Electrocatalytic properties of Pt-Bi electrodes towards the electrooxidation of formic acid

Formic acid oxidation was studied on two Pt-Bi catalysts, i.e., Pt2Bi and polycrystalline Pt modified by irreversible adsorbed Bi (Pt/Biirr) in order to establish the difference between the effects of Biirr and Bi in the alloyed state. The results were compared to pure Pt. It was found that both bimetallic catalysts were more active than Pt with the onset potentials shifted to more negative values and the currents at 0.0 V vs. saturated calomel electrode (under steady state conditions) improved by up to two order of magnitude. The origin of the high activity and stability of Pt2Bi was increased selectivity toward formic acid dehydrogenation caused by the ensemble and electronic effects and suppression of Bi leaching from the surface during formic acid oxidation. However, although Pt/Biirr also showed remarkable initial activity compared to pure Pt, dissolution of Bi was not suppressed and poisoning of the electrode surface induced by the dehydration path was observed. Comparison of the initial quasi-steady state and potentiodynamic results obtained for these two Pt-Bi catalysts revealed that the electronic effect, existing only in the alloy, contributed to the earlier start of the reaction, while the maximum current density was determined by the ensemble effect.Oksidacija mravlje kiseline ispitivana je na dva tipa Pt-Bi katalizatora: Pt2Bi elektrodi i na polikristalnoj Pt elektrodi modifikovanoj ireverzibilno adsorbovanim Bi (Pt/Biirr). Aktivnosti su upoređene sa rezultatima dobijenim na čistoj poli- kristalnoj Pt elektrodi. Cilj je bio da se objasni razlika u delovanju ireverzibilno adsorbovanog Bi (Biirr) i Bi u legiranom stanju. Pokazano je da su oba bimetalna katalizatora aktivnija od polikristalne Pt, početak reakcije je pomeren ka negativnijim vrednostima i u poređenju sa čistom Pt pri stacionarnim uslovima dobijene su do dva reda veličine veće gustine struje. Razlog za veliku aktivnost i stabilnost Pt2Bi elektrode u oksidaciji mravlje kiseline je odigravanje reakcije po glavnom reakcionom putu (dehidroganacija mravlje kiseline), što je izazvano efektom trećeg tela i elektronskim efektom, kao i sprečavanje izluživanja Bi iz elektrode. S druge strane, iako Pt/Biirr pokazuje značajnu početnu aktivnost u odnosu na Pt, ova elektroda nije stabilna tokom reakcije oksidacije HCOOH zbog kontinualnog rastvaranja Bi sa površine elektrode, kao i trovanja površine izazvanog tokom reakcije po indirektnom, dehidratacionom putu. Poređenjem rezultata dobijenih na ove dve Pt-Bi elektrode može se objasniti uloga efekta trećeg tela i elektronskog efekta u oksidaciji HCOOH. Naime, elektronski efekat, koji postoji samo kod legure, doprinosi ranijem početku reakcije, dok je maksimalna struja određena efektom trećeg tela. Tokom cikliziranja Pt/Biirr elektrode Bi odlazi sa površine i efekat trećeg tela se gubi tokom vremena. Hronoamperometrijska merenja ukazuju na prednost legure, odnosno neophodnost legiranja Bi sa Pt da bi se dobio koroziono stabilan katalizator

Factors affecting the microstructure of porous ceramics

In this study, porous ceramics were produced by using two methods: the polymeric sponge and foam method. Astudy of the effect of viscosity on the characteristics of the final product produced using the polymeric sponge method revealed that the microstructure of porous ceramics is highly affected by the viscosity of the slurry. The optimal ratio between porosity and the strength of the porous material was achieved by subsequently repeating the immersing and drying processes. Astudy of the porous material obtained using the foam method revealed that the pore size and foam volume can be controlled by varying the amounts of anhydride and thermal blowing agent. The problem related to foam collapsing was solved by using a thermal blowing agent. The microstructure of the samples was characterized by SEM

High Forest or Wood Pasture: A model of Large Herbivores' impact on European Lowland Vegetation

Natural forest dynamics is a foundational topic of forest science. A new Wood Pasture hypothesis considering large herbivore as driving force in forest ecosystem is now challenging the traditional High Forest hypothesis, in which vegetation is regarded as main driving force. In this study, a model-based approach is applied to investigate differences between these two hypotheses and the determine factors in the system. A theoretical landscape of 1 km²formed by 100*100 cells is set up with 100 vegetation patches and free moving herbivores on. Our null hypothesis that herbivores make no difference in vegetation dynamics especially at canopy level is rejected. It is found that synchronization of herbivore behaviors is the most influencing factor of how a landscape might be shaped. It is also found that landscape could be a mosaic of both high forest and wood pasture depends on large herbivore’s herd size

Carbon Supported PtSn versus PtSnO2 Catalysts in Methanol Oxidation

Pt, PtSn and PtSnO2 catalysts supported on high surface area carbon synthesized by microwave assisted polyol procedure were tested for methanol oxidation. Based on TGA, EDX and XRD analysis, PtSn/C is composed of Pt and Pt3Sn phase while the rest of Sn is present in a form of very small tin oxide particles. This paper focuses on structure-activity relationships for CO tolerance and methanol oxidation reactions after addition of Sn to Pt catalysts. Alloying of Sn with Pt improves the rate of CO oxidation despite the fact that the pure Sn does not react with CO and therefore activity for methanol oxidation increases similar to 2 times in comparison to Pt/C catalyst. PtSn/C catalyst shows small advantage in comparison with PtSnO2/C catalyst due to the alloyed Sn and its electronic effect. Long term stability tests also confirmed that PtSn/C catalyst is somewhat better in comparison to PtSnO2/C

Relationships between Atomic Level Surface Structure and Stability/Activity of Platinum Surface Atoms in Aqueous Environments

The development of alternative energy systems for the clean production, storage, and conversion of energy is strongly dependent on our ability to understand, at atomic molecular levels, the functional links between the activity and stability of electrochemical interfaces. Whereas structure–activity relationships are rapidly evolving, the corresponding structure–stability relationships are still missing. This is primarily because there is no adequate experimental approach capable of monitoring the stability of well-defined single crystals in situ. Here, by utilizing the power of inductively coupled plasma mass spectrometry (ICP-MS) connected to a stationary probe and coupling this technique to the rotating disk electrode method, it was possible to simultaneously measure the dissolution rates of surface atoms (as low as 0.4 pg cm^–2 s^–1) and correlate them with the kinetic rates of electrochemical reactions in real time. Making use of this unique probe, it was possible to establish almost “atom by atom” structure–stability–activity relationships for platinum single crystals in both acidic and alkaline environments. We found that the degree of stability is strongly dependent on the coordination of surface atoms (less coordinated yields less stable), the nature of covalent and noncovalent interactions (i.e., adsorption of hydroxyl groups, oxygen atoms, and halide species vs interactions between hydrated Li cations and surface oxide), the thermodynamic driving force for Pt complexation (Pt ion speciation in solution), and the nature of the electrochemical reaction (the oxygen reduction/evolution and CO oxidation reactions). These findings open new opportunities for elucidating key fundamental descriptors that govern both activity and stability trends and will ultimately assist in the development of real energy conversion and storage systems