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Sharp, Ian D.

Publications and source records attributed to Sharp, Ian D..

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Modifikation eines Cu‐Pd‐Schaufelrad‐Metall‐Organischen Gerüsts für die selektive CO 2 ‐Elektroreduktion

Abstract Die Optimierung der Bindungsenergie zwischen dem Intermediat und dem aktiven Zentrum ist ein entscheidender Faktor, um die katalytische Produktselektivität und Aktivität bei der elektrochemischen Kohlendioxidreduktion (CO 2 RR) zu steuern. Es ist bekannt, dass Kupferatome als aktive Zentren CO 2 zu Kohlenwasserstoffen und Sauerstoffverbindungen reduzieren, jedoch unter schlechter Produktselektivität leiden, da mehrere Intermediate nur moderate Bindungsenergien aufweisen. Hier berichten wir über eine Ionenaustauschstrategie zur Konstruktion von Cu−Pd‐Schaufelrad‐Dimeren innerhalb von Cu‐basierten metallorganischen Gerüsten (MOFs), [Cu 3‐x Pdx(BTC) 2 ] (BTC=1,3,5‐Benzoltricarbonsäure), ohne die strukturellen Eigenschaften des MOFs zu verändern. Im Vergleich zum reinen Cu‐MOF ([Cu 3 (BTC) 2 ], HKUST‐1) verlagert der Cu−Pd‐MOF die Produkte der CO 2 ‐Elektroreduktion von einer Vielzahl chemischer Spezies hin zu einer selektiven CO‐Erzeugung. Eine in situ‐Röntgenabsorptions‐Feinstrukturanalyse der Oxidationsstufe des Katalysators und der lokalen Geometrie, kombiniert mit theoretischen Berechnungen, zeigt, dass die Einfügung von Pd in die Knotenpunkte der Cu‐Schaufelradstruktur des MOFs die Adsorption des Schlüsselintermediats COOH* am Cu‐Zentrum fördert. Dies ermöglicht CO‐selektive katalytische Mechanismen und verbessert somit unser Verständnis über das Zusammenspiel von Struktur und Aktivität bei der elektrochemischen CO 2 ‐Reduktion unter Verwendung molekularer Katalysatoren.

Zhang, Ruirui↗
DOE OSTI2024

Engineering a Cu‐Pd Paddle‐Wheel Metal–Organic Framework for Selective CO 2 Electroreduction

Optimizing the binding energy between the intermediate and the active site is a key factor for tuning catalytic product selectivity and activity in the electrochemical carbon dioxide reduction reaction. Copper active sites are known to reduce CO 2 to hydrocarbons and oxygenates, but suffer from poor product selectivity due to the moderate binding energies of several of the reaction intermediates. Here, we report an ion exchange strategy to construct Cu−Pd paddle wheel dimers within Cu-based metal–organic frameworks (MOFs), [Cu 3-x Pd x (BTC) 2 ] (BTC=benzentricarboxylate), without altering the overall MOF structural properties. Compared to the pristine Cu MOF ([Cu 3 (BTC) 2 ], HKUST-1), the Cu−Pd MOF shifts CO 2 electroreduction products from diverse chemical species to selective CO generation. In situ X-ray absorption fine structure analysis of the catalyst oxidation state and local geometry, combined with theoretical calculations, reveal that the incorporation of Pd within the Cu−Pd paddle wheel node structure of the MOF promotes adsorption of the key intermediate COOH* at the Cu site. This permits CO-selective catalytic mechanisms and thus advances our understanding of the interplay between structure and activity toward electrochemical CO 2 reduction using molecular catalysts.

CO2 electroreduction reaction↗
DOE OSTI2022

Strong Induced Circular Dichroism in a Hybrid Lead‐Halide Semiconductor Using Chiral Amino Acids for Crystallite Surface Functionalization

Abstract Chirality is a desired property in functional semiconductors for optoelectronic, catalytic, and spintronic applications. Here, introducing enantiomerically‐pure 3‐aminobutyric acid (3‐ABA) into thin films of the 1D semiconductor dimethylammonium lead iodide (DMAPbI 3 ) is found to result in strong circular dichroism (CD) in the optical absorption. X‐ray diffraction and grazing incidence small angle X‐ray scattering (GISAXS) are applied to gain molecular‐scale insights into the chirality transfer mechanism, which is attributed to a chiral surface modification of DMAPbI 3 crystallites. This study demonstrates that the CD signal strength can be controlled by the amino‐acid content relative to the crystallite surface area. The CD intensity is tuned by the composition of the precursor solution and the spin‐coating time, thereby achieving anisotropy factors ( g abs ) as high as 1.75 × 10 –2 . Grazing incidence wide angle scattering reveals strong preferential ordering that can be suppressed via tailored synthesis conditions. Different contributions to the chiroptical properties are resolved by a detailed analysis of the CD signal utilizing an approach based on the Mueller matrix model. This report of a novel class of chiral hybrid semiconductors with precise control over their optical activity presents a promising approach for the design of circularly polarized light detectors and emitters.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Exploiting heat transfer to achieve efficient photoelectrochemical CO 2 reduction under light concentration

Photoelectrochemical (PEC) conversion of carbon dioxide into valuable chemicals and fuels represents a promising path towards combating anthropogenic CO 2 emissions. However, the limited conversion efficiencies, operation lifetimes and CO 2 utilization efficiencies of PEC devices currently prohibit their application beyond the laboratory scale. Here, a wireless device converting CO 2 and water into carbon monoxide and hydrogen at a peak solar conversion efficiency exceeding 16% under an illumination intensity of 5 suns is demonstrated. A CO/H 2 product ratio between 10–20 is measured during a 17 h stability test. Fluctuations in device performance are rigorously analyzed via deconvolution of electrochemical and photoabsorber contributions. Furthermore, it is demonstrated that beneficial heat dissipation is enabled by wireless integration of the photoabsorber and electrocatalyst components, accounting for roughly 10% of the achieved conversion efficiency, an achievement unattainable with physically separated photoabsorber and electrolyzer components.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Solar fuel generator including a catalytic mesh

This disclosure provides systems, methods, and apparatus related to a solar fuel generator. In one aspect, a device includes a photovoltaic cell, the photovoltaic cell having a first surface and a second surface, a mesh disposed on the first surface of the photovoltaic cell, and a polymer disposed on the mesh and on the first surface of the photovoltaic cell. The mesh has a catalyst disposed thereon. The polymer covers the first surface of the photovoltaic cell, with at least a portion of the mesh not being covered with the polymer.

Walczak, Karl A.↗
DOE OSTI2021

Monolithic Photoelectrochemical CO 2 Reduction Producing Syngas at 10% Efficiency

We report increasing anthropogenic carbon dioxide emissions have prompted the search for photoelectrochemical (PEC) methods of converting CO 2 to useful commodity products, including fuels. Ideally, such PEC approaches will be sustained using only sunlight, water, and CO 2 as energetic and reactant inputs. However, low peak conversion efficiencies (< 5%) have made commercialization of fully-integrated PEC devices prohibitive. Here, a 4 cm 2 monolithic PEC device exceeding 10% solar-to-fuel efficiency with principal fuel products of carbon monoxide and hydrogen is reported. The corresponding solar-to-CO and solar-to-H 2 efficiencies are 7% and 3.5%, respectively. Screening of a range of operating conditions reveals a tunable product mixture of H 2 and CO using a gold electrocatalyst. Accordingly, it is shown that device optimization yields a H 2 -to-CO ratio of 1:2 commonly present in synthesis gas (syngas). Notably, the modularity and facile fabrication of this device permit the incorporation of a broad array of materials for various applications. For example, the electrocatalyst may easily be swapped to target a different set of products.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Revealing Nanoscale Chemical Heterogeneities in Polycrystalline Mo-BiVO 4 Thin Films

The activity of polycrystalline thin film photoelectrodes is impacted by local variations of the material properties due to the exposure of different crystal facets and the presence of grain/domain boundaries. Here a multi-modal approach is applied to correlate nanoscale heterogeneities in chemical composition and electronic structure with nanoscale morphology in polycrystalline Mo-BiVO 4 . By using scanning transmission X-ray microscopy, the characteristic structure of polycrystalline film is used to disentangle the different X-ray absorption spectra corresponding to grain centers and grain boundaries. Comparing both spectra reveals phase segregation of V 2 O 5 at grain boundaries of Mo-BiVO 4 thin films, which is further supported by X-ray photoelectron spectroscopy and many-body density functional theory calculations. Theoretical calculations also enable to predict the X-ray absorption spectral fingerprint of polarons in Mo-BiVO 4 . After photo-electrochemical operation, the degraded Mo-BiVO 4 films show similar grain center and grain boundary spectra indicating V 2 O 5 dissolution in the course of the reaction. Overall, these findings provide valuable insights into the degradation mechanism and the impact of material heterogeneities on the material performance and stability of polycrystalline photoelectrodes.

36 MATERIALS SCIENCE↗