Michael J. Janik

Optoelectronic properties of organic photovoltaics, including light absorption, intramolecular and intermolecular charge transfer, depend on the energetics of the frontier molecular orbitals of constituent organic materials. We develop a tight-binding model for an indacenodithiophene-based small molecule non-fullerene acceptor – IDTBR, which gives a high-efficiency organic photovoltaic cell in combination with poly(3-hexylthiophene) as donor. By choosing stiff conjugated ring moieties as sites, we obtain tight-binding parameters that are local to each moiety, and transferable to other chain architectures. In particular, parameters from homo-oligomers and alternating co-oligomers of constituent moieties can be used, without adjustment, to define the tight-binding model for IDTBR, which reasonably predicts the energies and wavefunctions of its frontier molecular orbitals. Transferability of model parameters will enable …

The affinity difference between lithium and potassium ions for the adsorption to a titanosilicate adsorbent is quantified. Experimental and computational methods examine the thermodynamics of Na+–K+ and Na+–Li+ ion exchange from dilute aqueous solution using modified ETS-10 titanosilicate. Equilibrium uptake data were analyzed with a modified Langmuir isotherm that accounts for ion exchange involving the desorption of Na+ from the modified ETS-10 framework together with the adsorption of Li+ or K+ to the framework. The equilibrium constant for ion exchange of Na+ from the modified ETS-10 framework with K+ from aqueous solution is 6-fold greater than the equilibrium constant for Li+ exchange. This affinity difference is supported by density functional theory (DFT) calculations of ion affinity to the modified ETS-10 framework. Energy differences from DFT were interpreted using a thermochemical cycle to …

Activation barriers for elementary electrochemical reactions can show strong dependence on the composition and structure of the electrode–electrolyte interface, the electrochemical double layer (EDL), due to the highly polar nature of ion/electron transfer transition states. A compartmentalized analytical framework, built upon DFT calculations, is developed to consider complex interactions between reaction intermediates and the EDL. The approach analytically captures how altering interfacial properties, such as the dielectric constant or distribution of electrolyte charges, impact electrocatalytic activation barriers. Dipole moment change along the reaction path plays the largest role in dictating the extent to which interfacial properties impact elementary electrochemical kinetics. The compartmentalization and uncertainty quantification capability of the developed framework is illustrated employing a Helmholtz model …

We explore the crystal structure and ionic conductivity of unfilled and cellulose nanowhisker‐filled polymer electrolytes, based on high molecular weight PEO and LiClO4 at a concentration EO:Li = 6:1 (EO = ether oxygen). At this concentration, the polymer electrolyte forms crystalline PEO6 (PEOy—the crystal structure co‐crystallizes “y” PEO ether oxygens to one Li‐anion pair). While the diffraction patterns for PEO3 and PEO6 with LiClO4 are available, their structures are not. Thus, we optimize these structures using density functional theory and show agreement between simulated and experimental diffraction patterns. The PEO6 crystal shows insufficient Li‐ion conductivity due to a lack of percolated conduction paths, and the crystal structure is unstable following 2 months after annealing. Cellulose nanowhiskers, with their patterned surface OH groups, extend the length of PEO6 tunnels, stabilize these …

Connecting active-site chemistry with observed macroscopic kinetic behaviour is required to rationally design active sites of heterogeneous catalysts. Isolated active sites limit co-adsorption complexities, which challenge reconciling elementary reaction mechanisms and rate constants to observed macroscopic kinetics. The Pd–Zn γ-brass intermetallic phase enables the controlled synthesis of Pd1 monomer and Pd3 trimer sites isolated in an inert Zn matrix. Here we utilize these isolated sites, combining experimental kinetic measurements, density functional theory (DFT) calculations and a fully coverage-enumerated microkinetic model (MKM) to provide detailed mechanistic understanding of elementary reaction chemistry for ethylene hydrogenation. With isolated sites reducing the complexity of co-adsorption coverage effects, remarkable agreement between experimental and DFT-MKM kinetics is reached. The …

CuO-based catalysts are active for the oxygen evolution reaction (OER), although the active form of copper for the OER is still unknown. We combine operando Raman experiments and density functional theory (DFT) electronic structure calculations to determine the form of Cu(O)xOHy present under OER conditions. Raman spectra show a distinct feature related to the active “Cu3+” species, which is only present under highly oxidizing conditions. DFT is used to produce theoretical Raman standards and match the unique Raman feature of copper under OER potentials. This method identifies a range of Cu3+-containing compounds which match the distinct Raman feature. We then integrate experimental electrochemistry to progressively eliminate possible structures and determine the stoichiometry of the active form as CuOOH, which likely takes the form of a surface-adsorbed hydroxide on a CuO surface. Bader …

Water polarizability at a metal interface plays an essential role in electrochemistry. We devise a classical molecular dynamics approach with an efficient description of metal polarization and a novel ac field method to measure the local dielectric response of interfacial water. Water adlayers next to the metal surface exhibit higher-than-bulk in-plane and negative out-of-plane dielectric constants, the latter corresponding physically to overscreening of the applied field. If we account for the gap region at the interface, the average out-of-plane dielectric constant is quite low (ε⊥≈ 2), in agreement with reported measurements on confined thin films.

Ion-pair high-temperature polymer electrolyte membranes (HT-PEMs) paired with phosphonic acid ionomer electrode binders have substantially improved the performance of HT-PEM electrochemical hydrogen pumps (EHPs) and fuel cells. Blending poly(pentafluorstyrene-co-tetrafluorostyrene phosphonic acid) (PTFSPA) with Nafion™, and using this blend as an electrode binder, improved proton conductivity in the electrode layer resulting in a 2 W cm−2 peak power density of fuel cells at 240 °C (a HT-PEM fuel cell record). However, much is unknown about how phosphonic acid ionomers blended with perfluorosulfonic acid materials affect electrode kinetics and gas transport in porous electrodes. In this work, we studied the proton conductivity, electrode kinetics, and gas transport resistances of 3 types of phosphonic acid ionomers, poly(vinyl phosphonic acid), poly(vinyl benzyl phosphonic acid), and PTFSPA by …

Electrolyte cations can have significant effects on the kinetics and selectivity of electrocatalytic reactions. We show an atypical mechanism through which electrolyte cations can impact electrocatalyst performance─direct incorporation of the cation into the oxide electrocatalyst lattice. We investigate the transformations of copper electrodes in alkaline electrochemistry through operando X-ray absorption spectroscopy in KOH and Ba(OH)2 electrolytes. In KOH electrolytes, both the near-edge structure and extended fine-structure agree with previous studies; however, the X-ray absorption spectra vary greatly in Ba(OH)2 electrolytes. Through a combination of electronic structure modeling, near-edge simulation, and postreaction characterization, we propose that Ba2+ cations are directly incorporated into the lattice and form an ordered BaCuO2 phase at potentials more oxidizing than 200 mV vs the normal hydrogen …

2,4,6-Trinitrotoluene (TNT) degradation is of interest in environmental remediation, demilitarization, and national security. Electrochemical TNT reduction to 2,4,6-triaminotoluene is potentially energy efficient and operable at ambient conditions. Determining an elementary reduction mechanism and rate limiting steps is needed to rationally develop TNT electroreduction catalysts. Density functional theory methods determine the TNT reduction mechanism for non-catalyzed and late-transition metal catalyzed paths. The non-catalyzed mechanism is limited by slow initial NO2 group reduction. The outer-sphere mechanism is more competitive to electrocatalytic reduction on Au (111) and Fe (110) surfaces, which wasn't observed in our previous work on nitrobenzene electroreduction. An inverse tradeoff between the initial reduction of the NO2-R* group and reduction of surface hydroxyls suggests relative catalytic activity …

ConspectusDespite the growing deployment of renewable energy conversion technologies, a number of large industrial sectors remain challenging to decarbonize. Aviation, heavy transport, and the production of steel, cement, and chemicals are heavily dependent on carbon-containing fuels and feedstocks. A hopeful avenue toward carbon neutrality is the implementation of renewable carbon for the synthesis of critical fuels, chemicals, and materials. Biomass provides an opportune source of renewable carbon, naturally capturing atmospheric CO2 and forming multicarbon linkages and useful chemical functional groups. The constituent molecules nonetheless require various chemical transformations, often best facilitated by catalytic nanomaterials, in order to access usable final products.Catalyzed transformations of renewable biomass compounds may intersect with renewable energy production by offering a …

Metal oxides have structurally complex surfaces on which a variety of adsorption site types can occur, including cation sites, anion sites, oxygen vacancy sites, and Brønsted acid sites. These sites can catalyze the catalytic transformation of organic molecules via diverse routes, thus enabling H abstraction, O abstraction, C–C bond formation, and other reactions. This Perspective provides an update on recent advances and future directions for various organic reactions on metal oxide catalyst surfaces, particularly for C–H activation of alkanes and for C–C bond formation with organic oxygenate reactants. We put emphasis on the molecular scale details, on the active site structures required to enable the formation of kinetically relevant transition states, energetic descriptors, as well as contemporary ideas to enable low activation energies. This progress has been enabled by specialized experiments and the increased …

Ultra-deep desulfurization of transformer oil is of great demand among power industry. In this work, the effective and deep removal of various types of organosulfurs, including mercaptan, sulfide and disulfide via catalytic adsorptive desulfurization (CADS) using bifunctional Ti-based adsorbent is reported. Compared to adsorptive desulfurization (ADS), dramatically improvement of the organosulfur uptakes were achieved under CADS process. The equilibrium adsorption capacity at 5 μg∙g−1 S reached up to 15.7, 33.4, 11.6 and 11.9 mg∙g−1 for propyl mercaptan(n-PM), dimethyl sulfide(DMS), di-t-butyl disulfide (DTBDS) and dibenzyl disulfide (DBDS), which was 262, 477, 97 and 128 times to that of ADS process, respectively, and was the highest among the reported desulfurization adsorbents. Moreover, it achieved superior breakthrough capacity of 2050, 530 and 210 ml F·(g A)−1 at the breakthrough S concentration …

The thermodynamics of hydrogen bonds in aqueous and acidic solutions significantly impacts the kinetics and thermodynamics of acid reaction chemistry. We utilize in this work a multiscale approach, combining density functional theory (DFT) with classical molecular dynamics (MD) to model hydrogen bond thermodynamics in an acidic solution. Using thermodynamic cycles, we split the solution phase free energy into its gas phase counterpart plus solvation free energies. We validate this DFT/MD approach by calculating the aqueous phase hydrogen bond free energy between two water molecules (H2O–···–H2O), the free energy to transform an H3O+ cation into an H5O2+ cation, and the hydrogen bond free energy of protonated water clusters (H3O+–···–H2O and H5O2+–···–H2O). The computed equilibrium hydrogen bond free energy of H2O–···–H2O is remarkably accurate, especially considering the large …

Pd–Zn intermetallic catalysts show encouraging combinations of activity and selectivity on well-defined active site ensembles. Thermodynamic description of the Pd–Zn system, delineating phase boundaries and enumerating site occupancies within intermediate alloy phases, is essential to determining the ensembles of Pd–Zn atoms as a function of composition and temperature. Combining the present extensive first-principles calculations based on density functional theory (DFT) and available experimental data, the Pd–Zn system was remodeled using the CALculation of PHAse Diagrams (CALPHAD) approach. High throughput modeling tools with uncertainty quantification, i.e., ESPEI and PyCalphad, were incorporated in the phase analysis. The site occupancies across the γ phase composition region were given special attention. A four-sublattice model was used for the γ phase owing to its four Wyckoff positions …

A cyclic process of selective adsorption‐reactive regeneration over bifunctional Z‐sorb was proposed for desulfurization of heavy mercaptan from gasoline under ambient conditions. A pronounced adsorption capacity (25.7 mg‐S/g‐adsorbent) and selectivity (206.1, ~10 times over 1‐hexene) of heptanethiol over bifunctional Z‐sorb were achieved, which can be attributed to the strong adsorbate–adsorbent interaction calculated as high as −44.6 kJ/mol. Catalytic reactive regeneration was proposed to remove stubbornly adsorbed heptanethiol, which achieved complete recovery of Z‐sorb in multiple cycles under room temperature. With the aid of minor H2O2, the strongly adsorbed heptanethiol in the form of metal‐thiolate (Zn‐SR) transformed to readily desorbed disulfide, which was elucidated via the combined experiment and density functional theory calculations. The developed process provides insights to …

Water electrolysis using renewable energy inputs is being actively pursued as a green route for hydrogen production. However, it is limited by the high energy consumption due to the sluggish anodic oxygen evolution reaction (OER) and safety issues associated with H2 and O2 mixing. Here, we replaced the OER with an electrocatalytic oxidative dehydrogenation (EOD) of aldehydes for bipolar H2 production and achieved industrial-level current densities at cell voltages much lower than during water electrolysis. Experimental and computational studies suggest a reasonable barrier for C–H dissociation on Cu surfaces, mainly through a diol intermediate, with a potential-dependent competition with the solution-phase Cannizzaro reaction. The kinetics of the EOD reaction was further enhanced using a porous CuAg catalyst prepared from a galvanic replacement method. Through Ag incorporation and its modification …

Converting CO2 into value-added chemicals and fuels is one of the promising approaches to alleviate CO2 emissions, reduce the dependence on nonrenewable energy resources, and minimize the negative environmental effect of fossil fuels. This work used density functional theory (DFT) calculations combined with microkinetic modeling to provide fundamental insight into the mechanisms of CO2 hydrogenation to hydrocarbons over the iron carbide catalyst, with a focus on understanding the energetically favorable pathways and kinetic controlling factors for selective hydrocarbon production. The crystal orbital Hamiltonian population analysis demonstrated that the transition states associated with O–H bond formation steps within the path are less stable than those of C–H bond formation, accounting for the observed higher barriers in O–H bond formation from DFT. Energetically favorable pathways for CO2 …

Atomically dispersed organometallic clusters can provide well-defined nuclearity of active sites for both fundamental studies as well as new regimes of activity and selectivity in chemical transformations. More recently, dinuclear clusters adsorbed onto solid surfaces have shown novel catalytic properties resulting from the synergistic effect of two metal centers to anchor different reactant species. Difficulty in synthesizing, stabilizing, and characterizing isolated atoms and clusters without agglomeration challenges allocating catalytic performance to atomic structure. Here, we explore the stability of dinuclear rhodium and iridium clusters adsorbed onto layered titanate and niobate supports using molecular precursors. Both systems maintain their nuclearity when characterized using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Statistical analysis of …

The separation of butanes and butenes using MOF-74 (with two reticular MOFs with different pore sizes, Ni-IRMOF-74-I and Ni-IRMOF-74-II) was evaluated computationally using density functional theory. We identified that C4 alkene versus alkane selectivity stems from π–d chemical interactions, whereas selectivity differences among butenes stem from steric implications.