No abstract

No abstract

Heterogeneous catalysis performed in wall-coated reactors and electrocatalysis require homogeneous catalytic coatings with high surface area and good accessibility of the active sites. Conventional coating methods necessitate the use of binder components that often block pores and active sites, which limits catalytic efficiency, and utilization of expensive active metals. We report an approach for the direct and binder-free synthesis of chemically, mechanically, and thermally stable catalytic coatings based on ordered mesoporous carbon films employed as catalyst support. The synthesis relies on the codeposition of a structure-directing agent and small clusters of polymeric carbon precursors along with ionic metal species on a substrate. A sequence of thermal treatments converts the polymer into partly graphitized carbon, decomposes the structure-directing agent, and converts the metal precursor into highly active nanoparticles. Syntheses and catalytic applications are exemplarily demonstrated for palladium on carbon, a system widely used in heterogeneous catalysis and electrocatalysis. The obtained catalysts provide significantly higher space–time yields in the selective gas-phase hydrogenation of butadiene than all reported Pd/C catalysts while at the same time retaining isothermal reactor conditions. Moreover, when they were tested in the electrocatalytic hydrogen evolution reaction (HER), the catalysts outperformed reported Pd/C catalysts by a factor of 3, which underlines the benefits of the developed binder-free catalyst system.

Dedicated to Prof.D r. Wolfgang Schuhmann on the occasiono fh is 60th birthday. 1IntroductionThei ncreasing availability of fluctuating renewable energy like wind or solar power calls for efficient means of energy storage in times of excess power combined with the ability to provide the stored energy in times of shortage.E lectrochemical energy conversion, i.e.t he conversion of electrical energy into storable chemical energy and vice versa,e merges as am ajor contribution to solve this challenge with water splitting into hydrogen and oxygen by electrolysis and theirr econversion into water and electricale nergy in fuel cells as ap romising technique.C ombining both electrolysis and fuel cell in one single device,aso called reversible fuel cell, would be highly desirable.F rom an electrochemical point of view, major challenges are both the oxygen evolution reaction (OER)a nd the oxygen reduction reaction (ORR). Similar to metal-air-batteries [1],i ti sac onsiderablec hallenge to find materials whichc atalyze both reactionse fficiently, which however would be aprerequisite for high-efficiency reversible fuel cells.Among the various materials investigated towards this application,s pinel transition metalo xides were shown to be promising catalysts for both OER and ORR [2][3][4][5].Because of their large variety,s pinel type materials offer opportunities for synthesis and optimization towards active electrocatalysts.Another material extensively investigated towards electrocatalytic applications are carbon nanotubes (CNTs), whichi s, amongsto therr easons,d ue to their high surface area and high electrical conductivity.I t has frequently been shown that nitrogen dopingo ft he CNTs to formN CNTse nhances their activity towards the ORR, which is attributed to alterationsi nt he electronic structure and enhancedb asicity [6][7][8].N CNTsa re com-Abstract:Afacile way to prepare ab ifunctional electrocatalyst, which is active for both the oxygen evolution reaction (OER) and the oxygen reduction reaction( ORR) in alkaline media, is presented.ANi 0.9 Co 0.1 Fe 2 O 4 mixed oxide,w hich is synthesized usingapolyol mediateds ynthesis route,i sc ombinedw ith nitrogen doped carbon nanotubes (NCNT) known as electrically conducting material with high activity for the ORR. Thec ombined bifunctional catalystw as investigated towards its structural properties using TEM, XRD,X PS and Raman spectroscopy and studied withr elevante lectrochemical characterization techniques,n amely rotating disk electrode measurements for ORR and linears weepv oltammetry for OER as well as with scanning electrochemical microscopy (SECM). Thed ifference between onsetp otentials for OER and for ORR was similar to that of other published bifunctional catalysts,i ndicatingt hat the simple synthetic approachy ields materials well suited for bifunctional catalysis applications.F or ORR investigations the redox competition mode of SECM indicated high selectivity of the materials towards 4-electron reduction of oxygen to water. Them ixed material showed an enhan...

Functionalized high purity carbon nanotubes (CNTs) with various amounts of oxygen containing surface groups were investigated towards the relevant redox reactions of the all‐vanadium redox flow battery. The quinone/hydroquinone redox peaks between 0.0 and 0.7 V vs. Ag|AgCl|KClsat. were used to quantifying the degree of functionalization and correlated to XPS results. Cyclic voltammetry in vanadyl sulfate‐containing 3 M H2SO4 as a common supporting electrolyte showed no influence of the amount of surface groups on the V(IV)/V(V) redox system. In contrast, the reactions occurring at the negative electrode (V(II)/V(III) and V(III)/V(IV)) are strongly affected by oxygen surface groups. However, under modified experimental conditions, SECM experiments detecting the consumption of VO2+ molecules by CNT thin films in pH=2 solution show improved onset potentials with increased surface oxygen content up to ∼ 3 at%. Further increase in surface oxygen up to 8 at% led to minor improvement. These dissimilar results under different experimental conditions are rationalized by suggesting that oxygen functional groups do not form the active site for the V(IV)/V(V) reaction but wetting of the catalyst layer is of high importance.