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Efficient electrochemical transformations of molecular oxygen (oxygen reduction and evolution) for energy conversion/storage rely largely on the effective design of heterogeneous electrocatalysts. ...

Alkali metal–O2 batteries (i.e., Li/Na–O2) with high specific energies are promising alternatives to state-of-the-art metal-ion batteries. However, they are plagued by challenges arising from the u...

Shaping the energy landscape through development of more efficient electrochemical energy conversion and storage devices requires significant advancements in the catalysis of key electrochemical processes involving oxygen. This is especially the case for the oxygen evolution reaction (OER), which is largely challenged by the cost-ineffectiveness of the best performing electrocatalysts (i.e., Ru, Ir), along with their limited stability under acidic conditions. This presents a roadblock in the development of robust acid-based polymer exchange membrane electrochemical systems, currently the most advanced technologies for electrochemical energy conversion. Approaches such as dilution of Ru/Ir into flexible mixed metal oxide frameworks have been used as alternative strategies in designing robust OER electrocatalysts. Herein, we discuss the state of research in this area and detail the effect of the composition and structure of mixed metal oxides on their acidic OER activity and stability. Future directions for developing mixed metal oxide electrocatalysts suitable for acidic electrochemical environments are devised.

Recent advances in the use of nonstoichiometric mixed metal oxides belonging to the perovskite family as cost-effective catalysts for various oxygen-related heterogeneous thermochemical and electro...

Tuning catalysis at solid–solid interfaces is critical for the development of next-generation energy storage devices such as Li–O2 batteries, where solid lithium–oxygen species are formed and dissociated on a solid catalyst. Herein, atomically controlled synthesis is combined with theoretical calculations, electrochemical studies, and detailed characterization measurements to show that the interface between an oxide catalyst and the solid products is key to selectively control discharge product distribution, consequently affecting charge overpotentials. A surface structure-dependent electrochemical performance for nonprecious metal-containing, nanostructured lanthanum nickelate oxide (La2NiO4+δ, LNO) electrocatalysts is demonstrated. LNO nanostructures with (001) NiO-terminated surfaces exhibit lower charge overpotentials, as opposed to irregularly terminated polyhedral-shaped oxides of the same composition. It is found that these LNO nanostructures, with controlled surface structure, enhance the performa...

Electrocatalysis of oxygen reduction and evolution (ORR and OER) have become of significant importance due to their critical role in the performance of electrochemical energy conversion and storage devices, such as fuel cells, electrolyzers, and metal air batteries. While efficient ORR and OER have been reported using noble-metal based catalysts, their commercialization is cost prohibitive. In this Perspective, we discuss the potential of nonprecious metal based, mixed electronic–ionic conducting oxides (i.e., perovskites, double perovskites, and Ruddlesden–Popper (R-P) oxides) for efficient oxygen electrocatalysis at high and low temperatures. The nonstoichiometry of oxygen in these materials provides key catalytic properties that facilitate efficient ORR/OER electrocatalysis. We discuss the importance of surface structure and composition as critical parameters to understand and tune the ORR/OER activity of these oxides. We argue that techniques facilitating controlled synthesis and characterization of t...

Advancing our understanding of solid–solid interfacial electrocatalysis is central for engineering the next generation energy storage technologies. Li-O2 batteries provide the highest energy density among all battery technologies, making them attractive for the widespread electrification of the transportation (>500 miles) and the aviation sectors.1 These regenerative systems rely on the reversible redox chemistry between metallic Li and molecular O2 leading to the formation and dissociation of solid Li x O2species (xLi+ + O2 + xe– -> Li x O2; E0 = 3.0 V vs. Li/Li+; 1=< x =< 2). Although promising, these systems suffer from large overpotential losses potentially stemming from challenges in electron transport through Li x O2 species, consequently resulting in reduced round-trip efficiencies (55-60%).1 Various catalysts have been used to overcome these losses. However, lack of a fundamental understanding on the interfacial factors that dictate selective formation of Li x O2 species on an electrocatalyst surface, has hindered systematic optimization of the energetics for these processes. Therefore, development of a framework to investigate the atomistic interactions between an electrocatalyst surface and the formed Li x O2 solid products is key to enhancing their overall performance. In this contribution, atomically-controlled synthesis, detailed electrochemical and characterization studies, along with periodic density functional theory (DFT) calculations are combined to showcase the importance of the surface structure in tailoring the solid–solid interfacial catalysis for enhanced cell performance.2 This is demonstrated through the incorporation of non-precious 3d metal-based mixed metal oxide cathode electrocatalysts belonging to the first-series Ruddlesden-Popper (R-P) phase of the general form (A = La, Ca, Sr; B = Mn, Fe, Co, Ni).3 The flexibility in the A- and B-site compositions, can be explored to tune the geometric and the electronic structure of the catalysts, thus making them appealing candidates.4-5 Initially, the experimental and theoretical calculations are benchmarked using La2NiO4 (LNO) as the catalyst. A significant enhancement in the overall performance (>0.7 V) is observed upon the incorporation of catalytically active (001) NiO terminated LNO. The discharge products formed on these surfaces are characterized using numerous techniques, including Raman spectroscopy, chemical titration and mass spectroscopy. These studies indicate that the enhanced performance of LNO stems from its ability to effectively stabilize electronically conductive lithium deficient LixO2 (x2O2. The developed combinatorial framework for LNO, is extended to various A- and B-site systems to identify the geometric and electronic factors that aid in selective perturbation of film formation energetics, that leads to enhanced performance. A framework for tuning solid–solid interfacial catalysis on these systems is devised; knowledge that is critical for enhancing the efficiency of next generation energy storage technologies. References (1) Aurbach, D.; McCloskey, B. D.; Nazar, L. F.; Bruce, P. G., Nat. Energy 2016, 1, 16128. (2) Samira, S.†; Deshpande, S.†; Roberts, C. A.; Nacy, A. M.; Kubal, J.; Matesic, K.; Oesterling, O.; Greeley, J.; Nikolla, E., Chem. Mater. 2019, 31, 7300-7310. (3) Gu, X. K.†; Samira, S.†; Nikolla, E., Chem. Mater. 2018, 30, 2860-2872. (4) Gu, X. K.; Carneiro, J. S. A.; Samira, S.; Das, A.; Ariyasingha, N. M.; Nikolla, E., J. Am. Chem. Soc. 2018, 140, 8128-8137. (5) Samira, S.†, Gu, X. K.†, Nikolla, E., ACS Catal. 2019, 9, 10575-10586.

The photocatalytic oxidation of crystal violet, a triphenyl methane dye in aqueous solutions was investigated with nanoanatase TiO2 containing Anatase and rutile phases in the ratio of 3:1, under UV light by using a 125 W high pressure mercury vapor lamp as the source. The dye degradation using Ag+ doped TiO2 and nanoanatase TiO2 was compared. An optimum catalyst dose of 1 g/L was used. It was found that nanoanatase TiO2 had a higher efficiency than the Ag+ doped Titanium di Oxide. Nanoanatase TiO2 was found to be easy to separate from the treated effluent by simple centrifuging. The degradation of the dye of initial concentration: 5×10-5 mol/L, using nanoanatase TiO2 was greater than 99.5% on UV illumination for 45 minutes and that with Ag+ doped Titanium di Oxide as catalyst, was found to be 75% for 45 minutes of illumination. The effects of various parameters such as pH; initial dye concentration and catalyst dose on the reaction rate were studied. The kinetics of degradation fit well to Langmuir- Hinshelwood rate law.