Membrane electrical modification

Two experimental poly(ether ether ketone) (PEEK) membranes for methanol fuel cell application, one with a zirconium modification to reduce the methanol crossover (samples PEEK-sn-0 and PEEK-sn-Zr, respectively), which were prepared and kindly submitted by Dr. S. Nunes (GKSS, Germany) (Nunes et al. 2002 Silva et al. 2006). To observe the electrical changes only due to membrane material modification, impedance measurements with these membranes were performed both in contact with the NaCl solutions and in a dry state. 

All these attempts to improve the membrane characteristics by decreasing the methanol crossover and increasing their temperature resistance gave encouraging results. However, modification of the existing membranes (e.g., with barrier screens) without decreasing the electrical... 

In our approach to membrane breakdown we have only taken preliminary steps. Among the phenomena still to be understood is the combined effect of electrical and mechanical stress. From the undulational point of view it is not clear how mechanical tension, which suppresses the undulations, can enhance the approach to membrane instability. Notice that pore formation models, where the release of mechanical and electrical energy is considered a driving force for the transition, provide a natural explanation for these effects [70]. The linear approach requires some modification to describe such phenomena. One suggestion is that membrane moduli should depend on both electrical and mechanical stress, which would cause an additional mode softening [111]. We hope that combining this effect with nonlocality will be illuminating. 

Another method used to vary the AG° of the recombination reaction without chemical modification of the centers, consists of placing the system in an electric field whose orientation and intensity are well defined [141]. However, the energy level shifts induced by the field also change the electronic factors, so that the interpretation of the experimental results is not straightforward. Bixon and Jortner have proposed using electric field effects to elucidate the nature of the primary electron step in bacterial photosystems [142], a problem that will be discussed in Sect. 3.5. One basic difficulty encountered in this method is the evaluation of the internal field effectively seen by the redox centers in the membrane. 

We may extrapolate from these basic considerations in two ways. We may evaluate the extracellular electric gradients associated with intrinsic or imposed tissue fields against the magnitude of the gradients in the membrane potential, both in resting conditions and in association with modification of the membrane potential during synaptic excitation. In this way, we may appraise the probability of direct effects of extracellular tissue fields in excitation of nerve cells. A second approach will consider the observed biological sensitivities to these fields. This will lead to the crux of our current dilemma. A... 

Due to their simplicity of construction, ease of modification, electrical methods of detection, fast response time and the fact that they are the principal structural component of all biomembranes, conventional bilayer lipid membrane (BLM) arises as an ideal system for biosensor technology [88] and they have been studied regarding the possibility of developing DNA biosensors consisting of a glassy carbon electrode-modified by a BLM with incorporated ssDNA [89]. 

The overall energy conversion efficiency for the complete process of mathanol chemical energy conversion dc electric energy will be similar (43%) for a system with an RAFC operating at 0.70 V and a DMFC operating at 0.55 V, provided the fuel efficiency in the DMFC is raised to 90% (the latter requirement could be possibly achieved by combination of anodic effects and membrane modification). 

When a thin membrane of glass separates two solutions, an electric potential difference that depends on the ions present in the solutions is established across the glass. Glass electrodes responding chiefly to ions have become common laboratory tools (Bates 1973). Modification of the glass composition has led to the development of electrodes selective for a variety of cations other than (Belford and Owen, 1989 Eisenmann, 1967). 

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