Note: Times Cited: 875 Reference EPFL-ARTICLE-206025doi:10.1021/cr0501846View record in Web of Science URL: ://WOS:000249839900009 Record created on 2015-03-03, modified on 2017-05-12

Complex Hydrides for Hydrogen Storage

The air electrode, which reduces oxygen (O2), is a critical component in energy generation and storage applications such as fuel cells and metal/air batteries. The highest current densities are achieved with platinum (Pt), but in addition to its cost and scarcity, Pt particles in composite electrodes tend to be inactivated by contact with carbon monoxide (CO) or by agglomeration. We describe an air electrode based on a porous material coated with poly(3,4-ethylenedioxythiophene) (PEDOT), which acts as an O2 reduction catalyst. Continuous operation for 1500 hours was demonstrated without material degradation or deterioration in performance. O2 conversion rates were comparable with those of Pt-catalyzed electrodes of the same geometry, and the electrode was not sensitive to CO. Operation was demonstrated as an air electrode and as a dissolved O2 electrode in aqueous solution.

High Rates of Oxygen Reduction over a Vapor

The emerging demand for electronic and transportation technologies has driven the development of rechargeable batteries with enhanced capacity storage. Especially, multivalent metal (Mg, Zn, Ca, and Al) and metal-ion batteries have recently attracted considerable interests as promising substitutes for future large-scale energy storage devices, due to their natural abundance and multielectron redox capability. These metals are compatible with nonflammable aqueous electrolytes and are less reactive when exposed in ambient atmosphere as compared with Li metals, hence enabling potential safer battery systems. Luckily, green and sustainable organic compounds could be designed and tailored as universal host materials to accommodate multivalent metal ions. Considering these advantages, effective approaches toward achieving organic multivalent metal and metal-ion rechargeable batteries are highlighted in this Review. Moreover, organic structures, cell configurations, and key relevant electrochemical parameters are presented. Hopefully, this Review will provide a fundamental guidance for future development of organic-based multivalent metal and metal-ion rechargeable batteries.

Recent Progress in Multivalent Metal (Mg, Zn, Ca, and Al) and Metal‐Ion Rechargeable Batteries with Organic Materials as Promising Electrodes

Photoelectrochemical (PEC) water splitting is an attractive strategy for the large-scale production of renewable hydrogen from water. Developing cost-effective, active and stable semiconducting photoelectrodes is extremely important for achieving PEC water splitting with high solar-to-hydrogen efficiency. Perovskite oxides as a large family of semiconducting metal oxides are extensively investigated as electrodes in PEC water splitting owing to their abundance, high (photo)electrochemical stability, compositional and structural flexibility allowing the achievement of high electrocatalytic activity, superior sunlight absorption capability and precise control and tuning of band gaps and band edges. In this review, the research progress in the design, development, and application of perovskite oxides in PEC water splitting is summarized, with a special emphasis placed on understanding the relationship between the composition/structure and (photo)electrochemical activity.

Perovskite Oxide Based Electrodes for High-Performance Photoelectrochemical Water Splitting.

Conjugated polymer chains have many degrees of conformational freedom and interact weakly with each other, resulting in complex microstructures in the solid state. Understanding charge transport in such systems, which have amorphous and ordered phases exhibiting varying degrees of order, has proved difficult owing to the contribution of electronic processes at various length scales. The growing technological appeal of these semiconductors makes such fundamental knowledge extremely important for materials and process design. We propose a unified model of how charge carriers travel in conjugated polymer films. We show that in high-molecular-weight semiconducting polymers the limiting charge transport step is trapping caused by lattice disorder, and that short-range intermolecular aggregation is sufficient for efficient long-range charge transport. This generalization explains the seemingly contradicting high performance of recently reported, poorly ordered polymers and suggests molecular design strategies to further improve the performance of future generations of organic electronic materials.

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-020288.pdf

A general relationship between disorder, aggregation and charge transport in conjugated polymers

We report the use of polyterthiophenes (PTTh) as a rare, combined light-harvester and catalyst for the hydrogen evolution reaction at high pH. Illuminated PTTh in combination with a MnOx anode in a two-electrode setup exhibited stable water-splitting at a bias-potential of only 0.3 V at pH 12. This confirms that PTTh used as photocathode can produce photovoltages of at least 900 mV for the hydrogen evolution reaction at high pH and is therefore a suitable match for traditional water-oxidation catalysts such as MnOx, CoOx, and RuOx. Films of PTTh were fabricated using a novel, metal-free method where iodine vapor is used as oxidant; thus, previously observed interference from metal residuals was omitted and thereby a gravimetric photo electrocatalytic conversion rate of 330 mmol(H2) h−1 g−1 was achieved in phosphate buffer (pH 7) at 0 V vs. RHE. A striking property of this new strand of polythiophene was an “inverse” correlation (compared to that predicted using the Nernstian relationship) between the onset potential for the light-assisted water reduction reaction and pH: the potential (vs. RHE) required for a given current was more positive at higher pH, which is not observed for other (photo-) electrocatalytic materials, and indicates that the charge neutralization of PTTh (rather than the pH) guides the onset potential.

Light-assisted electrochemical water-splitting at very low bias voltage using metal-free polythiophene as photocathode at high pH in a full-cell setup

Poly(vinyldibenzothiophenesulfone): Its Redox Capability at Very Negative Potential Toward an All‐Organic Rechargeable Device with High‐Energy Density

Proton exchange membrane fuel cells (PEMFCs) are promising clean energy conversion devices in residential, transportation, and portable applications. Currently, a high-pressure tank is the state-of-the-art mode of hydrogen storage; however, the energy cost, safety, and portability (or volumetric hydrogen storage capacity) presents a major barrier to the widespread dissemination of PEMFCs. Here we show an ‘all-polymer type’ rechargeable PEMFC (RCFC) that contains a hydrogen-storable polymer (HSP), which is a solid-state organic hydride, as the hydrogen storage media. Use of a gas impermeable SPP-QP (a polyphenylene-based PEM) enhances the operable time, reaching up to ca. 10.2 s mgHSP−1, which is more than a factor of two longer than that (3.90 s mgHSP−1) for a Nafion NRE-212 membrane cell. The RCFCs are cycleable, at least up to 50 cycles. The features of this RCFC system, including safety, ease of handling, and light weight, suggest applications in mobile, light-weight hydrogen-based energy devices. Hydrogen for fuel cells is commonly stored in pressurized tanks, whereby safety and portability can be problematic. Here, a rechargeable proton exchange membrane fuel cell with an internal hydrogen storage polymer that is cyclable up to 50 times is presented.

/pdf/rechargeable-proton-exchange-membrane-fuel-cell-containing-2s3j9can0v.pdf

Rechargeable proton exchange membrane fuel cell containing an intrinsic hydrogen storage polymer

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/aenm.202003724

Kouki Oka

Papers

Light-assisted electrochemical water-splitting at very low bias voltage using metal-free polythiophene as photocathode at high pH in a full-cell setup

Poly(vinyldibenzothiophenesulfone): Its Redox Capability at Very Negative Potential Toward an All‐Organic Rechargeable Device with High‐Energy Density

Rechargeable proton exchange membrane fuel cell containing an intrinsic hydrogen storage polymer

Organic π-Conjugated Polymers as Photocathode Materials for Visible-Light-Enhanced Hydrogen and Hydrogen Peroxide Production from Water

Characterization of PEDOT-Quinone conducting redox polymers in water-in-salt electrolytes for safe and high-energy Li-ion batteries