The recent advances in electrocatalysis for oxygen reduction reaction (ORR) for proton exchange membrane fuel cells (PEMFCs) are thoroughly reviewed. This comprehensive Review focuses on the low- and non-platinum electrocatalysts including advanced platinum alloys, core–shell structures, palladium-based catalysts, metal oxides and chalcogenides, carbon-based non-noble metal catalysts, and metal-free catalysts. The recent development of ORR electrocatalysts with novel structures and compositions is highlighted. The understandings of the correlation between the activity and the shape, size, composition, and synthesis method are summarized. For the carbon-based materials, their performance and stability in fuel cells and comparisons with those of platinum are documented. The research directions as well as perspectives on the further development of more active and less expensive electrocatalysts are provided.

http://repository.ust.hk/ir/bitstream/1783.1-77094/1/acs.chemrev.5b00462_withlink.pdf

Recent Advances in Electrocatalysts for Oxygen Reduction Reaction

Hydrogen sensors are of increasing importance in connection with the development and expanded use of hydrogen gas as an energy carrier and as a chemical reactant. There are an immense number of sensors reported in the literature for hydrogen detection and in this work these sensors are classified into eight different operating principles. Characteristic performance parameters of these sensor types, such as measuring range, sensitivity, selectivity and response time are reviewed and the latest technology developments are reported. Testing and validation of sensor performance are described in relation to standardisation and use in potentially explosive atmospheres so as to identify the requirements on hydrogen sensors for practical applications.

Hydrogen Sensors - A review

Microwave-assisted preparation of inorganic nanostructures in liquid phase.

Composites of intrinsically conducting polymers (ICPs) are materials that utilize conjugated polymers and at least one secondary component that can be inorganic or organic materials or biologically active species. The goal is to produce a new composite material that has distinct properties that were not observed in the individual components. This may include either new or improved chemical properties that can be exploited for chemical or biological sensing. For example, adding carbon nanotubes tends to drastically influence the electrical and thermal conductivity of ICPs. A secondary aspect concerns the stabilization of the secondary component in the polymer matrix. Enhanced optical, electrical, or mechanical properties such as stiffness and strength are common. In some cases, the physical and chemical properties of the secondary component are much different after composite formation. For the purpose of this review we will primarily focus on the ICPs such as polyaniline, polypyrrole, and polythiophene and their derivatives. The resonance-stabilized structure of ICPs allows, for example, incorporation of ions, nanoparticles, or nanowires of metals, metal oxides, carbon, or molecular species such as metallophthalocyanines or biologically active components such as enzymes, antibodies, and antigens. 1 I some cases, the ICP will simply act as a template for the incorporation of the secondary component. In that case, the secondary component will impart the chemical properties required for chemical sensing. In other cases the materials are linked through electrostatic interactions which influence the electronic and physical properties of the materials used to prepare the composite.

Composites of Intrinsically Conducting Polymers as Sensing Nanomaterials

A review on production, storage of hydrogen and its utilization as an energy resource

Microwave assisted synthesis of surfactant stabilized platinum/carbon nanotube electrocatalysts for direct methanol fuel cell applications

A compact hydrogen gas sensor based on solid polymer electrolyte (Nafion 117), working under amperometric conditions at room temperature with minor water maintenance, has been developed. Electrodes were prepared chemically by using the impregnation–reduction method. The polymer was platinized by using a platinum chloro amino complex and sodium tetrahydro borate as impregnating salt and reducing agent, respectively. The thin Pt films were characterized by XRD, infrared spectroscopy, optical microscopy, scanning electron microscopy and EDAX. Sensor measurements were performed under amperometric short-circuit current conditions. A maximum sensitivity of about 0.01 μA cm−2 ppm−1 was obtained. The response time was observed to be in the range of 10–50 s. A reproducible response with an approximately linear current versus P H 2 has been observed for the range of hydrogen concentration from 1 to 10%.

Development of a hydrogen sensor based on solid polymer electrolyte membranes

Several commercial carbons were tested with respect to their thermal stability and electrochemical activity as Pt catalyst support for oxygen reduction reaction (ORR). TGA analysis revealed that carbons with low BET surface such as graphite nanoparticles (GNP500, 100 m² g−1) are less prone to degradation than ordered mesoporous carbon (OMC, 1000 m²g−1). Moreover, high Pt loading favored considerably carbon oxidation rate in air. Best results in terms of activity for ORR and stability during electrochemical accelerated degradation tests (ADT) were yielded by Pt/GNP500 and Pt/OMC, respectively. High graphitization level and mesoporous surface structure of carbon were found to be determinant for sustainable Pt stability. Addition of certain amount of PTFE to Nafion as binder in gas diffusion electrode (GDE) catalyst layer clearly improved electrochemical surface area (ECSA) retention. Comparative identical location TEM images of electrochemically-aged Pt on Vulcan and OMC demonstrated positive influence of mesoporous carbon surface on immobilization of catalyst particles and consequently on ECSA retention. After 10,000 ADT cycles, ECSA retention was close to 30% for Pt/OMC compared to about 1% for Pt/Vulcan. This was due to dramatic increase of Pt particle size on Vulcan support up to 40 nm compared to about 15 nm for Pt on OMC.

An extensive study about influence of the carbon support morphology on Pt activity and stability for oxygen reduction reaction

In conventional low temperature PEM fuel cells, catalyst activity and stability rely on adequate structure and morphology of carbon support material, especially at the cathode that is exposed to high potential values. Degree of graphitization as well as pore distribution are decisive parameters for corrosion resistivity, catalyst utilization and mass transport. In this work, hollow graphitized carbon spheres (HGS) with mesoporous structure were tested as catalyst support in middle temperature (90–110 °C) direct methanol fuel cell (DMFC) cathode. Influence of catalyst loading and concentration as well as working temperature on power density was studied in a 5 cm 2 laboratory cell. Best results in terms of MEA performance were achieved with a catalyst loading of 2 mg Pt  cm −2 at both electrodes and an extremely dense Pt concentration on carbon support of 50 and 40 wt% at the anode and cathode, respectively at 110 °C. Additionally, thermal pretreatment of carbon-supported catalyst up to 850 °C led to increase in particle size up to 7 nm and as a consequence to substantial higher ECSA retention during accelerated degradation test (ADT) under half-cell conditions.

Investigation of mesoporous carbon hollow spheres as catalyst support in DMFC cathode

E in oxygen decreased down to 0.57 V thatis the lowest value ever reported in the literature. However, phase segregation and loss in ORR activity was observed during cycling.© The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative CommonsAttribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/),whichpermitsnon-commercialreuse,distribution,andreproductioninanymedium,providedtheoriginalworkisnotchangedinanyway and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0081506eel]All rights reserved.

M. Sakthivel

Papers

Microwave assisted synthesis of surfactant stabilized platinum/carbon nanotube electrocatalysts for direct methanol fuel cell applications

Development of a hydrogen sensor based on solid polymer electrolyte membranes

An extensive study about influence of the carbon support morphology on Pt activity and stability for oxygen reduction reaction

Investigation of mesoporous carbon hollow spheres as catalyst support in DMFC cathode

On Activity and Stability of Rhombohedral LaNiO3 Catalyst towards ORR and OER in Alkaline Electrolyte