Volume 227, Issue 5 -

The direct methanol fuel cell is the most interesting fuel cell for mobile applications. The state-of-the-art materials in a practical direct methanol fuel cell are Nafion 115 as membrane, carbon black as catalyst support and PtRu and Pt, respectively, as electrocatalyst. However, many materials were under investigation as alternatives to these materials in the last two decades. The most promising materials are reviewed in this paper. In addition, the catalyst preparation methods are summarized for chemical and electrochemical methods separately. Furthermore, a new electrodeposition technique with a gel-type electrolyte is highlighted. By the use of this method, the catalyst loading on the cathode side can be reduced by 25%.

A theory for the anodic oxidation of a metal under linear potentiodynamic conditions is derived based upon the Point Defect Model (PDM), by considering two contributions to the current; that from the metal oxidation reaction and that from capacitive charging. The veracity of the theory is demonstrated by analyzing linear potentiodynamic polarization curves for platinum in the oxide formation potential region. By optimizing the derived potential sweep rate-dependent current density expression on the measured i vs. V polarization data for the electrochemical oxidation of platinum in 0.1 M KOH solution at ambient temperature (22 ± 2 ºC) as a function of potential sweep rate, kinetic parameters for the growth and dissolution of the anodic film on platinum are extracted. The growth and dissolution rates of the oxide film are of the order of × 10 12 m/s (0.001 nm/s). The structure and electronic properties of the anodic film on platinum are also discussed. The film is n -type in electronic character, and is postulated to be a nano-crystalline structure probably comprising columnar, tetragonal unit cells or half cells (monolayer of oxygen) oriented with the c -axis perpendicular to the metal surface for an optimal epitaxial relationship with the substrate metal. For the very thinnest films ( <0.1 nm thick), the film is postulated to comprise “buried” oxygen atoms or ions in the platinum surface.

In this paper on high-throughput optical screening for the discovery and optimization of electrocalatysts for potential application in polymer electrolyte membrane and direct methanol fuel cells the present state-of-the-art in literature is reviewed focussing on non-optical and optical fast serial, semi-parallel or truly parallel screening techniques as well as actual improvements of the fluorescence based testing method to a semi-quantitative or even quantitative method are described. The modifications of the method are concerning hindrance of fluorescing colorant interdiffusion, optimization of system parameters concerning colorant, electrolyte and other measurement components, and application of correction procedures. With fluorescence based setups especially adapted to both anodic and cathodic half-cell reactions methanol oxidation as well as oxygen reduction reaction electrocatalysts have been screened. By iteratively passing through high-throughput optimization workflows several hundreds of precious metal-free as well as Pt containing compositions were synthesized, tested and validated by conventional cyclovoltammetric measurements. For electrocatalysts to oxidize methanol on the anodic side of the fuel cell a small amount of Pt seems to be indispensable to result in stable catalysts. For the oxygen reduction reaction active compositions performing comparable or even better than the reference PtO x catalyst contained the elements Co and Mn, which correspond to primary activity descriptors already specified in literature.

This review describes main strategies for the development of sulfonated aromatic polymers (SAP) with optimal properties for medium temperature (90–120 ºC) polymer electrolyte membrane fuel cell applications. SAP are promising economical polymer electrolytes, but there still exist some challenges about these materials due mainly to excessive swelling in water, poor mechanical strength and low dimensional stability. Here, the state-of-the-art of SAP is reviewed and the main focus will be directed to properties of SAP, including proton conductivity, water uptake, mechanical strength, permeability. Especially three approaches to improve the performances are addressed: the formation of copolymers, the formation of hybrid materials and the polymer reticulation.

The performance of Polymer Electrolyte Membrane Fuel Cells (PEM-FCs) is directly related to the interfacial resistance between the membrane and Gas Diffusion Electrodes (GDEs), the catalyst availability in the 3-phase zone and the micro structure of the catalyst containing porous layer. Therefore we have deposited a hydrophobic porous layer, containing Sulfonated PolyEtherEtherKetone (SPEEK), onto a Gas Diffusion Layer (GDL), we have electrodeposited Pt electrocatalysts, and in this way we have prepared GDEs particularly suited for fuel cells with SPEEK as membrane (as an alternative to Nafion as the standard membrane material). High degree of catalyst utilization as well as availability is assured by our Pulsed Potentiostatic catalyst ElectroDeposition method (PPED) using a Hydrogen Depolarized Anode (HDA). Characterization of the prepared GDEs containing SPEEK is done via in-situ and ex-situ electrochemical techniques, X-ray diffraction and electron microscopy. The fuel cell performance is evident from polarization curves recorded at different temperatures and at different relative humidity of the reactant gases.

At medium term, electricity could be partially provided by the utilization of carbon in high temperature fuel cells. The thermodynamic efficiency of a direct carbon fuel cell (DCFC) slightly exceeds 100% in a wide temperature range due to the positive value of the reaction entropy change. Thus, the thermodynamic efficiency is higher than those of conventional fuel cell types for gaseous fuels. In DCFC technology, three different main electrolyte concepts are used up to now: two types of liquid salt electrolytes (molten carbonate or molten hydroxide) and a solid oxide electrolyte (solid ceramic layer). For instance, it has been reported that power densities up to 210 mW cm -2 can been achieved at 750 ºC in a molten carbonate based cell, resulting to a real practical efficiency of about 60%. Recently, also combined technologies have been developed in which a maximum power density of 500 mW cm -2 is possible. In this paper, the actual state of technology will be discussed for the different concepts of direct carbon fuel cells.

Industrial chlor-alkali electrolysis represents one of the most energy- and resource-intensive technological applications of electrocatalysis. Improving process efficiency becomes a critical issue for the sustainable development and for alleviating the energy and environmental crisis. Rational design in the morphology of RuO 2 -based anodic electrocatalytic coatings and the control in the coating microstructure can contribute to massive energy saving compared to the current commercial Ru 0.3 Ti 0.7 O 2 coating. This review covers recent developments in the anodic coatings. Performance enhancement for RuO 2 -based anodic coatings is achieved by using alternative preparation routes of sol-gel and electrodeposition. The target control in the coating surface morphologies and the increase in the utilization of active Ru species are demonstrated.

This review describes the input of sol-gel chemistry to the immobilization of polyol dehydrogenases on electrodes, for applications in bioelectrocatalysis. The polyol dehydrogenases are described and their application for biosensing, biofuel cell and electrosynthesis are briefly discussed. The immobilization of proteins via sol-gel approaches is described, including a discussion on the difficulty to maintain the activity of proteins in a silica matrix and the strategies developed to offer a proper environment to the proteins by developing optimal organic-inorganic hybrid materials. Finally, the co-immobilization of the NAD + co-factor and of mediators for the elaboration of reagentless devices is presented, based on published and original data. All-in-all, sol-gel approaches appear to be a very promising for development of original electrochemical applications involving dehydrogenases in near future.

In Biology, numerous cellular signalling and control networks are centred around redox active chalcogen species, such as the thiol group of cysteine, the sulfide of methionine and the selenol(ate) of the unusual amino acid selenocysteine. These amino acids form part of peptides, proteins and enzymes, which they endow with a distinct ( i.e. chalcogen) redox activity. Compared to the biological redox chemistry of metal ions ( e.g. iron, copper, manganese), the redox behaviour of such chalcogen-based systems is considerably more diverse, complex and difficult to study. Not surprisingly, there have been few interactions between electrochemists and biological chalcogen redox chemists in the past. Nonetheless, electrochemistry provides several interesting leads: Impedance measurements enable cell biologists to ‘watch cells grow’ in real time and in a continuous manner, which forms the basis for innovative drug profiling. Voltammetry can be used to monitor the formation of (oxygen and nitrogen based) reactive species at the level of individual macrophages without the need of elaborate staining techniques. At the same time, Cyclic Voltammetry provides access to the redox properties of various cysteine proteins and enzymes, and hence may assist in unravelling some of the remaining mysteries of the cellular thiolstat. And finally, electrochemical methods are extraordinarily powerful and useful in the characterization and ultimately also the design of redox-modulating natural products and drugs, including potential antioxidants and anticancer agents.