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Stability of ferrate species, produced electrochemically for on‐site treatment of drinking water, has been thoroughly studied for a number of important conditions including: pH, temperature, initial concentration effects, and the presence of impurities, in order to assess the degradation process quantitatively. The limited number of ferrate degradation studies reported to this date have all focused on the chemically‐produced ferrate species and have examined conditions which are unsuitable for drinking water treatment. Degradation of electrochemical ferrates over a wide temperature range of 5 °C to 80 °C shows an Arrhenius‐type reaction behaviour with an activation energy of 27.3 ± 0.6 kJ mol−1. Initial rate analysis of ferrate degradation reveals a reaction order of about 1. The impacts of potential water impurities, such as salts and natural organic matter, and the source water (e.g. tap, deionized, and natural lake) have been studied and are presented. Degradation of ferrates in the pH range of 5 to 13 appears to have a first‐order kinetic behaviour with rate constants ranging from 1.02 × 10−3 s−1 to 6.67 × 10−5 s−1. Understanding the stability properties is important for further development and deployment of on‐site generated ferrates for the purposes of drinking water treatment. [ABSTRACT FROM AUTHOR]

The microporous layer (MPL) is a key cathodic component in proton exchange membrane fuel cells owing to its beneficial influence on two-phase mass transfer. However, its performance is highly dependent on material properties such as morphology, porous structure, and electrical resistance. To improve water management and performance, electrochemically exfoliated graphene (EGN) microsheets are considered as an alternative to the conventional carbon black (CB) MPLs. The EGN-based MPLs decrease the kinetic overpotential and the Ohmic potential loss, whereas the addition of CB to form a composite EGN+CB MPL improves the mass-transport limiting current density drastically. This is reflected by increases of approximately 30 and 70 % in peak power densities at 100 % relative humidity (RH) compared with those for CB- and EGN-only MPLs, respectively. The composite EGN+CB MPL also retains the superior performance at a cathode RH of 20 %, whereas the CB MPL shows significant performance loss. [ABSTRACT FROM AUTHOR]

In this paper a direct hydrogen fuel cell is operated in the absence of a membrane and at ultra-low Pt content using an aqueous iron redox species electrolyte as the oxidant. The liquid iron redox oxidant allowed for the use of a 3-D carbon cathode structure which in conjunction with a liquid electrolyte was used to eliminate the membrane and the need for precious metals on the cathode. Non-optimized maximum power density up to 250 mW/cm² (330 mW/cm² iR-corrected) and a current density in excess of 1000 mA/cm² were achieved with a total Pt content of the fuel cell as low as 0.05 mg/cm². In addition the membrane-less electrode assembly demonstrated superior performance to the conventional PEM-based MEA. The membrane-less direct hydrogen redox fuel cell (DHRFC) has the potential to be performance competitive with conventional polymer electrolyte membrane fuel cell (PEMFC) technology but be significantly superior on a cost basis and with balance of plant benefits. [ABSTRACT FROM AUTHOR]

The article examines the use of noncarbon support materials for the electrocatalysts of polymer electrolyte membrane (PEM) fuel cell. It notes the determination of carbon oxidation or corrosion that was driven by carbon dioxide and/or high potential of electrode as a failure mode for PEM fuel cell degradation. It presents some drawbacks for noncarbon-based supports such as electronic conductivity, solubility, and chemical and electrochemical stability.

Ba2In2O5 is one of the oxygen deficient ceramic materials widely investigated for both oxygen ion conduction and proton conduction in oxidizing atmospheres. However, its electrochemical properties have not been studied in hydrogen containing atmospheres. In this work, the electrical conductivity of Ba2In2O5 in hydrogen containing atmospheres was investigated by ac impedance spectroscopy in the temperature range between 100 and 500°C and compared to its conductivity in air and nitrogen in order to estimate the contribution of proton conductivity to the total conductivity. A stable electrical conductivity of over 0.3 S/cm was achieved in the temperature range of 300-480°C in a 50% vol H2/50% vol N2 atmosphere. Electromotive force measurements (and complimentary open circuit cell voltage measurements) revealed high proton transport numbers over the temperature range. Ba2In2O5 shows chemical stability in hydrogen containing atmospheres at temperatures up to 480°C, while decomposing at higher temperatures. Mechanical instability was noticed in humid atmospheres at 400°C and above. This previously unreported high conductivity in H2 atmosphere creates an opportunity for use of Ba2In2O5 as a proton conductive material for a range of intermediate temperature electrochemical devices [ABSTRACT FROM AUTHOR]

dvancements in the performance of the direct methanol redox fuel cell (DMRFC) were made through anolyte/catholyte composition and cell temperature studies. Catholytes prepared with different iron salts were considered for use in the DMRFC in order to improve the catholyte charge density (i.e., iron salt solubility) and fuel cell performance. Following an initial screening of different iron salts, catholytes prepared with FeNH(SO), Fe(ClO) or Fe(NO) were selected and evaluated using electrolyte conductivity measurements, cyclic voltammetry and fuel cell testing. Solubility limits at 25 °C were observed to be much higher for the Fe(ClO) (>2.5 M) and Fe(NO) (>3 M) salts than FeNH(SO) (~1 M). The Fe(ClO) catholyte was identified as a suitable candidate due to its high electrochemical activity, electrochemical reversibility, observed half-cell potential (0.83 V vs. SHE at 90 °C) and solubility. DMRFC testing at 90 °C demonstrated a substantial improvement in the non-optimized power density for the perchlorate system (79 mW cm) relative to that obtained for the sulfate system (25 mW cm). Separate fuel cell tests showed that increasing the cell temperature to 90 °C and increasing the methanol concentration in the anolyte to 16.7 M (i.e., equimolar HO/CHOH) yield significant DMRFC performance improvements. Stable DMRFC performance was demonstrated in short-term durability tests. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical production of hydrogen (H2) from liquid methanol in acidic aqueous media was investigated in a proton exchange membrane (PEM) electrolyser, comprising a two-compartment glass cell with a membrane electrode assembly (MEA) composed of a Nafion® 117 membrane and gas diffusion electrodes (GDE). Methanol electrolysis was studied at concentrations ranging from 0 to 16M, where 0M corresponds to water electrolysis. The influence of catalysts (Pt and Pt–Ru), catalyst support (C or black), operating temperatures (23, 50 and 75°C) and operating modes (dry and wet cathode) were evaluated in the static mode. A theoretical thermodynamic analysis of the system was done as a function of temperature. The limiting current densities, kinetic parameters, including the Tafel slopes and current exchange density, and apparent activation energies were determined. [Copyright &y& Elsevier]

Abstract: In this paper a single electrode supported direct methanol fuel cell (DMFC) is fabricated and tested. The novel architecture combines the elimination of the polymer electrolyte membrane (PEM) and the integration of the anode and cathode into one component. The thin film fabrication involves a sequential deposition of an anode catalyst layer, a cellulose acetate electronic insulating layer and a cathode catalyst layer onto a single carbon fibre paper substrate. The single electrode supported DMFC has a total thickness of 3.88×10−2 cm and showed a 104% improvement in volumetric specific power density over a two electrode DMFC configuration under passive conditions at ambient temperature and pressure (1atm, 25°C). [Copyright &y& Elsevier]

Abstract: A significant amount of work has been done in the field of the transition metal (TM) macrocyclic-catalyzed oxygen reduction reaction (ORR), but not as a function of temperature and substitution in an acidic electrolyte to simulate the environment of an operating PEM fuel cell. The electrocatalytic activity of several iron-based phthalocyanine macrocycles for the ORR were evaluated using cyclic voltammetric (CV) and rotating disc electrode (RDE) techniques. The activities of these substituted iron phthalocyanines were compared to those of the unsubstituted species in the temperature range of 20–80°C. The activity was also evaluated in the presence of hydrogen peroxide, both a possible by-product of the ORR and potential de-activator of iron phthalocyanines. The kinetics and corresponding parameters such as overall ORR electron transfer numbers, reaction rate constants, Tafel slopes, electron transfer numbers in the rate-determining step, and electron transfer coefficients were all measured in the temperature range of 20–80°C. A mechanism for the different FePc-catalyzed ORR''s was suggested based on the experimental results. The effect of substitution and temperature on ORR kinetics was also studied in this paper. [Copyright &y& Elsevier]

Abstract: A conventional membrane electrode assembly (MEA) for a direct methanol fuel cell (DMFC) consists of a polymer electrolyte membrane (PEM) compressed between an anode and cathode electrode. Limitations with this conventional design include: cost, fuel crossover, membrane degradation or contamination, ohmic losses and reduced active triple phase boundary (TPB) sites for catalyst located away from the electrode/membrane interface. In this work, ex situ and in situ characterization of a novel electrode assembly based on a membraneless architecture and advanced 3D anodes was investigated. The approach was shown to be fuel independent and scaleable to a conventional bi-polar fuel cell arrangement. The membraneless configuration exhibits comparable performance to a conventional ambient (25°C, 1atm) air-breathing DMFC. However, it has the additional advantages of a simplified design, the elimination of the membrane (a significant component expense) and enhanced fuel and catalyst utilization through the extension of the active catalyst zone. [Copyright &y& Elsevier]

Discusses the emergence of fuel cells as an electrochemical solution to global warming in the 21st century. Impact of air quality issues; Cost projections for manufacturing fuel cells; Future directions and challenges for fuel cells.

A correction to the article "Analytical quantification of electrochemical ferrates for drinking water treatments" is presented.

Abstract: Water management is a major issue in the operation of PEM fuel cells. Two-phase flow has been commonly observed in PEM fuel cell channels from experiments. One of the two-phase flow patterns, the slug flow, has great negative impacts on the fuel cell performance. In this work, the impact of two-phase flow patterns, especially the slug flow, on the fuel cell performance was simulated using a 3D volume fluid model (VOF) coupling with a 1D membrane electrode assembly (MEA) model. The proposed model is capable of describing the two-phase flow patterns, especially the slug flow in the cathode side gas flow channels. The comparison of fuel cell performance between single phase flow and two-phase flow shows that the presence of slug flow decreases the cell voltage output in the mass transport region, but has little effect in the kinetic and ohmic region. However, the slug flow causes great increase of overall pressure drop, which should be avoided during the PEM fuel cell operation. Effects of gas stoichiometric flow ratios on the fuel cell performance were then simulated. Increasing the gas flow rate significantly broadens the ohmic region, enabling the fuel cell to be operated at higher current densities. However, given a fixed current density during fuel cell operation, too high a gas flow rate will result in high pressure drops with little improvement in the fuel cell performance. Changing channel wall or MEA surface wettability also has great impact on the PEM fuel cell performance and two-phase flow pattern in the channel. Using a more hydrophobic MEA surface is helpful to extend the ohmic region and increase PEM fuel cell performance. Using too hydrophilic or too hydrophobic channel wall is not recommended, since either reduces the cell output voltage. [Copyright &y& Elsevier]

A novel rotating disk electrode (RDE) tip capable of characterizing catalyst coated substrates and compatible with commercial RDE systems is presented. The RDE tip, which uses a top-oriented Ti-based current collector, is demonstrated with Pt foil and commercial catalyst coated membranes (CCM). The specific activity of the platinum foil for oxygen reduction reaction is about 1.55 mA kinetic cm Pt −2 in 0.1 M HClO 4 at room temperature (20°C), which is in agreement with the measurements reported for polycrystalline Pt. The Ti-based current collector leads to a very small (≈ 5.6%) loss in the electrochemical surface area (ECSA). Hydrodynamic calculations and oxygen reduction measurements confirm that even at the fastest rotation speeds used in this type of measurement (i.e., 1600 rpm), the laminar flow regime (Re ≈ 56) is maintained, allowing one to apply classical RDE analysis. Repeatable and high quality cyclic voltammograms (CVs), oxygen reduction curves, and mass and specific activities for commercial CCMs were obtained in 0.1 M HClO 4 at room temperature (20°C). The activities determined from these experiments are in agreement with those of the H 2 /O 2 fuel cell measurements under equivalent operating conditions. Degradation of the CCM’s catalyst during a 30,000 potential cycling accelerated degradation test (ADT) is performed using a 0.4 mg Pt cm −2 commercial CCM and shows an ECSA loss of ≈ 0.0010 m 2 g Pt −1 cycle −1 and a mass activity loss of ≈ 1.8 × 10 −6 A mg Pt −1 cycle −1 . Details of the design, implementation, and results of this economical and novel approach for characterization of CCMs are presented and discussed. [ABSTRACT FROM AUTHOR]

Abstract: A colloidal silica incorporated porous anodic aluminum oxide (AAO) was utilized as a dual-template to prepare mesoporous carbon nanofibers (MCNFs). Such a strategy is simple because it takes advantage of commercially available materials (i.e., colloidal silica and AAO) and the templates can be removed in one step. The as-prepared MCNF shows a hierarchical nanostructure consisting of open macroporous channel connected with large mesopores and micropores. As a result of the large surface area and unique hierarchical nanoarchitecture which facilitates fast mass and electron transport, the MCNF reveals a discharge capacity of 679 mA h g−1 at 25 mA g−1. This value is significantly greater than that (i.e., 394 mA h g−1) observed for an ordered mesoporous carbon (OMC) with a similar specific surface area. Furthermore, at 3000 mA g−1, the MCNF demonstrates a discharge capacity of 585 mA h g−1, which is about twice that (i.e., 256 mA h g−1) of the OMC. [Copyright &y& Elsevier]

Abstract: Numerous transition metal–carbon composite catalysts (M=V, Zn, Ni, Sn, Ce, Ba, Fe, Cu) have been synthesized and tested for electroreduction of O2 to H2O2, The activity and selectivity of all synthesized catalysts for electrosynthesis of H2O2 were determined by the rotating ring-disk electrode method in acidic and neutral electrolytes. The Co-based catalysts in general showed the highest activity towards H2O2 formation. Experiments with different loading contents of Co showed that the activation overpotential losses of oxygen reduction to H2O2 reduces as loading increases to about 4wt% Co. Addition of Co beyond this level did not seem to impact the overpotential losses. The cobalt-based catalysts, were spray-coated onto 120μm thick Toray® graphite substrates, and were studied in bulk electrolysis cells for up to 100h at potentiostatic conditions (0.25V vs. RHE) in pH 0, 3, and 7 electrolytes. At (25°C and 1bar) with a catalysts loading of about and using dissolved O2 in 0.5M H2SO4, typical H2O2 electrosynthesis rates of about were reached with current efficiencies of about 85±5% at 0.25V (vs. RHE). [Copyright &y& Elsevier]

Abstract: Nitrogen-doped (N-doped) carbon, denoted as Fe–UF–CNx, is synthesized through nitridation of an iron-doped gel precursor on the Vulcan support. It exhibits a legitimate activity on catalyzing oxygen reduction reaction (ORR). Its polarization curve, measured with a rotating disk electrode in O2-saturated H2SO4, indicates Fe–UF–CNx has a widely distributed ORR activity and a high onset potential 0.859 V. The widely distributed activity originates from its complex nitrogen sites on the graphitic sheet, evidenced by the broad N1s spectrum of Fe–UF–CNx, which is featured with twin peaks of nearly equal intensity for pyridinic and pyrrolic nitrogens. The high onset potential suggests, despite an overall mediocre activity, the Fe–UF–CNx activity involves a small fraction of very active sites. When properly joining with the RuSe2 pyrite nanoparticles, the high potential active sites of Fe–UF–CNx uplift the ORR activity to the level of carbon-supported Pt catalyst. The platinum–level activity is manifested by a small half-wave potential difference 0.03–0.04 V between the joint catalyst of RuSe2–Fe–UF–CNx and the commercially available Pt/C catalyst. Additional merits of RuSe2–Fe–UF–CNx, such as high stability, methanol tolerance, low peroxide yield, are also measured and discussed. [Copyright &y& Elsevier]

Abstract: There are several compelling technological and commercial reasons for operating H2/air PEM fuel cells at temperatures above 100°C. Rates of electrochemical kinetics are enhanced, water management and cooling is simplified, useful waste heat can be recovered, and lower quality reformed hydrogen may be used as the fuel. This review paper provides a concise review of high temperature PEM fuel cells (HT-PEMFCs) from the perspective of HT-specific materials, designs, and testing/diagnostics. The review describes the motivation for HT-PEMFC development, the technology gaps, and recent advances. HT-membrane development accounts for ∼90% of the published research in the field of HT-PEMFCs. Despite this, the status of membrane development for high temperature/low humidity operation is less than satisfactory. A weakness in the development of HT-PEMFC technology is the deficiency in HT-specific fuel cell architectures, test station designs, and testing protocols, and an understanding of the underlying fundamental principles behind these areas. The development of HT-specific PEMFC designs is of key importance that may help mitigate issues of membrane dehydration and MEA degradation. [Copyright &y& Elsevier]