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Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS	Revealing the pH dependent activities and surface instabilities for Ni-based electrocatalysts during the oxygen evolution reaction Chunzhen Yang , Maria Batuk , Quentin Jacquet , Gwenaëlle Rousse , Wei Yin , Leiting Zhang , Joke Hadermann , Artem Abakumov , Giannantonio Cibin , Alan Chadwick , Jean-marie Tarascon , Alexis Grimaud Acs Energy Letters DOI: 10.1021/acsenergylett.8b01818 Diamond Proposal Number(s): [12559] Show Abstract ▼ Abstract: Multiple electrochemical processes are involved at the catalyst/electrolyte interface during the oxygen evolution reaction (OER). With the purpose of elucidating the complexity of surface dynamics upon OER, we systematically studied two Ni-based crystalline oxides (LaNiO3-δ and La2Li0.5Ni0.5O4) and compared them with the state-of-the-art Ni-Fe (oxy)hydroxide amorphous catalyst. Electrochemical measurements such as rotating ring disk electrode (RRDE) and electrochemical quartz microbalance microscopy (EQCM), coupled with a series of physical characterizations including transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) are conducted to unravel the exact pH effect on both the OER activity and the catalyst stability. We demonstrate that for Ni-based crystalline catalysts the rate for surface degradation depends on the pH and is greater than the rate for surface reconstruction. This behavior is unlike for amorphous Ni oxyhydroxide catalyst which is found more stable and pH independent.	Nov 2018
	Correlated polyhedral rotations in the absence of polarons during electrochemical insertion of lithium in ReO3 Nicholas H. Bashian , Shiliang Zhou , Mateusz Zuba , Alex M. Ganose , Joseph W. Stiles , Allyson Ee , David S. Ashby , David O. Scanlon , Louis F. J. Piper , Bruce S. Dunn , Brent C. Melot Acs Energy Letters DOI: 10.1021/acsenergylett.8b01179 Show Abstract ▼ Abstract: Understanding the structural transformations that materials undergo during the insertion and deinsertion of Li-ions is crucial for designing high performance intercalation hosts as these deformations can lead to significant capacity fade over time. Here we present a study of the metallic defect perovskite ReO3, with the goal of determining whether these distortions are driven by polaronic charge transport (i.e. the electrons and ions moving through the lattice in a coupled way) due to the semiconducting nature of most oxide hosts. Employing a range of techniques including galvanostatic/potentiometric electrochemical probes, operando X-ray diffraction, X-ray photoelectron spectroscopy, and density functional theory calculations we nd that the cubic structure of ReO3 experiences multiple phase changes involving the correlated twisting of rigid octahedral subunits during the insertion of two equivalents of Li-ions. This extensive rearrangement of the structure results in exceptionally poor long-term cyclability due to large strains that result within the structure, all in spite of the fact that the phase retains its metallic character for all values of Li content from ReO3 to Li2ReO3. These results suggest that phase transformations during alkali ion intercalation are the result of local strains in the lattice and not exclusively due to polaron migration.	Sep 2018
I07-Surface & interface diffraction	Layered mixed tin-lead hybrid perovskite solar cells with high stability Daniel Ramirez , Kelly Schutt , Zhiping Wang , Andrew J. Pearson , Edoardo Ruggeri , Henry J. Snaith , Samuel D. Stranks , Franklin Jaramillo Acs Energy Letters DOI: 10.1021/acsenergylett.8b01411 Diamond Proposal Number(s): [17223] Show Abstract ▼ Abstract: Tin-lead mixed metal hybrid perovskites with tunable band gaps are attractive candidates to be used as the low-band gap cell in high efficiency tandem solar cells. Nevertheless, perovskites containing tin have a greater propensity to degrade due to the fast oxidation of Sn2+ to Sn4+, which is a restrictive factor in the development of these materials. Although significant improvements are achieved with Pb:Sn mixed-metal perovskites, in comparison to neat Sn perovskites, the intrinsic instability may still pose a threat to long-term operation. For neat Pb perovskites, two dimensional (2D) hybrid perovskites, where n layers of inorganic material are separated by a long chain organic cation, generally exhibit greater stability but have lower photovoltaic performance characteristics, motivating the study of 2D/3D mixed dimension systems to realize both high efficiency and stability. In this report we demonstrate such optimal compromise between performance and stability using formamidinium, cesium and t-butylammonium as A-site cations with Pb:Sn mixed metal low band gap perovskites. As determined by film structure measurements, the optimised 2D perovskite phases facilitate improved luminescence efficiency, which we infer to be via surface defect site passivation. Perovskite solar cells based on n = 4 and n = 5 lead-tin perovskites achieved power conversion efficiencies of up to 9.3% and 10.6%, respectively and correspondingly retained 47% and 29% of their initial efficiency during storage in nitrogen for 2000 hours. A similar stability trend for n = 4 over n = 5 was also observed for unencapsulated devices during continuous operation under combined air atmosphere and temperature for 10 hours, resulting in improved stability over the 3D lead-tin counterpart.	Aug 2018
I07-Surface & interface diffraction I12-JEEP: Joint Engineering, Environmental and Processing	Defect-Assisted Photoinduced Halide Segregation in Mixed-Halide Perovskite Thin Films Alex J. Barker , Aditya Sadhanala , Felix Deschler , Marina Gandini , Satyaprasad P. Senanayak , Phoebe M. Pearce , Edoardo Mosconi , Andrew Pearson , Yue Wu , Ajay Ram Srimath Kandada , Tomas Leitjens , Filippo De Angelis , Sian E. Dutton , Annamaria Petrozza , Richard H. Friend Acs Energy Letters DOI: 10.1021/acsenergylett.7b00282 Diamond Proposal Number(s): [11454, 12436] Show Abstract ▼ Abstract: Solution processable lead halide perovskites show immense promise for use in photovoltaics and other optoelectronic applications. The ability to tune their bandgap by alloying various halide anions (for example in CH3NH3Pb(I1-xBrx)3, 0	May 2017
	Can Pb-Free Halide Double Perovskites Support High-Efficiency Solar Cells? Christopher N. Savory , Aron Walsh , David O. Scanlon Acs Energy Letters 1, 949 - 955 DOI: 10.1021/acsenergylett.6b00471 Show Abstract ▼ Abstract: The methylammonium lead halides have become champion photoactive semiconductors for solar cell applications; however, issues still remain with respect to chemical instability and potential toxicity. Recently, the Cs2AgBiX6 (X = Cl, Br) double perovskite family has been synthesized and investigated as stable nontoxic replacements. We probe the chemical bonding, physical properties, and cation anti-site disorder of Cs2AgBiX6 and related compounds from first-principles. We demonstrate that the combination of Ag(I) and Bi(III) leads to the wide indirect band gaps with large carrier effective masses owing to a mismatch in angular momentum of the frontier atomic orbitals. The spectroscopically limited photovoltaic conversion efficiency is less than 10% for X = Cl or Br. This limitation can be overcome by replacing Ag with In or Tl; however, the resulting compounds are predicted to be unstable thermodynamically. The search for nontoxic bismuth perovskites must expand beyond the Cs2AgBiX6 motif.	Nov 2016

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