Electrocatalysts For Methanol Oxidation Reaction Research Articles

Porphyrinic MOF derived Single-atom electrocatalyst enables methanol oxidation

Electrochemical methanol oxidation reaction (MOR) serves as a key route for renewable energy technologies. However, unmet challenges remain in the preparation of low-cost, efficient and robust electrocatalysts for MOR. Herein, a porphyrinic metal–organic framework (MOF) with spatially isolated Ni centres is prepared. Upon pyrolysis, this affords a single-atom Ni implanted nitrogen-doped porous carbon (20% Ni-N-C). Integrating abundant and accessible single-atom Ni sites, hierarchical porosity, excellent conductivity with stable Ni-N4 moieties all in one, the derived ultra-stable 20% Ni-N-C exhibits high MOR activity, impressive durability and CO tolerance, thereby outperforming state-of-the-art nonprecious metal based electrocatalysts. Computational insights reveal a low energy barrier of 1.19 eV for the rate-determining step, in agreement with the experimental observations of superior MOR activity. As the first foray into improving MOR efficiency with nonprecious metal based single-atom electrocatalysts, the yet-unrealized potential for MOFs and related modular hybrids is demonstrated.

3D Nanohybrid of MoS2 nanocoils functionalized carbon xerogels for methanol electro-oxidation

Searching for suitable low-cost electro-catalysts for methanol oxidation with high stability is a big challenge. Here, we report the successful preparations of carbon xerogels (CX) derived from resorcinol and formaldehyde monomors. Carbon xerogel was further functionalized with transition metals and transition metal dichalcogenides namely; Mo, W, MoS2 and WS2 through the hydrothermal process in presence of nickel foam (NF). These binder free nanocomposites were employed as electro-catalysts for methanol oxidation reaction (MOR). An outstanding electrochemical activity for MoS2/CX/NF electro-catalyst for MOR was observed that delivered high current density of about 550 mA‧cm−2 and long-term stability. This outstanding electro-catalytic performance towards MOR for MoS2/CX are due to the unique nanocoil structure of MoS2, which increases mesoporosity and active surface area, allowing for sufficient electrical conductive channels and pathways for electrons. This work could introduce a promising electro-catalyst for large scale commercial fuel cell applications.

NiCoPd Inlaid NiCo-Bimetallene for Efficient Electrocatalytic Methanol Oxidation.

Pd-based metallenes have attracted great attention recently as newly burgeoning two-dimensional (2D) materials, attributed to their significantly increased active surface areas and intrinsic electrocatalytic activities. Therefore, they could be used as a potential candidate as the high-performance electrocatalyst for methanol oxidation reactions (MORs) in the direct methanol fuel cell. Herein, a new strategy is proposed to fabricate NiCoPd inlaid NiCo-bimetallene (NiCoPd/NiCo-bimetallene) by the structure directing effect of 18-crown-6 ether under an ultrasonic-pulse interface together with the HCHO reduction and atom-diffusion-aging process. NiCoPd ternary-alloys with uniformly dispersed Pd active sites are decorated onto NiCo-bimetallenes, achieving remarkably enhancing the effective utilization of Pd atoms. What is more, the intrinsic activity is enhanced by the "bifunctional mechanism" of NiCo-bimetallene adsorption of intermediate species and increased Pd-active sites. Moreover, the anti-CO poisoning ability is optimized through the "alloying ligand effect" of NiCoPd. Therefore, the NiCoPd/NiCo-bimetallene exhibits excellent mass activity for MOR, which is higher than commercial Pd/C. This work suggests a new way of the Pd-based metallenes catalyst approach to the efficient electrocatalytic MOR.

Hierarchical NiCo2O4/CuO-C nanocomposite derived from copper-based metal organic framework and Ni/Co hydroxides: Excellent electrocatalytic activity towards methanol oxidation

In this work, a metal-organic framework (Cu-MOF) and two none-precious metals (Ni and Co) are used for preparation of a highly efficient electrocatalyst for methanol oxidation reaction. Nickel/cobalt hydroxides are coprecipitated on Cu-MOF in alkaline solution. The composite is then calcinated at 350 °C to obtain a carbonaceous framework and flower-like NiCo2O4 deposits (CuO-C/NiCo2O4). The obtained composite is characterized by several methods (XRD, XPS, FT-IR, SEM, TEM, and electrochemical techniques). The presence of metal oxides CuO and NiCo2O4 in the prepared electrocatalyst is confirmed by XRD and XPS methods. CuO-C/NiCo2O4 shows excellent catalytic activity towards MOR in alkaline solution (NaOH, 1 M). The electrocatalytic activity of CuO-C/NiCo2O4 is compared to stepwise composites (CuO-C/NiO, CuO/CoO, NiCo2O4) and commercial Pt/C, which confirms the superiority of the proposed catalyst in terms of current density (208.1 mA cm−2) and amperometric stability (7000 s) in methanol oxidation reaction. The observed benefits are attributed to synergistic effects between the porous conductive carbonaceous material and multi transition-metal oxides (CuO and NiCo2O4).

Boron and nitrogen codoped carbon nanohorn-supported Pt nanocrystals as highly-efficient methanol oxidation electrocatalysts

The large-scale commercialization of direct methanol fuel cells (DMFCs) largely depends on the design and synthesis of advanced Pt-based anode catalysts with excellent electrocatalytic performance and acceptable costs. Herein, we propose a controllable and scalable method to the construction of ultrafine Pt nanocrystals supported by boron and nitrogen codoped carbon nanohorns (Pt/BN-CNH) as electrocatalysts for methanol oxidation reaction. The as-derived Pt/BN-CNH architectures are endowed with a series of interesting physicochemical properties, such as accessible internal pores, numerous active conical tips, coexistence of B and N atoms, and homogeneous Pt distribution. Consequently, the resulting Pt/BN-CNH catalysts present high catalytic activity, reliable long-term stability as well as strong antipoisoning capacity towards methanol oxidation, all of which are superior to those of conventional Pt/carbon black, Pt/carbon nanotube, Pt/graphene and Pt/undoped CNH catalysts, thus offering great potentials in the next-generation DMFC devices.

Facile and Surfactant‐Free Routed Spherical Au@Pt Core–Shell–Satellite Nanoparticles as High‐Efficient and Stable Electrocatalyst for Methanol Oxidation

The spherical Au@Pt core–shell–satellite nanoparticles (NPs) are fabricated via a facile, efficient, and surfactant‐free method of seed‐mediated growth, and the electrocatalytic performance toward the methanol oxidation reaction (MOR) is systematically researched by cyclic voltammetry. Compared with commercial Pt/C, all the obtained Au@Pt NPs with such a core–shell–satellite structure exhibit greatly enhanced electrocatalytic activity and long‐term stability toward MOR. Among them, Au90@Pt10 NPs with less loading of Pt exhibit the most significantly enhanced electrocatalytic performance with a mass activity of 1.470 A mgPt−1, approximately 13 times that of commercial Pt/C (0.111 A mgPt−1) and specific activity (1.469 mA cm−2) approximately 9 times that of commercial Pt/C (0.157 mA cm−2). Au95@Pt5 NPs have the highest value of the oxidation current density (0.2615 mA cm−2), corresponding to 62.8% of its initial maximum value (0.4165 mA cm−2), showing higher stability at approximately 4000 s. Such a surfactant‐free synthesis technique of Au@Pt bimetallic NPs may be a simple method to prepare self‐supported bimetallic nanostructures, which is important to develop highly effective electrocatalysts for MORs.

Highly Loaded Independent Pt0 Atoms on Graphdiyne for pH-General Methanol Oxidation Reaction.

The emergence of platinum‐based catalysts promotes efficient methanol oxidation reactions (MOR). However, the defects of such noble metal catalysts are high cost, easy poisoning, and limited commercial applications. The efficient utilization of a low‐cost, anti‐poisoning catalyst has been expected. Here, it is skillfully used N‐doped graphdiyne (NGDY) to prepare a zero‐valent platinum atomic catalyst (Pt/NGDY), which shows excellent activity, high pH adaptability, and high CO tolerance for MOR. The Pt/NGDY electrocatalysts for MOR with specific activity 154.2 mA cm−2 (1449.3 mA mgPt −1), 29 mA cm−2 (296 mA mgPt −1) and 22 mA cm−2 (110 mA mgPt −1) in alkaline, acid, and neutral solutions. The specific activity of Pt/NGDY is 9 times larger than Pt/C in alkaline solution. Density functional theory (DFT) calculations confirm that the incorporation of electronegativity nitrogen atoms can increase the high coverage of Pt to achieve a unique atomic state, in which the shared contributions of different Pt sites reach the balance between the electroactivity and the stability to guarantee the higher performance of MOR and durability with superior anti‐poisoning effect.

Review and Development of Anode Electrocatalyst Carriers for Direct Methanol Fuel Cell

Direct methanol fuel cell (DMFC) can be used as a promising portable power device due to its excellent energy conversion efficiency and low pollutant emissions. The performance of DMFC largely depends on the anode electrocatalyst for methanol oxidation reaction (MOR). As an important part of the electrocatalyst, the carrier greatly affects the activity and stability of the electrocatalyst. Herein, the research progress of carbonaceous carriers (such as activated carbon, nanostructured carbon), noncarbonaceous carriers (metal compounds), and conducting polymers in DMFC is reviewed. Furthermore, an overview of the development of self‐supporting carriers for flexible DMFC electronics is presented. Its role as the most ideal DMFC carrier in the future provides new ideas for the challenges and development of the commercialization of flexible DMFC.

Laser-Assisted synthesis of Bi-Decorated Pt aerogel for efficient methanol oxidation electrocatalysis

Improving the activity and stability of electrocatalysts for methanol oxidation reaction (MOR) is key important for the large-scale application of direct methanol fuel cells (DMFCs). Herein, we provide a novel scheme to firstly build Bi-decorated Pt aerogel through the structural reconstruction of Pt/Bi2O3 interface, which demonstrates an excellent mass activity of 7.99 A mg-1Pt in MOR (8-fold higher than that of commercial Pt/C). Experimental results show that the synergistic effect between Bi0 species and Pt aerogel is the major cause of the improvement of the catalytic activity. In-suit Fourier transform infrared (FTIR) Spectroscopy results indicated that the generation and transformation of HCOO– intermediate are accelerated. Density functional theory (DFT) calculations indicate that the decorated Bi enhances the adsorption of OH species on the adjacent Pt site, which can facilitate the dehydrogenation of methanol and the removal of poisonous CO species. Thus, the electro-catalytic performance can be improved. This strategy can be extended to construct other types of interfaces, which may open new routes for the synthesis of highly efficient electrocatalysts.

Silk‐Derived N‐Doped Fe@NPC as Efficient Bifunctional Electrocatalyst for Direct Methanol Fuel Cell (DMFC)

AbstractThe development of economic and efficient bifunctional electrocatalysts, which can boost both the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) is quite necessary for the evolution of direct methanol fuel cell (DMFC). Herein, a novelty of precious metal‐free, iron, nitrogen and phosphorus‐doped porous carbon (Fe@NPC) was prepared by using cheap and renewable biomass silk as basic nitrogen sources, as an efficient ORR and MOR electrocatalyst with its high nitrogen content (8.16 wt%). The Fe@NPC catalyst exhibits extremely high onset potential (1.125 V vs RHE), current density (−6.089 mA cm−2) and methanol tolerance for ORR, even exceeds the corresponding values of Pt/C (1.007 V vs RHE, 5.068 mA cm−2). Furthermore, it also served as a good carrier for Pt nanoparticles (NPs). Pt/Fe@NPC shows high catalytic activity and stability for MOR in acidic condition.

Design of Co-Sn bimetallic nanoalloys as electrocatalyst for alkaline methanol oxidation reaction: Exploring the effect of electroactivation process

The engineering of cost-effective and durable electrocatalysts for the methanol oxidation reaction (MOR) is required for the commercialization of direct methanol fuel cells (DMFCs). Herein, a series of Cox-Sn100-x alloy nanoparticles were synthesized to optimize the Co/S ratio, and the alloy nanoparticle which offered the best electrochemical performance towards MOR was employed as electrocatalyst for further experiments. Moreover, two different electroactivation approaches including i) activation in phosphate buffer medium, and ii) in-situ activation were explored to enlighten their effect on electrochemical characteristics of nanocatalyst. In this regard, the chronoamperometry measurements were carried out at a constant potential over a fixed period of 300 s. Additionally, the pH of the phosphate buffer solution in a range of 3–12, the activation potential ranging −0.7 V to −2.0 V were optimized by evaluating the recorded cyclic voltammograms. Moreover, to predict the effect of phosphate buffer pH in the activation process on the electrocatalytic activity of catalyst were artificial neural network (ANN) approach was implemented. Amongst the various nanoalloys, Co65-Sn35 nanoparticles were determined as the optimal one thanks to their uniform dispersion and less aggregation feature. In the activation process with phosphate buffer at pH of 10 was determined as the optimal, and at this condition a hydrogen evolution reaction also occurred in the range of applied activation potential. The findings revealed that activation in phosphate buffer solution led to the formation of more –OH species, thereby boosting the electrocatalytic activation towards MOR in alkaline media. Similarly, for the in-situ activation approach, the optimum potential was determined as −1.3 V to achieve the maximum current density. The findings offered that the electroactivation in phosphate buffer solution (pH = 10) at −1.3 V could result in a highly active electrocatalyst to be utilized in alkaline DMFCs. This research lays the door for tailoring high-performance, low-cost electrocatalysts that could be used in energy conversion systems instead of commercial noble-metal-based electrocatalysts.

Promoting Effect of Gd2O3 in Pt-Gd2O3/C Electrocatalyst for Methanol Oxidation Reaction

Metal oxides have been used as supports and promoters to enhance the electrocatalytic activity of Pt/C for methanol oxidation reaction (MOR). In this work, Gd2O3 prepared by simple precipitation method (Gd2O3(PC)) and polymer-assisted method (Gd2O3(PL)) is examined as support for Pt/C. The Gd2O3 samples are characterized by FTIR, HR-SEM, and PXRD. The ease of surface oxygen exchange and formation of surface –OH groups are better in the case of Gd2O3(PC) for MOR activity. The microwave-assisted polyol reflux method is used to prepare Pt-Gd2O3(PC)/C and Pt-Gd2O3(PL)/C) electrocatalysts. Electrocatalysts are characterized by XPS, ICP, TEM, PXRD, and examined by cyclic voltammetry (CV), CO stripping experiments, chronopotentiometry (CP), and chronoamperometry (CA) in acidic media. The MOR activity of Pt-Gd2O3(PC)/C is found to be 2.8 times higher than commercial Pt/C with good anti-poisoning activity. This result is further corroborated by the first principle calculations which show that there is significant electron transfer from Pt/Gd2O3 to adsorbed CO. This electron transfer reduces the Gibbs free energy for CO adsorption and decreases the CO poisoning. The overall benefit of Gd2O3 is to increase the performance of Pt electrocatalyst for methanol oxidation.

Enhanced methanol electrooxidation by electroactivated Pd/Ni(OH)2/N-rGO catalyst

Direct methanol fuel cells, in which electrocatalytic oxidation of methanol takes place, are one of the most promising technologies for facilitating the shift to renewable energy sources. However, they still suffer from high-catalyst-prices, as well as sluggish kinetics of methanol oxidation reaction (MOR). Therefore, herein, palladium/Nickel(II) hydroxide/nitrogen doped reduced graphene oxide (Pd/Ni(OH)2/N-rGO) hybrid was fabricated via facile two-step solution method and utilized as electrocatalyst for MOR. The in-situ electrochemical activation pre-treatment was proposed to engineer a highly active electrocatalyst. The Pd/Ni(OH)2/N-rGO, which had distinctive structural features along with robust synergistic effects, outperformed the commercial Pd electrocatalyst in terms of catalytic activity towards MOR, with elevated anodic peak current density values. The in-situ electrochemical activation pre-treatment lead to 3.3, 3.0, and 2.0-fold increase in activity of Pd/Ni(OH)2/N-rGO, Pd/N-rGO, and Pd/C, respectively. This research lays the door for a unique technique to manufacture high-performance, low-cost electrocatalysts that might be used in fuel cell technology instead of existing Pd electrocatalysts.

Rational design ternary platinum based electrocatalysts for effective methanol oxidation reaction

Exploring effective, durable, and affordable electrocatalysts of methanol oxidation reaction (MOR) is of vital significance for the industrial application of direct methanol fuel cells. Herein, an efficient, general, and expandable method is developed to synthesis two-dimensional (2D) ternary PtBiM nanoplates (NPLs), in which various M (Co, Ni, Cu, Zn, Sn) is severed as the third component to the binary PtBi system. The MOR performance of PtBiM NPLs is entirely investigated, demonstrating that both the MOR activity and durability is enhanced with the introduction of the additional composition. Pt3Bi3Zn NPLs shows much higher MOR activity and stability than that of the PtBi counterparts, not to mention the current advanced PtRu/C and Pt/C catalysts. The prominent performances are attributed to the modulated electronic structure of the surface Pt in PtBi NPLs by the addition of Zn, resulting in a weakened affination between Pt and the adsorbed poisoning species (mainly CO) compared with PtBi NPLs, verified by density functional theory (DFT) calculations. In addition, the absorbed OH can be generated on the surface of Zn atom due to its favorable water activation properties, thus the CO removal on the adjacent Pt atoms is accelerated, further leading to a high activity and anti-poisoning performance of the resulting Pt3Bi3Zn catalyst. This work provides new insights and robust strategy for highly efficient MOR electrocatalyst with extraordinary anti-poisoning performance and stability.

Rhombic dodecahedral PtCo nanocrystals as a highly active electrocatalyst for methanol oxidation reaction

Platinum-based alloys have always been considered as more efficient and economical electrocatalysts for methanol oxidation reaction (MOR) compared with the traditional monometallic Platinum catalysts. Among them, PtCo bimetallic alloys are typical representatives which in many cases display prominent catalytic properties. Herein, rhombic dodecahedral PtCo nanocrystals (PtCo RDs) were obtained by a simple solvothermal method by using ascorbic acid as the reducing agent and cetyltrimethylammonium chloride (CTAC) as the stabilizing and structure-directing agent. The resultant PtCo RDs exhibit remarkably enhanced catalytic activity toward MOR in comparison with the commercial Pt/C catalyst. Its specific and mass activities are 3.8 mA/cm2 and 0.76 A/mg, respectively, which are 6.3 times and 2.5 times that of Pt/C catalyst. Moreover, the PtCo RDs show improved catalytic stability. We hope that this research can provide new insight into the design of catalysts in this field.

Three-dimensional Ni-MoN nanorod array as active and non-precious metal electrocatalyst for methanol oxidation reaction

• Three-dimensional Ni-MoN nanorod array electrocatalyst is facilely designed and synthesized. • The nitridation process ensures the uniform distribution of active Ni sites across the robust MoN nanorods. • The constructed Ni-MoN nanorod array exhibits a promising electrocatalytic activity towards methanol oxidation reaction. The development of direct methanol fuel cells requires low-cost, non-noble-metal electrocatalysts. However, it has not been widely used because of its limited activity, poor durability, and slow kinetics. Herein, the 3D nanostructured arrays of Ni-MoN composite nanorods were facilely prepared on the nickel foam (Ni-MoN NR/NF), which involves the direct hydrothermal synthesis of NiMoO 4 on NF and further nitridation treatment in the atmosphere of ammonia. The nitridation ensures the uniform distribution of active Ni sites across the robust MoN nanorods. Owing to the collaborative effect of Ni and the specific 3D MoN nanorod structure, the Ni-MoN NR/NF exhibits a promising electrocatalytic activity towards methanol oxidation reaction (MOR), which shows excellent activity (374 mA cm −2 @0.8 V vs. Hg/HgO), fast kinetics (40 mV dec −1 for the Tafel slope) and good stability. This work has shed light on the design of high-performance non-noble-metal electrocatalysts for MOR.

Construction of Bi-component CoNi nanosheet coated TiO2 nanotube arrays for photocatalysis-assisted poisoning tolerance toward methanol oxidation reaction

Transition metal-based materials are an excellent alternative high cost Pt and Pt-group metals as the anode material in direct methanol fuel cells (DMFCs). However, similar to Pt-based anode, these catalysts can also be poisoned by the by-product intermediates produced by methanol oxidation reaction (MOR). In this study, CoNi bi-component nanosheets were anchored onto the wall of spaced TiO2 nanotube arrays (TiO2 @CoNi) using a hydrothermal modification strategy and acted as a nonprecious metal electrocatalyst for MOR. Importantly, benefitting from the construction of the p-n heterojunction, the photogenerated electron-hole pairs can be effective separated. The holes are utilized for the decomposition of intermediate species adsorbed on the catalyst surface, thus releasing the occupied active sites. The as-formed TiO2 @CoNi hybrid displays remarkably improved intermediate-poisoning resistance ability and elevated electrocatalytic stability for MOR with the assistance of solar-light irradiation. This study provides an innovative strategy to design catalysts with tolerance for poisoning intermediates in MOR application, thus slowing down the drop of catalyst activity.

CoFe2O4 NPs supported on graphitic carbon nitride as inexpensive electrocatalysts for methanol oxidation reaction

Electrochemical methanol oxidation (MOR) is considered an efficient route for generating clean energy with low pollutant emissions. In this study, we synthesized graphitic carbon nitride (GCN/g-C3N4) supported CoFe2O4 with different weights (100, 200, and 300 mg) of GCN by using the hydrothermal synthesis method; the synthesized cost-effective electrocatalysts have been denoted as g-CF1, g-CF2, and g-CF3 respectively. The electrochemical performance of the synthesized catalysts was studied using cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) techniques. In an alkaline medium, the g-CF2 electrocatalyst showed the best MOR activity, a larger electrochemically active surface area, and better stability compared to those of pure GCN, g-CF1, and g-CF3 electrocatalysts.

Physicochemical properties and antibacterial activity of Pt nanoparticles on TiO2 nanotubes as electrocatalyst for methanol oxidation reaction

TiO2 nanotubes were prepared electrochemically as pure Ti sheet in 0.5% HF anodized and annealed under nitrogen acquiring the TiO2 NTs-N2 support. By chemical deposition method using NaBH4 as reducing agent, platinum was deposited on TiO2 NTs-N2 support to gain the Pt NPs/TiO2 NTs-N2 electrocatalyst.Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were applied for the physicochemical characterization of TiO2 NTs-N2 and Pt NPs/TiO2 NTs-N2. The XRD exhibited the an existence of platinum nanoparticles with an average crystallite size of 12 nm, which was regularly combined with TiO2 nanotubes. The Pt NPs/TiO2 NTs-N2 catalyst indicated considerably high electrocatalytic activity and stability for methanol electrocatalytic oxidation reaction in basic medium of KOH. The catalyst Pt NPs/TiO2 NTs-N2 was electrochemically characterized in a basic solution of methanol using cyclic voltammetry (CV) measurement in the absence and an existence of light. The higher poison tolerance and higher methanol oxidation current density observed for the Pt NPs/TiO2 NTs-N2 catalyst suggest that this catalyst supported on TiO2 NTs-N2 has a promising potential applications in the electro catalyst reactions. In addition, the synthesized platinum nanoparticles deposited on TiO2 nanotubes revealed a tremendous antibacterial effects against pathogenic microorganismm.

Low-temperature N-anchored ordered Pt3Co intermetallic nanoparticles as electrocatalysts for methanol oxidation reaction.

To enhance nanocatalyst performance and durability for the methanol oxidation reaction (MOR) in a direct methanol fuel cell, small-sized (2.1 nm) and structurally ordered Pt3Co intermetallic nanoparticles are uniformly anchored onto nitrogen-doped carbon nanotubes (N-CNTs) via a low-temperature N-anchoring method, and the N-doping abilities of different N-containing reagents are compared. After investigating the microstructure of Pt3Co/N-CNTs and evaluating their catalytic activity for the MOR, the results show that N-doping facilitates the uniform loading of Pt3Co NPs and plays a crucial role in improving the electrocatalytic activity of Pt3Co NPs supported on CNTs. Pt3Co/N-CNT-M with melamine as the N dopant exhibits the highest MOR activity and stability among all N-CNT-supported Pt3Co NPs and Pt/N-CNT-M. Density functional theory calculations suggest that the doping of N enhances the binding energy of CNTs to Pt3Co NPs, and the MOR mechanism shows that the introduction of Co is the reason for the enhancement of MOR reaction kinetics. The excellent electrochemical performance of Pt3Co/N-CNT-M is mainly attributed to the synergistic effect of N and Pt3Co intermetallic nanoparticles. The combination of ordered alloy nanoparticles and high-performance carrier N-CNT-M described herein exhibits great potential for fuel cells and may provide an unequivocal direction for the optimization of catalyst performance.