Constant-Phase Elements (CPE) are often used to fit impedance data arising from a broad range of experimental systems. Four approaches were used to interpret CPE parameters associated with the impedance response of human skin and two metal oxides in terms of characteristic frequencies and film thickness. The values obtained with each approach were compared against independent measurements. The power-law model developed recently by Hirschorn et al. 1,2 provided the most reliable interpretation for systems with a normal distribution of properties. Readers are cautioned that the CPE parameter Q does not provide an accurate value for capacitance, even when the CPE exponent α is greater than 0.9.Electrical circuits invoking constant-phase elements (CPE) are often used to fit impedance data arising from a broad range of experimental systems. The impedance for a film-covered electrode showing CPE behavior may be expressed in terms of ohmic resistance R e , a parallel resistance R || , and CPE parameters α and Q aswhere f is the frequency in units of Hz. When α = 1, the system is described by a single time-constant, and the parameter Q has units of capacitance; otherwise, Q has units of s α / cm 2 or F/s (1−α) cm 2 . 3 Under conditions that (2πf ) α R || Q 1,

The translation of batch chemistries to high-throughput flow methods addresses scaling concerns associated with the implementation of colloidal nanoparticle (NP) catalysts for industrial processes. A literature procedure for the synthesis of Ni-NPs was adapted to a continuous millifluidic (mF) flow method, achieving yields >60%. Conversely, NPs prepared in a batch (B) reaction under conditions analogous to the continuous flow conditions gave only a 45% yield. Both mF- and B-Ni-NP catalysts were supported on SiO2 and compared to a Ni/SiO2 catalyst prepared by traditional incipient wetness (IW) impregnation for the hydrodeoxygenation (HDO) of guaiacol under ex situ catalytic fast pyrolysis conditions (350 °C, 0.5 MPa). Compared to the IW method, both colloidal NPs displayed increased morphological control and narrowed size distributions, and the NPs prepared by both methods showed similar size, shape, and crystallinity. The Ni-NP catalyst synthesized by the continuous flow method exhibited similar H-adsorption site densities, site-time yields, and selectivities toward deoxygenated products compared to the analogous batch-prepared catalyst, and it outperformed the IW catalyst with respect to higher selectivity to lower oxygen content products and a 31-fold decrease in deactivation rate. These results demonstrate the utility of synthesizing colloidal Ni-NP catalysts using flow methods that can produce >27 g/day of Ni-NPs (equivalent to >0.5 kg of 5 wt % Ni/SiO2), while maintaining the catalytic properties displayed by the batch equivalent.

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Skin impedance measurements are sensitive to irreversible damage caused by exposure to puncture with a needle.