Polymer semiconductors are fascinating materials that could enable delivery of chemical fuels from water and sunlight, offering several potential advantages over their inorganic counterparts. These include extensive synthetic tunability of optoelectronic and redox properties and unique opportunities to tailor catalytic sites via chemical control over the nanoenvironment. Added to this is proven functionality of polymer semiconductors in solar cells, low-cost processability, and potential for large-area scalability. Herein we discuss recent progress on soft photoelectrochemical systems and define three critical knowledge gaps that must be closed for these materials to reach their full potential. We must (1) understand the influence of electrolyte penetration on photoinduced charge separation, transport, and recombination, (2) learn to exploit the swollen polymer/electrolyte interphase to drive selective fuel formation, and (3) establish co-design criteria for soft materials that sustain function in the face of harsh chemical challenges. Achieving these formidable goals would enable tailorable systems for driving photoelectrochemical fuel production at scale.

The hybrid electronic-ionic transport property of pi-conjugated polymers enables new (opto)electrochemical device constructs for energy conversion and storage and biosensing applications. One major challenge is separating the energy and frequency dependence of Faradaic events-those involving charge transfer and the redox processes of the conjugated backbone-from the non-Faradaic components, such as ionic motion. Herein, we combine optical spectroscopy with electrochemical impedance spectroscopy (EIS) to resolve the frequency response of ionic- electronic coupling as a function of electrochemical doping potential. First, using EIS, we identify two different frequency regimes resulting in potential-dependent capacitive elements on the order of similar to 10 mu F/cm(2) in a high-frequency regime and similar to 50-150 mu F/cm(2) in a low-frequency regime. Given the larger magnitude and greater potential dependence, we posit that polaronic motion is more likely to occur at low frequencies (<1 kHz) and overlaps with ionic motion. The use of color impedance spectroscopy (CIS) enables observation of polaronic motion with frequency modulation. We observe that higher doping potentials show a greater motion of polarons above the DC-bias baseline concentration for onset in electrochemical doping, but all potentials considered demonstrate a critical frequency at which the polaronic motion is "frozen" (similar to 40 Hz). This critical information obtained from CIS in highly dielectric environments offers a unique figure of merit for future studies on electronic-ionic coupling by which to compare across polymer/electrolyte interfaces, including the role of a charge-supporting electrolyte, a solvent, and alternative Faradaic processes (e.g., electrocatalysis).

The mechanical flexibility of conductive polymer electrodes coupled with their hybrid electronic-ionic transport properties enables a wide range of technologies from biology to energy conversion, including biosensors, flow batteries, and photo-electrochemical cells. Herein, we focus on a prototypical material to better understand hybrid transport properties - poly(3-hexylthiophene) (P3HT) - which has been widely studied in organic semiconductors and photovoltaics. In solid-state studies, the electronic transport within P3HT is limited by localized states induced by disordered regions and the mechanism is described by the multiple trapping and release (MTR) model. Recent electrochemical impedance spectroscopy (EIS) results have demonstrated anomalous diffusion of ions in regioregular and regiorandom P3HT films, indicative of ionic trapping. However, EIS has been historically equated with ambiguity, as interpretation is limited to equivalent circuit models to extract chemical parameters of interest. Herein we combine EIS and color impedance spectroscopy (CIS) to further understand the hybrid transport mechanism. Specifically, electrochemical doping of conductive polymers results in the formation of polarons – electronic free carriers that can be observed spectroscopically due to the reorganization of chemical bonds to support the radical cations. Thus, CIS allows us to combine the sensitivity of chemical phenomena attributed to optical signatures with the in operando control afforded by application of electrochemical potential. In particular, this approach allows us to resolve mixed transport properties in subpopulations (i.e. crystallites versus aggregates) that exist at nanometer length scales.

Conductive polymers are exceptionally promising for modular electrochemical applications including chemical sensors, bioelectronics, redox-flow batteries, and photoelectrochemical systems due to considerable synthetic tunability and ease of processing. Despite well-established structural heterogeneity in these systems, conventional macroscopic electroanalytical methods-specifically cyclic voltammetry-are typically used as the primary tool for structure property elucidation. This work presents an alternative correlative multimicroscopy strategy. Data from laboratory and synchrotron-based microspectroscopies, including conducting-atomic force microscopy and synchrotron nanoscale infrared spectroscopy, are combined with potentiodynamic movies of electrochemical fluxes from scanning electrochemical cell microscopy (SECCM) to reveal the relationship between electrode structure and activity. A model conductive polymer electrode system of tailored heterogeneity is investigated, consisting of phase-segregated domains of poly(3-hexylthiophene) (P3HT) surrounded by contiguous regions of insulating poly(methyl methacrylate) (PMMA), representing an ultramicroelectrode array. Isolated domains of P3HT are shown to retain bulk-like chemical and electronic structure when blended with PMMA and possess approximately equivalent electron-transfer rate constants compared to pure P3HT electrodes. The nanoscale electrochemical data are used to model and predict multiscale electrochemical behavior, revealing that macroscopic cyclic voltammograms should be much more kinetically facile than observed experimentally. This indicates that parasitic resistances rather than redox kinetics play a dominant role in macroscopic measurements in these conductive polymer systems. SECCM further demonstrates that the ambient degradation of the P3HT electroactivity within P3HT/PMMA blends is spatially heterogeneous. This work serves as a roadmap for benchmarking the quality of conductive polymer films as electrodes, emphasizing the importance of nanoscale electrochemical measurements in understanding macroscopic properties.

SiO2/SiC coatings were deposited onto ceramics disks using plasma-enhanced chemical vapor deposition. The effects of deposition pressure and gas-flow ratio on the refractive index, extinction coefficient, and SiC composition were studied. For the highest studied SiH4 to CH(4 )gas-flow ratio of 1.5, the refractive index increased by 17% from 2.53 (at the wavelength of 845 nm) to 2.96 (at the wavelength of 400 nm). For the lowest studied SiH4 to CH(4 )gas-flow ratio of 0.5, the refractive index only increased by 4% from 2.11 (at the wavelength of 845 nm) to 2.20 (at the wavelength of 400 nm). At higher deposition pressures, the variation in refractive index of the SiC coatings was significantly lower showing a slight increase from 1.93 (at a wavelength of 845 nm) to 1.96 at a wavelength of 400 nm. Except for the case of a low SiH4 to CH4 gas-flow ratio of 0.5, for light with wavelengths <= 650 nm, the extinction coefficient of the SiC coatings increased significantly. Light with a wavelength >650 nm had an extinction coefficient near 0 in all cases. After annealing the sample at 400 degrees C for 4 hours, hydrogen-related bonds broke and the stress of the film was reduced from -245 to -71 MPa. By utilizing different thicknesses of SiC, the full standard dental shade guide was matched with the Delta E of each coated disk being less than 3.3 compared to the shade guide.

Trimethyl borate (TMB) and triethyl borate (TEB) are used as film-forming electrolyte additives for high voltage Lithium nickel manganese oxide (LNMO) cathode. DFT calculation and initial charge curve of LNMO reveal that the oxidation activity of TEB is higher than that of TMB. Addition of 2% TMB and 2% TEB effectively improve the capacity retention of high voltage LNMO from 23.4% to 85.3% and 72.6% after 600 cycles, respectively. The film generated in TMB-containing electrolyte shows better ability on suppressing the LNMO shedding in comparison with that of TEB, resulting in higher capacity retention of LNMO in TMB-containing electrolyte at high voltage. The superior performance of LNMO with TMB-containing electrolyte should be ascribed to its less intense film-forming reaction which generates a denser protective surface film on LNMO surface. However, why LNMO shows catalyzation effect on TEB oxidation but not on TMB is unclear, which needs further intensive investigation. (C) 2017 Elsevier Ltd. All rights reserved.

In this work, trimethylboroxine is used as electrolyte additive to improve the electrode/electrolyte interface stability of LiNi1/3Co1/3Mn1/3O2 (LNCM) cathode for high voltage lithium ion battery. Charge/discharge tests show that addition of 3% TMB is the optimal amount for LNCM. After 300 cycled at 1C rate under the cut-off charge voltage of 4.5 V, the LNCM with 3% TMB achieves a capacity retention of 99%, compared to the 40% of that using STD electrolyte (1 M LiPF6 in ethylene carbonate/diethyl carbonate/dimethyl carbonate). The results from LSV, EIS and physical characterizations, including SEM, TEM, XPS and ICP-MS, demonstrate that TMB oxidizes preferentially to the STD electrolyte, and catalyzes the decomposition of base electrolyte subsequently, generating a thin and low impedance film on the LNCM surface, which effectively stabilizes the electrode/electrolyte interface by suppressing the continuous oxidation of STD electrolyte and the dissolution of LNCM, and hence, improves the cyclic and rate performances of LNCM under high voltage. (C) 2015 Elsevier Ltd. All rights reserved.