size for the first time. In 0.5 m H₂ SO₄ , the overpotential of Pt-Ru/CNT (Pt: 4.94 at %) is only 12 mV. What's more, it also has much larger electrochemical surface area and intrinsic activity than Pt/C. Pt-Ru/CNT still has an ultra-small overpotential under high current density (113 mV at 500 mA cm^-2 , 155 mV at 1000 mA cm^-2 ). At the same time, it possesses excellent stability regardless of high current or low current after the durability test of 100 h. Theoretical calculation also deeply reveals that Ru is the main adsorption site of H⁺ . The comparison of the electronic structure of a series of noble metals adjusted by Ru shows that Pt has the most excellent Gibbs free energy of the adsorbed hydrogen and promotes the desorption of the product.

Enhanced Oxygen Evolution Reaction with a Ternary Hybrid of Patronite-Carbon Nanotube-Reduced Graphene Oxide: A Synergy between Experiments and Theory

This work reports the hybridization of patronite (VS₄) sheets with reduced graphene oxide and functionalized carbon nanotubes (RGO/FCNT/VS₄) through a hydrothermal method. The synergistic effect divulged by the individual components, i.e., RGO, FCNT, and VS₄, significantly improves the efficiency of the ternary (RGO/FCNT/VS₄) hybrid toward the oxygen evolution reaction (OER). The ternary composite exhibits an impressive electrocatalytic OER performance in 1 M KOH and requires only 230 mV overpotential to reach the state-of-the-art current density (10 mA cm^-2). Additionally, the hybrid shows an appreciable Tafel slope with a higher Faradaic efficiency (97.55 ± 2.3%) at an overpotential of 230 mV. Further, these experimental findings are corroborated by the state-of-the-art density functional theory by presenting adsorption configurations, the density of states, and the overpotential of these hybrid structures. Interestingly, the theoretical overpotential follows the qualitative trend RGO/FCNT/VS₄ < FCNT/VS₄ < RGO/VS₄, supporting the experimental findings.

Size-controlled Ag quantum dots decorated on binder-free hierarchical NiCoP films by magnetron sputtering to boost electrochemical performance for supercapacitors

This paper reports novel binder-free and self-supported electrodes of hierarchical nickel-cobalt phosphide (NiCoP) films decorated with size-controlled Ag quantum dots by magnetron sputtering (Ag/NiCoP). Ag quantum dots with an average particle size of 7.90 nm uniformly distribute over the nanosheet-assembled architecture of NiCoP films. Benefitting from the good ohmic contact in the interfaces between Ag quantum dots and NiCoP nanosheets, Ag/NiCoP exhibits an ultrahigh specific capacitance of 6150 mF cm-2 (3050 F g-1 at 1 A g-1) higher than the 3445 mF cm-2 (1722 F g-1 at 1 A g-1) of bare NiCoP at 2 mA cm-2. The specific areal capacitance has been increased by 78.5% after introducing Ag quantum dots. 34% capacitance retention rate is achieved while the current density increases from 2 to 30 mA cm-2. The cycling stability displays a remarkable capacitance retention of 73% for 4000 cycles at 30 mA cm-2. These boosted electrochemical performances are mainly attributed to the synergistic effects of enough electroactive sites, high electronic conductivity, and easy electrolyte ion diffusion. An asymmetric supercapacitor is fabricated using hierarchical Ag/NiCoP as the positive electrode and activated carbon as the negative electrode. The supercapacitor delivers an energy density of 0.254 mW h cm-2 (1.81 mW h cm-3) at a power density of 1.88 mW cm-2 (13.4 mW cm-3). At a power density of 18.8 mW cm-2 (134 mW cm-3), an energy density of 0.115 mW h cm-2 (0.82 mW h cm-3) can still be maintained. This study provides an avenue to design a novel generation of supercapacitors for energy storage devices.

Nanostructured metal phosphides: from controllable synthesis to sustainable catalysis

Metal phosphides (MPs) with unique and desirable physicochemical properties provide promising potential in practical applications, such as the catalysis, gas/humidity sensor, environmental remediation, and energy storage fields, especially for transition metal phosphides (TMPs) and MPs consisting of group IIIA and IVA metal elements. Most studies, however, on the synthesis of MP nanomaterials still face intractable challenges, encompassing the need for a more thorough understanding of the growth mechanism, strategies for large-scale synthesis of targeted high-quality MPs, and practical achievement of functional applications. This review aims at providing a comprehensive update on the controllable synthetic strategies for MPs from various metal sources. Additionally, different passivation strategies for engineering the structural and electronic properties of MP nanostructures are scrutinized. Then, we showcase the implementable applications of MP-based materials in emerging sustainable catalytic fields including electrocatalysis, photocatalysis, mild thermocatalysis, and related hybrid systems. Finally, we offer a rational perspective on future opportunities and remaining challenges for the development of MPs in the materials science and sustainable catalysis fields.

Molecular dynamics investigation on the nano-mechanical behaviour of C60 fullerene and its crystallized structure

C₆₀ fullerene has been utilized in various applications, including low friction and wear coatings, due to its unique molecular structure. In this work, molecular dynamics simulations were conducted to assess the nano-mechanical behaviour of a single C₆₀ fullerene and its crystallized structure. A single C₆₀ model and a model of a face-centred cubic structured C₆₀ crystal with a one-unit-cell thickness were prepared for compression and unloading simulations based on the adaptive intermolecular reactive empirical bond-order potential for carbon. Force-displacement curves and molecule-averaged virial stresses were obtained during the simulation. The models applied during the compression and unloading processes were visualized to confirm the deformation behaviour. Both the single and crystal C₆₀ models showed a perfectly reversible deformation before the point of force decrease that occurred during compression. In particular, the face-centred cubic structure of the crystal C₆₀ model was severely altered during compression before the individual C₆₀ molecules experienced permanent deformation. The maximum values of the normal virial stress in the compression direction before the permanent deformation of the molecules were almost same for both the single and crystallized models.

Core–shell-structured MOF-derived 2D hierarchical nanocatalysts with enhanced Fenton-like activities

The fabricated core–shell-structured MOF-derived 2D nanocatalysts with Co/Co-N_x co-doping N-CNTs enhance Fenton-like activities for the water remediation of benzene-derived contaminants.

Hierarchical Bimetallic Ni-Co-P Microflowers with Ultrathin Nanosheet Arrays for Efficient Hydrogen Evolution Reaction over All pH Values

Designing efficient nonprecious catalysts with pH-universal hydrogen evolution reaction (HER) performance is of importance for boosting water splitting. Herein, a self-template strategy based on Ni-Co-glycerates is developed to prepare bimetallic Ni-Co-P microflowers with ultrathin nanosheet arrays. The highly porous core-shell structure gives rise to affluent mass transfer channels and availably prevents the aggregation of nanosheets, while the ultrathin nanosheets are favorable for producing abundant active sites. Besides, the produced CoP/NiCoP heterostructure in the bimetallic Ni-Co-P catalyst has excellent HER performance in a wide pH range. The as-prepared catalyst shows low potentials of 90, 157, and 121 mV to deliver a current density of 10 mA cm^-2 in 0.5 M H₂SO₄, 0.5 M PBS, and 1 M KOH solution, respectively. Meanwhile, negligible overpotential decay is achieved in the polarization curves after a long-term stability determination. This work supplies a promising strategy for developing pH-universal HER electrocatalysts based on solid-state metal alkoxides.

Augmenting Intrinsic Fenton-Like Activities of MOF-Derived Catalysts via N-Molecule-Assisted Self-catalyzed Carbonization

To overcome the ever-growing organic pollutions in the water system, abundant efforts have been dedicated to fabricating efficient Fenton-like carbon catalysts. However, the rational design of carbon catalysts with high intrinsic activity remains a long-term goal. Herein, we report a new N-molecule-assisted self-catalytic carbonization process in augmenting the intrinsic Fenton-like activity of metal-organic-framework-derived carbon hybrids. During carbonization, the N-molecules provide alkane/ammonia gases and the formed iron nanocrystals act as the in situ catalysts, which result in the elaborated formation of carbon nanotubes (in situ chemical vapor deposition from alkane/iron catalysts) and micro-/meso-porous structures (ammonia gas etching). The obtained catalysts exhibited with abundant Fe/Fe-Nx/pyridinic-N active species, micro-/meso-porous structures, and conductive carbon nanotubes. Consequently, the catalysts exhibit high efficiency toward the degradation of different organic pollutions, such as bisphenol A, methylene blue, and tetracycline. This study not only creates a new pathway for achieving highly active Fenton-like carbon catalysts but also takes a step toward the customized production of advanced carbon hybrids for diverse energy and environmental applications.

Scalable synthesis of self-assembled bimetallic phosphide/N-doped graphene nanoflakes as an efficient electrocatalyst for overall water splitting

In order to achieve clean hydrogen energy through overall water splitting, it is vitally important but still challenging to develop highly efficient and low-cost electrocatalysts to replace the noble metal-based electrocatalysts (e.g. Pt- and Ru-based catalysts). To address this issue, herein, we present a facile and scalable spray drying and subsequent phosphorization approach to synthesize iron-cobalt bimetallic nanoflakes encapsulated in N-doped graphene (FCP@NG). The optimized FCP@NG exhibits excellent performance in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting. It demonstrates remarkable performance in the HER and superior activity in the OER, even outperforming the state-of-the-art RuO₂ catalyst. Being employed as both the cathode and anode on nickel foams, this FCP@NG hybrid demonstrates promising performance in overall water splitting with a very low potential of 1.63 V to deliver a current density of 10 mA cm^-2, which is superior among most of the recently reported transition-metal-based catalysts and comparable to the commercial Pt/RuO₂ cell. The outstanding electrocatalytic performance of FCP@NG is attributed to a synergistic effect of its bi-metallization, unique nanoflake structure and conductive N-doped graphene encapsulation. This work provides a scalable and low-cost strategy to synthesize nonprecious and bi-functional transition-metal-based catalysts with unique nanoarchitecture and outstanding catalytic performance for overall water splitting.

Synergistic Effect of Co-Ni Hybrid Phosphide Nanocages for Ultrahigh Capacity Fast Energy Storage

Rational design of metal compounds in terms of the structure/morphology and chemical composition is essential to achieve desirable electrochemical performances for fast energy storage because of the synergistic effect between different elements and the structure effect. Here, an approach is presented to facilely fabricate mixed-metal compounds including hydroxides, phosphides, sulfides, oxides, and selenides with well-defined hollow nanocage structure using metal-organic framework nanocrystals as sacrificial precursors. Among the as-synthesized samples, the porous nanocage structure, synergistic effect of mixed metals, and unique phosphide composition endow nickel cobalt bimetallic phosphide (NiCo-P) nanocages with outstanding performance as a battery-type Faradaic electrode material for fast energy storage, with ultrahigh specific capacity of 894 C g-1 at 1 A g-1 and excellent rate capability, surpassing most of the reported metal compounds. Control experiments and theoretical calculations based on density functional theory reveal that the synergistic effect between Ni and Co in NiCo-P can greatly increase the OH- adsorption energy, while the hollow porous structure facilitates the fast mass/electron transport. The presented work not only provides a promising electrode material for fast energy storage, but also opens a new route toward structural and compositional design of electrode materials for energy storage and conversion.

Flexible vanadium-doped Ni2P nanosheet arrays grown on carbon cloth for an efficient hydrogen evolution reaction

Tuning the electronic structure, morphology, and structure of electrocatalysts is of great significance to achieve a highly active and stable hydrogen evolution reaction (HER). Herein, combining hydrothermal and low temperature phosphidation methods, V-doped Ni2P nanosheet arrays grown on carbon cloth (V-Ni2P NSAs/CC) were successfully prepared for the HER. It is found that the prepared V-Ni2P NSAs/CC exhibits preeminent performance for the HER. Specifically, it only requires an overpotential of 85 mV to achieve a current density of 10 mA cm-2 in 1.0 M KOH solution. Moreover, the V-Ni2P NSAs/CC shows superior electrochemical stability, maintaining its HER performance up to 3000 cyclic voltammetry cycles. This work affords a guiding strategy for the synthesis of a high-performance and stable electrocatalyst for the HER.

Low-cost high-performance hydrogen evolution electrocatalysts based on Pt-CoP polyhedra with low Pt loading in both alkaline and neutral media

Low-cost Pt-CoP hollow polyhedra exhibited prominent performance for the HER in both basic and neutral solutions.