Perovskite catalysts are of great interest as replacements for precious metals and oxides used in the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Perovskite electrocatalysts have been shown to have greater specific activities than precious metals and their oxides, but high mass activities have not yet been realized due to vague or incomplete mechanistic understanding of catalysts active sites coupled with inadequate synthesis techniques which often result in unwanted phase impurities and micron-scale materials. Herein, we demonstrated precise control over the synthesis of essentially phase pure perovskite nanocrystals with mass activities exceeding that of IrO2 and possessing comparable or greater bifunctional character than leading precious metals such as Ir and Pt. The robust aqueous synthesis of ABO3 perovskites such as LaCoO3, LaMnO3, LaNixFe1-xO3 and Ba0.5Sr0.5Co0.8Fe0.2O3-δ will be demonstrated, and the resulting electrocatalytic activities of these materials will be presented. We will examine these results in the context of proposed perovskite activity descriptors, surface hydroxylation, oxygen vacancies and mechanistic pathways for the OER and ORR. Catalytic activity is determined using electroanalytical techniques such as rotating disk electrochemistry and cyclic voltammetry in conjunction with materials characterization enabled by dynamic light scattering, electron microscopy, nitrogen sorption, X-ray photoelectron spectroscopy and X-ray diffraction. It is demonstrated that these highly active perovskite catalysts are an emerging replacement for the precious metals used not just for the OER and ORR, but also for the chlor-alkali and oxygen depolarized cathode industries as well.
Metal oxides have gained significant interest aspseudocapacitor electrodes due to reversible faradaicsurface reactions that allow for high power density andgreater energy storage than carbon based electric doublelayer capacitors. However, classically investigatedmaterials like RuO2, MnO2, and Ni(OH)2 suffer from highcost, low life cycles, or limited potential windows,respectively.1-3 As such, there is growing demand for newmaterials with improved energy storage and stability.Herein, we demonstrate the capacitive characteristics ofthree lanthanum based perovskite type oxides, LaMnO3,LaNiO3, and LaCoO3. Based on the inherent nature ofperovskites to contain oxygen vacancies, we demonstratethrough cyclic voltammetry that perovskites store chargethrough anions in alkaline electrolytes, likely in the formof hydroxides. This hypothesis was tested by inducingextrinsic oxygen vacancies in LaMnO3 through a lowtemperature reduction in H2/Ar. It was found thatsubstoichiometric LaMnO3-δ exhibits ~20% greatercapacitance, highlighting the significance of oxygenvacancies as charge-storage sites in these perovskite typeoxides. Importantly, due to the well-known oxide andproton ionic conduction characteristics of perovskites, wedemonstrate that charge storage is not limited to thesurface of these materials. Rather, it may extend into thebulk of the structure, leading to higher energy storagethan traditional psuedocapacitors which are inherentlylimited by surface confined reactions. As the first study ofthese materials for pseudocapacitor applications, onlymoderate structural and electrochemical optimizationshave been carried out. As such, the high specificcapacitances of >500F/g and high cycling stability for thematerials of this study imply a promising future forperovskite structured pseudocapacitors.
This paper demonstrates the capabilities and benefits of using dynamic traffic assignment (DTA) to analyze traffic impacts caused by transit services. The City of Austin’s proposed urban rail system is used as a case study. The urban rail connects the CBD, the University of Texas at Austin campus, and other large traffic generators. The majority of the rail system shares right-of-way with traffic. However, several segments have completely dedicated guideway. Previous analyses have focused either on microsimulation (which is limited in spatial area and does not consider route choice changes) or regional planning (which typically lacks detailed inputs and does not directly model transit impedances in the traffic assignment process). DTA provides a connection between these two methods: it can model route choice behavior using realistic inputs at a fine time scale across a large spatial area. Five scenarios with varying mode split percentages were modeled. At low ridership levels, corridors with major geometric modifications experienced more congestion. This caused travel pattern changes, increasing the volume on nearby parallel corridors.