Xiangdong Yao

• Griffith University

Defect engineering is widely regarded as a promising strategy to enhance the performance of electrocatalysts for water splitting. In this work, defective NiFe layered double hydroxide (NiFe LDH) with a high density of edge sites (edge‐rich NiFe LDH) is synthesized via a simple reduction process during the early stages of nucleation. The introductio...

Substituent-modulation induced electronic perturbations can fine-tune the charge cloud distribution around carbon defects. The transfer of electron from electron-donating substituent to carbon defects will lead to lower p z band center...

Defect engineering is an effective method for tuning the performance of thermoelectric materials and shows significant promise in advancing thermoelectric performance. Given the rapid progress in this research field, this Review summarizes recent advances in the application of defect engineering in thermoelectric materials, offering insights into h...

Hydrogen, a clean resource with high energy density, is one of the most promising alternatives to fossil. Proton exchange membrane water electrolyzers are beneficial for hydrogen production because of their high current density, facile operation, and high gas purity. However, the large‐scale application of electrochemical water splitting to acidic...

Defect‐engineered bimetallic oxides exhibit high potential for the electrolysis of small organic molecules. However, the ambiguity in the relationship between the defect density and electrocatalytic performance makes it challenging to control the final products of multi‐step multi‐electron reactions in such electrocatalytic systems. In this study,...

Optimizing the local electronic structure of electrocatalysts can effectively lower the energy barrier of electrochemical reactions, thus enhancing the electrocatalytic activity. However, the intrinsic contribution of the electronic effect is still experimentally unclear. In this work, the electron injection‐incomplete discharge approach to achieve...

Nanoscale defects can induce the effective modulation of carrier concentration, mobility, and phonon scattering to secure high thermoelectric performance in semiconductors. However, it is still limited to effectively controlling nanoscale defects in thermoelectric materials. Here, argon plasma bombardment is employed to introduce a large number of...

On 16 June 2023, the United Nations Environment Programme highlighted the severity of nitrogen pollution faced by humans and called for joint action for sustainable nitrogen use. Excess nitrogenous waste (NW: NO, NO2, NO2-, NO3-, etc.) mainly arises from the use of synthetic fertilisers, wastewater discharge, and fossil fuel combustion. Although th...

The interactions between the catalyst and support are widely used in many important catalytic reactions but the construction of strong interaction with definite microenvironments to understand the structure‐activity relationship is still challenging. Here, strongly‐interacted composites are prepared via selective exsolution of active NiSe2 from the...

Active sites identification in metal-free carbon materials is crucial for developing practical electrocatalysts, but resolving precise configuration of active site remains a challenge because of the elusive dynamic structural evolution process during reactions. Here, we reveal the dynamic active site identification process of oxygen modified defect...

Oxygen defects play a critical role in the electrocatalytic oxygen evolution reaction (OER). Therefore, in-depth understanding the structure-activity-mechanism relationship of these defects is the key to design efficient OER electrocatalysts. This relationship needs to be understood dynamically due to the potential for irreversible phase transition...

Metal-free carbon-based materials are considered as promising oxygen reduction reaction (ORR) electrocatalysts for clean energy conversion, and their highly dense and exposed carbon active sites are crucial for efficient ORR. In this work, two unique quasi-three-dimensional cyclotriphosphazene-based covalent organic frameworks (Q3CTP-COFs) and thei...

Abstract An efficient and economical electrocatalyst as kinetic support is key to electrochemical reactions. For this reason, chemists have been working to investigate the basic changing of chemical principles when the system is confined in limited space with nanometer‐scale dimensions or sub‐microliter volumes. Inspired by biological research, the...

In the past decades, remarkable progress has been achieved in the exploration of electrocatalysts with high activity, long durability, and low cost. Among these, defective graphene (DG)‐based catalysts are considered as one of the most potential substitutes for precious metal‐based electrocatalysts. DG‐based catalysts contain abundant active center...

Designing a facile strategy to prepare catalysts with highly active sites are challenging for large‐scale implementation of electrochemical hydrogen production. Herein, a straightforward and eco‐friendly method by high‐energy mechanochemical ball milling for mass production of atomic Ru dispersive in defective MoS2 catalysts (Ru1@D‐MoS2) is develop...

ConspectusOwing to climate change and over-reliance on fossil fuels, the study and development of sustainable energy is of essential importance in the next few decades. In recent years, rapid advances have been witnessed in various power to gas electrocatalysis technologies including oxygen reduction reaction (ORR), oxygen evolution reaction (OER),...

Electrocatalytic hydrogenation (ECH) is a burgeoning strategy for the sustainable utilization of hydrogen. However, how to effectively suppress the competitive hydrogen evolution reaction (HER) is a big challenge to ECH catalysis. In this study, amine (NH2R)‐coordinated Pd nanoparticles loaded on carbon felt (Pd@CF) as a catalyst is successfully sy...

Herein, we report the method of molecular-beam-epitaxial growth (MBE) for precisely regulating the terminal surface with different exposed atoms on indium telluride (InTe) and studied the electrocatalytic performances toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The improved performances result from the exposed In o...

Proton exchange membrane water electrolyzers (PEMWEs) for water electrolysis have received tremendous attention due to their immediate response, high proton conductivity, low ohmic losses and gas crossover rate. Design high-performance,...

Carbon materials are widely used in various industrial applications due to their outstanding stability and robustness in diverse structures, yet it remains a revolutionary and challenging task in activating carbon materials for efficient and low-cost catalysis. Herein, inspired by the successful experimental studies, we for the first-time exploited...

Covalent organic frameworks (COFs) have attracted extensive interest due to their unique structures and various applications. However, structural diversities are still limited, which greatly restricts the development of COF materials. Herein, we report two unusual cubic (8-connected) building units and their derived 3D imine-linked COFs with bcu ne...

Defective carbons have recently been considered as one of the most promising alternatives to precious metal electrocatalysts. However, atomic structural tailoring of carbon defects poses challenges, especially in regulating defect density to maximize the active sites. Herein, we report an interfacial self-corrosion strategy to control the removal a...

Comprehensive Summary Three‐dimensional (3D) covalent organic frameworks (COFs) are crystalline porous polymers with potential in numerous high‐tech applications, but the linkages involved in their synthesis are still rather limited. Herein, we report novel 3D sp ² carbon‐linked COFs fabricated by the formation reaction of C=C bonds and their appli...

Cancers heavily threaten human life, therefore, the high‐accuracy diagnosis is vital to protect human beings from the suffer of cancers. While the biopsy and imaging methods have been widely used as current technologies for cancer diagnosis, new detection platform by metabolic analysis is expecting due to the significant advantages of fast, simple,...

Developing efficient hydrogen storage materials and the corresponding methods is the key to successfully realizing the "hydrogen economy". The ideal hydrogen storage materials should be capable of reversibly ab-/desorbing hydrogen under mild temperatures with high hydrogen capacities. To achieve this target, the ideal enthalpy of adsorption is dete...

The heterogeneous electro-Fenton (Hetero-EF) system is characterized by in situ generation of hydrogen peroxide (H2O2). Then, the hydroxyl radicals (•OH) formed by activization of H2O2 can strongly oxidize and mineralize pollutants in wastewater. Single-site heterogeneous catalysts (SSHCs) have the essence of isolated active single sites anchored o...

Active center reconstruction is essential for high performance oxygen reduction reaction (ORR) electrocatalysts. Usually, the ORR activity stems from the electronic environment of active sites by charge redistribution. We introduce an asymmetry strategy to adjust the charge distribution of active centers by designing conjugated polymer (CP) catalys...

Atomic metal catalysis

Active center reconstruction is essential for searching high performance oxygen reduction reaction (ORR) electrocatalysts. Usually, the ORR activity stems from the special electronic environment of active sites through charge redistribution. In this work, we introduce “asymmetry” strategy to adjust the charge distribution of active centers by preci...

Defective carbon-based materials (DCMs) have recently been considered as one of the most promising alternatives to precious metal electrocatalysts owing to their irreplaceable advantages, such as environmentally friendly, low cost and high structural tunability. Despite remarkable progress has been achieved, grand challenges of their further develo...

a>Three-dimensional (3D) covalent organic frameworks (COFs) are crystalline porous polymers with potential in numerous high-tech applications, but the linkages involved in their synthesis are still rather limited. Herein we report the first case of 3D sp² carbon-linked COFs fabricated by the formation reaction of C=C bonds and their appl...

Water electrolysis is a promising option for pure hydrogen production, but it is limited by the high cost. Developing superb and low‐cost electrocatalysts for hydrogen evolution reaction (HER) is critical for cost reduction. Heterostructures are demonstrated with excellent HER activities, but still inferior to commercial Pt/C. Herein, vacancy type...

Electrocatalysis plays a deciding role in various energy-related applications. Engineering the active sites of electrocatalysts is an important aspect to promote their catalytic performance. In particular, defect engineering provides a feasible and efficient approach to improve the intrinsic activities and increase the number of active sites in ele...

Catalysts play a critical role in accelerating the electrochemical reactions. Engineering the electronic structures and surface properties of electrocatalysts is a feasible approach to improve their catalytic performance. Introducing defects such as anion and cation vacancies into transition metal‐based materials to enhance their activity for vario...

The oxygen vacancies of defective iron–cobalt oxide (FeCoOx‐Vo) nanosheets are modified by the homogeneously distributed sulfur (S) atoms. S atoms can not only effectively stabilize oxygen vacancies (Vo), but also form the Co−S coordination with Co active site in the Vo, which can modulate the electronic structure of the active site, enabling FeCoO...

Manipulating the surface structure of electrocatalysts at the atomic level is of primary importance to simultaneously achieve the activity and stability dual‐criteria in oxygen reduction reaction (ORR) for proton exchange membrane fuel cells. Here, a durable acidic ORR electrocatalyst with the “defective‐armored” structure of Pt shell and Pt–Ni cor...

A known doping atomic-level functionalization strategy achieves the breakthrough of ferromagnetism in carbon.

The defective iron–cobalt oxide nanosheet is developed into a highly efficient OER catalyst through modulating its electron structure by oxygen vacancy creation and sulfur atom modification. Pairing with CoP3/Ni2P, its current density can reach up to 406.0 mA cm⁻² at 2.3 V, meeting well with the industrial water splitting requirement. Abstract The...

Metal-free oxygen reduction reaction (ORR) catalysts have been intensively studied during the past decade. For heteroatom-modified carbon materials, the influence of heteroatoms on the ORR remains unclear. Here, we use computational simulations to probe the role of heteroatoms in catalyzing the ORR; graphene with the pentagonal carbon (C5) defect i...

Metal-free carbon catalysts, especially with rich topological defects, have exhibited extraordinary performance in various electrochemical reactions. To fundamentally understand the relation of activity with specific defect, control of defect type in carbon is indispensable and unfortunately still remains a great challenge to date. Here, we develop...

Controllable design and synthesis of catalysts with the target active sites are extremely important for their applications such as for the oxygen reduction reaction (ORR) in fuel cells. However, the controllably synthesizing electrocatalysts with a single type of active site still remains a grand challenge. In this study, we developed a facile and...

Developing efficient catalysts toward both oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) is the core task for rechargeable metal-air batteries. Although integration of two active components should be an effective method to produce the bifunctional catalysts in principle, traditional techniques still can not attain fine tunable s...

Defective or heteroatoms-doped metal-free carbon materials (MFCMs) are regarded as efficient oxygen reduction reaction (ORR) catalysts in the past decade. However, the active site structures for ORR in MFCMs are hard to be precisely confirmed and controllably synthesized through the common methods such as high temperature pyrolysis or heteroatom do...

Exploring safe and efficient hydrogen storage materials has been one of the toughest challenges for the upcoming hydrogen economy. High capacity, mild dehydrogenation conditions and good stability at room temperature endow liquid-phase chemical hydrides the great potential to be utilized as the next generation of hydrogen storage medium. In this re...

Controllably constructing nitrogen‐modified divacancies (ND) in carbon substrates to immobilize atomic Fe species and unveiling the advantageous configuration is still challenging, but indispensable for attaining optimal Fe−N−C catalysts for the oxygen reduction reaction (ORR). Herein, a fundamental investigation of unfolding intrinsically superior...

The family of atomic catalysts in defective carbons is now of increasing interest for diverse reactions. In this issue of Chem, Liu and co-workers unveil the nature of M–N–C (M = Mn, Fe, Co, Ni, and Cu) as active sites that can finely tune the oxygen reduction reaction (ORR) pathways spanning 1e–4e transfer processes.

Atomic metal catalysis (AMC) provides an effective way to enhance activity for the oxygen reduction reaction (ORR). Cobalt anchored on nitrogen‐doped carbon materials have been extensively reported. The carbon‐hosted Co‐N4 structure was widely considered as the active site; however, it is very rare to investigate the activity of Co partially coordi...

Increasing the active site density of single-atomic catalysts (SACs) is expected to generate the closely neighboring atomic sites with the potential synergetic interaction. However, the synthesis of SACs with high active site density still remains a great challenge due to the easy aggregation of high density metal atoms during the synthesis. In the...

Die Aktivität von Co-N4−xCx mit einer abstimmbaren Koordinationsumgebung wurde im Hinblick auf aktive Zentren für die Katalyse der Sauerstoffreduktion studiert. Der Defekt an Kohlenstoff ist wesentlich für die Bildung von Co-N4−xCx. Co-koordiniertes N verändert die Reaktivität durch Modifizierung der Elektronenverteilung, und N fängt mehr Co ab, wo...

Five isostructural, new bimetallic ZIF precursor with various Zn/Co ratios were successfully synthesized to derive a series of N-doped porous carbons embedded with Co nanoparticles. We systematically investigated the effect of different bimetals ratios in ZIF precursors on electrocatalytic properties of the obtained porous carbon catalysts. The opt...

Metal–organic framework (MOFs) two‐dimensional (2D) nanosheets have many coordinatively unsaturated metal sites that act as active centres for catalysis. To date, limited numbers of 2D MOFs nanosheets can be obtained through top‐down or bottom‐up synthesis strategies. Herein, we report a 2D oxide sacrifice approach (2dOSA) to facilely synthesize ul...

Owing to the difficulty in controlling the dopant or defect types and their homogeneity in carbon materials, it is still a controversial issue to identify the active sites of carbon-based metal-free catalysts. Here we report a proof-of-concept study on the active-site evaluation for a highly oriented pyrolytic graphite catalyst with specific pentag...

Denk schlank: Ein sogenannter 2D-Opferoxid-Ansatz wurde entwickelt, um Liganden an Metallzentren amorpher Metalloxid-Nanoschichten zu koordinieren und so Nanoschichten von Metall-organischen Gerüstverbindungen (MOF) zu synthetisieren. Aufgrund der hohen Anzahl an koordinativ ungesättigten Metallzentren und der Heteroatom-Synergie zeigen die erhalte...

A defect‐based carbon hollow sphere catalyst with dual‐atomic Co‐Pt species trapped in a multilayered carbon shell was synthesized by electrochemical activation. In their Communication (DOI: 10.1002/anie.201902107), X. Yao et al. investigated the synergistic effect between the atomic metals on the adjacent carbon layers and showed how charge polari...

Atomic metal species‐based catalysts (AMCs) show remarkable possibilities in various catalytic reactions. The coordination configuration of the metal atoms has been widely recognized as the determining factor to the electronic structure and the catalytic activity. However, the synergistic effect between the adjacent layers of the multilayered AMCs...

The exploitation of highly efficient, low-cost, and stable electrocatalysts is a key issue of the broad application of green electrocatalytic reactions and efficient energy devices. Recently, modulating the surface structure of electrocatalysts to improve the catalytic activity has attracted a lot of attention. In particular, defect engineering is...

Ein Kohlenstoff‐Hohlkugelkatalysator mit Co‐Pt‐Spezies, die in einer mehrlagigen Kohlenstoffhülle eingeschlossen sind, wurde durch elektrochemische Aktivierung synthetisiert. In ihrer Zuschrift (DOI: 10.1002/ange.201902107) untersuchen X. Yao et al. den synergistischen Effekt zwischen den atomaren Metallen auf die angrenzenden Kohlenstoffschichten...

Atomic metal species based catalysts (AMCs) show remarkable potential in various catalytic reactions. The coordination configuration of the metal atoms has been widely recognized as the determining factor to the electronic structure and the catalytic activity. However, the synergistic effect between the adjacent layers of the multilayered AMCs is a...

Metal‐free and carbon‐based catalysts are emerging as a promising alternative to conventional metallic catalysts. As summarized in article number 1805717 by Josue Ortiz‐Medina, Feng Wang, Xiangdong Yao, Mauricio Terrones, Morinobu Endo, and co‐workers, the engineered defect and doped sites in nanostructured carbon materials provide increased activi...

Correction for ‘Exfoliation of amorphous phthalocyanine conjugated polymers into ultrathin nanosheets for highly efficient oxygen reduction’ by Wenping Liu et al. , J. Mater. Chem. A , 2019, 7 , 3112–3119.

The development of advanced catalysts for efficient electrochemical energy conversion technologies to alleviate the reliance on fossil fuels has attracted considerable interest in the last decades. Insight into the roles of reactive sites in nanomaterials is significant for understanding and implementing the design principles of nanocatalysts. Rece...

Great effort has been contributed to exploring efficient and cost‐effective oxygen reduction reaction (ORR) catalysts for fuel cell applications in the past decades. Now various electrocatalysts can be synthesized for high‐performance ORR catalysis. However, the identification of the ORR active sites in many nonprecious metal‐based catalysts is sti...

With the advent of carbon nanotechnology, which initiated significant research efforts more than two decades ago, novel materials for energy harvesting and storage have emerged at an amazing pace. Nevertheless, some fundamental applications are still dominated by traditional materials, and it is especially evident in the case of catalysis, and envi...

It is a significant challenge to develop high-efficiency synthetic methodology to access fully conjugated 2D conjugated polymers (CPs)/covalent organic frameworks (COFs) nanosheets (NSs) that are of great application potential for electronics and energy. Herein, we report the exfoliation of a series of amorphous ethynyl-linked phthalocyanine (Pc) C...

The polar surface of (001) wurtzite-structured MnO possesses substantial electrostatic instabilities that facilitate a wurtzite to graphene-like sheet transformation during the lithiation/delithiation process when used in battery technologies. This transformation results in cycle instability and loss of cell efficiency. In this work, we synthesized...

In this communication, N-doped carbon shell encapsulated Co3O4@Co nanoparticles (NPs) were assembled on N-doped reduced graphene oxide to form non-precious metal aerogels (Co3O4@Co/N-r-GO) for oxygen reduction. In alkaline medium, the aerogels exhibit comparable oxygen reduction reaction (ORR) performances to the commercial Pt/C in aspects of half-...

Rational design and synthesis of hetero‐coordinated moieties at the atomic scale can significantly raise the performance of the catalyst and obtain mechanistic insight into the oxygen‐involving electrocatalysis. Here, a facile plasma‐photochemical strategy is applied to construct atomically coordinated Pt–Co–Se moieties in defective CoSe2 (CoSe2−x)...

Various strategies, such as increasing active site numbers, structural and surface engineering, have been used to improve the oxygen evolution reaction (OER) performance of transition metal dichalcogenide. However, it is still a grand challenge to combine these strategies in one material system to realize the full catalytic potential. Herein, we fi...

Various strategies, such as increasing active site numbers, structural and surface engineering, have been used to improve the oxygen evolution reaction (OER) performance of transition metal dichalcogenide. However, it is still a grand challenge to combine these strategies in one material system to realize the full catalytic potential. Herein, we fi...

The exploration of highly active and durable cathodic oxygen reduction reaction (ORR) catalysts with economical production costs is still the bottleneck to realize the large-scale commercialization of fuel cells. In recent years, remarkable progress has been achieved in fabricating effective non-precious metal based ORR catalysts. In particular, mo...

Herein, a general strategy is developed to synthesize atomic metal catalysts using sustainable and earth-abundant sodium alginate (Na-Alg), a common seaweed extract, as a precursor. The “egg-box” structure in Na-Alg after ion-exchange with metal cations (Zn²⁺, Co²⁺, Ni²⁺, Cu²⁺ etc) is the key to achieve the scalable and controllable synthesis of hi...

At present, the biggest hurdle for the commercialization of fuel cells is the correlated manufacturing cost, where the expense on the cathodic oxygen reduction electrocatalysts holds a large portion. It is because the precious platinum (Pt) and its alloys are still the most effective oxygen reduction reaction (ORR) catalysts, which play an essentia...

The inhibitively high cost of the noble‐metal‐containing materials has become a major obstacle for the large‐scale application of rechargeable zinc‐air batteries (ZABs). To solve this problem in a practical way, a green and scalable method to prepare sandwich‐like reduced graphene oxide /carbon black/amorphous cobalt borate nanocomposites (rGO/CB/C...

Platinum (Pt) is the state-of-the-art catalyst for oxygen reduction reaction (ORR), but its high cost and scarcity limit its large-scale use. However, if the usage of Pt reduces to a sufficiently low level, this critical barrier maybe overcome. Atomi-cally dispersed metal catalysts with high activity and high atom efficiency endow them with the pos...

Cobalt diselenide (CoSe2) has been demonstrated to be an efficient and economic electrocatalyst for oxygen evolution reaction (OER) both experimentally and theoretically. However, the catalytic performance of up-to-now reported CoSe2-based OER catalysts is still far below commercial expectation. Herein, we report a hybrid catalyst consisting of CoS...

Newly N-S-C coordination-structured active sites, originating from the integrity of edged thiophene S, graphitic N, and pentagon defects, were reconstructed by N-modified S defects in carbon aerogel with a 3D hierarchical macro-meso-microporous structure. This metal-free material exhibited outstanding oxygen reduction reaction (ORR) activity (e.g.,...

Sustainable hydrogen production is an essential prerequisite for realizing the future hydrogen economy. The electrocatalytic hydrogen evolution reaction (HER), as the cornerstone of exploring the mechanism of water electrolysis, has attracted extensive interest in the past decades. Carbon‐based materials with significant merits such as abundance, l...

Sonagashira-Hagihara coupling reaction is utilized to fabricate the ethynyl-linked phthalocyanine (Pc) 2D conjugated polymers (CPs), affording the unprecedented heterometallic compound Fe0.5Co0.5Pc-CP and homometallic analogues MPc-CPs (M = Fe, Co) as comparisons. It is confirmed that the Fe and Co ions are well-defined/distributed with one metal i...

Defects in the catalyst are considered to be important for generating the active sites for electrocatalytic reactions, due to the changed distribution of the charge density. In this work, Li vacancy defects are purposely created in a series of one-dimensional (1D) porous multi-shell Li(NixCoyMnz)O2 hollow fibers by a facile electrochemical lithium...

Carbon-based materials have been attracting numerous interests for electrocatalysis due to various merits such as abundance, low cost, high conductivity and tunable molecular structures. However, to date, the electrochemical activities of these electrocatalysts are mainly attributed to different active dopants (e.g., N, B, P or S), leading to a com...

The oxygen evolution reaction (OER) represents the rate-determining step of electrocatalytic water splitting into hydrogen and oxygen. Creating oxygen vacancies and adjusting their density has proven to be an effective strategy to design high-performance OER catalysts. Herein, a hydrogenation method is applied to treat a two-dimensional (2D) iron-c...

Transition metal phosphides (TMPs) have emerged as highly active catalysts for the hydrogen evolution reaction (HER). Herein, we report a novel excellent CoP3/Ni2P catalyst for the HER with a small onset potential of 51 mV vs. RHE, a low Tafel slope of 49 mV dec⁻¹, a small over-potential value of 115 mV at 10 mA cm⁻², and outstanding long-term stab...

Perovskite-type borohydride, NH4Ca(BH4)3, is considered as a promising hydrogen storage material due to its high gravimetric hydrogen capacity (15.7 wt%). In this work, the dehydrogenation performance and reaction pathway of NH4Ca(BH4)3 have been systematically investigated. It is found that the initial decomposition temperature is only 65 °C, sugg...

Efficient yet cost-effective electrode materials play deciding roles in the widespread application of fuel cells, as precious metals, such as platinum (Pt), remain the main component of the cathodic oxygen reduction reaction (ORR) electrocatalyst. Herein, a type of biomass, macadamia nut shell (MNS), is utilized for synthesizing ORR catalysts, aimi...

Downsizing the catalyst to atomic scale provides an effective way to maximize the atom efficiency and enhance activity for electrocatalysis. Here, we report a concept whereby graphene defects trap atomic Ni species (aNi) inside to form an integrity (aNi@defect). X-ray adsorption characterization and density-functional-theory calculation revealed th...

Biomass product 5-hydroxymethylfurfural (5-HMF) can be used to synthesize a broad range of value added compounds currently derived from petroleum. Thus, the effective conversion of glucose or cellulose (the major components of biomass) into fuels and chemical commodities has been capturing increasing attentions. Previous studies have been extensive...