Electrocatalyst For Oxidation Research Articles

Harvesting high-performance electro-water oxidation and selective MB degradation through dual functional Gd2O3–La2O3 photo-electrocatalysts

Interestingly, catalytic oxygen evolution reaction (OER) in an alkaline medium with minimizing the overpotential is the most trustworthy electrocatalyst for the output of hydrogen energy from copious water electrochemical activity. Currently, amalgamated trivalent cations metal oxides have gained desirability as a low-cost anode electrocatalyst to replace noble metal-supported electrocatalysts for water oxidation and are also used for photo-degradation applications. In the present work, we have successfully synthesized Gd2O3 supported La2O3 composites via hydrothermal pathways for efficient OER and selective methylene blue (MB) degradation applications. XRD, UV–Vis DRS, FT-IR, XPS, SEM-EDX, HR-TEM, DLS, and BET analyzers confirmed the successful synthesis of photo-electrocatalysts. Gd2O3–La2O3 composites achieved 5.66 and 3.37-fold larger surface areas than La2O3 and Gd2O3, respectively. The results of the Gd2O3 supported La2O3 composite electrode demonstrated better OER performance under 1 M KOH, and it exhibited a lower Tafel slope and overpotential of 72 mV dec−1 and 310 mV at 10 mA cm−2. A chronoamperometry examination confirms that the fabricated Gd2O3–La2O3 electrode has good stability at a fixed potential of 1.540 V vs. RHE for water oxidation. Although the, Gd+3 inspired La2O3 electrode actively takes part in OER activity owing to its high Cdl value of 40.222 μF cm−2. The selective degradation of MB dye using the Gd2O3–La2O3 composite achieved an acceptable degradation efficiency of 84.80 % compared to other pollutants under UV-light irradiation for 120 min, and the specified pH condition is 9 for the degradation of MB dye, and it follows the first-order kinetics model. Notably, post-OER and photocatalytic results exhibited good stability and reusability characteristics. Therefore, the Gd2O3–La2O3 catalyst can be used for real-time water oxidation and MB dye removal from polluted water.

Ultrasonic-assisted Fenton reaction inducing surface reconstruction endows nickel/iron-layered double hydroxide with efficient water and organics electrooxidation

Nickel/iron-layered double hydroxide (NiFe-LDH) tends to undergo an electrochemically induced surface reconstruction during the water oxidation in alkaline, which will consume excess electric energy to overcome the reconstruction thermodynamic barrier. In the present work, a novel ultrasonic wave-assisted Fenton reaction strategy is employed to synthesize the surface reconstructed NiFe-LDH nanosheets cultivated directly on Ni foam (NiFe-LDH/NF-W). Morphological and structural characterizations reveal that the low-spin states of Ni2+ (t2g6eg2) and Fe2+ (t2g4eg2) on the NiFe-LDH surface partially transform into high-spin states of Ni3+ (t2g6eg1) and Fe3+ (t2g3eg2) and formation of the highly active species of NiFeOOH. A lower surface reconstruction thermodynamic barrier advantages the electrochemical process and enables the NiFe-LDH/NF-W electrode to exhibit superior electrocatalytic water oxidation activity, which delivers 10 mA cm−2 merely needing an overpotential of 235 mV. Besides, surface reconstruction endows NiFe-LDH/NF-W with outstanding electrooxidation activities for organic molecules of methanol, ethanol, glycerol, ethylene glycol, glucose, and urea. Ultrasonic-assisted Fenton reaction inducing surface reconstruction strategy will further advance the utilization of NiFe-LDH catalyst in water and organics electrooxidation.

Synthesis of spinel Nickel Ferrite (NiFe2O4)/CNT electrocatalyst for ethylene glycol oxidation in alkaline medium

Nickel-iron-based spinel oxide was prepared and supported on multi-walled carbon nanotubes to enhance the electrochemical oxidation of ethylene glycol in an alkaline medium. NiFe2O4 was prepared using facile sol-gel techniques. Then the prepared material was characterized using different bulk and surface techniques like powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and transmitted electron microscope (TEM). Different electrodes of NiFe2O4/CNT ratios were prepared to find out the optimum spinel oxide/CNT ratio. The activity of the metal spinel oxides composite was characterized toward ethylene glycol conversion by different electrochemical techniques like cyclic voltammetry (CV), Chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The modified electrode reached an oxidation current of 43 mA cm−2 in a solution of 1.0 M ethylene glycol and 1.0 M NaOH. Furthermore, some kinetics parameters (like diffusion coefficient, and rate constant) were calculated to evaluate the catalytic performance. Additionally, the electrode showed extreme stability for long-term ethylene glycol oxidation.

CeVO4 Nanosheets as Bifunctional Electrocatalysts for Glycerol Oxidation and Hydrogen Peroxide Sensing

CeVO₄ Nanosheets as Bifunctional Electrocatalysts for Glycerol Oxidation and Hydrogen Peroxide Sensing

Covalent Transition Metal Borosilicides: Reaction Pathways in Molten Salts for Water Oxidation Electrocatalysis.

The properties of transition metal borides and silicides are intimately linked to the covalent character of the chemical bonds within their crystal structures. Bringing boron and silicon together within metal borosilicides can then engender different competing covalent networks and complex charge distributions. This situation results in unique structures and atomic environments, which can impact charge transport and catalytic properties. Metal borosilicides, however, hold the status of unusual exotic species, difficult to synthesize and with poor knowledge of their properties. Our strategy consists of developing a redox pathway to synthesize transition metal borosilicides in inorganic molten salts as high-temperature solvents. By studying the formation of Ni6Si2B, Co4.75Si2B, Fe5SiB2, and Mn5SiB2 with in situ X-ray diffraction, we highlight how new reaction routes, maintaining covalent structural building blocks, draw a general scheme of their formation. This pathway is driven by the covalence of the chemical bonds within the boron coordination framework. Next, we demonstrate high efficiency for water oxidation electrocatalysis, especially for Ni6Si2B. We ascribe the strongly increased resistance to corrosion, high stability, and electrocatalytic activity of the Ni6Si2B-derived material to three factors: (1) the two entangled boron and silicon covalent networks; (2) the ability to codope with boron and silicon an in situ generated catalytic layer; and (3) a rare electron enrichment of the transition metal by back-donation from boron atoms, previously unknown within this compound family. With this work, we then unveil a new chemical dimension for Earth-abundant water oxidation electrocatalysts by bringing to light a new family of materials.

Impact of Fe2(MoO4)3 and ZnMoO4 on CO Tolerance of Pt/C catalysts for enhanced methanol electrooxidation efficiency

Success of Pt/C catalyst in electrooxidation of methanol is highly influenced by its ability to withstand the poisoning effects of carbonaceous species adsorbed on the catalytic surface. Covalently bonded CO molecules occlude the active sites of the catalytic surface, impeding methanol adsorption. In this study, Pt/C-based nanocomposite catalysts were synthesized incorporating Fe2(MoO4)3 and ZnMoO4 to form heterojunctions through intermittent microwave-assisted polyol method to augment the CO oxidation pathway by introducing hydroxy groups adsorbed on their surfaces. Thorough characterization of the catalysts elucidated their chemical and phase purity, bonding configurations, and oxidation states, with various electroanalytical techniques employed to probe the mechanism of activity enhancement. Furthermore, the distinctive electron density profiles of these molybdate species have been identified as potential facilitators of methanol adsorption on the platinum surface. Equimolar composition in formulating the composite catalysts yielded a fivefold increase in catalytic activity (with ZnMoO4) and a 1.5-fold increase (with Fe2(MoO4)3). This approach demonstrates promise for tailoring Pt/C catalysts to develop industrially viable CO-tolerant and highly stable electrocatalysts.

Oxygen-deficient annealing boosts performance of CoNiFe oxide electrocatalyst in oxygen evolution reaction

Mixed oxides of transition metals have emerged as promising catalysts for the oxygen evolution (OER) reaction in alkaline water electrolysis. Since OER is significantly slower than hydrogen evolution, developing stable and easily accessible materials that effectively promote OER is one of the keys to improving overall efficiency. In this context, we present a promising method for preparing Co-Ni-Fe oxides which is based on a straightforward sol–gel procedure. Key to success is a thermal treatment under oxygen-deficient atmosphere, which renders superior electrocatalytic properties compared to a treatment under reductive and aerobic conditions, respectively. Attractive performance characteristics are thereby obtained, e.g., a η10 value of 291 mV and a Tafel slope of 32 mV dec−1. The impact of the annealing conditions on the material properties has been elaborated using cyclic voltammetry, impedance spectroscopy, and structural analyses. Stability and strong performance under practical conditions were confirmed in long-term studies using an AEM electrolyzer.

Transfer learning guided discovery of efficient perovskite oxide for alkaline water oxidation

Perovskite oxides show promise for the oxygen evolution reaction. However, numerical chemical compositions remain unexplored due to inefficient trial-and-error methods for material discovery. Here, we develop a transfer learning paradigm incorporating a pre-trained model, ensemble learning, and active learning, enabling the prediction of undiscovered perovskite oxides with enhanced generalizability for this reaction. Screening 16,050 compositions leads to the identification and synthesis of 36 new perovskite oxides, including 13 pure perovskite structures. Pr0.1Sr0.9Co0.5Fe0.5O3 and Pr0.1Sr0.9Co0.5Fe0.3Mn0.2O3 exhibit low overpotentials of 327 mV and 315 mV at 10 mA cm−2, respectively. Electrochemical measurements reveal coexistence of absorbate evolution and lattice oxygen mechanisms for O-O coupling in both materials. Pr0.1Sr0.9Co0.5Fe0.3Mn0.2O3 demonstrates enhanced OH- affinity compared to Pr0.1Sr0.9Co0.5Fe0.5O3, with the emergence of oxo-bridged Mn-Co conjugate facilitating charge redistribution and dynamic reversibility of Olattice/VO, thereby slowing down Co dissolution. This work paves the way for accelerated discovery and development of high-performance perovskite oxide electrocatalysts for this reaction.

Manganese-Mediated Electrochemical Oxidation of Thioethers to Sulfoxides Using Water as the Source of Oxygen Atoms.

Oxygen-atom transfer reactions are a prominent class of synthetic redox reactions that often use high-energy oxygen-atom donor reagents. Electrochemical methods can bypass these reagents by using water as the source of oxygen atoms through pathways involving direct or indirect (mediated) electrolysis. Here, manganese porphyrins and related mediators are shown to be effective molecular electrocatalysts for selective oxidation of thioethers to sulfoxides, without overoxidation to the sulfone. The reactions proceed by proton-coupled oxidation of a MnIII-OH2 species to generate a MnIV-OH and MnV═O species. This methodology is compared to direct electrolysis methods initiated by single-electron oxidation of the thioether, and chloride-mediated electrochemical oxidation of thioethers. The Mn-mediated reactions operate at lower applied potential and exhibit improved substrate scope and functional group compatibility relative to direct electrolysis, and the tunability of the Mn-based mediators allows for improved performance relative to chloride-mediated electrolysis. An electrochemical parallel screening platform is developed and applied to a library of pharmaceutically relevant thioethers.

Self-Assembly of a Hierarchical Metal-Organic Framework at the Liquid/Liquid Interface via π-π Stacking Manipulations in Organoplatinum(IV) Complexes for Methanol Fuel Cells.

This study focuses on the facile synthesis of the hierarchical architecture of zeolitic imidazolate framework-8 (ZIF-8) films containing an ultrasmall amount of Pt(0) by investigating the synthesis of different organoplatinum complexes and manipulating the π-π stacking effect in these complexes at the liquid/liquid interface. The organometallic Pt(IV) precursors were complexes with a formula of [PtXMe2(R)(bpy)] (bpy = 2,2'-bipyridine; for complex 2, R = CH2CH═CHC6H5 and X = Br; for complex 3, R = CH2CH═CH2 and X = Br; for complex 4, R = Me and X = I) prepared by oxidative addition of cinnamyl bromide, allyl bromide, or methyl iodide to [PtMe2(bpy)] (complex 1). Different thin films were synthesized starting from three organometallic Pt(IV) precursors (i) by reduction of the Pt complexes at the toluene/water interface (TF2-TF4), (ii) by encapsulation of the Pt precursors in a ZIF-8 (TF5-TF7), and (iii) by reduction of the Pt precursors onto a ZIF-8 (TF8-TF10). The self-assembly of ZIF-8 and different organoplatinum precursors at the interface of two immiscible liquids leads to the preparation of films with well-engineered structures such as rhombic dodecahedra, nanorods, hierarchical architectures, and nanowires, which are very difficult and complicated to synthesize under normal conditions. The ultralow loading of platinum complexes with different degrees of π-π stacking of dangling moieties has a great impact on the structure and morphology (directing agent), which in turn drastically changes the catalytic properties. The obtained films were applied as electrocatalysts for methanol oxidation in fuel cells. The electrocatalytic performance of organoplatinum containing a cinnamyl group in hierarchical architecture TF8 was found to be superior to those of nonhierarchical structures.

Pd nanoparticles supported on silver, zinc, and reduced graphene oxide as a highly active electrocatalyst for ethanol oxidation

In this manuscript, we present a facile approach to synthesize a highly active catalyst for the electro-oxidation of ethanol using Pd nanoparticles supported on a Ag–Zn alloy on reduced graphene oxide. This nanocomposite material was fabricated via a two-step process of incineration followed by sol-gel synthesis. The physical properties of the catalyst were evaluated using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning and transmission electron microscopies. To understand the catalyst's activity for ethanol oxidation, we performed a series of cyclic voltammetry and electrochemical impedance spectroscopy experiments in alkaline medium. The catalyst exhibited good catalytic activity with a current density of 13.01 mA cm−2, a value seven times higher than the commercial standard Pd/C catalyst and higher than any other previously reported Pd-based catalyst. The results were attributed synergistic effects between the Pd and alloy support along with the large electrochemically active surface area of the material. Taken together, these results suggest that ethanol electrocatalysts based on nanocomposites of Pd, Ag, and Zn is promising candidates for future ethanol fuel cells.

Component leaching of water oxidation electrocatalysts

AbstractMost electrocatalysts are known to experience structural change during the oxygen evolution reaction (OER) process. Considerable endeavors have been dedicated thus far to comprehending the catalytic process and uncovering the underlying mechanism. During the dynamic evolution of catalyst structure, component leaching of electrocatalysts is the most common phenomenon. This article offers a concise overview of recent findings and developments related to the leaching phenomena in the OER process in terms of fundamental understanding of leaching, advanced characterization techniques used to investigate leaching, leaching of inactive components, and leaching of active components. Leaching behaviors and the induced effects in various kinds of OER catalysts are discussed, progress in manipulating leaching amount/degree toward a tunable surface evolution is spotlighted, and finally, three representative types of structure transformations induced by leaching metastable species in OER condition are proposed. By understanding the process of component leaching in the OER, it will provide more guidance for the rational design of superior electrocatalysts.image

One-step hydrothermal preparation of CeMo-codoped Ni3S2 as robust bifunctional electrocatalyst for urea oxidation and methanol oxidation

The production of hydrogen via electrolytic water splitting is mainly limited by the high overpotential of the oxygen evolution reaction (OER). Thus, the replacement of OER with more thermodynamically favorable urea oxidation (UOR) and methanol oxidation (MOR) reactions shows good promise. In this paper, a CeMo-Ni3S2/NF bifunctional electrocatalyst for UOR and MOR electrolysis was prepared by a one-step hydrothermal method. The experiments reveal that the doped Ce and Mo cations significant modulate the morphology of Ni3S2, and thus significant boost the electrochemically active surface area and increase the UOR and MOR performance. At a current density of 100 mA cm−2, UOR requires a potential of 1.35 V (vs. RHE) and MOR requires 1.38 V (vs. RHE), which are both significantly lower than the potential of 1.59 V (vs. RHE) required for OER. The UOR reaction produces NO2- with a Faradaic efficiency of 69.0 %, while the MOR reaction produces formate with a Faradaic efficiency of 81.5 %. These results provide strategies for the development of advanced MOR and UOR electrode materials.

Nickel-modified poly(aniline-co-pyrrole) as electrocatalyst for electrochemical oxidation of methanol in direct methanol fuel cell application

Nickel-modified poly(aniline-co-pyrrole) as electrocatalyst for electrochemical oxidation of methanol in direct methanol fuel cell application

Rationally Designed L12-Pt2RhFe Intermetallic Catalyst with High CO-Tolerance for Alkaline Methanol Electrooxidation.

It is a grand challenge to deep understanding of and precise control over functional sites for the rational design of highly efficient catalysts for methanol electrooxidation. Here, an L12-Pt2RhFe intermetallic catalyst with integrated functional components is demonstrated, which exhibits exceptional CO tolerance. The Pt2RhFe/C achieves a superior mass activity of 6.43 A mgPt -1, which is 2.23-fold and 3.53-fold higher than those of PtRu/C and Pt/C. Impressively, the Pt2RhFe/C exhibits a significant enhancement in durability owing to its high CO-tolerance and stability. Density functional theory calculations reveal that high performance of Pt2RhFe intermetallic catalyst arises from the synergistic effect: the strong OH binding energy (OHBE) at Fe sites induce stably adsorbed OH species and thus facilitate the dehydrogenation step of methanol via rapid hydrogen transfer, while moderate OHBE at Rh sites promote the formation of the transition state (Pt-CO···OH-Rh) with a low activation barrier for CO removal. This work provides new insights into the role of OH binding strength in the removal of CO species, which is beneficial for the rational design of highly efficient catalysts.

Lithium cation-doped tungsten oxide as a bidirectional nanocatalyst for lithium-sulfur batteries with high areal capacity

Lithium-sulfur (Li-S) batteries are promising for high energy-storage applications but suffer from sluggish conversion reaction kinetics and substantial lithium sulfide (Li2S) oxidation barrier, especially under high sulfur loadings. Here, we report a Li cation-doped tungsten oxide (LixWOx) electrocatalyst that efficiently accelerates the S↔Li2S interconversion kinetics. The incorporation of Li dopants into WOx cationic vacancies enables bidirectional electrocatalytic activity for both polysulfide reduction and Li2S oxidation, along with enhanced Li+ diffusion. In conjunction with theoretical calculations, it is discovered that the improved electrocatalytic activity originates from the Li dopant-induced geometric and electronic structural optimization of the LixWOx, which promotes the anchoring of sulfur species at favourable adsorption sites while facilitating the charge transfer kinetics. Consequently, Li-S cells with the LixWOx bidirectional electrocatalyst show stable cycling performance and high sulfur utilization under high sulfur loadings. Our approach provides insights into cation engineering as an effective electrocatalyst design strategy for advancing high-performance Li-S batteries.

Research on carbon black and cerium co-doped Ti4O7-CB-Ce electrocatalytic oxidation of tetracycline-based antibiotics.

Elemental doping is a promising way for enhancing the electrocatalytic activity of metal oxides. Herein, we fabricate Ti/ Ti4O7-CB-Ce anode materials by the modification means of carbon black and cerium co-doped Ti4O7, and this shift effectively improves the interfacial charge transfer rate of Ti4O7 and •OH yield in the electrocatalytic process. Remarkably, the Ti4O7-CB-Ce anode exhibits excellent efficiency of minocycline (MNC) wastewater treatment (100% removal within 20 min), and the removal rate reduces from 100 to 98.5% after five cycles, which is comparable to BDD electrode. •OH and 1O2 are identified as the active species in the reaction. Meanwhile, it is discovered that Ti/ Ti4O7-CB-Ce anodes can effectively improve the biochemical properties of the non-biodegradable pharmaceutical wastewater (B/C values from 0.25 to 0.44) and significantly reduce the toxicity of the wastewater (luminescent bacteria inhibition rate from 100 to 26.6%). This work paves an effective strategy for designing superior metal oxides electrocatalysts.

Nickel-based metal-organic-frameworks as electrocatalysts for electrochemical oxidation of ammonia

Electrochemical oxidation of ammonia can produce hydrogen by splitting the ammonia molecules, not merely facilitating the elimination of ammonia but also augmenting sustainable hydrogen-based technological systems. However, the anode reaction is sluggish and the development of novel electrocatalysts is the major method to overcome this demerit. Herein, three kinds of Ni-based MOFs (Ni-BDC, Ni-BTC, and Ni-NH2-BDC) were prepared and used as electrocatalysts towards electrochemical oxidation of ammonia for the first time. At optimized working condition (0.5 V), Ni-NH2-BDC presents the response current density of 2.12 mA/cm2 with the current efficiency of 92.6%, both of which are significantly higher than those of Ni-BDC and Ni-BTC, indicating the better performance of Ni-NH2-BDC. EIS tests and the measurement of conductivity revealed that the good performance of Ni-NH2-BDC could be attributed to the lower charge transfer resistance at the electrode/electrolyte interface and the significantly improved conductivity which is caused by the introduction of NH2 groups.This work shed lights on the development of MOFs electrocatalysts for ammonia oxidation as well as other electrochemical reactions.

Dynamic in situ reconstruction of NiSe2 promoted by interfacial Ce2(CO3)2O for enhanced water oxidation

Understanding and manipulating the structural evolution of water oxidation electrocatalysts lays the foundation to finetune their catalytic activity. Herein, we present a synthesis of NiSe2-Ce2(CO3)2O heterostructure and demonstrate the efficacy of interfacial Ce2(CO3)2O in promoting the formation of catalytically active centers to improve oxygen evolution activity. In-situ Raman spectroscopy shows that incorporation of Ce2(CO3)2O into NiSe2 causes a cathodic shift of the Ni2+→Ni3+ transition potential. Operando electrochemical impedance spectroscopy reveals that strong electronic coupling at heterogeneous interface accelerates charge transfer process. Furthermore, density functional theory calculations suggest that actual catalytic active species of NiOOH transformed from NiSe2, which is coupled with Ce2(CO3)2O, can optimize electronic structure and decrease the free energy barriers toward fast oxygen evolution reaction (OER) kinetics. Consequently, the resultant NiSe2-Ce2(CO3)2O electrode exhibits remarkable electrocatalytic performance with low overpotentials (268/304 mV @ 50/100 mA cm−2) and excellent stability (50 mA cm−2 for 120 h) in the alkaline electrolyte. This work emphasizes the significance of modulating the dynamic changes in developing efficient electrocatalyst.

Pumpkin shell-derived activated carbon-supported S-incorporated transition metal oxide electrocatalyst for hydrogen evolution reaction

In the pursuit of a more sustainable future and to combat the environmental impact of fossil fuels, green hydrogen production through water electrolysis is gaining traction. While noble metals currently dominate electrocatalyst design, their expense limits widespread adoption. This study proposes a solution by outlining a method for designing efficient and affordable electrocatalysts based on non-precious metals. Herein, we introduce a novel S-incorporated Ni2O3 supported on biowaste-derived activated carbon (S-Ni2O3@AC) synthesized from pumpkin shells. This facile and sustainable approach utilizes readily available resources. The S-Ni2O3@AC nanocomposite demonstrates excellent HER performance with low overpotential and high durability. This is attributed to a high surface area of the composite, fast charge transfer, optimal hydrogen adsorption, and lowered energy barrier for water dissociation facilitated by sulfur incorporation, which is demonstrated by density functional theory (DFT) calculations. This research paves the way for cost-effective and sustainable hydrogen evolution electrocatalysts.