Alexis T. BELL

Integrated solar fuels devices for CO2 reduction (CO2R) are a promising technology class towards reducing carbon emissions. Designing integrated CO2R solar fuels devices requires careful co-design of electrochemical and photovoltaic components as well as consideration of the diurnal and seasonal effects of solar irradiance, temperature, and other meteorological factors expected for ‘on-sun’ deployment. Using a photovoltaic-electrochemical (PV-EC) platform, we developed a temperature and potential-dependent diurnal and annual model using experimentally-determined CO2R performance of Cu-based electrocatalysts, local meteorological data from the National Solar Radiation Database (NSRD), and modeled performance of commercial c-Si PVs. We simulated gaseous diurnal product outputs with and without the effects of ambient temperature. From these outputs, we observed seasonal variation in …

Recent research has found that dealuminated zeolite BEA (DeAlBEA) is an attractive support for the dispersion of Pt and PtSn species that serve as catalysts for propane dehydrogenation (PDH). In this study, we report the preparation, structural characterization, and PDH activities of Pt-Sn-DeAlBEA catalysts as a function of the Pt/Al ratio (here Al represents the amount of Al present in the parent zeolite H-BEA). The support Sn-DeAlBEA was prepared by introduction of Sn to DeAlBEA. Characterization of this material by X-ray absorption spectroscopy (XAS) and UV–vis spectroscopy revealed that the Sn incorporated into the BEA framework as Sn(IV) cations. Pt-Sn-DeAlBEA catalysts were prepared with Pt/Al ratios (0.001–0.026) and were characterized with infrared (IR) spectroscopy of adsorbed probe molecules and XAS to understand the effect of changing Pt loading on the structure of Pt in Pt-Sn-DeAlBEA. Pt …

Bipolar membranes (BPMs) enable control of ion concentrations and fluxes in electrochemical cells suitable for a wide range of applications. Here we present the multi-scale physics of BPMs in an electrochemical engineering context and articulate design principles to drive the development of advanced BPMs. The chemistry, structure, and physics of BPMs are illustrated and related to the thermodynamics, transport phenomena, and chemical kinetics that dictate ion and species fluxes and selectivity. These interactions give rise to emergent structure–property–performance relationships that yield design criteria for BPMs that achieve high permselectivity, durability, and voltaic efficiency. The resulting performance trade-offs for BPMs are presented in the context of emerging applications in energy conversion or storage, and environmental remediation. By connecting the fundamental physical phenomena in BPMs to …

This work presents the effects of ≡Ti–OH site distortion in Ti/SiO2 on the kinetics and mechanism of gas-phase cyclohexene (C6H10) epoxidation to form cyclohexene oxide (C6H10O). We utilize an experimentally validated computational method to calculate enthalpies of adsorption and transition states along a well-established mechanism for the catalytic cycle. We discover that adsorption enthalpies correlate with the facet area of the tetrahedral O–Ti–O facets of the ≡Ti–OH group through which the adsorbate binds to Ti. In contrast, enthalpies of H2O2 activation and O atom transfer are relatively insensitive. We then develop a steady-state microkinetic model (MKM) to investigate the effects of distortion on predicted kinetic observables (apparent activation energy (Ea) and reaction orders in the partial pressures of C6H10 and H2O2) and to establish whether the mechanism is consistent with observed kinetics …

Zn Lewis acid centers were grafted onto the silanol nest created by dealumination of H-BEA zeolite (DeAlBEA). The resulting material was characterized and investigated for propane dehydrogenation to propene and n-butane dehydrogenation to 1,3-butadiene (1,3-BD). For Zn/Al molar ratios (Al is the molar amount in H-BEA) below 0.12, Zn sites are present as isolated (≡SiOZn–OH) species, but for Zn/Al ratios between 0.12 and 0.60, the ≡SiOZn–OH species form nests in which enhanced electron transfer between Zn and O atoms of the neighboring ≡SiOZn–OH group and H-bonding interaction between adjacent Zn–OH groups occur. The turnover frequency (TOF) for both propane and n-butane dehydrogenation is virtually identical for Zn-DeAlBEA for Zn/Al < 0.12 and then increases almost linearly with increasing Zn/Al ratio from 0.12 to 0.36, indicating the superior activity of Zn atoms in ≡SiOZn–OH nests. In …

The electrochemical reduction of the CO2 reaction (CO2RR) offers an attractive means for converting the carbon content of CO2, released from a stationary source or the atmosphere, into fuels and chemicals [1]. Utilization of CO2 captured from the atmosphere, and energy provided by electricity sourced from wind or solar energy, are particularly appealing because they enable sustainable production of carbon-containing products. The most attractive type of CO2 electrolyzer for commercial application is a membrane electrode assembly (MEA), as shown in Fig. 1 a [2, 3]. This device consists of an anion-exchange membrane (AEM) sandwiched between two gas diffusion electrodes (GDEs), each of which comprises a gas diffusion layer (GDL) and a catalyst layer (CL). The cathode CL contains metal nanoparticles, typically Ag or Cu, that promote the electrochemical reduction of CO2 using water vapor as the source of …

The synthesis, thermolysis, and surface organometallic chemistry of thermolytic molecular precursors based on a new germanosilicate ligand platform, –OGe[OSi(OtBu)3]3, is described. Use of this ligand is demonstrated with preparation of complexes containing the first-row transition metals Cr, Mn, and Fe. The thermolysis and grafting behavior of the synthesized complexes, Fe{OGe[OSi(OtBu)3]3}2 (FeGe), Mn{OGe[OSi(OtBu)3]3}2(THF)2 (MnGe) and Cr{OGe[OSi(OtBu)3]3}2(THF)2 (CrGe), was evaluated using a combination of thermogravimetric analysis; nuclear magnetic resonance (NMR), ultraviolet-visible (UV-Vis), and electron paramagnetic resonance (EPR) spectroscopies; and single-crystal X-ray diffraction (XRD). Grafting of the precursors onto SBA-15 mesoporous silica and subsequent calcination in air led to substantial changes in transition metal coordination environments and oxidation states, the …

Heterogeneous catalysis is driven by the interaction of reactant molecules and the catalyst surface. The locus of this interaction as well as the surrounding ensemble of atoms is referred to as the catalyst active site. Active site characterization attempts to distinguish active catalytic sites from inactive surface sites, to elucidate the structural and chemical nature of active sites, and to quantify active site concentration. Numerous techniques have been demonstrated to provide compositional and structural information about the active sites within a catalyst. However, each technique has its own limitations and experimental pitfalls that can lead to data misinterpretation or irreproducible results. This work aims to provide an overview of the types of data that can be collected, to outline common experimental challenges and how to avoid them, and to assemble relevant references for the most used active site characterization …