Abstract:A special in situ PEM fuel cell has been developed to allow X-ray absorption measurements during real fuel cell operation. and electronic (atomic XAFS) structure of the anode catalyst, are monitored as a function of the current. In hydrogen, the NPt-Ru coordination number increases much slower than the NPt-Pt with increasing current, indicating a more reluctant reduction of the surface Pt atoms near the hydrous Ru oxide islands. In methanol, both O[H] and CO adsorption are separately visible with the ∆µ technique and reveal a drop in CO and an increase in OH coverage in the range of 65-90 mA/cm 2 . With increasing OH coverage, the Pt-O coordination number and the AXAFS intensity increase. The data allow the direct observation of the preignition and ignition regions for OH formation and CO oxidation, during the methanol fuel cell operation. It can be concluded that both a bifunctional mechanism and an electronic ligand effect are active in CO oxidation from a PtRu surface in a PEM fuel cell.

The fabrication of three-dimensional assemblies consisting of large quantities of nanowires is of great technological importance for various applications including (electro-)catalysis, sensitive sensing, and improvement of electronic devices. Because the spatial distribution of the nanostructured material can strongly influence the properties, architectural design is required in order to use assembled nanowires to their full potential. In addition, special effort has to be dedicated to the development of efficient methods that allow precise control over structural parameters of the nanoscale building blocks as a means of tuning their characteristics. This paper reports the direct synthesis of highly ordered large-area nanowire networks by a method based on hard templates using electrodeposition within nanochannels of ion track-etched polymer membranes. Control over the complexity of the networks and the dimensions of the integrated nanostructures are achieved by a modified template fabrication. The networks possess high surface area and excellent transport properties, turning them into a promising electrocatalyst material as demonstrated by cyclic voltammetry studies on platinum nanowire networks catalyzing methanol oxidation. Our method opens up a new general route for interconnecting nanowires to stable macroscopic network structures of very high integration level that allow easy handling of nanowires while maintaining their connectivity.

CO reduction is of significant interest for the production of nonfossil fuels. The reactivity of eight Cu foams with substantially different morphologies was comprehensively investigated by analysis of the product spectrum and in situ electrochemical spectroscopies (X-ray absorption near edge structure, extended X-ray absorption fine structure, X-ray photoelectron spectroscopy, and Raman spectroscopy). The approach provided new insight into the reactivity determinants: The morphology, stable Cu oxide phases, and *CO poisoning of the H formation reaction are not decisive; the electrochemically active surface area influences the reactivity trends; macroscopic diffusion limits the proton supply, resulting in pronounced alkalization at the CuCat surfaces (operando Raman spectroscopy). H and CH formation was suppressed by macroscopic buffer alkalization, whereas CO and C H formation still proceeded through a largely pH-independent mechanism. C H was formed from two CO precursor species, namely adsorbed *CO and dissolved CO present in the foam cavities.

In situ X-ray absorption spectroscopy (XAS) measurements, including both X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS), were carried out on commercially produced Pt and PtRu bimetallic electrocatalysts as well as on a mechanically mixed PtRu bimetallic electrocatalyst in an operating fuel cell in H 2 doped with 150 ppm CO. By use of the novel ∆XANES technique, the coverages of CO and ontop and n-fold H (overpotential deposited and underpotential deposited hydrogen) are obtained and compared for the three catalysts, and the results are correlated with PtRu cluster morphology. The mechanical mixing process used to create the bimetallic PtRu catalyst is found to maximize CO tolerance, although the PtRu commercial electrocatalyst exhibits an increased electronic effect, most probably due to the presence of Ru(O) x islands at the catalyst surface. The mobility of the CO on both Ru and Pt is found to be sharply dependent on the CO coverage, decreasing dramatically beyond 0.4 fractional coverage.

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The recently emerging metal-air batteries equipped with advanced oxygen electrodes have provided enormous opportunities to develop the next generation of wearable and bio-adaptable power sources. Theoretically, neutral electrolyte-based Mg-air batteries possess potential advantages in electronics and biomedical applications over the other metal-air counterparts, especially the alkaline-based Zn-air batteries. However, the rational design of advanced oxygen electrode for Mg-air batteries with high discharge voltage and capacity under neutral conditions still remains a major challenge. Inspired by fibrous string structures of bufo-spawn, it is reported here that the scalable synthesis of atomic Fe-N coupled open-mesoporous N-doped-carbon nanofibers (OM-NCNF-FeN ) as advanced oxygen electrode for Mg-air batteries. The fabricated OM-NCNF-FeN electrodes present manifold advantages, including open-mesoporous and interconnected structures, 3D hierarchically porous networks, good bio-adaptability, homogeneously coupled atomic Fe-N sites, and high oxygen electrocatalytic performances. Most importantly, the assembled Mg-air batteries with neutral electrolytes reveal high open-circuit voltage, stable discharge voltage plateaus, high capacity, long operating life, and good flexibility. Overall, the discovery on fabricating atomic OM-NCNF-FeN electrode will not only create new pathways for achieving flexible, wearable, and bio-adaptable power sources, but also take a step towards the scale-up production of advanced nanofibrous carbon electrodes for a broad range of applications.

Two key problems inhibiting the commercialization of direct methanol fuel cells (DMFCs) are the cost of the precious metals employed and the sluggish kinetics and catalyst poisoning by CO or CHO species. Research to solve the first drawback [1][2][3][4] focuses on the reduction of precious metal loading, which is achieved by increasing the catalysts specific surface area and its accessibility. For the second problem, advanced electrocatalyst design relies on the "bifunctional approach", [5][6][7][8][9][10] in which a second compound such as ruthenium or RuO 2 ·x H 2 O assists the oxidation of CO or CHO species by adsorption of oxygen-containing species close to the poisoned Pt sites. In contrast to previous work on PtRu alloy catalysts, [11][12][13] Rolison and co-workers [14,15] emphasized the importance of hydrous ruthenium oxides because the RuO 2 ·x H 2 O speciation of Ru in nanoscale PtRu blacks shows both high electron and proton conductivity, which results in a much more active catalyst for methanol oxidation. However, direct evidence of the catalytic function of hydrous oxides is very scarce.Mixed proton-electron conducting materials should be ideal catalyst supports for DMFCs since they allow for low ohmic resistance in both the proton and electron conduction at the same time. As hydrous ruthenium(IV) oxide has been reported to contain liquid or liquid-like regions of water to

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