Electrocatalytic Oxidation Reaction Research Articles

Platinum-Based Electrocatalysts for Direct Alcohol Fuel Cells: Enhanced Performances toward Alcohol Oxidation Reactions.

In the past few decades, Pt-based electrocatalysts have attracted great interests due to their high catalytic performances toward the direct alcohol fuel cell (DAFC). However, the high cost, poor stability, and the scarcity of Pt have markedly hindered their large-scale utilization in commerce. Therefore, enhancing the activity and durability of Pt-based electrocatalysts, reducing the Pt amount and thus the cost of DAFC have become the keys for their practical applications. In this minireview, we summarized some basic concepts to evaluate the catalytic performances in electrocatalytic alcohol oxidation reaction (AOR) including electrochemical active surface area, activity and stability, the effective approaches for boosting the catalytic AOR performance involving size decrease, structure and morphology modulation, composition effect, catalyst supports, and assistance under other external energies. Furthermore, we also presented the remaining challenges of the Pt-based electrocatalysts to achieve the fabrication of a real DAFC.

Synergy between Nickel Nanoparticles and N-Enriched Carbon Nanotubes Enhances Alkaline Hydrogen Oxidation and Evolution Activity

Electrocatalytic hydrogen oxidation (HOR) and evolution (HER) reactions under alkaline conditions are kinetically sluggish processes even when Pt catalysts are employed. Despite having markedly slo...

Regulating the Local Charge Distribution of Ni Active Sites for the Urea Oxidation Reaction

AbstractIn electrochemical energy storage and conversion systems, the anodic oxygen evolution reaction (OER) accounts for a large proportion of the energy consumption. The electrocatalytic urea oxidation reaction (UOR) is one of the promising alternatives to OER, owing to its low thermodynamic potential. However, owing to the sluggish UOR kinetics, its potential in practical use has not been unlocked. Herein, we developed a tungsten‐doped nickel catalyst (Ni‐WOx) with superior activity towards UOR. The Ni‐WOx catalyst exhibited record fast reaction kinetics (440 mA cm−2 at 1.6 V versus reversible hydrogen electrode) and a high turnover frequency of 0.11 s−1, which is 4.8 times higher than that without W dopants. In further experiments, we found that the W dopant regulated the local charge distribution of Ni atoms, leading to the formation of Ni3+ sites with superior activity and thus accelerating the interfacial catalytic reaction. Moreover, when we integrated Ni‐WOx into a CO2 flow electrolyzer, the cell voltage is reduced to 2.16 V accompanying with ≈98 % Faradaic efficiency towards carbon monoxide.

Regulating the Local Charge Distribution of Ni Active Sites for the Urea Oxidation Reaction.

In electrochemical energy storage and conversion systems, the anodic oxygen evolution reaction (OER) accounts for a large proportion of the energy consumption. The electrocatalytic urea oxidation reaction (UOR) is one of the promising alternatives to OER, owing to its low thermodynamic potential. However, owing to the sluggish UOR kinetics, its potential in practical use has not been unlocked. Herein, we developed a tungsten-doped nickel catalyst (Ni-WOx ) with superior activity towards UOR. The Ni-WOx catalyst exhibited record fast reaction kinetics (440 mA cm-2 at 1.6 V versus reversible hydrogen electrode) and a high turnover frequency of 0.11 s-1 , which is 4.8 times higher than that without W dopants. In further experiments, we found that the W dopant regulated the local charge distribution of Ni atoms, leading to the formation of Ni3+ sites with superior activity and thus accelerating the interfacial catalytic reaction. Moreover, when we integrated Ni-WOx into a CO2 flow electrolyzer, the cell voltage is reduced to 2.16 V accompanying with ≈98 % Faradaic efficiency towards carbon monoxide.

Single Co-Atoms as Electrocatalysts for Efficient Hydrazine Oxidation Reaction.

Single-atom catalysts (SACs) have aroused great attention due to their high atom efficiency and unprecedented catalytic properties. A remaining challenge is to anchor the single atoms individually on support materials via strong interactions. Herein, single atom Co sites have been developed on functionalized graphene by taking advantage of the strong interaction between Co2+ ions and the nitrile group of cyanographene. The potential of the material, which is named G(CN)Co, as a SAC is demonstrated using the electrocatalytic hydrazine oxidation reaction (HzOR). The material exhibits excellent catalytic activity for HzOR, driving the reaction with low overpotential and high current density while remaining stable during long reaction times. Thus, this material can be a promising alternative to conventional noble metal-based catalysts that are currently widely used in HzOR-based fuel cells. Density functional theory calculations of the reaction mechanism over the material reveal that the Co(II) sites on G(CN)Co can efficiently interact with hydrazine molecules and promote the NH bond-dissociation steps involved in the HzOR.

In-situ loading synthesis of graphene supported PtCu nanocube and its high activity and stability for methanol oxidation reaction

A perfect PtCu nanocube with partial hollow structure was prepared by hydrothermal reaction and its electrocatalytic methanol oxidation reaction (MOR) was studied. The appropriate concentration of shape-control additives KI and triblock pluronic copolymers, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO19-PPO69-PEO19) (P123) play crucial roles in the final product morphology. The PtCu nanocubes can be perfectly in situ immobilizedonto graphene under the action of P123 while the structure and cubic morphologyremain unchanged. The electrochemical tests suggest that the obtained PtCu nanocube (PtCu-NCb) exhibits better MOR activity and stability than PtCu hexagon nanosheet (PtCu-NSt), PtCu nanoellipsoid (PtCu-NEs) and commercial Pt/C in alkaline medium. When in situ immobilized onto graphene, the MOR catalytic activity and stability of PtCu cubes are further improved. The markedly enhanced electrocatalytic activity and durability maybe attributed to the special cubic morphology with partial hollow structure enclosed by highly efficient facet and the probably the synergistic effect of PtCu and intermediate state CuI decorated on the surface and graphene.

The formation of wrapping type Pt–Ni alloy on three-dimensional carbon nanosheet for electrocatalytic oxidation of methanol

In this paper, the PtNi alloy was embedded into the surface layer of three-dimensional carbon nanosheets (CNSs) with a special layered structure. We controllably adjusted the ratio of Pt/Ni to form large particle alloy with Pt coating Ni and a small number of hollow PtNi alloy pellets. The electro-catalytic methanol oxidation activity and durability of the catalysts were estimated by cyclic voltammetry and chronoamperometric techniques. The results indicated that the doping of Ni effectively improved the activity and anti-poisoning of the catalyst in the methanol electrocatalytic oxidation reaction (MOR). Transmission electron microscopy (TEM), Raman spectroscopy, nitrogen adsorption-desorption techniques, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to explore the composition, morphology and structure of these catalysts. It is discovered that the Pt–Ni/CNSs (2:1) sample exhibits the best MOR activity with a peak current density of 15.03 mA cm−2 at the forward scan due to the excellent lamellar structure, good crystallinity and abundant pore structure of CNSs, which is benefit to form ultrahigh specific surface area, superb electron and ionic conductivity.

Synthesis and Physicochemical Properties of Pt on TiO2 nanotubes as electro catalyst for Methanol Oxidation Reaction

In this paper, TiO2 nanotubes were synthesized electrochemically by anodization of pure Ti sheet in 0.5% HF and annealed in N2 atmosphere to obtain (TONTs-N2) then the platinum was deposited on the support TONTs-N2 by chemical deposition method using NaBH4 as reducing agents to obtain the electrocatalyst Pt-B/TONTs-N2.
 The physicochemical characterizations of Pt-B/TONTs-N2 were performed by scanning electron microscopy (SEM), X-ray diffraction (XRD analysis.
 The catalyst Pt-B/TONTs-N2 was electrochemically characterized in basic solution of methanol by cyclic voltammetry (CV) measurement. XRD characterization indicates the presence of platinum nanoparticles with diameter less than 54.8 nm and regularly combined into TiO2 nanotubes. Pt-B/TONTs-N2 catalyst exhibited a remarkably high electrocatalytic activity and has high electrocatalytic stability for methanol electrocatalytic oxidation reaction.
 In addition, the Pt-B/TONTs-N2 catalyst exhibits better poison tolerance and higher methanol oxidation current density than that reported for Pt/carbon catalyst.
 This suggests that the Pt-B/TONTs-N2 catalyst supported on TONTs-N2 has promising potential applications in electro catalyst reactions.
 Pt supported on the conductive support TONTs-N2 is used as electrocatalyst in alkaline fuel cells. Results showed best improvement in physico-chemical properties of these catalysts in comparison with previous studies.

Recent Progress in Electrocatalytic Glycerol Oxidation

Glycerol, as the major by‐product of biodiesel, can be oxidized into diverse value‐added chemical products via either traditional chemical methods or electrochemical routes. Electrocatalytic glycerol oxidation reaction (GOR) driven by renewable‐derived electricity (e.g., wind and solar) is a promising pathway for fine chemicals production. In an electrochemical cell, GOR can be coupled with various cathodic reactions, including hydrogen evolution reaction (HER), CO2 reduction reaction (CO2RR), and oxygen reduction reaction (ORR); in this manner, different benefits of either energy effectiveness or additional value‐added products can be obtained depending on the cathode reduction reaction selected. Comprehensively understanding of electrocatalytic GOR and the associated processes is of great significance to promote its industrial application. Herein, recent progress of GOR is focused on. The background of biomass‐derived glycerol valorization to energy and value‐added chemicals as well as the electrochemical conversion techniques via GOR is introduced. Then, the electrocatalytic reaction pathways, the potential application of GOR, and the measurement method for products are also discussed and summarized. Special emphasis is put on the design and the development of high‐selectivity and high‐activity electrocatalysts for GOR. Finally, the challenges and the future prospects in the fields of GOR are highlighted.

Integration of Marigold 3D flower-like Ni-MOF self-assembled on MWCNTs via microwave irradiation for high-performance electrocatalytic alcohol oxidation and oxygen evolution reactions

Fabrication of metal-organic frameworks (MOFs) on carbon nanostructure arrays is extremely challenging. Here, we successfully fabricated three-dimensional (3D) flower-like Ni-MOFs on multiwalled carbon nanotubes (MWCNTs) through a highly efficient and rapid microwave synthetic protocol and studied their applicability in electrocatalytic alcohol oxidation reaction (AOR) and oxygen evolution reaction (OER). Morphological studies using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) images suggested the formation of marigold-like Ni-MOF decorated on the MWCNTs. Surface coverage of Ni-MOF@CNT (1.11 × 10−7 mol g-1) was higher than that of the pristine Ni-MOF (9.35 × 10-8 mol g-1) electrocatalyst. The higher electrochemical active surface area (ECSA) of Ni-MOF@CNT (494.3 cm2) compared to the pristine Ni-MOF (203.5 cm2) electrocatalyst resulted in the availability of large active sites in the Ni-MOF@CNT to catalyze AOR and OER. Ni-MOF@CNT exhibited a higher electrooxidation performance in AOR than the pristine Ni-MOF and its OER activity was far superior.

Spinel CuxCo1−xMn2O4 electrode for effectively cleaning organic wastewater via electrocatalytic oxidation

Development of anodes with high electrocatalytic activity, electrochemical stability and low cost is a key to clean organic wastewater via electrocatalytic oxidation. Here, spinel CuxCo1−xMn2O4 (CCM-X) was prepared by introducing copper with high catalytic activity into the structurally stable spinel CoMn2O4. The CCM-X were coated on the surface of titanium plate and used as anodes to study their electrocatalytic oxidation performance for cleaning simulated organic wastewater (tetracycline hydrochloride aqueous solution). The maximum removal ratio of 20 mg L−1 tetracycline hydrochloride was 91.3% in 120 min and still reached 84.9% after 5-times’ reusing of the anode, which was attributed to the high electrocatalytic activity, oxygen evolution potential (1.70 V vs. Ag/AgCl) and stable structure of multi-metal oxide CCM-X anode. In addition, free radical trapping experiments showed that hydroxyl radicals played a major role in electrocatalytic oxidation process. Electrochemical tests showed that redox of Co(III)/Co(IV) and Mn(III)/Mn(IV) participated in the electrocatalytic oxidation reaction, and doping Cu can effectively improve the electron transfer ability and electrocatalytic activity of CCM-X. Therefore, CCM-X/Ti electrodes perform attractive application prospects in cleaning organic wastewater via electrocatalytic oxidation.

Advances and Fundamental Understanding of Electrocatalytic Methane Oxidation

AbstractMethane utilization is one of the promising energy‐efficient conversions which can potentially control its emissions as an additional benefit. In this regard, electrochemically methane conversion is particularly attractive as a fossil‐free and sustainable strategy to generate power and fuels of global importance. However, it is relatively less explored. This review aims to highlight the feasibility of the electro‐conversion approach via electrocatalytic methane oxidation (EMO) reaction. The recent progress regarding power generation as well as value‐added fuel/chemical production, such as hydrocarbons, alcohols, acids, and ketones, is summarized. Additional mechanistic insights to increase the fundamental understanding of the EMO reaction pathways underlying various catalytic modes and their challenges are provided. Theoretical modeling focusing on the reactivity trends and performance kinetics is also presented, along with key recommendations for the material design that need to be addressed. Suggesting some insights on catalysts‐related developing directions and chances in the EMO field is concluded.

Unravelling the role of polyoxovanadates in electrocatalytic water oxidation reaction: Active species or precursors

Exploring the role of polyoxometalates (POMs) in electrocatalytic oxygen evolution reaction (OER) is greatly significant for developing efficient electrocatalyst towards the sustainable energy production. Herein, three polyoxovanadate (POV)-based inorganic–organic hybrid compounds with formula of [Ni2(BBTZ)(H2O)4]V4O12·2H2O(1), [Co2(BBTZ)(H2O)4]V4O12·2H2O(2), [Ni(BBTZ)2]V2O6·2H2O(3) (BBTZ = 1,4-bis-(1,2,4-triazol-1-ylmethyl)benzene) were synthesized as electrocatalysts to explore their roles for OER. Structural analysis showed that compounds 1–2 are isomorphic 2-D wave-like layer structures, while compound 3 features 3-D framework with a 5-fold interpenetrating metal–organic moiety. Experiments showed that the three compounds can keep their structural integrities after soaking in 1 M KOH electrolyte, and compound 1 exhibited the best catalytic activity towards OER with low overpotential of 353 mV at current density of 10 mA cm−2 and small Tafel slope of 77.8 mV dec−1. However, a series of technical characterizations clearly implied that there are structural conversion processes of compounds 1–3 on electrode surface accompanying the electrocatalytic reation. The organic ligands and most of polyoxovanadate species were electrochemically extracted under anodic potential, leaving the V-doping metal oxyhydroxides as OER-active species. This work confirmed that polyoxovanadates are not active sites but precursors for generating active species of OER, and suggested an available route for designing new nanosized vanadium-doped metal oxide electrocatalysts.

Electrochemical oxidation of Rhodamine B with cerium and sodium dodecyl benzene sulfonate co-modified Ti/PbO2 electrodes: Preparation, characterization, optimization, application

Schematic diagram of electrode preparation procedure and application. Regulation of the electronic structure and interface property becomes a major strategy in the preparation of electro-catalyst. This paper reports the synthesis of cerium (Ce) and sodium dodecyl benzene sulfonate (SDBS) co-modified Ti/PbO 2 electrodes (Ti/PbO 2 -Ce-SDBS). Ce and SDBS could greatly change the electronic structure and interface property of PbO 2 . Ti/PbO 2 -Ce-SDBS exhibited excellent electrocatalytic activity and stability in Rhodamine B (RhB) electrocatalytic oxidation reaction. The improved electrocatalytic activity associates with the synergistic effect of electronic and interface factors. In the electrochemical degradation of RhB, the removal efficiencies of RhB and COD are about 0.880 and 0.694 respectively after the electrolysis of 220 min with Ti/PbO 2 -Ce-4-SDBS-40, which are higher than the contrast Ti/PbO 2 electrodes. In the meantime, the accelerated lifetime of Ti/PbO 2 -Ce-4-SDBS-40 is more than 6.2 times than that of Ti/PbO 2 .

One‐Pot Synthesized Nickel‐Doped Hierarchically Porous Beta Zeolite for Enhanced Methanol Electrocatalytic Oxidation Activity

AbstractHierarchically porous zeolites have been widely explored for catalytic applications owing to their high specific surface area, large pore volume, favorable mass transfer capability and abundant acidic sites. Herein we report the facile synthesis of Ni‐doped hierarchically Beta zeolite (Ni−H‐beta) via one‐pot hydrothermal method, in which Ni is uniformly doped into the zeolite crystalline skeleton in the form of Ni3+ without any nickel oxides being found. The prepared Ni−H‐beta zeolite shows high performance towards the electrocatalytic methanol oxidation reaction (MOR) with a high current density of 1450 A g−1 at 1.65 V vs RHE, which is higher than most non‐precious MOR electrocatalysts. More importantly, the electrochemical MOR performance has been identified to be closely related to the acidic property of the prepared samples. The increase in Al concentration resulted in the formation of strong acid sites, and the consequent MOR activity enhancement. These results provide valuable knowledge and favor the application of transition metals doped hierarchical zeolite for electrocatalytic MOR.

Cost-effective and efficient water and urea oxidation catalysis using nickel-iron oxyhydroxide nanosheets synthesized by an ultrafast method

The synthesis of earth-abundant, low-cost, and stable electrocatalysts with high efficiency in the oxygen evolution reaction (OER) is a necessary requirement for improving the effectiveness of electrochemical water splitting approach. To date, expensive electrode materials and time-consuming synthesis procedures have generally been used for the electrocatalysts applied in water splitting, which limits their efficiency. Herein, nickel-iron oxyhydroxide nanosheets are fabricated by a scalable and ultrafast (requiring only 5 s) wet chemical strategy on a nickel foam substrate. The experimental results indicate that compared to recently reported catalysts, the prepared nickel-iron oxyhydroxide electrode has a high number of active sites and low reaction barrier, enabling efficient OER catalysis in an alkaline electrolyte. In particular, the prepared nickel-iron oxyhydroxide electrode requires an ultralow overpotential of 230 mV to reach a current density of 50 mA cm−2, with excellent long-term stability for 75 h. Moreover, the nickel-iron oxyhydroxide also performs well towards the electrocatalytic urea oxidation reaction (UEOR), with a very low potential of 1.38 and 1.41 V vs RHE (reversible hydrogen electrode) to reach 50 and 100 mA cm−2 current density in 1 M KOH with 0.33 M urea electrolyte. This ultrafast synthesis approach can be extended to prepare electrocatalysts used for other electrochemical reactions.

Ultrasensitive Detection of the Hepatitis E Virus by Electrocatalytic Water Oxidation Using Pt-Co3O4 Hollow Cages.

A sensitive virus detection method applicable for an early stage increases the probability of survival. Here, we develop a simple and rapid detection strategy for the detection of the hepatitis E virus (HEV) by an electrocatalytic water oxidation reaction (WOR) using a platinum (Pt)-incorporated cobalt (Co)-based zeolite imidazole framework (ZIF-67). The surface cavity of ZIF-67 enables the rich loading of Pt NPs, and subsequent calcination etches the cavity, promoting the electrocatalytic activity of Pt-Co3O4 HCs. The Pt-Co3O4 HCs show excellent behavior for the WOR due to the synergistic interaction of Pt and Co3O4, evaluated by voltammetry and chronoamperometry. The synthesized Pt-Co3O4 HCs are conjugated with anti-HEV antibody (Ab@Pt-Co3O4 HCs); the electrocatalytic activity of Ab@Pt-Co3O4 HCs is combined with that of antibody-conjugated magnetic nanoparticles (MNPs) for HEV detection by a magneto-and-nanocomposite sandwich immunoassay. The sensor is challenged to detect the HEV in spiked serum samples and HEV G7 genotypes collected from the cell culture supernatant, reaching a low limit of detection down to 61 RNA copies mL-1. This work establishes a free-indicator one-step approach with the controlled design of Pt-Co3O4 HCs, which presents an effective WOR technique for virus detection in a neutral pH solution, which can be extended to electrocatalytic studies in the future integrated biosensing systems.

Electrochemically Regenerable Hydrogen Atom Acceptors: Mediators in Electrocatalytic Alcohol Oxidation Reactions

A class of electrochemical mediators is described for electrocatalytic oxidation reactions that are catalyzed by metal hydrides. The octahedral ruthenium complex [Ru(acac)2(pyimN)] (RuIIIN 3) is sh...

Methanol electrocatalytic oxidation over Pt nanoparticles anchoring on three-dimensional carbon nanosheet rich in oxygen functional groups

In this paper, three-dimensional carbon nanosheets (CS) were treated at different temperatures in an atmosphere of ozone, then obtained a series of Pt/OCS-X catalysts through the loading of Pt, including Pt/CS, Pt/OCS-25, Pt/OCS-90, Pt/OCS-160 and Pt/OCS-200. To prove that ozone oxidation can effectively improve the activity of the catalyst, these catalysts were tested by methanol electrocatalytic oxidation reaction (MOR). It is discovered that ozone treatment could greatly increase the number of oxygen-containing functional groups, and the HO–CO content was greatly improved after the modulation of treated temperature. It is discovered that the Pt/OCS-160 sample exhibits the best activity with a peak current density of 37.7 mA cm−2 at the forward scan due to the excellent lamellar structure, good crystallinity, and abundant pore structure of CS, which is a benefit to form ultrahigh specific surface area, superb electron, and ionic conductivity. Meanwhile, the capacity of anti-poisoning of Pt/CS after O3 treatment is enhanced obviously.

Bulk Nanostructuring of Janus-Type Metal Electrodes.

The stable deposition of reactive nanostructures on metal electrodes is a key process for modern technologies including energy conversion/ storage, electrocatalysis or sensing. Here a facile, scalable route is reported, which allows the bulk nanostructuring of copper foam electrodes with metal, metal oxide or metal hydroxide nanostructures. A concentration‐gradient driven synthetic approach enables the fabrication of Janus‐type electrodes where one face features Cu(OH)2 nanowires, while the other face features CuO nanoflowers. Thermal or chemical conversion of the nanostructured surfaces into copper oxide or copper metal is possible whilst retaining the respective nanostructure morphologies. As proof of concept, the functionalized electrodes are promising in electrocatalytic water oxidation and water reduction reactions.