Rotating Ring Disk Electrode Research Articles

Neuroscience, Linguistics and Psycholinguistics Advances Applied to Early Literacy Teaching

I discuss the lack of linguistic and psycholinguistic fundamentals compromising the teaching-learning models of early literacy, as well as the ignorance of reading neuroscience most recent contributions, arguing with linguistic and neuroscience theories about perceptual invariant units, like phonemes and graphemes. I also explain the difference between phoneme and sound and between grapheme and letter as well as the existence of hierarchical linguistic levels. All those fundamentals pave the Scliar Early Literacy System (SSA), applied on an experiment run at Lagarto, Sergipe State, on the Brazilian Northeastern, that showed the lowest scores in the 2016 National Literacy Assessment (ANA). METHOD: José Humberto dos Santos Santana, distance SSA Course student, belonging to Lagarto municipal staff, organized the five researchers group to implement the SSA in two Lagarto schools. Teachers Patrícia Vieira Barbosa Faria and Jaqueline da Silva Nascimento were 75 children teaching pioneers, in February, 2017, using SSA, Module 1, method and materials, focusing on reading learning at the municipal schools Raimunda Reis, RR (two classes) and Manoel de Paula Menezes Lima, MPML (one class). On 2018, the same teachers followed the same children in the 2nd grade, applying SSA, Module 2, method and materials, focusing on writing learning. Educators received continuous distance training, first, fortnightly and, starting in 2018, twice every week: Tuesdays, for educators who worked with 2nd grade children and, on Wednesdays, for 1st grade educators, from Elementary School. Distant classes last one hour and a half each. RESULTS: The 2018 More Early Literacy Program assessment describes the lowest level 1, as the one where children barely identify one word or the other. In this level two Lagarto schools dropped to 8.7 (RR) and 9.1% (MPML), while at the highest level, dealing with children who have a desirable reading performance, they reached the percentages of 34.8 (RR) and 31.8 (MPML). Compare such results with the 2016 National Literacy Assessment (ANA) performance in the State of Sergipe: level 1, 45.28; highest level, 3.02. In 2018, Lagarto Municipal Education Secretariat expanded its adhesion to SSA, reaching an average of 490 children from the 1st (18 classes) and 2nd (3 classes) grades of Elementary School, taking into account reading and writing, respectively. The Secretariat guaranteed the continuous training of 18 teachers who attend the 1st year and the 5 who attend the 2nd year for applying the SSA. In 2019, given the proposal success, more than 1000 children benefited from the project.

Impact of Surface Functionalization on the Intrinsic Properties of the Resulting Fe–N–C Catalysts for Fuel Cell Applications

Herein, Fe–N–C catalysts are prepared from surface functionalized carbon nanotubes (CNTs) in combination with iron acetate and phenanthroline. An improved performance and structural composition is obtained by surface functionalization of the CNTs with indazole or pyridine. Catalyst composition and morphology are characterized by transmission electron microscopy, N2 sorption, photoelectron spectroscopy, and 57Fe transmission Mössbauer spectroscopy. However, activity and selectivity toward oxygen reduction reaction are determined from rotating ring disc electrode (RRDE) experiments. The durability and stability are evaluated by accelerated stress tests (0.0–1.2 V) and differential electrochemical mass spectroscopy (DEMS), respectively. It is shown that surface functionalization with indazole enables the direct attachment of FeN4 centers to CNTs so that no impurity species are detected and a high activity is achieved, that can be attributed to an improved turnover frequency and higher mass‐based site density. Even more striking is the excellent durability and stability of the realized catalyst. While these trends are well pronounced in RRDE and DEMS, challenges in the preparation of membrane electrode assemblies make the trend not as obvious in fuel cells (FCs).

Kinetic Analysis of Electrochemical Oxygen Reduction over a Fe/N/C Catalyst Considering the Chemical Decomposition of H2O2

Iron and nitrogen codoped carbon catalysts (Fe/N/C catalysts) are promising nonprecious-metal catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. Understanding the ORR kinetics over Fe/N/C catalysts is crucial for active catalyst development. Here, we propose an analytical method for rotating ring–disk electrode (RRDE) voltammetry to separate the ORR for O2 reduction to H2O via the 4-e pathway (k1), O2 reduction to H2O2 via the 2-e pathway (k2), H2O2 reduction to H2O via the 2-e pathway (k3), H2O2 chemical decomposition to O2 and H2O (k4), and H2O2 oxidation to O2 by the 2-e pathway (k–2). First, RRDE voltammetry in an H2O2 solution was performed, yielding k3, k4, and k–2. The obtained parameters were used to analyze the ORR voltammogram to calculate I1′, I2′, I3′, I4′, k1′, and k2′. These currents and kinetic constants were corrected by studying the effect of the catalyst loading density to obtain I10, I20, I30, I40, k10, and k20, thus avoiding the overestimation of I10 and k10 caused by the quasi-four-electron reduction of O2. The contribution of k4 during the ORR is negligible at considerable anodic and cathodic overpotentials but was detected at 0.8 V, for which k3 and k–2 are relatively small.

Synergistic Catalytic Effect of Hollow Carbon Nanosphere and Silver Nanoparticles for Oxygen Reduction Reaction

AbstractDeveloping low‐cost and high‐performance catalysts for oxygen reduction reaction (ORR) is critical for fuel cell applications. In this study, hollow carbon nano‐spheres (HCNS) are synthesized by a hydrothermal method and used as the support for silver nano‐particles (Ag@HCNS) as the ORR catalyst. The morphology of Ag@HCNS is investigated by the transmission electron microscopy (TEM), scanning electron microscopy (SEM) and other methodologies. Results show that the silver nanoparticles with a diameter from 3 to 6 nm are evenly distributed on the surface of HCNS. The catalytic performances of the HCNS and Ag@HCNS for ORR are investigated by cyclic voltammetry, linear sweeping voltammetry, rotating disc and rotating ring disc electrode tests. The synergistic effect between HCNS and Ag nanoparticles plays the major role on the high catalytic activity of Ag@HCNS for ORR. The onset potential of Ag@HCNS (0.82 V v.s. RHE) catalyzed ORR is close to that of Pt/C catalyst. In addition, the reaction kinetics study shows that the Ag@HCNS catalyzed ORR major proceeds through 4‐electron style. This paper promotes the understanding of the happening mechanism of ORR on the surface of novel carbon supported metal nanoparticles.

Synthesis of Ti4O7/Ti3O5 Dual-Phase Nanofibers with Coherent Interface for Oxygen Reduction Reaction Electrocatalysts.

Electrocatalysts play an important role in oxygen reduction reaction (ORR) in promoting the reaction process. Although commercial Pt/C exhibits excellent performance in ORR, the low duration, high cost, and poor methanol tolerance seriously restrict its sustainable development and application. TinO2n−1 (3 ≤ n ≤ 10) is a series of titanium sub-oxide materials with excellent electrical conductivity, electrochemical activity, and stability, which have been widely applied in the field of energy storage and catalysis. Herein, we design and synthesize Ti4O7/Ti3O5 (T4/T3) dual-phase nanofibers with excellent ORR catalytic performance through hydrothermal growth, which is followed by a precisely controlled calcination process. The H2Ti3O7 precursor with uniform size can be first obtained by optimizing the hydrothermal growth parameters. By precisely controlling the amount of reducing agent, calcination temperature, and holding time, the T4/T3 dual-phase nanofibers with uniform morphology and coherent interfaces can be obtained. The orientation relationships between T4 and T3 are confirmed to be , , and , respectively, based on comprehensive transmission electron microscopy (TEM) investigations. Furthermore, such dual-phase nanofibers exhibit the onset potential and half-wave potential of 0.90 V and 0.75 V as the ORR electrocatalysts in alkaline media, respectively, which illustrates the excellent ORR catalytic performance. The rotating ring-disk electrode (RRDE) experiment confirmed the electron transfer number of 3.0 for such catalysts, which indicates a mixture of two electron and four electron transfer reaction pathways. Moreover, the methanol tolerance and cycling stability of the catalysts are also investigated accordingly.

Detection of protons using the rotating ring disk electrode method during electrochemical oxidation of battery electrolytes

Knowledge of the degradation mechanisms inside lithium-ion batteries (LIBs) is critical in designing robust next-generation materials. While significant efforts have led to advances in characterization techniques and in our general understanding of the numerous decomposition reactions, the complex, multicomponent nature of batteries has hindered our progress towards developing a complete picture of these processes. In this work, we present a method for the detection of protons—one of the commonly proposed products of battery electrolyte decomposition at high potentials—using the rotating ring disk electrode (RRDE) method. Using the H2 oxidation reaction (HOR) as a model reaction, we first determine that protons generated at the disk electrode can be detected in organic carbonate-based electrolyte at the ring electrode with a ring collection efficiency close to the theoretical value. We then show that protons are indeed generated during the electrochemical decomposition of the battery electrolyte on Pt(111) at high potentials. Furthermore, quantitative detection of protons provided a valuable insight into the mechanism of oxidation for the electrolyte used. Overall, our work demonstrates the value of RRDE as a complementary method for studying potential-dependent electrolyte stability.

Effects of fulvic acids on the electrochemical reactions and mass transfer properties of organic cation toluidine blue: Results of measurements by the method of rotating ring-disc electrode

This study examined effects of aquatic and soil natural organic matter (NOM) exemplified by standard Suwannee River fulvic acid (SRFA) and Pahokee Peat fulvic acid (PPFA), respectively, on the electrochemical (EC) reactivity and mass transfer properties of the cationic organic probe toluidine blue (TB) that forms complexes with NOM. EC measurements that were carried out using the method of rotating ring-disc electrode (RRDE) showed that for disc potentials below −0.4 V vs. the standard Ag/AgCl reference electrode, TB molecules undergo EC reduction accompanied by the formation of EC-active products that undergo oxidation at the ring electrode. EC reactions of TB in the range of potentials −0.2 to −0.4 V were determined to involve free TB+ cations and TB species adsorbed on the electrode surface. The EC reduction of TB species at the disc potentials < −0.4 V was controlled by the mass transfer of the free TB+ cations and TB/NOM complexes to the electrode surface. Formation of TB/NOM complexes caused the mass transfer-controlled TB currents to undergo a consistent decrease. The observed changes were correlated with the extent of TB/NOM complexation and decreases of the diffusion coefficients of TB/NOM complexes that have higher molecular weights (MW) than the free cations. Properties of the intermediates formed upon the reduction of TB+ cations were also affected by NOM. These results demonstrate that RRDE measurements of EC reactions of TB or possibly other EC active probes allow probing the complexation of EC-active organic species with NOM and mass transfer properties of NOM complexes and ultimately NOM itself.

Low Pd loadings onto Printex L6: Synthesis, characterization and performance towards H2O2 generation for electrochemical water treatment technologies

In order to enhance hydrogen peroxide (H2O2) electrogeneration, a catalyst based on less than 1 wt% of Pd nanoparticles dispersed onto commercially available Printex L6 carbon black (PCL6) is proposed and synthetized. The material was characterized by physico-chemical and electroanalytical methods, demonstrating high activity with a 320 mV lower onset potential compared to pristine PCL6 and high stability after 5000 potential cycles. Its performance places it among the most efficient bi- and monometallic electrocatalysts for H2O2 production. When testing the accumulation of H2O2, a 1.69-fold molar increase was observed for Pd1%/PCL6 compared to PCL6. Different electrochemical advanced oxidation processes based on H2O2 generation have been performed to oxidize and remove pollutants as exemplarily shown on methyl paraben in Na2SO4 solution as model pollutant. A boron-doped diamond electrode was used as anode while Pd1%/PCL6 was tested in a rotating ring disk electrode (RRDE) and gas diffusion setup. Pollutant degradation followed a pseudo-first-order reaction kinetic in the following order: anodic oxidation along with H2O2 generation (AO-H2O2) < AO-H2O2/UVC < electro-Fenton (EF) < photoelectro-Fenton (PEF). The best mineralization performance was found for PEF due to the photodecarboxylation of Fe (III) complexes with UVC light, while the process with lowest energy consumption per order was EF with 0.488 kWh m−3 order−1. At the end of the work a route for pollutant mineralization was suggested.

The oxygen reduction reaction on palladium with low metal loadings: The effects of chlorides on the stability and activity towards hydrogen peroxide

Hydrogen peroxide is considered one of the most important commodity chemicals worldwide but its main production method, the anthraquinone process, poses serious logistical, environmental and safety challenges. Electrocatalytic synthesis through the reduction of molecular oxygen is a promising H2O2 production route. However, the reduction of molecular oxygen is kinetically hindered and stable electrocatalysts with a high activity and selectivity towards the 2-electron transfer reaction are needed. In this work, we evaluated the influence of chloride on catalysts with low palladium loadings on the ORR selectivity towards H2O2. We report the factors and dynamics that influence H2O2 production and highlight synthesis strategies to obtain close to 100% selectivity. By probing the electrode surface after various degradation cycles, we evaluate the role of adsorbing species and the catalysts oxidation states on the hydrogen peroxide selectivity. We systematically modified the catalyst synthesis using different Pd-precursors that were reduced and supported on high surface area graphene nanoribbons. Identical location transmission electron microscopy was used to probe catalyst dynamics during reaction and the activities and selectivities were measured by a rotating ring disk electrode. We probe the potential boundary conditions that lead to catalyst degradation during accelerated stress tests and potentiostatic polarisation and demonstrate how the catalytically active surface can be revived after degradation. The obtained insights can be used as guideline for the development of active, selective and stable catalysts with low noble metal loadings.

Conversion of Methane into Methanol Using the [6,6'-(2,2'-Bipyridine-6,6'-Diyl)bis(1,3,5-Triazine-2,4-Diamine)](Nitrato-O)Copper(II) Complex in a Solid Electrolyte Reactor Fuel Cell Type.

The application of solid electrolyte reactors for methane oxidation to co-generation of power and chemicals could be interesting, mainly with the use of materials that could come from renewable sources and abundant metals, such as the [6,6′- (2, 2′-bipyridine-6, 6′-diyl)bis (1,3,5-triazine-2, 4-diamine)](nitrate-O)copper (II) complex. In this study, we investigated the optimal ratio between this complex and carbon to obtain a stable, conductive, and functional reagent diffusion electrode. The most active Cu-complex compositions were 2.5 and 5% carbon, which were measured with higher values of open circuit and electric current, in addition to the higher methanol production with reaction rates of 1.85 mol L–1 h–1 close to the short circuit potential and 1.65 mol L–1 h–1 close to the open circuit potential, respectively. This activity was attributed to the ability of these compositions to activate water due to better distribution of the Cu complex in the carbon matrix as observed in the rotating ring disk electrode experiments.

Electrochemically Generated Interfacial pH Change: Application to Signal‐Triggered Molecule Release

AbstractElectron transfer processes during redox reactions are frequently accompanied with protonation/deprotonation processes, thus changing H+/OH− concentrations. When the redox reactions proceed at electrode surfaces, being electrochemically processed, changes in local interfacial pH are possible, particularly when the electrolyte solution is not strongly buffered. The pH gradient can be produced in the diffusion layer and its thickness depends on the rate of electrochemical process, which is measured as the current density, diffusion rates, and buffer capacity. While conventional techniques for measuring pH values are not applicable to a very thin diffusional layer, special methods have been developed for the interfacial pH measurements, including scanning electrochemical microscopy (SECM), rotating ring‐disk electrode (RRDE) measurements, various optical methods, particularly using confocal fluorescent microscopy, and others. Dramatic pH changes proceeding in a near‐electrode layer have been reported for H2O reduction/oxidation, O2 reduction, and some other electrochemical electron/proton transfer processes. These pH changes can be used to trigger some other physical processes, particularly (bio)molecule release processes from modified electrodes, which can be destabilized upon the electrochemically generated pH changes, thus releasing entrapped/loaded target molecules. This review‐type article overviews the formation and analysis of locally produced interfacial pH changes and their use for electrochemically triggered (bio)molecule release. The paper briefly reviews the research area, then concentrating on the systems designed recently by the authors.

The influence of hydrogen sulphide contamination on platinum catalyst used in polymer electrolyte membrane fuel cells during potential cycling at 0.05–1.05 V vs RHE: An RRDE study

The effect of H2S contamination on platinum catalyst has been investigated in terms of rotating ring disk electrode measurements (RRDE) in 0.1 M HClO4. The electrochemical surface area (ECSA) was determined by hydrogen underpotential deposition (HUPD) and CO stripping methods before and after accelerated stress tests (AST). The observed reduced losses of ECSA of the catalyst in the presence of H2S were associated to adsorbed sulphuric compounds on the catalyst surface which changed electrochemical characteristics of the materials surface. The RRDE experiments revealed that for oxygen reduction reaction (ORR) mass and specific activities were essentially decreased after AST with H2S contamination which was attributed to the interstitial defect on platinum atom sites due to adsorbed sulphuric compounds. Identical location and high resolution transmission electron microscopy (TEM) analysis have revealed only slightly different catalyst surface morphology and particle sizes before and after the AST indicating rather atomic scale deterioration of the platinum catalyst surface due to the adsorbed sulphur species.

Low-Noble-Metal-Loading Hybrid Catalytic System for Oxygen Reduction Utilizing Reduced-Graphene-Oxide-Supported Platinum Aligned with Carbon-Nanotube-Supported Iridium

Hybrid systems composed of the reduced graphene oxide-supported platinum and multiwalled carbon nanotube-supported iridium (both noble metals utilized at low loadings on the level of 15 and ≤2 µg cm−2, respectively) were considered as catalytic materials for the reduction of oxygen in acid media (0.5-mol dm−3 H2SO4). The electrocatalytic activity toward reduction of oxygen and formation of hydrogen peroxide intermediate are tested using rotating ring–disk electrode (RRDE) voltammetric experiments. The efficiency of the proposed catalytic systems was also addressed by performing galvanodynamic measurements with gas diffusion electrode (GDE) half-cell at 80 °C. The role of carbon nanotubes is to improve charge distribution at the electrocatalytic interface and facilitate the transport of oxygen and electrolyte in the catalytic systems by lowering the extent of reduced graphene oxide restacking during solvent evaporation. The diagnostic electrochemical experiments revealed that—in iridium-containing systems—not only higher disk currents, but also somehow smaller ring currents are produced (when compared to the Ir-free reduced graphene oxide-supported platinum), clearly implying formation of lower amounts of the undesirable hydrogen peroxide intermediate. The enhancement effect originating from the addition of traces of iridium (supported onto carbon nanotubes) to platinum, utilized at low loading, may originate from high ability of iridium to induce decomposition of the undesirable hydrogen peroxide intermediate.

Prussian-blue-modified reduced-graphene-oxide as active support for Pt nanoparticles during oxygen electroreduction in acid medium

Abstract Platinum nanoparticles have been deposited onto hybrid carriers composed of iron hexacyanoferrate (Prussian Blue) pretreated or functionalized reduced graphene oxide (rGO), and the resulting system’s electrocatalytic activity has been investigated during oxygen reduction reaction in acid solution. Physicochemical properties of the Pt nanoparticle-containing materials have been obtained using transmission electron microscopy, X-ray diffraction and various electrochemical diagnostic techniques including cyclic voltammetry and rotating ring-disk electrode (RRDE) voltammetry. Although functionalization of rGO carriers with Prussian Blue, followed by the system’s thermal treatment at 300°C, does not change activity of Pt catalytic centers in terms of the electroreduction potential of oxygen in 0.5 mol dm−3 H2SO4 (under rotating disk voltammetric conditions), the presence of cyanide-bridged iron ionic sites tends to decrease formation of the undesirable hydrogen peroxide intermediate, as demonstrated by monitoring ring currents during RRDE measurements. The results imply usefulness of PB-modified rGO supports for dispersed Pt nanoparticles at the low loading of 10 μg cm−2 in the oxygen reduction electrocatalysis. In addition to the possible metal-support activating interactions, the mechanism, in which oxygen reduction is initiated at Pt centers and the hydrogen peroxide intermediate is reductively decomposed at reactive PB-modified rGO supports, is feasible.

Development of CuAg/Cu2O nanoparticles on carbon nitride surface for methanol oxidation and selective conversion of carbon dioxide into formate

Herein we report a catalyst consisting of CuAg/Cu2O nanoparticles (NPs), synthesized on the two-dimensional carbon nitride (CN) surface via galvanic exchange route for electrocatalytic methanol oxidation and carbon dioxide reduction. The lower reduction potential of copper ([Cu+(aq) + e− → Cu(s)], + 0.52 eV) compared to Ag ([Ag+(aq) + e− → Ag(s)], +0.80 eV) makes Cu(0) easily exchangeable by Ag+ ions via galvanic exchange without applying any external bias. In a two-step process, the Cu NPs are synthesized first on CN surface by adsorbing Cu2+ precursors and reducing them by NaBH4. Due to unstable nature of Cu2+ in aqueous medium some Cu2O NPs (a mixed phase of Cu/CuO) were also formed. Thereafter in the second step, Ag+ precursors are brought in contact with the already synthesized Cu and Cu2O nanoparticles (NPs). The Cu and Cu2O NPs present on the surface of CN are partially exchanged by Ag atoms to generate bimetallic CuAg/Cu2O NPs. Two atoms of Ag are expected to be deposited for every Cu atom replaced. As galvanic replacement occurs on the solid surface of carbon nitride, there is only a partial replacement of Cu and Cu2O atoms. The catalysts CN/Cu/Cu2O and CN/CuAg/Cu2O were evaluated for their performance towards methanol oxidation and carbon dioxide reduction. CN/CuAg/Cu2O showed twice the current density for methanol oxidation than CN/Cu/Cu2O in a 0.5 M methanol solution. Probably the reason for high activity of Ag than Cu is related to the weak bond of oxygen on silver substrate for oxidation reactions and strong binding affinity on copper substrate. In case of carbon dioxide reduction (CO2 reduction) the product was identified to be formate by oxidizing the product (formate) on a Pt ring electrode. The results revealed CN/CuAg/Cu2O shows a better selectivity towards formic acid formation than CN/Cu/Cu2O using the rotating ring disc electrode (RRDE). A probable reason may be the strain induced by alloy formation which could favor a reduced coverage of adsorbed hydrogen and a decrease in oxophilicity of the compressively strained copper.

How key characteristics of carbon materials influence the ORR activity of LaMnO3- and Mn3O4-carbon composites prepared by in situ autocombustion method

In this work we studied the effect of carbon in LaMnO3- and Mn3O4- carbon composites synthesized through the In Situ Auto Combustion (ISAC) route for the Oxygen Reduction Reaction (ORR). For this study, we prepared LaMnO3 perovskite and Mn3O4 spinel composites using different types of carbon materials: carbon blacks, pyrolytic carbons, and catalytic filamentous carbon. Various analytical methods such as cyclic voltammetry, rotating ring disc electrode, Brunauer-Emmett-Teller (BET) method, X-Ray Powder Diffraction (XRD), thermogravimetric analysis (TGA), X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) and Electron Energy Loss Spectroscopy (EELS) were used to shed light on the influence of carbon in LaMnO3- and Mn3O4 - carbon composites during the ORR. These allowed us to define key characteristics of carbon materials, which determine the ORR activity and selectivity of the composites, among them sub-structural characteristics of carbon materials and pore accessibility. We conclude that (i) the ISAC route allows to significantly increase the number of accessible oxide sites and the ensuing ORR activity, (ii) the oxidation degree of Mn in LaMnO3 depends on the type and wt.% of carbon material and sub-structural order of carbon. (iii) We further claim that sub-structural characteristics of carbon materials, their pore size and size distribution affect the ORR activity of LaMnO3- and Mn3O4 - carbon composites. (iv) We see that an optimum combination of the carbon and the metal oxide allows obtaining the highest ORR activity. (v) Vulcan XC72 carbon seems to be the best suited for the ISAC synthesis of metal oxide-carbon composites due to its high structure consisting of highly branched flexible reticulate agglomerates.

Catalytic Performances of NiCuP@rGO and NiCuN@rGO for Oxygen Reduction and Oxygen Evolution Reactions in Alkaline Electrolyte

AbstractIn this paper, the reduced graphene oxide (rGO) supported nickel‐copper phosphide (NiCuP@rGO) nanotube and nickel‐copper nitride (NiCuN@rGO) nano‐rods were synthesized and the catalytic performances of them for oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) in alkaline electrolyte were reported. Structure investigations show that the NiCuP@rGO has a nanotube structure, whereas NiCuN@rGO has aggregated nanorods structure. The catalytic performance of NiCuP@rGO and NiCuN@rGO for ORR and OER were investigated by cyclic voltammetry (CV), Tafel, rotating disc electrode (RDE) and rotating ring disc electrode (RRDE) tests and other methodologies. Results showed that both NiCuP@rGO and NiCuN@rGO had good catalytic performance for ORR, which major happened through 4‐electron pathway. Thus, the catalytic performance of NiCuP@rGO for OER was much higher than that of NiCuN@rGO. The great difference in the catalytic performance should be attributed to the different electronegativity of nitrogen and phosphorus. The higher negativity of nitrogen facilitates the electron transfer from catalyst to oxygen molecules but inhibits the acceptance of electron from hydroxide ions in the alkaline electrolyte. On the other hand, the nanotube structure of NiCuP@rGO with superior electron conductivity facilitates the OER reaction on the catalyst surface. This paper provides a reference for the design of novel catalysts for ORR and OER.

Development of Nanosized Mn3O4-Co3O4 on Multiwalled Carbon Nanotubes for Cathode Catalyst in Urea Fuel Cell

Double-oxide Mn3O4-Co3O4 nanoparticles were synthesized and anchored on multiwalled carbon nanotubes (MWCNTs) via a single-step solvothermal method. The largest specific area (99.82 m2g−1) of the catalyst was confirmed via a nitrogen adsorption isotherm. Furthermore, the uniform coating of the Mn3O4-Co3O4 nanoparticles on the surface of the MWCNTs was observed via scanning electron microscopy and transmission electron microscopy; the uniform coating provided an effective transport pathway during the electrocatalytic activities. The rotating disk electrode and rotating ring disk electrode measurements indicated that the electron transfer number was 3.96 and the evolution of H2O2 was 2%. In addition, the Mn3O4-Co3O4/MWCNT catalyst did not undergo urea poisoning and remained stable in an alkaline solution. Conversely, commercial Pt/C could not withstand urea poisoning for long. The performance cell achieved a power density of 0.4226 mW cm−2 at 50 °C. Therefore, Mn3O4-Co3O4/MWCNT is an efficient and inexpensive noble-metal-free cathodic catalyst for direct urea fuel cells.

(Invited) Oxygen Reduction Reactivity at Fe- and Cu-Codoped Carbon Nanostructures

Polymer electrolyte fuel cells (PEFCs), which can efficiently convert hydrogen into electricity without using fossil fuels, are a promising energy conversion device. At the cathodes of PEFCs, oxygen reduction reaction (ORR) occurs via 4-electrons' and 4-protons' transfer. Due to its low reaction rate limiting the performance of PEFCs, the electrocatalysts are necessary and the platinum-based electrocatalysts for ORR are mainly used because of its highest electrocatalystic activity in the metals. Since platinum metal is expensive and rare, there is a need to develop non-platinum-based electricatalysts based on iron and/or copper with high ORR activity1,2,3,4). A cytochrome c oxidase (CcO), which is a metalloenzyme and contains iron and copper metal ions, catalyzes the ORR efficiently to produce ATP in mitochondria5) and its activity is higher than that of artificial platinum-based electrocatalysts6). Metalloenzymes are not practical because of their stability, size, and difficulty to isolate and purify.In this study, iron and copper co-doped carbon electrocatalysts, synthesized from the mixtures of Fe and/or Cu complexes and carbon nanotubes in heat treatment inspired by the CcO’s active center, were developed. Synthetic conditions of Fe : Cu metal ratios and heating temperatures were optimized. The ORR activity was evaluated by hydrodynamic voltammetry using a rotating ring disk electrode in 0.05 M sulfuric acid aqueous solution saturated with oxygen. The activity of Fe/Cu/CNT catalyst was compared with two catalysts: iron-doped carbon carbon catalyst (Fe/CNT) and copper-doped carbon catalyst (Cu/CNT). The Fe/Cu/CNT catalyst showed more positive onset potential for the oxygen reduction in acidic media than Fe/CNT and Cu/CNT, indicating that Fe/Cu/CNT is more active, and we figure out that the coexistence of iron and copper in CNTs contributes to the improvement of ORR activity.

One-Pot Synthesis of Pt-Free 3D-Catalyst for PEMFC

Pt-free catalysts for Oxygen Reduction Reaction (ORR) are broadly studied for Proton Exchange Membrane Fuel Cells (PEMFC) in order to widely develop hydrogen as a fuel for individual transportation. To reduce the performance gap between noble and non-noble catalysts, kinetics and thermodynamics are to be considered. The kinetics of the reaction is influenced by both the turn over frequency of the catalytic site and the density of said sites in the materials. The diffusion of gaseous reactants and liquid water produced is equally important as it modifies the thermodynamic of the reaction. For a long time now, Fe-C-N materials have been identified as the most promising Pt-free electrocatalysts for ORR despite the limited knowledge on the actual structure of the involved sites. Several approaches are currently studied to produce materials with high active site density and high porosity. Different carbon structures are modified to include active sites. The most reported and promising routes are Metal Organic Frameworks, polymers on carbon nanoparticles and silica templated organic structures.In this new approach, carbon cryogels are chosen for their tunability and high specific surface area. Porous Fe-C-N catalysts are synthesized in one step by a modified resorcinol-formaldehyde aerogel method. Gelation, drying and pyrolysis steps are carefully studied and optimized to obtain a high density of accessible catalytic sites. The porosity of the formed materials is measured with nitrogen adsorption. Values of the Brunauer Emmett Teller (BET) surface area up to 800 m2/g are obtained. The impact of different synthesis parameters on catalytic activity is studied. To assess the catalyst’s performances toward ORR, rotating ring Disk Electrode measurements as well as Fuel Cell polarization curves will be reported.