30 results found
Wang T, Zhang Y, Huang B, et al., 2021, Enhancing oxygen reduction electrocatalysis by tuning interfacial hydrogen bonds, NATURE CATALYSIS, Vol: 4, Pages: 753-762, ISSN: 2520-1158
Corby S, Rao R, Steier L, et al., 2021, The kinetics of metal oxide photoanodesfrom charge generation to catalysis, Nature Reviews Materials, ISSN: 2058-8437
Generating charge carriers with lifetimes long enough to drive catalysis is a critical aspect for both photoelectrochemical and photocatalytic systems and a key determinant of their efficiency. This review addresses the charge carrier dynamics underlying the performance of metal oxides as photoanodes and their ability to drive photoelectrochemical water oxidation, alongside wider comparison with metal oxide function in photocatalytic and electrocatalytic systems. We start by highlighting the disparity between the ps–ns lifetimes of electron and holes photoexcited in bulk metal oxides versus the ms –s timescale of water oxidation catalysis. We go onto review recent literature of the dominant kinetic processes determining photoanode performance, namely charge generation, polaron formation and charge trapping, bulk and surface recombination, charge separation and extraction, and finally the kinetics of water oxidation catalysis. With each topic, we review current understanding and note areas of remaining uncertainty or controversy. We discuss the potential for material selection and examine approaches such as doping, nanostructuring, junction formation and/or co-catalyst deposition to enhance performance. Critically, we examine how such performance enhancements can be understood from analyses of carrier dynamics and propose design guidelines for further material or device optimisation.
Hwang J, Rao RR, Giordano L, et al., 2021, Regulating oxygen activity of perovskites to promote NOx oxidation and reduction kinetics, NATURE CATALYSIS, Vol: 4, Pages: 663-673, ISSN: 2520-1158
Rao RR, Huang B, Katayama Y, et al., 2021, pH- and Cation-Dependent Water Oxidation on Rutile RuO2(110), JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 125, Pages: 8195-8207, ISSN: 1932-7447
Bucci A, Garcia-Tecedor M, Corby S, et al., 2021, Self-supported ultra-active NiO-based electrocatalysts for the oxygen evolution reaction by solution combustion, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 9, Pages: 12700-12710, ISSN: 2050-7488
Huang B, Myint KH, Wang Y, et al., 2021, Cation-Dependent Interfacial Structures and Kinetics for Outer-Sphere Electron-Transfer Reactions, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 125, Pages: 4397-4411, ISSN: 1932-7447
Rao RR, Stephens IEL, Durrant JR, 2021, Understanding What Controls the Rate of Electrochemical Oxygen Evolution, JOULE, Vol: 5, Pages: 16-18, ISSN: 2542-4351
Katayama Y, Kubota R, Rao RR, et al., 2021, Direct Observation of Surface-Bound Intermediates during Methanol Oxidation on Platinum under Alkaline Conditions, Journal of Physical Chemistry C, ISSN: 1932-7447
Direct methanol fuel cells (DMFCs) using alkaline electrolytes are of interest due to the applicability of nonprecious metal-based materials for electrocatalysts. However, the lack of understanding of the methanol oxidation reaction (MOR) mechanism in alkaline media hinders the development of active catalysts for the MOR. In this work, ambient-pressure XPS and in situ surface-enhanced infrared spectroscopy were performed on the Pt surface in order to gain experimental insights into the reaction pathway for the MOR. We present a comprehensive reaction mechanism for the MOR in alkaline media and show that the MOR proceeds via two different pathways depending on the electrode potential. We confirmed the formation of partially hydrogenated CO adsorbates [HxCOad···(OH) (1 < x < 3)] via water and/or hydroxide ion-mediated dissociation of methanol. The HxCOad···(OH) species were further dehydrogenated to COad in the potential range of 0.40-0.60 VRHE and subsequently oxidized to CO2 by reactive OHad on the Pt surface at 0.65 VRHE (pathway I). Furthermore, H3C-Oad intermediates were observed at potentials higher than 0.9 VRHE, at which the MOR proceeds mainly via H3C-Oad instead of COad intermediates (pathway II). The oxidation current related to this conversion from H3C-Oad to CO2 (pathway II) dominates the overall MOR current, suggesting that the H3C-Oad pathway could be one of the keys to enhancing the MOR activity in an alkaline environment. Our findings pave the way toward a design strategy for MOR electrocatalysts with improved activity based on the experimental reaction mechanisms that have been identified.
Mesa CA, Rao RR, Francas L, et al., 2020, Reply to: Questioning the rate law in the analysis of water oxidation catalysis on haematite photoanodes, NATURE CHEMISTRY, Vol: 12, Pages: 1099-+, ISSN: 1755-4330
Kawaguchi T, Rao RR, Lunger JR, et al., 2020, Stern layers on RuO2 (100) and (110) in electrolyte: Surface X-ray scattering studies, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, Vol: 875, ISSN: 1572-6657
Rao RR, Tulodziecki M, Han B, et al., 2020, Reactivity with Water and Bulk Ruthenium Redox of Lithium Ruthenate in Basic Solutions, ADVANCED FUNCTIONAL MATERIALS, Vol: 31, ISSN: 1616-301X
Rao RR, Kolb MJ, Giordano L, et al., 2020, Operando identification of site-dependent water oxidation activity on ruthenium dioxide single-crystal surfaces, NATURE CATALYSIS, Vol: 3, Pages: 516-525, ISSN: 2520-1158
Escudero-Escribano M, Biegel CM, Kamat PV, 2020, Women Scientists at the Forefront of Energy Research: A Virtual Issue, Part 2, ACS ENERGY LETTERS, Vol: 5, Pages: 623-633, ISSN: 2380-8195
Hwang J, Feng Z, Charles N, et al., 2019, Tuning perovskite oxides by strain: Electronic structure, properties, and functions in (electro)catalysis and ferroelectricity, MATERIALS TODAY, Vol: 31, Pages: 100-118, ISSN: 1369-7021
Mezzavilla S, Katayama Y, Rao R, et al., 2019, Activity-or Lack Thereof-of RuO2-Based Electrodes in the Electrocatalytic Reduction of CO2, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 123, Pages: 17765-17773, ISSN: 1932-7447
Katayama Y, Nattino F, Giordano L, et al., 2019, An In Situ Surface-Enhanced Infrared Absorption Spectroscopy Study of Electrochemical CO2 Reduction: Selectivity Dependence on Surface C-Bound and O-Bound Reaction Intermediates, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 123, Pages: 5951-5963, ISSN: 1932-7447
Wei C, Rao RR, Peng J, et al., 2019, Recommended Practices and Benchmark Activity for Hydrogen and Oxygen Electrocatalysis in Water Splitting and Fuel Cells, Advanced Materials, ISSN: 0935-9648
© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Electrochemical energy storage by making H 2 an energy carrier from water splitting relies on four elementary reactions, i.e., the hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Herein, the central objective is to recommend systematic protocols for activity measurements of these four reactions and benchmark activities for comparison, which is critical to facilitate the research and development of catalysts with high activity and stability. Details for the electrochemical cell setup, measurements, and data analysis used to quantify the kinetics of the HER, HOR, OER, and ORR in acidic and basic solutions are provided, and examples of state-of-the-art specific and mass activity of catalysts to date are given. First, the experimental setup is discussed to provide common guidelines for these reactions, including the cell design, reference electrode selection, counter electrode concerns, and working electrode preparation. Second, experimental protocols, including data collection and processing such as ohmic- and background-correction and catalyst surface area estimation, and practice for testing and comparing different classes of catalysts are recommended. Lastly, the specific and mass activity activities of some state-of-the-art catalysts are benchmarked to facilitate the comparison of catalyst activity for these four reactions across different laboratories.
Zhu ZH, Strempfer J, Rao RR, et al., 2019, Anomalous Antiferromagnetism in Metallic RuO2 Determined by Resonant X-ray Scattering, PHYSICAL REVIEW LETTERS, Vol: 122, ISSN: 0031-9007
Stoerzinger KA, Wang XR, Hwang J, et al., 2018, Speciation and Electronic Structure of La1-xSrxCoO3-delta During Oxygen Electrolysis, TOPICS IN CATALYSIS, Vol: 61, Pages: 2161-2174, ISSN: 1022-5528
Rao RR, Kolb MJ, Hwang J, et al., 2018, Surface Orientation Dependent Water Dissociation on Rutile Ruthenium Dioxide, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 122, Pages: 17802-17811, ISSN: 1932-7447
Roy C, Rao RR, Stoerzinger KA, et al., 2018, Trends in activity and dissolution on RuO2 under oxygen evolution conditions: particles versus well-defined extended surfaces, ACS Energy Letters, Vol: 3, Pages: 2045-2051, ISSN: 2380-8195
Rutile RuO2 catalysts are the most active pure metal oxides for oxygen evolution; however, they are also unstable toward dissolution. Herein, we study the catalytic activity and stability of oriented thin films of RuO2 with (111), (101), and (001) orientations, in comparison to a (110) single crystal and commercial nanoparticles. These surfaces were all tested in aqueous solutions of 0.05 M H2SO4. The initial catalyst activity ranked as follows: (001) > (101) > (111) ≈ (110). We complemented our activity data with inductively coupled plasma mass spectroscopy, to measure Ru dissolution products occurring in parallel to oxygen evolution. In contrast to earlier reports, we find that, under our experimental conditions, there is no correlation between the activity and stability.
Katayama Y, Giordano L, Rao RR, et al., 2018, Surface (Electro)chemistry of CO2 on Pt Surface: An in Situ Surface-Enhanced Infrared Absorption Spectroscopy Study, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 122, Pages: 12341-12349, ISSN: 1932-7447
Kuznetsov DA, Han B, Yu Y, et al., 2018, Tuning Redox Transitions via Inductive Effect in Metal Oxides and Complexes, and Implications in Oxygen Electrocatalysis, JOULE, Vol: 2, Pages: 225-244, ISSN: 2542-4351
Stoerzinger KA, Hong WT, Wang XR, et al., 2017, Decreasing the Hydroxylation Affinity of La1-xSrxMnO3 Perovskites To Promote Oxygen Reduction Electrocatalysis, CHEMISTRY OF MATERIALS, Vol: 29, Pages: 9990-9997, ISSN: 0897-4756
Rao RM, Kolb MJ, Halck NB, et al., 2017, Towards identifying the active sites on RuO2 (110) in catalyzing oxygen evolution, Energy and Environmental Science, Vol: 10, Pages: 2626-2637, ISSN: 1754-5692
While the surface atomic structure of RuO2 has been well studied in ultra high vacuum, much less is known about theinteraction between water and RuO2 in aqueous solution. In this work, in situ surface X-ray scattering measurementscombined with density functional theory (DFT) was used to determine the surface structural changes on single-crystalRuO2 (110) as a function of potential in acidic electrolyte. The redox peaks at 0.7, 1.1 and 1.4 V vs. reversible hydrogenelectrode (RHE) could be attributed to surface transitions associated with the successive deprotonation of -H2O on thecoordinatively unsaturated Ru sites (CUS) and hydrogen adsorbed to the bridging oxygen sites. At potentials relevant tothe oxygen evolution reaction (OER), an –OO species on the Ru CUS sites was detected, which was stabilized by aneighboring -OH group on the Ru CUS or bridge site. Combining potential-dependent surface structures with theirenergetics from DFT led to a new OER pathway, where the deprotonation of the -OH group used to stabilize –OO wasfound to be rate-limiting.
Stoerzinger KA, Rao RR, Wang XR, et al., 2017, The Role of Ru Redox in pH-Dependent Oxygen Evolution on Rutile Ruthenium Dioxide Surfaces, CHEM, Vol: 2, Pages: 668-675, ISSN: 2451-9294
Stoerzinger KA, Diaz-Morales O, Kolb M, et al., 2017, Orientation-Dependent Oxygen Evolution on RuO2 without Lattice Exchange, ACS ENERGY LETTERS, Vol: 2, Pages: 876-881, ISSN: 2380-8195
Giordano L, Han B, Risch M, et al., 2016, pH dependence of OER activity of oxides: Current and future perspectives, CATALYSIS TODAY, Vol: 262, Pages: 2-10, ISSN: 0920-5861
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