9 Search Results

Abstract Electrochemical CO ₂ reduction (CO ₂ R) is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent progress in fundamental understanding, catalyst development, and in engineering and scale-up. We discuss the outstanding challenges towards commercialization of electrochemical CO ₂ R technology: energy efficiencies, selectivities, low current densities, and stability. We highlight the opportunities in establishing rigorous standards for benchmarking performance, advances in in operando characterization, the discovery of new materials towards high value products, the investigation of phenomena across multiple-length scales and the application ofmore » data science towards doing so. We hope that this collective perspective sparks new research activities that ultimately bring us a step closer towards establishing a low- or zero-emission carbon cycle.« less

Raffaella Buonsanti and Wilson Smith are leaders of their fields considering the careful design of materials and engineering, respectively. In this backstory, they share their view of the field of electrochemical synthesis both as it is now, and in the future.

At the outermost surface of colloidal QDs are organic surface ligands which dynamically bind and release in solution to control the growth kinetics, control the size/shape of the crystals, passivate surface states, and provide colloidal stability through favorable interactions with the solvent. However, the dynamicity comes at the expense of the stability of the QD suspension. Here, we show that ligands can be permanently locked on the QD surface by a thin layer of an inert metal oxide which forms within the ligand shell, over the headgroup. By interrogating the surface chemistry with different spectroscopic methods, we prove the ligandmore » locking on the QD surface. As a result, an exceptional stability of the coated QD inks is achieved in a wide concentration range, even in the presence of chemically competing surface ligands in solution. We anticipate that this critical breakthrough will benefit different areas related to colloidal QDs, spanning from single-particle studies to displays and solar cells and biological applications. Furthermore, the same chemistry could be easily translated to surface treatments of bulk materials and thin films.« less

Förster resonant energy transfer (FRET)-mediated exciton diffusion through artificial nanoscale building block assemblies could be used as an optoelectronic design element to transport energy. However, so far, nanocrystal (NC) systems supported only diffusion lengths of 30 nm, which are too small to be useful in devices. In this work, we demonstrate a FRET-mediated exciton diffusion length of 200 nm with 0.5 cm²/s diffusivity through an ordered, two-dimensional assembly of cesium lead bromide perovskite nanocrystals (CsPbBr₃ PNCs). Exciton diffusion was directly measured via steady-state and time-resolved photoluminescence (PL) microscopy, with physical modeling providing deeper insight into the transport process. This exceptionallymore » efficient exciton transport is facilitated by PNCs' high PL quantum yield, large absorption cross section, and high polarizability, together with minimal energetic and geometric disorder of the assembly. This FRET-mediated exciton diffusion length matches perovskites' optical absorption depth, thus enabling the design of device architectures with improved performances and providing insight into the high conversion efficiencies of PNC-based optoelectronic devices.« less

Heterostructured nanocomposites offer promise for creating systems exhibiting functional properties that exceed those of the isolated components. For solar energy conversion, such combinations of semiconducting nanomaterials can be used to direct charge transfer along pathways that reduce recombination and promote efficient charge extraction. However, interfacial energetics and associated kinetic pathways often differ significantly from predictions derived from the characteristics of pure component materials, particularly at the nanoscale. Here, the emergent properties of TiO₂/BiVO₄ nanocomposite photoanodes are explored using a combination of X-ray and optical spectroscopies, together with photoelectrochemical (PEC) characterization. Application of these methods to both the pure components andmore » the fully assembled nanocomposites reveals unpredicted interfacial energetic alignment, which promotes ultrafast injection of electrons from BiVO₄ into TiO₂. Physical charge separation yields extremely long-lived photoexcited states and correspondingly enhanced photoelectrochemical functionality. This work highlights the importance of probing emergent interfacial energetic alignment and kinetic processes for understanding mechanisms of solar energy conversion in complex nanocomposites.« less

Inorganic nanocomposites synthesized by combination of colloidal nanocrystals (NCs) and inorganic clusters have recently emerged as new materials with novel and unique functionalities. Much of the demonstrated promise of nanocomposites derives from the unique interactions between NC and matrix components—this generates new material properties, which direct unique transport behavior in the overall solid or nanocomposite—be it mass, charge, or heat. While measured empirically, it has remained largely impossible to take an a priori look at material properties and use those as a guideline to design desired transport behavior. Fundamentally, this is because the structural and electronic changes manifest at thosemore » interfaces have remained hidden from examination. We provide experimental evidence that transport behavior in nanocrystal-in-matrix (NIM) composites is dictated primarily by interfacial charge transfer associated with electronic and structural reconstructions as the composite forms. Our approach building continuous composite superlattices serves as a starting point for systematic probing of the nanointerface of NIM composites via ultrathin films. A combination of field effect transistor device characterization and photoemission spectroscopy reveals the systematic dependence of the polarity of charge transfer on the selection of matrix materials in NIM composites. We use this insight to combine, by design, different components to tune the carrier type in NIM composites.« less

Favoring the CO₂ reduction reaction (CO₂RR) over the hydrogen evolution reaction and controlling the selectivity towards multicarbon products are currently major scientific challenges in sustainable energy research. It is known that the morphology of the catalyst can modulate catalytic activity and selectivity, yet this remains a relatively underexplored area in electrochemical CO₂ reduction. In this study, we exploit the material tunability afforded by colloidal chemistry to establish unambiguous structure/property relations between Cu nanocrystals and their behavior as electrocatalysts for CO₂ reduction. Our study reveals a non-monotonic size-dependence of the selectivity in cube-shaped copper nanocrystals. Among 24 nm, 44 nm andmore » 63 nm cubes tested, the cubes with 44 nm edge length exhibited the highest selectivity towards CO₂RR (80 %) and faradaic efficiency for ethylene (41 %). Finally, statistical analysis of the surface atom density suggests the key role played by edge sites in CO₂RR.« less

Abstract Favoring the CO ₂ reduction reaction (CO2RR) over the hydrogen evolution reaction and controlling the selectivity towards multicarbon products are currently major scientific challenges in sustainable energy research. It is known that the morphology of the catalyst can modulate catalytic activity and selectivity, yet this remains a relatively underexplored area in electrochemical CO ₂ reduction. Here, we exploit the material tunability afforded by colloidal chemistry to establish unambiguous structure/property relations between Cu nanocrystals and their behavior as electrocatalysts for CO ₂ reduction. Our study reveals a non‐monotonic size‐dependence of the selectivity in cube‐shaped copper nanocrystals. Among 24 nm, 44 nm andmore » 63 nm cubes tested, the cubes with 44 nm edge length exhibited the highest selectivity towards CO2RR (80 %) and faradaic efficiency for ethylene (41 %). Statistical analysis of the surface atom density suggests the key role played by edge sites in CO2RR.« less

In this paper, we show that sub-micron coatings of zeolitic imidazolate frameworks (ZIFs) and even ZIF-ZIF bilayers can be grown directly on polymers of intrinsic microporosity from zinc oxide (ZnO) nanocrystal precursor films, yielding a new class of all-microporous layered hybrids. The ZnO-to-ZIF chemical transformation proceeded in less than 30 min under microwave conditions using a solution of the imidazole ligand in N,N-dimethylformamide (DMF), water, or mixtures thereof. By varying the ratio of DMF to water, it was possible to control the morphology of the ZIF-on-polymer from isolated crystallites to continuous films. Grazing incidence X-ray diffraction was used to confirmmore » the presence of crystalline ZIF in the thin films, and X-ray absorption spectroscopy was used to quantify film purity, revealing films with little to no residual ZnO. Finally, the role solvent plays in the transformation mechanism is discussed in light of these findings, which suggest the ZnO nanocrystals may be necessary to localize heterogeneous nucleation of the ZIF to the polymer surface.« less