Transition Metal Chalcogenides for Oxygen Reduction

Abstract

Chalcogenide materials are considered as the promising catalysts for oxygen reduction reaction (ORR).1,2 However, their usage is hindered mainly by poor conductivity, which results a substantial decrease in activity upon cycling. Carbon supports such as vulcan and activated carbon generally used to increase the conductivity, but, the issue associated with the stability of the material still not solved. In this work, we have synthesized TM1xTM2yXz (TM = transition metal; X = S, Se, Te) nanoparticles with different morphologies (Figure a). The morphology of the particle have also been simulated using BFDH morphology code and exposed planes were extracted. The materials were characterized in detail using various techniques such as PXRD, EXAFS, XPS, TEM and FESEM-EDAX. The electrochemical catalytic activity of the material was checked using vulcan as the conducting carbon support. The material showed good catalytic activity towards ORR and found electrochemically stable even at the end of 50000 cycles with negligible shift in the E1/2 value (Figure b), which is better than the state-of-the-art material platinum on carbon. Better activity of the catalyst has been linked with dissolution of chalcogen from the bulk to the surface of the catalyst. On the surface chalcogen forms XO32-/XO42-. The presence of chalcogen at the surface has a dual role. Firstly, the oxygen removal process from active sites becomes much easier than without additives. Secondly, hydrogen adsorption and desorption suppresses which prevents the active site from blocking, thus preventing a competitive reaction to take place.

Co7Se8 Nanostructures as Catalysts for Oxygen Reduction Reaction with High Methanol Tolerance

“…Typically it has been observed that changing from transition-metal oxide to transition-metal selenide leads to an increase of the conduction and valence band edges, making them closer to the water oxidation–reduction levels. − The relative closeness of the band positions will expectedly lead to better charge transfer at the catalyst–electrolyte interface, thus enhancing the catalytic efficiency. Similar effect has been also reported by Alonso-Vante in a comprehensive report comparing the ORR activity of transition-metal chalcogenide catalysts where they have shown the favorable effect of selenization in increasing the ORR catalytic activity for both Pt-group metals as well other transition metals, especially Co . Similar effect has also been reported for Co 9 Se 8 through theoretical as well as experimental study .…”

“…20−22 The relative closeness of the band positions will expectedly lead to better charge transfer at the catalyst−electrolyte interface, thus enhancing the catalytic efficiency. Similar effect has been also reported by Alonso-Vante in a comprehensive report comparing the ORR activity of transition-metal chalcogenide catalysts where they have shown the favorable effect of selenization in increasing the ORR catalytic activity for both Pt-group metals as well other transition metals, especially Co. 23 Similar effect has also been reported for Co 9 Se 8 through theoretical as well as experimental study. 24 Additionally, these nonstoichiometric compositions such as Co 0.85 Se (i.e., Co 7 Se 8 ), being less Se rich and containing the metal in a mixed valent state, might be more beneficial for this kind of catalytic reactions because it can easily support variation of the metal oxidation state, thereby facilitating the reaction pathway.…”

Physical and Chemical Considerations for Improving Catalytic Activity and Stability of Non-Precious-Metal Oxygen Reduction Reaction Catalysts

“…A possible path to solve the economic and geological constraints associated with the use of platinum when deploying PEMFCs consists in developing catalysts based on nonprecious metals. Many materials such as transition-metal oxides, nitrides, and/or carbides, transition-metal chalcogenides, − nanostructured carbon materials, nitrogen-, sulfur-, boron-, and phosphorus-doped carbon materials, , and transition-metal/nitrogen/carbon (metal–NC) catalysts − have been investigated for ORR electrocatalysis in acid and/or alkaline medium. Metal–NC catalysts synthesized by pyrolysis of a transition metal (Fe, Co), nitrogen and carbon precursors have demonstrated initial ORR activity approaching that of Pt/C in rotating disk electrode (RDE) or PEMFC. − ,, Their ORR activity strongly depends on their physical and chemical structure, namely the nature and coordination of the metal centers, metal content, , redox potential, basicity of the N-containing groups, ,,, and pore size distribution in the carbon phase .…”

Oxygen reduction catalyzed by nanocomposites based on graphene quantum dots-supported copper nanoparticles

“…These include monometallic nanoparticles [4][5][6][7], alloy nanoparticles [8][9][10], metal oxides nanoparticles [11][12][13][14][15], and transition metal chalcogenide nanoparticles [16] that are supported on diverse substrates including metal structures [17], metal oxides [18], or carbon-based materials such as carbon black, standard carbon fibers [19], single-or multi-walled carbon nanotubes [20], and graphene sheets [21][22][23][24]. As summarized in several recent reviews [25][26][27], these supporting materials play important roles in, for instance, preventing nanoparticle aggregation and increasing the corresponding surface areas; manipulating electronic energy of the metal nanoparticles and hence interactions with O 2 molecules via intimate electronic interactions with the supporting substrates; enhancing electronic conductivity and serving as current collectors; as well as improving structural stability of the catalysts in extreme acidic or basic environments.…”