Electrode For Oxygen Reduction Reaction Research Articles

Ni-doped Fe-based perovskite to obtain multifunctional and highly efficient electrocatalytic active IT-SOFC electrode

This paper systematically studies Ni doping at Fe sites in La0.6Sr0.4Co0.3Fe0.7O3-δ (LSCF) as an intermediate temperature solid oxide fuel cell (IT-SOFC) electrode. The electrocatalytic activity of Ni-doped electrodes in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) modes was analyzed, rather than individual cathode or anode. The results indicate that Ni doping increases the internal vacancies, ORR activity, and charge transfer ability of La0.6Sr0.4Co0.3Fe0.6Ni0.15O3-δ (LSCFN15). In addition, compared to LSCF, LSCFN15 also reduces the energy barriers for surface oxygen exchange and bulk diffusion, thereby increasing the overall ORR kinetic rate. Combined with the distribution of relaxation time (DRT) analysis, it was confirmed that Ni-doped LSCFN15 increased the adsorption and dissociation rates of oxygen. At 750 ℃, the area-specific resistance (ASR) of LSCFN15 reached 0.045 Ω cm2, which is only 58.4 % of LSCF (0.077 Ω cm2). As a SOFC cathode, the peak power density (PPD) reached 1175 mW cm−2, 1.31 times that of LSCF (898 mW cm−2). As a SOFC anode, the current exchange density of LSCFN15 in OER mode reaches 164 mA cm−2, which is higher than the 125 mA cm−2 of LSCF, indicating that LSCFN15 also has the potential to serve as an anode for SOFC. In addition, Ni doping reduces the thermal expansion coefficient of the electrode and improves its thermal compatibility with traditional electrolytes. As an electrode, LSCFN15 exhibits excellent long-term stability in both SOFC and SOEC modes. Overall, Ni-doped Fe-based perovskite can improve the ORR and OER activities while enhancing the stability of cell operation and is expected to obtain multifunctional SOFC electrode materials.

Electrocatalytic degradation of Favipiravir by heteroatom (P and S) doped biomass-derived carbon with high oxygen reduction reaction activity

In this study, a biomass-derived carbon block with heteroatoms (P and S) self-doped graphene structure was successfully synthesized by spent coffee grounds (SCG) directly sintered method. The spent coffee grounds biomass-derived carbon (SCC) block was used as electrocatalytic electrode to effectively degrade the antiviral drug of Favipiravir (FAV) in water, which represented excellent oxygen reduction reaction (ORR) activity with the H2O2 production. The doped heteroatoms in the graphene structure of SCC provided many active sites in the electrocatalytic electrode for ORR as well as more production of reactive OH･. Based on the structural characterization, radical species identification and intermediate products analysis, the reaction mechanism of FAV degradation by the SCC block electrode was proposed. This catalytic system also showed high ecological safety that the ecological toxicity for Vibrio fischeri was significantly reduced with the degradation process of FAV. The degradation of FAV in recycle test and in real sample of lake water, well water, tap water all demonstrated high stability of structure and catalytic activity of SCC. The electrocatalytic system based on SCC block electrode has realized the recycling and utilization of biomass resources and has promising application on the removal of environmental pollutants.

New Materials for Alkaline Fuel Cells from Electroplating Industries Waste Solution Oxygen Reduction Reaction Catalyzed by Pd on Carbon Nanotubes, Graphene and Carbon Black

Issues concerning the energy sector are the focus of international discussions; the progressive depletion of fossil reserves and the increase in energy demand have led to the rise in fuel and electricity prices. In this context, fuel cells are promising candidates for a sustainable future. Oxygen Reduction Reaction (ORR) is the bottle-neck strategic reaction ruling the fuel cell efficiency process. This reaction allows the release of chemical energy in the form of electricity without producing any waste. However, the slow kinetics of ORR require highly effective electrocatalysts for proper boosting. It is well known that best available catalysts, in terms of raw bulk elements, belong to the so-called platinum group metals (PGMs). PGMs are very expensive, hence lowering the PGM content of ORR catalysts is among the most prevalent research focuses [1,2].We propose two different ways to obtain carbon-based ORR catalyst with a low continent of PMGs. The first approach involves the use of Single-Ion catalysts designed by carbon nanotubes functionalized with palladium(II) complexes show [3]. The second approach is totally innovative and aims at recovering precious metals to reduce industrial waste and promote the development of a circular economy. Large quantities of wastewater are produced in electroplating industries. This wastewater not only has to be properly processed before it is released into the environment, but also contains metals like palladium [4]. Using carbon materials and an electroless deposition, palladium can be recovered from the wastewater of the electroplating industry. We focus on carbon black (CB) and two different types of graphene-type materials named as (G4) and (G7). It was found that CB and G4 can recover up to 97% palladium. In this way we obtained hybrid materials containing palladium that could be promising candidates for use as catalysts for the ORR in alkaline fuel cells.New catalysts were treated by preparing a nafion polymeric dispersion and tested with electroanalytical techniques. Rotating ring-disk electrode (RRDE) experiments were performed to investigate the catalytic pathway of ORR and asses the number of exchanged electrons per oxygen molecule. Results confirm that tested materials promote the four-electron reaction pathway and reduce the formation of hydrogen peroxide. These approaches provide the basis for further developments to improve the efficiency of future low-cost catalysts for alkaline fuel cells.[1] Passaponti, M.; Lari, L.; Bonechi, M.; Bruni, F.; Giurlani, W.; Sciortino, G.; Rosi, L.; Fabbri, L.; Vizza, M.; Lazarov, V.K.; et al. Optimisation Study of Co Deposition on Chars from MAP of Waste Tyres as Green Electrodes in ORR for Alkaline Fuel Cells. Energies 2020, 13, 5646, doi:10.3390/en13215646.[2] Bonechi, M.; Giurlani, W.; Vizza, M.; Savastano, M.; Stefani, A.; Bianchi, A.; Fontanesi, C.; Innocenti, M. On the Oxygen Reduction Reaction Mechanism Catalyzed by Pd Complexes on 2D Carbon. A Theoretical Study. Catalysts 2021, 11, 764, doi:10.3390/catal11070764.[3] Savastano, M.; Passaponti, M.; Giurlani, W.; Lari, L.; Calisi, N.; Delgado-Pinar, E.; Serrano, E.S.; Garcia-España, E.; Innocenti, M.; Lazarov, V.K.; et al. Linear, Tripodal, Macrocyclic: Ligand Geometry and ORR Activity of Supported Pd(II) Complexes. Inorganica Chim. Acta 2021, 518, 120250, doi:10.1016/j.ica.2021.120250.[4] De Beni, E.; Giurlani, W.; Fabbri, L.; Emanuele, R.; Santini, S.; Sarti, C.; Martellini, T.; Piciollo, E.; Cincinelli, A.; Innocenti, M. Graphene-Based Nanomaterials in the Electroplating Industry: A Suitable Choice for Heavy Metal Removal from Wastewater. Chemosphere 2022, 292, 133448, doi:10.1016/j.chemosphere.2021.133448.

Biochar catalysts from animal manure: Production and application

Biochar is a sustainable functional material rich in carbon, derived from renewable resources such as biowaste (e.g., animal manure). It has unique chemical structure, large surface area and porosity, and tailored surface functional groups via proper activation and/or functionalization, thereby having high potential as heterogeneous catalytic materials applied to different chemical processes. Therefore, using animal manure-derived biochar as catalytic materials could be key to sustainable agriculture and chemical industries. Recent recognition of animal manure-derived biochars as versatile media of catalytic applications has encouraged rudimentary studies on their catalytic capabilities; however, the use of animal manure-derived biochar as catalytic materials has not been systematically reviewed yet. This review gives an overview of recent achievements in producing biochar from animal manure and subsequent modification methods. The catalytic properties of the biochar with respect to its production/modification recipes are also discussed. Furthermore, the catalytic performances of animal manure-derived biochars for different catalytic applications, such as transesterification, hydrogen production, hydrolysis, C–C coupling reactions, and electrodes for oxygen reduction reaction, supercapacitor, and lithium-ion battery, are evaluated.

Pore surface engineering of FeNC for outstanding power density of alkaline hydrazine fuel cells

In alkaline hydrazine fuel cells (AHFCs), the rapid kinetics of hydrazine oxidation contribute to their superior power density compared to other liquid fuel cells. However, the optimization of oxygen reduction reaction (ORR) electrodes in AHFCs has received limited attention, despite the potential importance of ORR as a rate-determining step. The wettability and pore structure of ORR catalysts are critical factors in facilitating reactant supply (O2 and H2O) and improving catalyst utilization. In this study, we synthesized a hierarchical pore structure in a FeNC catalyst by excess iron incorporation and steam activation, and adjusted its water/oxygen gas contact property by oxalic acid treatment. The modified catalyst exhibited improved wettability and optimized triple-phase boundaries. Remarkably, utilizing a 25 cm2 electrode size and non-noble electrocatalysts, the resulting AHFC achieved a significant power density improvement from 630 to 1240 mW cm−2, setting a new record for AHFCs. This research highlights the importance of pore structure and surface engineering, including the role of excess iron, in enhancing the performance of ORR electrodes in AHFCs.

Effect on percolation threshold of catalytic layer: Pt/N‐Doped graphene shell onto SWCNT for ORR electrode

AbstractA high‐rate oxygen reduction reaction (ORR) is necessary for polymer electrolyte membrane fuel cells (PEMFC). In this work, by using a solution plasma technique, Pt catalytic particles coated with N‐doped graphene (Pt‐NG) were effectively produced at 25°C. According to transmission electron microscope images, the average diameter of Pt particles was 4 nm, while the graphene layer thickness was less than 1 nm. A catalytic layer of Pt‐NG supported on single‐walled carbon nanotubes (Pt‐NG/SWCNT) was synthesized. Cyclic voltammetry was used to assess the ORR characteristics of Pt‐NG/SWCNT catalytic layers. Only at a density of SWCNT to solvent ratio of 0.75 mg ml−1 were the ORR peaks clearly visible. Because of the high resistivity of SWCNT layers, the ORR peaks in other ranges, 0.4 mg ml−1 to 2.0 mg ml−1, were not clearly observed. The effect of SWCNT concentration on conductivity was proven to follow the basic concept of the percolation threshold.

Tetraphenylporphyrin Decorated Bi2MoO6 Nanocomposite: Its Twin Affinity of Oxygen Reduction Reaction and Electrochemical Detection of 4-Nitrophenol.

A selective electrode for oxygen reduction reaction (ORR) and electrocatalytic reduction of 4-nitrophenol (p-NP) was fabricated on a glassy carbon electrode using organic-inorganic Bi2MoO6/H2TPP nanocomposites with different weight percentages of tetraphenylporphyrin, synthesized by the solvothermal process. Materials thus synthesized were characterized through UV-Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) analysis. The electrocatalytic performance of the modified electrode toward ORR in the 0.1 M KOH solution, the onset potential Eonset (0.942 V), E1/2 (0.704 V) vs RHE, Jd (-5.545 mA cm-2), and n = 4 physicochemical parameters were well appreciable. It exhibits good catalytic activity toward ORR through a four-electron pathway with excellent stability and high active site density, and thus, the in situ Porphy-decorated metal oxide system facilitates the electron transport process. High selectivity and efficacy for the oxygen reduction reaction (ORR) are a significant measure for several energy-converting applications. The decorated electrode, glassy carbon electrode (GCE)/Bi2MoO6/3 wt % Porphy, serves as an electrochemical sensor that exhibited good sensitivity (0.4683 μAμM-1 cm-2), good reproducibility, a low detection limit (0.0940 μM), and long-term stability in the aqueous phase without any appreciable effect in the presence of some common organic and inorganic interferences for the detection of p-NP in a linear concentration range of 0.5-350 μM. Therefore, the material performs as an effective electrode for both the ORR and the electrocatalytic reduction of p-NP with real matrix samples at room conditions.

Tuning the wettability of advanced mesoporous Fe[sbnd]N[sbnd]C catalysts for optimizing the construction of the gas/liquid/solid three-phase interface in air-cathodes

To explore high-efficient FeNC oxygen reduction reaction (ORR) catalysts, remarkable efforts have been made to search the active sites with superior ORR activity and increase the site density and exposure. However, the active sites are not utilized in fuel cells unless they are located at the gas/liquid/solid three-phase interface that can simultaneously get in touch with ions and oxygen. Tuning the wettability of the catalyst layer (CL) is a key to enlarging the three-phase interface. Here, we adjusted the wettability of FeNC catalysts and thus obtained a series of ORR electrodes with different CL wettability. Various electrochemical methods were linked and carried out to quantitatively investigate how the wettability influences the electrode behaviors including current response, electrochemical surface area, impedance, and oxygen and ion diffusion coefficient. The results revealed that the electrode behaviors are quite sensitive to the wettability of CL. Moreover, the construction of the three-phase interface that requires a coupling development of gas and liquid channels ultimately determines the electrode performance. In detail, the liquid channels of the water superwettable electrode and the gas channels of the gas superwettable electrode were both overdeveloped, which caused that the electrolyte-wetted surfaces of the former are not fully exposed to gas and lots of gas-exposed surfaces of the latter cannot be wetted by electrolytes. While the electrode with moderate gas and water wettability succeeded in a sufficient coupling development of gas and liquid channels and thus exhibited an optimal three-phase interface and a boosted cathode performance.

Easy enrichment of graphitic nitrogen to prepare highly catalytic carbons for oxygen reduction reaction

One of the biggest challenges in producing fuel cells at affordable prices is to synthesize carbon materials selectively doped with graphitic nitrogen, as it is considered the most active nitrogen species for the oxygen reduction reaction (ORR). So far, all strategies focus on the use of nitrogen-containing carbon precursors, which limits the functionalization of commercially available carbon materials. Here, we present a post-functionalization method to boost the catalytic properties of carbon materials for the ORR by selectively enriching activated carbons with nitrogen graphitic species. A commercial high-surface area activated carbon was post-functionalized by a two-step procedure. First, the commercial carbon was mixed with different carbon/urea weight ratios and heated in air at 350 °C. Then, the functionalized materials were heat-treated at high temperature (from 700 to 1300 °C) to tailor the amount and distribution of the different nitrogen species in the resulting carbon structure. Nitrogen functionalization using a carbon to urea weight ratio of 1:2 and heat-treatment at 1100 °C led to highly selective doping in graphitic nitrogen species, which provided the tools to individually asses the catalytic activity of these nitrogen species. In addition, this study presents a low-cost and easily feasible synthesis route to improve the catalytic activity of carbon materials, leading to an onset potential of almost 0.9 V compared to reversible hydrogen electrode for ORR in an alkaline electrolyte. Moreover, this study provides significant evidence for the key role of graphitic nitrogen.

MOF derived CeO2/CoFe2O4 wrapped by pure and oxidized g-C3N4 sheet as efficient supercapacitor electrode and oxygen reduction reaction electrocatalyst materials

In this work, MOF-derived metal oxide/spinel metal oxide nanocomposite was successfully synthesized. Then, different amounts of pure and oxidized g-C3N4 were introduced to nanocomposites as modification treatments using preserved shape and complex appropriate features of g-C3N4. After mixing CeO2/CoFe2O4 with pure and oxidized g-C3N4 sheets, the 10% Ox-g-C3N4/CeO2/CoFe2O4 hybrid exhibited excellent supercapacitor, and 20% g-C3N4/CeO2/CoFe2O4 shows good oxygen reduction reaction (ORR) performance. Accordingly, the 10% Ox-g-C3N4/CeO2/CoFe2O4 electrode exhibited a high specific capacitance (255.5 F/g). Asymmetric device (using the promising electrode as cathode and activated carbon as the anode), achieved a wide potential window up to 1.6 V with a high-power density of 11,904 W/kg and a good cycling performance with 91% capacitance retention after 3000 charge/discharge cycling test. Furthermore, the as-prepared 20% g-C3N4/CeO2/CoFe2O4 showed good comparable to those of commercially available Pt/C electrodes in oxygen reduction reaction (ORR) performance. The enhanced capacitive and electrocatalytic properties and stability are due to the synergistic interactions between the porous pure or oxidized g-C3N4 sheets and CeO2/CoFe2O4. The results indicate that introducing pure or oxidized g-C3N4 to MOF-derived metal oxide could be a useful strategy for improving the performance of energy storage devices supercapacitor and ORR catalysts.

Selection of oxygen reduction catalysts for secondary tri-electrode zinc\u2013air batteries

Oxygen reduction reaction (ORR) electrocatalysts, which are highly efficient, low-cost, yet durable, are important for secondary Zn–air cell applications. ORR activities of single and mixed metal oxide and carbon electrocatalysts were studied using rotating disc electrode (RDE) measurements, Tafel slope and Koutecky–Levich plots. It was found that MnOx combined with XC-72R demonstrated high ORR activity and good stability—up to 100 mA cm−2. The performance of the selected ORR electrode and a previously optimised oxygen evolution reaction (OER) electrode was thereafter tested in a custom-built secondary Zn–air cell in a tri-electrode configuration, and the effects of current density, electrolyte molarity, temperature, and oxygen purity on the performance of the ORR and OER electrode were investigated. Finally, the durability of the secondary Zn–air system was assessed, demonstrating energy efficiencies of 58–61% at 20 mA cm−2 over 40 h in 4 M NaOH + 0.3 M ZnO at 333 K.

Tetraphenolphthalein Cobalt(II) Phthalocyanine Polymer Modified with Multiwalled Carbon Nanotubes as an Efficient Catalyst for the Oxygen Reduction Reaction.

Oxygen reduction reaction (ORR) is the main reaction at the cathode of a fuel cell that utilizes Pt/C as the benchmark catalyst. Due to sluggish activity, high cost, rare abundance, and durability issues, Pt/C must be replaced by nonprecious, stable, and easily synthesizable materials. This work involves the synthesis of novel, simple, low-cost, and environmentally friendly phenolphthalein-bearing cobalt(II) phthalocyanine polymer, poly(CoIITPpPc) dyad, as an efficient catalyst for ORR. The results of analytical characterizations reveal the formation of the poly(CoIITPpPc) polymer in the pure state. To further enhance the catalytic response of poly(CoIITPpPc), a hybrid composite is prepared using poly(CoIITPpPc) and multiwalled carbon nanotubes (MWCNTs) that increase the surface area and conductivity. The poly(CoIITPpPc) and hybrid composite are separately deposited on the electrode surfaces. The electron microscopy images confirm the uniform distribution of the poly(CoIITPpPc) molecules on the electrode surface and MWCNTs. The poly(CoIITPpPc) and hybrid composite electrodes are evaluated for ORR, and the hybrid composite exhibits better onset potential at 0.803 V versus reversible hydrogen reference electrode for ORR according to linear sweep voltammograms (LSVs). The obtained data are superior compared to those of other carbon-based redox-active materials reported previously and nearer to those of the benchmark catalyst (Pt/C). The rotating disc electrode measurement of the hybrid composite electrode confirms the total number of electrons involved in ORR to be four. Furthermore, the hybrid composite electrode exhibits an excellent stability for 100 LSV scans. The synergistic effect of poly(CoIITPpPc) and MWCNTs leads to the surprisingly high ORR activity due to the improved surface area, conductivity, and interfacial confined surface.

Nanostructured, Metal-Free Electrodes for the Oxygen Reduction Reaction Containing Nitrogen-Doped Carbon Quantum Dots and a Hydroxide Ion-Conducting Ionomer.

In this work, we studied the combination of nitrogen-doped carbon quantum dots (N-CQD), a hydroxide-ion conducting ionomer based on polysulfone (PSU) and polyaniline (PANI), to explore the complementary properties of these materials in high-performance nanostructured electrodes for the oxygen reduction reaction (ORR) in alkaline solution. N-CQD were made by hydrothermal synthesis from glucosamine hydrochloride (GAH) or glucosamine hydrochloride and N-Octylamine (GAH-Oct), and PSU were quaternized with trimethylamine (PSU-TMA). The nanocomposite electrodes were prepared on carbon paper by drop-casting. Furthermore, we succeeded in preparing PSU-TMA + PANI + GAH-Oct fibers by electrospinning. The capacitance of the electrodes was investigated by cyclic voltammetry and impedance spectroscopy, which gave similar trends. The ORR was investigated by linear sweep voltammetry at rotating disk electrode speeds between 250 and 2000 rpm in an oxygen-saturated 1 M KOH solution. Koutecky–Levich plots showed that four electrons were exchanged for nanocomposite electrodes containing CQD. The highest reduction currents were measured for the electrodes containing GAH-Oct. The Tafel plots gave the lowest slope and the most positive half-wave potential for PSU-TMA + PANI + GAH-Oct fibers. The best electrocatalytic activity of this electrode could be related to the high amount of graphitic nitrogen in GAH-Oct. Long-term cycling tests showed no significant modification of the onset potential, but a change of the current in the mass transport limited region, indicated the evolution of the microstructure of the nanocomposite ORR electrode modifying the mass transport conditions during the first 400 cycles before reaching stationary conditions. FTIR spectra were used to study possible electrode degradation after the ORR in 1 M KOH: the only change was due to the reaction of PANI emeraldine salt to emeraldine base, whereas the other constituents of the multiphase electrode did not show any degradation.

Oxygen reduction reaction at conducting polymer electrodes in a wider context: Insights from modelling concerning outer and inner sphere mechanisms

AbstractPractical interest in oxygen reduction reaction (ORR) has traditionally been due to its application at fuel cells’ cathode following its complete 4e route to the water. In search of new electrode materials, it was discovered that conducting polymers (CPs) also are capable of driving ORR, though predominantly halting the process at 2e reduction leading to hydrogen peroxide generation. As alternative ways to produce this “green oxidant” are attracting increasing attention, a detailed study of the ORR mechanism at CP electrodes gains importance. Here, we summarize our recent theoretical work on the topic, which underscores the fundamental difference between CP and electrocatalytic metal ORR electrodes. Our insights also bring to us the attention of outer‐sphere electron transfer, not unknown but somewhat ignored in the field. We also put the action of CP electrodes in a more general context of chemical ORR and redox mediation responsible for the electrocatalytic ORR mechanism.

Direct thermal annealing synthesis of FeO nanodots anchored on N-doped carbon nanosheet for long-term electrocatalytic oxygen reduction

It is highly desired to exploit non-noble metal oxide catalysts for superseding the Pt-based material and achieving long-term oxygen reduction reaction (ORR). Herein, a FeO-based ORR catalyst is firstly designed and synthesized by a one-pot pyrolysis strategy using FeCl3 and N-doped carbon nanosheets (NCNSs) as precursors. The NCNSs substrate play the important role to control the size of gained FeO at nanodot level (near 2.5 nm). The supersmall FeO nanodots, uniformly dispersion on the NCNSs, which enhance the touching areas with the NCNSs substrate and expose richen active sites. The introduction of FeO nanodots improve the graphitization degree of the composite and form Fe-N bonds in FeO/NCNSs, then exhibiting excellent electrocatalytic performance and long-term stability. The catalyst displays a high half-wave potential and small Tafel slope of 0.94 V and 56.9 mV dec−1 in the 4 electron ORR process, respectively. Meanwhile, it demonstrates superior tolerance to methanol. Noting, after 150 h i t-test, the current density only drops by 10.7%, even better than the durability performance of many catalysts after 10 h. The theoretical calculations further reveal that the OH* adsorption on the surface of FeO/NCNSs in real reaction environment is beneficial for embedding the FeO NDs in N6 hollow of NCNSs, which sustains the highly efficient ORR activity under the long-term running conditions. Our work opens a new era for the novel FeO-based ORR catalysts and provides a design reference for the long-term ORR electrode.

High-performance carbon black electrode for oxygen reduction reaction and oxidation of atrazine by electro-Fenton process

The aim of this study is to produce an electrode that can be used in H2O2 production and Electro-Fenton (EF) process by an effective, cheap, and easy method. For this reason, a superhydrophobic electrode with a higher PTFE ratio and high thickness was produced with a simple press. The produced electrode was used in the production of H2O2 and mineralization of Atrazine. First, the effect of pH, cathode voltage, and operation time on H2O2 production was evaluated. The maximum H2O2 concentration (409 mg/L), the highest current efficiency (99.80%), and the lowest electrical energy consumption (3.16 kWh/kg) were obtained at 0.8 V, 7.0 of pH, and 120 min, and the stability of the electrode was evaluated up to 720 min. Then, the effects of the operational conditions (pH, cathode voltage, operating time, and catalyst concentration) in electro-Fenton were evaluated. The fastest degradation of Atrazine (>99%) was obtained at 2.0 V, 3.0 of pH, and 0.3 mM of Fe2+ in 15 min. In the final part of the study, the degradation intermediates were identified, and the characterization of the electrode was evaluated by SEM, XRD, FT-IR, tensiometer, potentiostat, and elemental analyzer.

Insights into surface alkaline-earth segregation on the surface of La0.3Me0.7Fe0.7Cr0.3O3−δ (Me = Sr, Ca) porous electrodes for oxygen reduction reaction

Surface alkaline-earth segregation is a common problem encountered for the cathodes of solid oxide fuels cells based on perovskites (ABO3) containing alkaline-earth acceptor dopants. In this work, the porous electrodes of La0.3Me0.7Fe0.7Cr0.3O3−δ (Me = Sr, Ca) were employed as the model specimens to look into the surface segregation issue. The two electrodes were cathodically polarized by continuously testing their cathodic current polarization curves. The electrocatalytic activity of the two electrodes was examined in relation with their cathodic polarization history. Moreover, the crystal and surface structures of the cathodically polarized electrodes were analyzed. An appreciable segregation of strontium onto the surface was detected for cathodically polarized La0.3Sr0.7Fe0.7Cr0.3O3−δ electrode, leading to an obvious deceleration of disassociative adsorption of molecular oxygen on the surface and thus degradation of the electrode activity. In contrast, La0.3Ca0.7Fe0.7Cr0.3O3−δ electrode displayed nearly negligible surface calcium segregation and degradation of the electrocatalytic activity after experiencing an identical cathodic polarization history. The disparity of the two electrodes was related to their A-site compositions. This work exemplifies the importance of minimizing A-site cation size mismatch in stabilizing the crystal structure of the perovskite electrodes under cathodic polarization conditions and therefore alleviating the segregation of A-site alkaline-earth cations onto the electrode surface.

A Facile Method to Realize Oxygen Reduction at the Hydrogen Evolution Cathode of an Electrolytic Cell for Energy-Efficient Electrooxidation.

Electrochemical oxidation, widely used in green production and pollution abatement, is often accompanied by the hydrogen evolution reaction (HER), which results in a high consumption of electricity and is a potential explosion hazard. To solve this problem, we report here a method for converting the original HER cathode into one that enables the oxygen reduction reaction (ORR) without having to build new electrolysis cells or be concerned about electrolyte leakage from the O2 gas electrode. The viability of this method is demonstrated using the electrolytic production of ammonium persulfate (APS) as an example. The original carbon black electrode for the HER is converted to an ORR electrode by first undergoing in situ anodization and then contacting O2 or air bubbled from the bottom of the electrode. With this sole change, APS production can achieve an electric energy saving of up to 20.3%. Considering the ease and low cost of this modification, such significant electricity savings make this method very promising in the upgrade of electrochemical oxidation processes, with wide potential applications.

The use of reactive binder for carbon-based oxygen reduction reaction catalyst in neutral medium

In this study, we report the use of reactive binding strategy to fix carbon-based oxygen reduction reaction (ORR) catalyst to metal current collector for the first time. Reactive binder, e.g. phenol-formaldehyde resin (PFR) oligomer, is developed as an alternative to the popularly used Nafion binder to bond carbon-based ORR catalyst, e.g. Pt/C (Pt loaded on VulcanX C72R carbon black), onto stainless steel (SS) current collector for use as cathode in microbial fuel cells. The ORR electrocatalytic performance of the Pt/C electrode bonded by PFR (Pt/C-PFR) is studied in neutral medium and compare with that bonded by the Nafion binder (Pt/C-Nafion). Results show that the dosage of PFR binder in the Pt/C-PFR could be only half that of Nafion binder in the Pt/C-Nafion, and the resulted Pt/C-PFR shows superior ORR electrocatalytic performance and stability to that of Pt/C-Nafion on the SS current collector. A strong interaction is developed between the SS and the PFR binder, which is four times of that between the SS and the Nafion binder. X-ray photoelectron spectroscopy results reveal that the higher bonding strength can be attributed to the formation of C−O−Fe bonds between the PFR and the SS. This study offers a low-cost and effective binding strategy for generating high-performance and scalable ORR electrode.

Fabrication and Characterization of Metal‐Free Composite Electrodes Based on Few‐Layer‐Graphene Nanoplatelets for Oxygen Reduction Reaction Applications

The fabrication of advanced graphene‐based electrodes is currently an open research topic because of their potential in a broad range of applications, such as in light‐emitting diodes, field‐effect transistors, solar cells, supercapacitors, batteries, electrochemical energy storage, and sensors, which can be traced back to their remarkable electronic, mechanical, optical, and thermal properties. Herein, the fabrication and characterization of metal‐free few layer graphene‐based composite electrodes for oxygen reduction reaction (ORR) applications is reported. Electrodes’ characterization and performance are assessed using Raman spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The electrocatalytic activity for ORR is elucidated by determination of the reaction onset potential at different pH values. The best formulation shows cathodic peak current density up to −469 μA cm−2, accompanied by the lowest potential peak separation of 0.17 V and the lowest charge transfer resistance of 1657 Ω cm−2, which is almost five times lower if compared with the composite electrode without graphene. The results suggest that similar nanocomposites electrodes might be potentially exploited in life processes such as biological respiration, and in energy converting systems such as fuel cells or microbial fuel cells.