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Electrochemical Impedance Spectroscopy: A Noninvasive Tool for Performance Assessment of Bioelectrochemical Systems
Published in Sonia M. Tiquia-Arashiro, Deepak Pant, Microbial Electrochemical Technologies, 2020
Namita Shrestha, Govind Chilkoor, Bhuvan Vemuri, Venkataramana Gadhamshetty
The slow kinetics of electrochemical reactions on the surfaces of counter electrodes, e.g., oxygen reduction reactions (ORR), in BES represents a dominant bottleneck to the commercialization of BES technologies. The rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) are typically used to evaluate the performance of the ORR catalysts (Géniès et al. 2003). The DC analysis is disadvantageous as it offers summative manifestations of multiple polarization effects on the cathode surface and fails to differentiate them. Conversely, EIS can distinguish the charge transfer resistance from mass transfer impedances (kinetic, ohmic and diffusion) to ORR as they elicit different EIS spectra at different frequency ranges. EIS can characterize a range of mass and charge transfer processes associated with the ORR (Raistrick 1990; Singh et al. 2015; Springer et al. 1996). A classic model that serially combines flooded-agglomerate electrode model with a thin electrolyte film model is commonly used to study the ORR activity on porous electrodes (Raistrick 1990; Springer et al. 1996). At higher frequencies, the current density increases with the increase in the steady state concentration of participating reactants of ORRs. At lower frequencies, the current density decreases because of the mass transport limitations. A study by Springer et al. demonstrates the use of EIS for characterizing the effects of mass transfer limitations and humidification on the performance of air breathing cathodes (Springer et al. 1996). Their EIS study revealed two unique features of the air breathing cathode: (i) the interfacial charge transfer resistance and the catalyst layer properties appeared in the higher frequency range and (ii) the gas-phase transport limitations appeared in the lower frequency range. The EIS studies can also be used to understand the impacts of electrolyte crossover on the ORR activity (Perez et al. 1998; Piela et al. 2006). Table 2b shows a typical EIS behavior of the air breathing cathodes that sustain ORRs.
Synthesis, characterisation and performance analysis of multi-walled carbon nanotubes supported platinum catalyst for proton exchange membrane fuel cells
Published in Indian Chemical Engineer, 2019
Shaik Shadulla, K. Satish Raj, S. V. Naidu
Linear sweep voltammetry measurements were done using a rotating ring disk electrode (RRDE) setup for the working electrode. The rotating ring disk electrode system is generally used to study the oxygen reduction reaction (ORR) which significantly affects PEM fuel cell performance. When O2 was dissolved in acidic media and reduced at a platinum electrode, water formation is the desired reaction. In this experimental setup, the RRDE (working electrode) was placed in a 0.1 M HClO4 solution and was operated at rotation rates varying from 1000 to 1600 rpm. Initially, both the ring and the disk electrodes were held at a positive potential so that no reaction occurs. From the steady-state current–potential curves shown in Figure 5, as the potential was slowly swept at 50 mV/s, a cathodic current was observed which corresponds to the ORR. As ORR progressed, the reduced species was swept radially from the disk electrode towards the ring electrode. The ring electrode was held constant at a positive (oxidising) potential throughout. It is to be noted that as the rotation speed increased while the potential was swept from 0.70 V towards negative potential (−0.025 V), the cathodic current increased.