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Half-cell gas diffusion electrode (GDE) setups have recently been shown to allow characterization of oxygen reduction reaction (ORR) catalysts at fuel cell relevant current densities and potentials while offering the advantage of fast screening and requiring only minimal sample usage. Most recently, publications suggesting best practices for GDE half-cell characterization have highlighted key challenges in running GDE experiments and have presented measurement protocols that allow excellent Inter-lab comparability. This step can be seen as the cornerstone for broad-based utilization of GDE half-cells. However, what is still missing, is an understanding of what limits the maximum achievable current density in GDE measurements. In this study we highlight the influence of various setup parameters (electrode area, electrolyte concentration, as well as size and position of the counter electrode) on the maximum achievable current density in an automated GDE setup. Furthermore, we present the metrics that need to be considered when adapting the electrochemical protocol for recording ORR polarization curves at higher current densities. The findings observed in this study are not limited to testing the ORR, but can be transferred to any other electrocatalytic reaction tested in a half-cell GDE at high current densities.

The oxygen reduction reaction (ORR) is pivotal for optimizing the energy output of fuel cells and metal-air batteries; however, their commercialization is precluded by the intolerable cost, instability, earth-scarcity of Pt that remains a prestigious catalyst for ORR. Porous ternary Pt-based branched nanostructures (PTB-Pt) with unique catalytic properties, low-density structural stability, multiple electronic effects, high surface area, and maximized atomic utilization can maximize the ORR catalytic activity at low Pt content. This review provides broad and balanced insights on the substantial progress on the rational design of porous PTB-Pt for ORR and their fundamental mechanisms besides the current challenges and perspectives on designing ideal PTB-Pt catalysts for efficient ORR and guidance for future development of real-device.

[Display omitted] • Poisoning effect of benzene-containing hydrocarbon-based ionomers on Pt catalysts. • Two types of orientation-dependent adsorption of benzenesulfonic acid anion for Pt. • Changes in PZTC of Pt surface according to the sequence of electrolyte replacement. • Combination of various electrochemical analyses and XPS/TPD measurements. • Time-dependent anion adsorption affecting the long-term stability of fuel cell electrodes. Membrane electrode assembly (MEA) is an essential component that mainly determines the performance of proton exchange membrane fuel cells (PEMFCs). In the electrodes of the MEA, ionomers are mixed with Pt-based nanoparticles to transfer protons to the Pt surface where electrochemical reactions take place. However, Pt catalysts suffer from the poisoning effect of ionomers with proton-conducting groups such as sulfonic acid (SA), resulting in performance deterioration. In particular, for emerging hydrocarbon-based ionomers, the benzene group, which is commonly used to improve their chemical structure, accelerates the poisoning effect. Herein, we experimentally simulate the adsorption of SA and benzenesulfonic acid (BSA) on Pt nanoparticles, revealing the orientation-dependent poisoning effect of BSA on the Pt surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • ORR reaction mechanism in CW-MFCs occurred through the 4-electrons pathway. • Maximum power density was produced with 1 mg/cm2 of G/TiO 2 in CW-MFCs. • Photosynthetic compounds were used as substrate for the anodic biofilm in CW-MFCs. Constructed wetlands-microbial fuel cells (CW-MFC) are an innovative technology used for simultaneous bioelectricity generation and wastewater treatment. This is possible due to the installation of macrophytes in an electrode configuration, in which electroactive microorganisms use organic substrates as biofuel. One way to improve the electrochemical performance of CW-MFCs is through the impregnation of cathodic electrocatalysts. Therefore, in this study the bioelectricity production capacity of CW-MFCs was evaluated from the oxygen reduction reaction (ORR). For this study, the concentrations 0 (CW-MFC1), 0.5 (CW-MFC2), and 1 mg/cm2 (CW-MFC3) of graphene/titanium dioxide (G/TiO 2) as electrocatalyst on the cathodes were evaluated. Using the Koutecky-Levich analysis, it was determined that the ORR transfer mechanism arises via a 4-electron pathway. The electrokinetic parameters of Tafel slope, charge transfer coefficient, and exchange current density determined the efficiency of the ORR, registering 92 mV/dec, 0.93 (α), and 2.30 x10-3 mA/cm2, respectively for CW-MFC3. The highest electrochemical performance was obtained at a concentration of 1 mg/cm2 (CW-MFC3) of G/TiO 2 , generating 144 mW/m2 of power density, 157 Ω of internal resistance, −150 mV of anodic potential, and 383 mV of cathodic potential. The surface modification carried out on the cathodes resulted in a catalytic increase in the ORR. [ABSTRACT FROM AUTHOR]

• Iodine and Fe-N x were simultaneously introduced into carbon (FeNI-CNS) by a solution plasma process. • Iodine dopants contribute to the oxygen reduction reaction rate with a higher current density. • A synergistic effect further enhances the catalytic activity of the FeNI-CNS. • FeNI-CNS exhibits better durability than commercial Pt/C catalysts. The oxygen reduction reaction (ORR) plays a critical role at the cathode of fuel cells and metal–air batteries. In this study, we report the one-pot synthesis of iodine- and Fe-N x impregnated carbon nanospheres (FeNI-CNS) using a solution plasma process and their effect on electrocatalytic activity. FeNI-CNS exhibits a fast four-electron transfer reaction with a high current density and superior durability in both alkaline and acidic media. The excellent catalytic performance is attributed to the synergetic effect between the iodine and Fe-N x sites, which provide a higher reaction rate and faster ORR, respectively. We believe that these findings represent a new approach for enhancing ORR catalytic performance and catalyst synthesis. [ABSTRACT FROM AUTHOR]

A heteroatom-doped carbon-based electrocatalyst for the oxygen reduction reaction (ORR) was prepared from a hybrid zeolitic imidazolate framework (ZIF) using a step-by-step approach. A bimetallic Co,Zn-ZIF was synthesized by a microwave-assisted method and then enriched with Fe and N. The resulting ZIF was pyrolysed at 700 °C in an inert atmosphere, producing a complex morphology including an amorphous carbon matrix, cobalt nanoparticles and bamboo-like nanotubes. A range of techniques were used to characterize the initial ZIF and the resulting catalyst. The catalytic activity and stability of the carbon-based electrocatalyst towards the ORR were investigated by cyclic voltammetry and chronoamperometry using a rotating disc electrode (RDE) in an acidic medium. The highest electrocatalytic activity for the ORR was reached when an equal weight of commercial carbon black (Vulcan XC-72) was added to the composite. Analysis of Koutecky–Levich plots showed that the reaction followed a four-electron transfer mechanism. A durability test over 1000 cycles showed no signs of decreasing catalytic activity. This catalyst appears to be a promising material for application in fuel cells. [ABSTRACT FROM AUTHOR]

Core-satellite gold nanoassemblies (CSNs) supported on carbon were fabricated by self-assembly using simple molecular cross-linkers and applied to the advanced oxygen reduction reaction (ORR). The as-prepared CSNs exhibited unexpectedly high catalytic activity and a dominant four-electron pathway towards the ORR. [ABSTRACT FROM AUTHOR]

Ag-Co 3 O 4 @N-doped carbon/carbon nanotubes composites are synthesized by dispersing Ag nanoparticles throughout the N-doped carbon derived from ZIF-67/CNT. In oxygen reduction reaction (ORR), the synthesized composites possess a one-step 4 electron pathway, and a synergistic effect between Ag nanoparticles and N-doped carbon is proposed. In the Mg-air fuel cell, the synthesized composites show the highest power density of 88.9 mW/cm 2 at current density of 140 mA/cm 2 , better than that of 20%Pt/C. This excellent performance ensures this composite a promising ORR catalyst for Mg-air fuel cell. [ABSTRACT FROM AUTHOR]

Sulfur doped reduced graphene oxide (S-rGO) is investigated for catalytic activity towards the oxygen reduction reaction (ORR) in acidic and alkaline electrolytes. X-ray photoelectron spectroscopy shows that sulfur in S-rGO is predominantly integrated as thiophene motifs within graphene sheets. The overall sulfur content is determined to be approximately 2.2 at.% (elemental analysis). The catalytic activity of S-rGO towards the ORR is investigated by both rotating disc electrode (RDE) and polymer electrolyte fuel cell (PEFC) measurements. RDE measurements reveal onset potentials of 0.3 V and 0.74 V (vs. RHE) in acidic and alkaline electrolyte, respectively. In a solid electrolyte fuel cell with S-rGO as cathode material, this is reflected in an open circuit voltage of 0.37 V and 0.78 V and a maximum power density of 1.19 mW/cm 2 and 2.38 mW/cm 2 in acidic and alkaline polymer electrolyte, respectively. This is the first report investigating the catalytic activity of a sulfur doped carbon material in both acidic and alkaline liquid electrolyte, as well as in both proton and anion exchange polymer electrolyte fuel cells. [ABSTRACT FROM AUTHOR]

• GDE measurements for evaluation of oxygen reduction reaction catalysts. • Avoiding current limitations in high-current density testing. • Guidelines for design of gas diffusion electrode half-cells. • Best practices for iR correction in high-current density testing. • Comparison of GDE and MEA. Half-cell gas diffusion electrode (GDE) setups have recently been shown to allow characterization of oxygen reduction reaction (ORR) catalysts at fuel cell relevant current densities and potentials while offering the advantage of fast screening and requiring only minimal sample usage. Most recently, publications suggesting best practices for GDE half-cell characterization have highlighted key challenges in running GDE experiments and have presented measurement protocols that allow excellent Inter-lab comparability. This step can be seen as the cornerstone for broad-based utilization of GDE half-cells. However, what is still missing, is an understanding of what limits the maximum achievable current density in GDE measurements. In this study we highlight the influence of various setup parameters (electrode area, electrolyte concentration, as well as size and position of the counter electrode) on the maximum achievable current density in an automated GDE setup. Furthermore, we present the metrics that need to be considered when adapting the electrochemical protocol for recording ORR polarization curves at higher current densities. The findings observed in this study are not limited to testing the ORR, but can be transferred to any other electrocatalytic reaction tested in a half-cell GDE at high current densities. [ABSTRACT FROM AUTHOR]

A Fe, N and S multielement co-doped reduced graphene oxide (Fe–N–S/rGO) was successfully prepared using a one-pot method by directly pyrolyzing a mixture of graphene oxide (GO), FeCl 3 , melamine and sulfur in N 2 flow, during which deoxidization of GO and multielement co-doping are realized simultaneously. This catalyst shows excellent oxygen reduction activity in an alkaline medium, with an onset potential of 0.95 V (vs. RHE) and a kinetic-limiting current density of 4.78 mA cm − 2 at 0.68 V (vs. RHE), which is superior to that of commercial Pt/C. Furthermore, it exhibits long-term stability, excellent methanol tolerance and high selectivity for the four-electron reduction pathway. [ABSTRACT FROM AUTHOR]

Abstract: The oxygen reduction reaction (ORR) has been investigated on fish-bone carbon nanotubes (F-CNTs) and parallel carbon nanotubes (P-CNTs). The results showed that the F-CNTs exhibited much higher activity than P-CNTs, which originated from the higher fraction of edge carbon atoms. The dependence of ORR peak potential on the fraction of edge carbon atoms was determined quantitatively for the first time. The density functional theory calculations clearly unveiled the mechanism of edge carbon atoms facilitating the ORR performance. [Copyright &y& Elsevier]

Abstract: The nitrogen-doped carbon nanotube (NCNT) bouquets have been synthesized by the pyrolysis of nitrogen-containing ion-exchange resin. The material shows excellent oxygen reduction performance after being supported by the Pt nanoparticles (Pt/NCNTs) compared with commercial Pt/C (46.7wt.% Pt, TKK, Japan) in terms of the onset potential, half-wave potential, mass activity and durability. The better ORR performance of the Pt/NCNTs indicates potential applications in PEMCs. [Copyright &y& Elsevier]

[Display omitted] • Highlighting the rational design of ternary Pt-based branched nanostructures (PTB-Pt) • Discussion the fabrication methods of PTB-Pt and their mechanisms. • Emphasizing the effect of shape and composition of PTB-Pt on oxygen reduction (ORR) activity. • Identifying the current limitations and perspectives direction on design PTB-Pt for ORR. The oxygen reduction reaction (ORR) is pivotal for optimizing the energy output of fuel cells and metal-air batteries; however, their commercialization is precluded by the intolerable cost, instability, earth-scarcity of Pt that remains a prestigious catalyst for ORR. Porous ternary Pt-based branched nanostructures (PTB-Pt) with unique catalytic properties, low-density structural stability, multiple electronic effects, high surface area, and maximized atomic utilization can maximize the ORR catalytic activity at low Pt content. This review provides broad and balanced insights on the substantial progress on the rational design of porous PTB-Pt for ORR and their fundamental mechanisms besides the current challenges and perspectives on designing ideal PTB-Pt catalysts for efficient ORR and guidance for future development of real-device. [ABSTRACT FROM AUTHOR]

Abstract: The degradation of a commercial platinum polymer electrolyte membrane (PEM) fuel cell catalyst has been studied under severe simulated start–stop conditions (50,000cycles from 0.2V to 1.4V vs. the reversible hydrogen electrode, RHE), employing a newly developed identical location scanning electron microscopy technique (IL-SEM). We show that significant platinum particle growth occurs on top of the catalyst film while platinum depletion takes place in the layers beneath. There is a possibility of misleading interpretation of thin film severe degradation experiments, when the catalyst loading and volume of electrolyte are neglected and when the non-identical location electron microscopy pictures are statistically analyzed. [Copyright &y& Elsevier]

Abstract: Graphene-xerogel-based Co–N cathode catalyst (Co–N-GX) for the oxygen reduction reaction (ORR) was prepared through a simple approach. The Co–N-GX shows a more positive onset potential, higher cathodic density for the ORR in alkaline media than graphene-sheet-based Co–N catalyst (Co–N-GS), highlighting the importance of high specific surface area for improving the ORR performance. The proposed approach makes the Co–N-GX catalyst a non-precious metal cathode catalyst for fuel cells. [Copyright &y& Elsevier]

Abstract: The oxygen reduction reaction (ORR) has been studied on graphene-supported electrocatalysts in alkaline media. Uniformly dispersed Pd nanoparticles with a mean diameter of ca. 1.8nm can be successfully obtained on graphene sheets (GNSs) through chemical synthesis, even at a high metal loading of 60wt.%. The ORR activity of these catalysts was investigated in a 0.1M NaOH solution, and the kinetic parameters were determined by the rotating disk electrode (RDE) technique. The GNS-supported Pd catalyst (Pd/GNS) shows significantly high catalytic activity for the ORR. For comparison, the GNS-supported Pt catalyst (Pt/GNS) was also synthesized and investigated under the same experimental conditions. [Copyright &y& Elsevier]

Abstract: Carbon-supported Pt–Ni alloy nanoparticles with various compositions were prepared by a borohydride reduction method in anhydrous ethanol solvent. Here, we surveyed effect of thermally induced de-alloying on activity of the oxygen reduction reaction (ORR). Especially, changes in surface and bulk structures were investigated through electrochemical and spectroscopic measurements. The activity of as-prepared Pt–Ni alloy nanoparticles showed a monotonous dependence on Pt content. However, heat-treatment induced the phase separation between Pt and NiO and the resultant enhancement in ORR activity without significant increase in surface Pt concentration. [ABSTRACT FROM AUTHOR]

Abstract: Cyanamide was used in the preparation series of metal–nitrogen–carbon (M–N–C) oxygen reduction catalysts. The best catalyst, treated at 1050°C, shows good performance versus previously reported non-precious metal catalysts with an OCV ~1.0V and a current density of 105mA/cm2 (iR-corrected) at 0.80V in H2/O2 fuel cell testing (catalyst loading: 4mgcm−2). Although nitrogen content has been previously correlated positively with ORR activity, no such trend is observed here for any nitrogen type. The combined effects of nitrogen and sulfur incorporation into the carbon may account for the high activity of the 1050°C catalyst. [ABSTRACT FROM AUTHOR]

Abstract: Oxygen reduction reaction (ORR) in alkaline medium at iron (II) tetrakis (diaquaplatinum) octacarboxyphthalocyanine (PtFeOCPc) catalyst supported on multi-walled carbon nanotubes (MWCNTs) has been described. The ORR followed the direct 4-electron transfer process, with a very low onset potential (approximately zero volts vs. Ag|AgCl, saturated KCl) and at a kinetic rate constant, 2.78×10−2 cms−1. The results clearly showed that the ORR activity at the MWCNT-PtFeOCPc platform is comparable or even better than recent reports with other electrocatalysts, thus a promising catalytic platform for cathodic process in fuel cell device. [ABSTRACT FROM AUTHOR]

Abstract: Electrochemical reduction of oxygen is studied over a novel nanowire network catalyst made of highly-dispersed Pt nanoparticles into electrospun Pt nanowire network architecture, which shows an excellent mass activity increase by 50% or higher per equal Pt mass than the conventional cathode electrocatalysts of Pt/C in polymer electrolyte membrane fuel cells. [Copyright &y& Elsevier]

Abstract: Pt–Pd/MWCNT with Pt:Pd atomic ratio 40:60 and Pt/MWCNT electrocatalyst were synthesized and evaluated as oxygen reduction reaction (ORR) cathodes for Direct Ethylene Glycol Fuel Cells (DEGFC) applications. As reference, a commercial Pt/C material was also tested. We found that Pt–Pd/MWCNT has high tolerance capability to EG and higher selectivity for the ORR compared to the Pt-alone materials. As a result, the shift in onset potential for the ORR, E onset, at Pt–Pd/MWCNT was considerably smaller than the shift at Pt/MWCNT or Pt/C. The average particle size (from XRD) was 3.5 and 4nm for Pt/MWCNT and Pt–Pd/MWCNT, respectively. A moderate degree of alloying was determined for the Pt–Pd material. An advantageous application of Pt–Pd electrocatalysts should be in DEGFCs. [Copyright &y& Elsevier]

Abstract: A new approach to test fuel cell catalysts under conditions of high mass transport and variable temperature is described. This approach relies upon utilising a 5μm thick gold grid to act as a catalyst support in contact with a perfluorsulfonic acid (PFSA) membrane in a true three electrode electrochemical configuration. The gold grid has 20μm×20μm sized holes in it which allow the reactant gas to reach the catalyst layer. The high electrical conductivity and low profile of the grid ensure that electrical and mass transport losses are minimal. We have used this configuration to look at the oxygen reduction reaction (orr) and the hydrogen oxidation reaction (hor) on a platinum-black and platinum on carbon catalyst at a loading of about 10μgcm−2. We find that for the orr we can measure kinetic currents over the entire range of relevant fuel cell operating potentials (0.55–1V). Although platinum-black shows higher specific catalytic activity towards the orr than platinum on carbon at high potentials, this performance benefit is reduced at lower potentials. For the hor we measure exchange current densities of 0.022Acm−2 and 0.026Acm−2 respectively on the Pt-Black and Pt/C. These values indicate that there does not appear to be a size effect for the hor, unlike the orr. [Copyright &y& Elsevier]

Abstract: The factors controlling the electrocatalytic activity for the oxygen reduction reaction (ORR) in fuel cells have been tuned and investigated systematically with the low cost carbon-supported Pd70Co30 nanoalloy. The catalytic activity decreases with increasing annealing temperature due to an increasing degree of alloying (Co content in the Pd lattice) and crystallite size. With a controlled crystallite size of ∼8nm, the activity is found to decrease with increasing degree of alloying from 18 to 30at.% Co. However, the catalyst durability increases considerably with annealing temperature due to the alloying of Pd with Co and an increase in crystallite size. [Copyright &y& Elsevier]

Abstract: An effective method was developed for preparing highly dispersed CeO2 nanoparticle on a Pt/C catalyst synthesized by a continuous two-step process. From the XRD patterns, the diffraction pattern of the 20Pt–10CeO2/C catalyst revealed that both crystalline Pt and CeO2 phases coexisted. The TEM images show that the Pt and CeO2 nanoparticles were well-dispersed on the surface of the carbon support, which is known to be important for activity in the ORR test. In the ORR and single-cell tests, the 20Pt–10CeO2/C catalyst showed higher performance than a commercial 20Pt/C catalyst, owing to the oxygen storage capacity of CeO2 and its ability to rapidly exchange oxygen with oxygen in the buffer. [Copyright &y& Elsevier]

Abstract: A solid-state cell is used to study the electrocatalysis of oxygen reduction at the silver/hydroxide-exchange membrane interface. The catalyst/membrane interface exhibits improved performance in comparison to a catalyst/aqueous sodium hydroxide interface. Surprisingly, the half-wave potential for oxygen reduction is shown to shift 185mV higher at the silver/hydroxide-exchange membrane interface than for the silver/aqueous hydroxide solution interface, and the exchange current density is significantly higher at 1.02×10−6 Am−2. On a cost per performance basis, silver electrocatalysts in a hydroxide-exchange membrane fuel cell may provide better performance than platinum in a proton-exchange membrane fuel cell. [Copyright &y& Elsevier]

Abstract: Carbon supported PtW alloy nanoparticles with well-controlled particle size, morphology, and dispersion have been synthesized by the thermal decomposition of carbonyl complexes at elevated temperatures. The synthesized alloy nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and electrochemically analyzed for activity towards molecular oxygen electroreduction in an acidic electrolyte. The influence of synthesis parameters on the size of PtW nanoparticles were also investigated. XRD results show that the structure of PtW nanoparticles is composition dependent with a predominate face centered cubic structure for tungsten content less than ∼65%. Phase segregation was observed for PtW alloys with higher tungsten content. The prepared PtW nanoparticles exhibit significantly higher platinum mass specific activity towards molecular oxygen electroreduction than commercially available Pt/C catalysts, hence, the amount of platinum used in fuel cell cathode could be reduced dramatically. [Copyright &y& Elsevier]

Abstract: The tungsten carbide nanocrystals promoted Ag composite electrocatalysts have been firstly prepared and used for the electroreduction of oxygen in alkaline solution. These Pt-free electrocatalysts show high activities similar to those of Pt-based electrocatalysts. The kinetic parameters and the reaction mechanism for ORR are determined by RRDE. The enhancement of the activity is the evidence of synergetic effect. The novel electrocatalyst shows unique selectivity towards the electroreduction of oxygen and is immune to methanol, ethanol, isopropanol and glycerol. Such low cost electrocatalysts can be potentially applied to anion exchange membrane alcohol fuel cells, alcohol monitors and metal-air batteries. [Copyright &y& Elsevier]

Abstract: This paper reports the findings of an investigation of the correlation between the catalytic activity and the bimetallic composition of carbon-supported gold–platinum (AuPt/C) nanoparticles (2–4nm diameters) for the electrocatalytic oxygen reduction reaction. The electrocatalytic activities were characterized using voltammetric and rotating disk electrode techniques, and were also compared with those obtained with Au/C and Pt/C catalysts under the same measurement conditions. The mass activities of the bimetallic catalysts were shown to be not only dependent on the composition, but also the nature of the electrolyte. The catalysts showed a relatively smooth transition from the low activity of Au to the high activity of Pt in the acidic electrolyte. In contrast, a maximized mass activity in the composition region (60–80% Au) of the bimetallic catalyst is revealed which is higher than those of Pt/C and Au/C in the alkaline electrolyte. This remarkable finding suggests a qualitative concurrence with findings from related theoretical modeling and experimental studies, which are discussed in terms of a synergistic activity by the participation of Au in the adsorption of oxygenated species. [Copyright &y& Elsevier]

Abstract: Microwave synthesis method was applied to prepare CoTMPP/BP oxygen reduction electrocatalysts. The influence of the pre-treatment of BP2000 carbon supports by 6M HNO3 and 30 wt% H2O2 on the activity of electrocatalysts for oxygen reduction was investigated by means of the measurements of their electrochemical characteristics and performances. Levich–Koutecky plot shows that the number of transferred electrons during oxygen reduction on CoTMPP/BP is found to be between 2 and 4. The observed evidence indicated that the production of hydrogen peroxide has occurred during oxygen reduction in two electrons, and further oxidation of hydrogen peroxide involving two other electrons in the higher potential may also occur. The fuel cell performance of single cells with the different CoTMPP/BP electrocatalysts was examined under actual PEM fuel cell conditions. For hydrogen–oxygen fuel cell system, the maximal output power density reached 150mW/cm2 at 50°C. Life test was carried out at a constant of the output current density of 200mA/cm2 for CoTMPP/BP electrocatalyst, the single cell output voltage maintains at about 0.5V for more than 900min, there was no obvious performance degradation under fuel cell conditions. [Copyright &y& Elsevier]

A nanoporous amorphous manganese oxide is investigated as electrocatalyst for the oxygen reduction reaction in alkaline solutions. Cyclic voltammetry of catalytic electrodes based on the amorphous manganese oxide in oxygen-saturated electrolytes indicates that the amorphous manganese oxide catalyzes a two-electron reduction of molecular oxygen to HO2−. An oxygen reduction current density of more than 100 mA/cm2 is attained with an oxygen back-feed gas diffusion electrode with a low-catalyst loading of ca. 0.85 mg/cm2. The significant catalytic activity might be due to high concentration of lattice defects and active sites of the amorphous material, which would have potential applications in metal–air batteries and low-power fuel cells. [Copyright &y& Elsevier]

[Display omitted] • Method for synthesizing metal-free electrocatalyst with highly ordered nanochannels. • Thermal treatment in NH 3 atmosphere for activation of catalyst surface toward oxygen reduction. • Improved performance after stability test owing to ordered nanostructure with activated surface. • Verification of variations in N-containing species during oxygen reduction reaction. Lowering the cost of electrocatalysts for the oxygen reduction reaction (ORR) is indispensable for the wider commercialization of fuel cells. Therefore, the development of non-Pt, especially metal-free, carbon-based electrocatalysts, has been encouraged as an alternative to Pt. Here, we report active N-doped nanocarbon electrocatalysts in ORR activated by thermal treatment of pristine carbon precursors with highly aligned mesopore channels under an NH 3 atmosphere. This NH 3 -activation process adopts N-containing carbon sites, leading to enhanced ORR performance in an alkaline electrolyte with negligible formation of peroxide species. The stability of the activated carbon electrocatalysts was confirmed by performing 40,000 rounds of potential cycles in the accelerated stress test (AST). The variations in the voltammograms during AST were analyzed using X-ray photoelectron spectroscopy. The correlation between electrochemical behavior and the N 1 s spectrum corroborates the contribution of N-related sites toward voltammetric responses in ORR. [ABSTRACT FROM AUTHOR]

• Pt and PtNi NPs on metal oxides evaluated as bifunctional ORR/OER catalysts. • Ni addition reduces the catalysts cost while increasing its ORR/OER activity. • Use of Mn 2 O 3 -NiO bimetal oxide support enhances the catalyst stability. Three different metal oxides based on Mn 2 O 3 with TiO 2 or NiO were synthesised. Pt or PtNi nanoparticles were anchored on each support, creating a set of nine samples that were tested for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). PtNi/Mn 2 O 3 -NiO showed the most promising results for ORR as evidenced by the lowest Tafel slope, the highest diffusion-limited current density and number of electrons exchanged, along with the highest stability. The best performance of PtNi/Mn 2 O 3 -NiO reflects its highest electrochemical surface area and the lowest charge-transfer resistance. Furthermore, this catalyst showed high activity for the OER as evidenced by the low Tafel slope and high current density at an overpotential of 400 mV. The present study indicated different active sites for the two reactions, i.e., PtNi NPs for the ORR and NiO for the OER. [ABSTRACT FROM AUTHOR]

[Display omitted] • Potential pulses prior to the ORR reactivate catalytic sites which were oxidized at high anodic potentials. • Optimisation of the pulse potential allows to stabilize ORR activity. • RRDE measurements demonstrate a change in the ORR mechanism after applying high anodic potentials. The stability of electrocatalysts is of great importance to ensure their applicability, but stability is generally only considered for catalysts polarised to a constant potential or current density. This excludes stability evaluation under start/stop conditions in a fuel cell or in reversible batteries in which the catalyst is alternately polarised to high opposite potentials. For example, the poor cyclability of metal-air batteries is mainly due to the decrease in the oxygen reduction activity of electrocatalysts during the high applied potentials for the oxygen evolution reaction during battery charging. To investigate and at least partially mitigate the loss of electrocatalytic activity for the oxygen reduction reaction, we employed reductive pulses with the aim of restoring the catalytic activity of the active sites for the oxygen reduction reaction. Optimisation of the reductive pulse parameters makes it possible to substantially prolong the oxygen reduction activity of a Fe-N x -doped carbon-based oxygen reduction electrocatalyst. [ABSTRACT FROM AUTHOR]

Abstract: For the first time, gas-phase electrolysis of HCl to chlorine was conducted in a fuel cell type reactor with an oxygen depolarized cathode. Very low cell voltages below −1V at industrially relevant current densities of 4kAm−2 were obtained. Compared to technical HCl electrolysis processes, this leads to a reduction in electrical energy demand of approximately 30%. The temperature and the relative humidity (rH) of the cathode inlet gas were identified as key parameters controlling the overall performance of the system. [Copyright &y& Elsevier]

Abstract: The cubic vanadium carbides with the size ranging from 5 to 15nm uniformly dispersed on the carbon matrix have been synthesized by a simple hydrothermal method for the first time. The XRD measurement shows that the cubic vanadium carbide is structured in the form of V8C7. The vanadium carbide cube grows along the {100} planes. The Pt nanoparticles with the average size of 3nm are uniformly dispersed on both the surfaces of carbon and cubic vanadium carbide (Pt/VC@C) as electrocatalyst for oxygen reduction reaction (ORR). The connection between Pt nanoparticles and the nanosized cubic vanadium carbides favors to enhance the synergistic effect. The mass activity of ORR at 0.9V versus a reversible hydrogen electrode (RHE) is 230mA mg−1 Pt on the Pt/VC@C which is 2.4 times larger than that of the benchmark on Pt/C electrocatalyst (97mA mg−1 Pt). [Copyright &y& Elsevier]

Abstract: In the presented work, the evaluation of an unsupported AuPt core–shell catalyst for the oxygen reduction reaction is introduced. Applying only basic chemicals in an upscalable synthesis route, it is demonstrated that uniform, flat, and complete Pt layers around a spherical Au core are obtained. The electrocatalytic measurements show that the surface area specific activity of the AuPt core–shell catalyst towards the important oxygen reduction reaction equals the one of polycrystalline bulk Pt. To our knowledge, this is the first time that the unfavorable particle size effect of Pt nanoparticles could be by-passed for a nanoscale catalyst. [ABSTRACT FROM AUTHOR]

• Method for rapid and comparable catalyst layer evaluation developed. • Successful benchmark experiments with commercial Fe-N-C catalyst and alkaline ionomer. • Optimized cathode performance after pre-conditioning for 48 h in 1 M KOH. • Fe-N-C catalyst layers show very high stability after 5000 cycles between 0.6 and 1.0 V vs. RHE. Anion exchange membrane fuel cells (AEMFC) are a promising technology to allow the application of non-precious metal catalysts. While many of such catalysts have been identified in numerous recent fundamental research studies, reports evaluating these catalysts in realistic AEMFC catalyst layers together with stability assessments are rare. In the present work we show that fast and reliable evaluation and optimization of Fe-N-C-based oxygen reduction reaction (ORR) catalyst layers can be achieved using a gas diffusion electrode (GDE) half-cell approach. To set a benchmark in such measurements, a commercial Pajarito Powder Fe-N-C catalyst and commercial AemionTM ionomer are used. It is demonstrated that the ORR performance can be increased significantly by fine-tuning of the ionomer activation time. Furthermore, the optimized Fe-N-C-based catalyst layer shows very high stability with no observable performance deterioration after 5000 cycles in the 0.6–1.0 V vs. RHE potential window. [ABSTRACT FROM AUTHOR]