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ACS Energy Letters

Yue Zhang, Lu Gao, Emiel J M Hensen, Jan P Hofmann
The evaluation of the stability of emerging earth-abundant metal phosphide electrocatalysts by solely electrochemical current-potential sweeps is often not conclusive. In this study, we investigated Co2 P to evaluate its stability under both acidic (0.5 M H2 SO4 ) and alkaline (1.0 M KOH) hydrogen evolution (HER) conditions. We found that the electrochemical surface area (ECSA) of Co2 P only slightly increased in acidic conditions but almost doubled after electrolysis in alkaline electrolyte. The surface composition of the electrode remained almost unchanged in acid but was significantly altered in alkaline during current-potential sweeps...
June 8, 2018: ACS Energy Letters
Ming Ma, Kai Liu, Jie Shen, Recep Kas, Wilson A Smith
In this work, the highly selective and stable electrocatalytic reduction of CO2 to CO on nanostructured Ag electrocatalysts is presented. The Ag electrocatalysts are synthesized by the electroreduction of Ag2 CO3 formed by in situ anodic-etching of Ag foil in a KHCO3 electrolyte. After 3 min of this etching treatment, the Ag2 CO3 -derived nanostructured Ag electrocatalysts are capable of producing CO with up to 92% Faradaic efficiency at an overpotential as low as 290 mV, which surpasses all of the reported Ag catalysts at identical conditions to date...
June 8, 2018: ACS Energy Letters
Wouter Vijselaar, Roald M Tiggelaar, Han Gardeniers, Jurriaan Huskens
Most photoanodes commonly applied in solar fuel research (e.g., of Fe2 O3 , BiVO4 , TiO2 , or WO3 ) are only active and stable in alkaline electrolytes. Silicon (Si)-based photocathodes on the other hand are mainly studied under acidic conditions due to their instability in alkaline electrolytes. Here, we show that the in-diffusion of nickel into a 3D Si structure, upon thermal annealing, yields a thin (sub-100 nm), defect-free nickel silicide (NiSi) layer. This has allowed us to design and fabricate a Si microwire photocathode with a NiSi interlayer between the catalyst and the Si microwires...
May 11, 2018: ACS Energy Letters
Yuljae Cho, Bo Hou, Jongchul Lim, Sanghyo Lee, Sangyeon Pak, John Hong, Paul Giraud, A-Rang Jang, Young-Woo Lee, Juwon Lee, Jae Eun Jang, Henry J Snaith, Stephen M Morris, Jung Inn Sohn, SeungNam Cha, Jong Min Kim
In a quantum dot solar cell (QDSC) that has an inverted structure, the QD layers form two different junctions between the electron transport layer (ETL) and the other semiconducting QD layer. Recent work on an inverted-structure QDSC has revealed that the junction between the QD layers is the dominant junction, rather than the junction between the ETL and the QD layers, which is in contrast to the conventional wisdom. However, to date, there have been a lack of systematic studies on the role and importance of the QD heterojunction structure on the behavior of the solar cell and the resulting device performance...
April 13, 2018: ACS Energy Letters
Dorottya Hursán, Csaba Janáky
Isotopic labeling experiments were performed to better understand the electrochemical reduction of carbon dioxide on nitrogen-doped porous carbon electrodes. By using nonequilibrated solutions of selectively labeled initial carbon sources (i.e., 13 CO2 and H13 CO3 - ), bicarbonate anion was identified as the predominant source of the carbon monoxide reduction product.
March 9, 2018: ACS Energy Letters
Franziska Krieg, Stefan T Ochsenbein, Sergii Yakunin, Stephanie Ten Brinck, Philipp Aellen, Adrian Süess, Baptiste Clerc, Dominic Guggisberg, Olga Nazarenko, Yevhen Shynkarenko, Sudhir Kumar, Chih-Jen Shih, Ivan Infante, Maksym V Kovalenko
Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and optoelectronic applications are hampered by the loss of colloidal stability and structural integrity due to the facile desorption of surface capping molecules during isolation and purification. To address this issue, herein, we propose a new ligand capping strategy utilizing common and inexpensive long-chain zwitterionic molecules such as 3-( N , N -dimethyloctadecylammonio)propanesulfonate, resulting in much improved chemical durability...
March 9, 2018: ACS Energy Letters
Tanmay Banerjee, Kerstin Gottschling, Gökcen Savasci, Christian Ochsenfeld, Bettina V Lotsch
Covalent organic frameworks (COFs) are a new class of crystalline organic polymers that have garnered significant recent attention as highly promising H2 evolution photocatalysts. This Perspective discusses the advances in this field of energy research while highlighting the underlying peremptory factors for the rational design of readily tunable COF photoabsorber-cocatalyst systems for optimal photocatalytic performance.
February 9, 2018: ACS Energy Letters
David Kiefer, Alexander Giovannitti, Hengda Sun, Till Biskup, Anna Hofmann, Marten Koopmans, Camila Cendra, Stefan Weber, L Jan Anton Koster, Eva Olsson, Jonathan Rivnay, Simone Fabiano, Iain McCulloch, Christian Müller
N-doping of conjugated polymers either requires a high dopant fraction or yields a low electrical conductivity because of their poor compatibility with molecular dopants. We explore n-doping of the polar naphthalenediimide-bithiophene copolymer p(gNDI-gT2) that carries oligoethylene glycol-based side chains and show that the polymer displays superior miscibility with the benzimidazole-dimethylbenzenamine-based n-dopant N-DMBI. The good compatibility of p(gNDI-gT2) and N-DMBI results in a relatively high doping efficiency of 13% for n-dopants, which leads to a high electrical conductivity of more than 10-1 S cm-1 for a dopant concentration of only 10 mol % when measured in an inert atmosphere...
February 9, 2018: ACS Energy Letters
Jarvist Moore Frost, Lucy D Whalley, Aron Walsh
Halide perovskites show unusual thermalization kinetics for above-bandgap photoexcitation. We explain this as a consequence of excess energy being deposited into discrete large polaron states. The crossover between low-fluence and high-fluence "phonon bottleneck" cooling is due to a Mott transition where the polarons overlap ( n ≥ 1018 cm-3 ) and the phonon subpopulations are shared. We calculate the initial rate of cooling (thermalization) from the scattering time in the Fröhlich polaron model to be 78 meV ps-1 for CH3 NH3 PbI3 ...
December 8, 2017: ACS Energy Letters
Francisco Palazon, Carmine Urso, Luca De Trizio, Quinten Akkerman, Sergio Marras, Federico Locardi, Ilaria Nelli, Maurizio Ferretti, Mirko Prato, Liberato Manna
Perovskite-related Cs4 PbBr6 nanocrystals present a "zero-dimensional" crystalline structure where adjacent [PbBr6 ]4- octahedra do not share any corners. We show in this work that these nanocrystals can be converted into "three-dimensional" CsPbBr3 perovskites by extraction of CsBr. This conversion drastically changes the optoelectronic properties of the nanocrystals that become highly photoluminescent. The extraction of CsBr can be achieved either by thermal annealing (physical approach) or by chemical reaction with Prussian Blue (chemical approach)...
October 13, 2017: ACS Energy Letters
Jimin Wang, Mikhail Askerka, Gary W Brudvig, Victor S Batista
Photosystem II (PSII) oxidizes water to produce oxygen through a four-step photocatalytic cycle. Understanding PSII structure-function relations is important for the development of biomimetic photocatalytic systems. The quantum mechanics/molecular mechanics (QM/MM) analysis of substrate water binding to the oxygen-evolving complex (OEC) has suggested a rearrangement of water ligands in a carousel mechanism around a key Mn center. Here, we find that the most recently reported X-ray free-electron laser (XFEL) crystallographic data obtained for the dark-stable S1 state and the doubly flashed S3 state at 2...
October 13, 2017: ACS Energy Letters
Quinten A Akkerman, Daniele Meggiolaro, Zhiya Dang, Filippo De Angelis, Liberato Manna
CsPbI3 nanocrystals are still limited in their use because of their phase instability as they degrade into the yellow nonemitting δ-CsPbI3 phase within a few days. We show that alloyed CsPb x Mn1- x I3 nanocrystals have essentially the same optical features and crystal structure as the parent α-CsPbI3 system, but they are stable in films and in solution for periods over a month. The stabilization stems from a small decrease in the lattice parameters slightly increasing the Goldsmith tolerance factor, combined with an increase in the cohesive energy...
September 8, 2017: ACS Energy Letters
Kara D Fong, Tiesheng Wang, Hyun-Kyung Kim, R Vasant Kumar, Stoyan K Smoukov
Conducting polymers show great promise as supercapacitor materials due to their high theoretical specific capacitance, low cost, toughness, and flexibility. Poor ion mobility, however, can render active material more than a few tens of nanometers from the surface inaccessible for charge storage, limiting performance. Here, we use semi-interpenetrating networks (sIPNs) of a pseudocapacitive polymer in an ionically conductive polymer matrix to decrease ion diffusion length scales and make virtually all of the active material accessible for charge storage...
September 8, 2017: ACS Energy Letters
Moritz H Futscher, Bruno Ehrler
Perovskite/Si tandem solar cells have the potential to considerably out-perform conventional solar cells. Under standard test conditions, perovskite/Si tandem solar cells already outperform the Si single junction. Under realistic conditions, however, as we show, tandem solar cells made from current record cells are hardly more efficient than the Si cell alone. We model the performance of realistic perovskite/Si tandem solar cells under real-world climate conditions, by incorporating parasitic cell resistances, nonradiative recombination, and optical losses into the detailed-balance limit...
September 8, 2017: ACS Energy Letters
He Huang, Maryna I Bodnarchuk, Stephen V Kershaw, Maksym V Kovalenko, Andrey L Rogach
This Perspective outlines basic structural and optical properties of lead halide perovskite colloidal nanocrystals, highlighting differences and similarities between them and conventional II-VI and III-V semiconductor quantum dots. A detailed insight into two important issues inherent to lead halide perovskite nanocrystals then follows, namely, the advantages of defect tolerance and the necessity to improve their stability in environmental conditions. The defect tolerance of lead halide perovskites offers an impetus to search for similar attributes in other related heavy metal-free compounds...
September 8, 2017: ACS Energy Letters
Eline M Hutter, Rebecca J Sutton, Sanjana Chandrashekar, Mojtaba Abdi-Jalebi, Samuel D Stranks, Henry J Snaith, Tom J Savenije
Metal halide perovskites such as methylammonium lead iodide (MAPbI3) are highly promising materials for photovoltaics. However, the relationship between the organic nature of the cation and the optoelectronic quality remains debated. In this work, we investigate the optoelectronic properties of fully inorganic vapour-deposited and spin-coated black-phase CsPbI3 thin films. Using the time-resolved microwave conductivity technique, we measure charge carrier mobilities up to 25 cm(2)/(V s) and impressively long charge carrier lifetimes exceeding 10 μs for vapour-deposited CsPbI3, while the carrier lifetime reaches less than 0...
August 11, 2017: ACS Energy Letters
Tejas S Sherkar, Cristina Momblona, Lidón Gil-Escrig, Jorge Ávila, Michele Sessolo, Henk J Bolink, L Jan Anton Koster
Trap-assisted recombination, despite being lower as compared with traditional inorganic solar cells, is still the dominant recombination mechanism in perovskite solar cells (PSCs) and limits their efficiency. We investigate the attributes of the primary trap-assisted recombination channels (grain boundaries and interfaces) and their correlation to defect ions in PSCs. We achieve this by using a validated device model to fit the simulations to the experimental data of efficient vacuum-deposited p-i-n and n-i-p CH3NH3PbI3 solar cells, including the light intensity dependence of the open-circuit voltage and fill factor...
May 12, 2017: ACS Energy Letters
Luis M Pazos-Outón, Ju Min Lee, Moritz H Futscher, Anton Kirch, Maxim Tabachnyk, Richard H Friend, Bruno Ehrler
After 60 years of research, silicon solar cell efficiency saturated close to the theoretical limit, and radically new approaches are needed to further improve the efficiency. The use of tandem systems raises this theoretical power conversion efficiency limit from 34% to 45%. We present the advantageous spectral stability of using voltage-matched tandem solar cells with respect to their traditional series-connected counterparts and experimentally demonstrate how singlet fission can be used to produce simple voltage-matched tandems...
February 10, 2017: ACS Energy Letters
Jimin Wang, Mikhail Askerka, Gary W Brudvig, Victor S Batista
Understanding structure-function relations in photosystem II (PSII) is important for the development of biomimetic photocatalytic systems. X-ray crystallography, computational modeling, and spectroscopy have played central roles in elucidating the structure and function of PSII. Recent breakthroughs in femtosecond X-ray crystallography offer the possibility of collecting diffraction data from the X-ray free electron laser (XFEL) before radiation damage of the sample, thereby overcoming the main challenge of conventional X-ray diffraction methods...
February 10, 2017: ACS Energy Letters
Javad Shamsi, Ahmed L Abdelhady, Sara Accornero, Milena Arciniegas, Luca Goldoni, Ajay Ram Srimath Kandada, Annamaria Petrozza, Liberato Manna
We report chemical routes for the synthesis of both nanocrystals and bulk crystals of methylammonium (MA) lead halide perovskites employing N-methylformamide (NMF) as a source of MA ions. Colloidal nanocrystals were prepared by a transamidation reaction between NMF and an alkyl amine (oleylamine). The nanocrystals showed photoluminescence quantum yields reaching 74% for MAPbBr3 and 60% for MAPbI3. Bulk crystals were grown at room temperature, with no need for an antisolvent, by the acid hydrolysis of NMF. Important advantages of using NMF instead of MA salts are that the syntheses involve fewer steps and less toxic and less expensive chemicals...
November 11, 2016: ACS Energy Letters
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